Sciencemadness Discussion Board - Slow high torque electric motors for stirrer?

Slow high torque electric motors for stirrer?

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Dr.Arz - 27-10-2014 at 13:39

Where can I get high torque low RPM electric motors, with or without rpm adjuster? I know brushless DC are most ideal and freely adjustable for stirring purposes and they give extremely high torque even too much but they tend to be expensive.

What I am looking is something OTC. I can get 600-1200 watt continous use eletric motors from pumps and other stuff for very low price (10-50) but they all work at 50hz which is just total kill for overhead stirrer.

Air fan motors turn slower than that but they are weak too. 40W may not be enough to turn against the vacuum seal friction.

Magpie - 27-10-2014 at 15:17

I agree that there is a need for such a stirrer. I have a Wheaton overhead stirrer but it is designed for tissue slicing, I believe. It's great if you want high rpm (500-1000) but not so good at low rpm, say around 100.

I would like to build my own stirrer. But, as you say, I need to identify the right motor. Ideally it would be controllable.

[Edited on 28-10-2014 by Magpie]

Oscilllator - 27-10-2014 at 16:23

I personally use a "WICTA DC GearMotor 12V" that I bought for an unrelated project. The thing is 12V but it runs fine on an 18V cordless drill battery and is virtually unstoppable. Seriously, if you want a motor to stir a 1L flask of wet concrete than this is the motor for you. It cost me $14AUD, but you might be able to get it for less, depending on where you look.

Magpie - 27-10-2014 at 17:19

Oscillator that sounds like a great price.

Perhaps you have identified a good source for all that is required, ie, a cordless drill. It would have everything: low rpm high torque motor with a chuck, speed controller, and battery.

(I'm assuming the above motor would be brushless, but I don't really know if it is or not.)

[Edited on 28-10-2014 by Magpie]

[Edited on 28-10-2014 by Magpie]

[Edited on 28-10-2014 by Magpie]

diddi - 28-10-2014 at 03:47

raid an old printer and get a stepper motor. the stepper motor driver circuits are available complete for about $5. infinitely variable speed and good torque.

Oxirane - 28-10-2014 at 07:14

Stepper motor sounds good too.

But if you have got common 220V electric motors, what if you put a reduction gear between it? A 5:1 ratio would already bring it to 600rpm. I use RPM around that for most everything I do and if you get 2-3 sizes of small gears you could vary the speed easily. Gearbox is not hard to construct and small gears suitable for that are available all around. If you go hardcore, 3D print them.

A small electric motor from drill, pump, fan etc. is very cheap and can probably be found from junk and with reduction it gives huge torque, most likely even that 40W fan motor would be enough. Beware it won't run your setup off the table it it gets stuck.

[Edited on 28-10-2014 by Oxirane]

[Edited on 28-10-2014 by Oxirane]

zed - 30-10-2014 at 15:03

Air motors are wonderful. Explosion proof too. Problem is, they require a lot of air.

I have a pretty nifty compressor, but at its maximum output, it still isn't really adequate to supply enough air to even a smaller air motor.

So, do you have a big-ass air compressor? Or, a couple of smaller, but pretty good ones?

[Edited on 30-10-2014 by zed]

jock88 - 30-10-2014 at 15:32

Cordless drills can be found in the dump sometimes as the batteries have given out.
The one with a torque setter on them would be great as you can limit the torque of needs be.

careysub - 31-10-2014 at 10:55

Although repurposing junk into something useful is an admirable and truly rewarding activity, the investment in time (finding that "cheap" motor, adapting it to the task) can be significant.

You can set an upper limit on cost at $19, and make the process of acquiring by considering the cheap Harbor Freight variable speed drill:
http://www.harborfreight.com/38-in-variable-speed-reversible...

Using the trigger lock you can set it run at a continuous, fairly slow speed.

Magpie - 31-10-2014 at 14:28

I looked at some cordless drills at Ace recently. These were brand-name drills like Milwaukee, etc, and were about 3-5 times as expensive as the HF Drillmaster.

The Ace drills had a 17 or 18 position ring that is used to set the speed. Then there is a high and low range switch giving you a total of 34-36 different speed settings. I assume that these drills are DC brushless.

The HF Drillmaster has a cord so I'm assuming it is an AC motor likely with brushes. I think that we agree that for lab stirring brushless is desireable (or mandatory) as many of our concoctions are flammable. Correct me if I'm wrong.

careysub - 31-10-2014 at 14:41

Brushless is no doubt better - but if this really is absolutely necessary you must also confirm all your electrics are sparkless (fume hood fan, lighting, hot plate if using, etc.).

Checking some cordless drill specs (like 12V Black and Decker) I see that they are NOT brushless. So being cordless is no guarantee.

diddi - 31-10-2014 at 14:58

stepper motor controllers are externally clocked which means that you can control the RMP infinitely from 1 rev per day to thousands RPM (eg hard drive 7200rpm) a lot of steppers use 4 wires which is a common output config for the generic stepper control boards. you can obtain quite high resolution of angular step with very little investment. many steppers have a resolution of 1.8degrees/step (200 steps per rev) but the stepper control circuitry is able to generate a series of microsteps (which sort of feels counterintuitive to a digital motor) by tweeking the overlap of power to the motor coils . so you can get smooth stepping rotation with up to 200 x 16 increments per 360 degrees. torque is good, but the holding strength is compromised at the pseudo analog positions between native digital steps (but this would not be a problem in your application)

violet sin - 31-10-2014 at 15:05

I service our ac screw guns at work. They have brushes for sure. Same goes with the rotozip (drywall router by dremel). I don't know of a single brushless version we use.

Also magpie, the 17-18 position twist ring is most likely setting the torque before the clutch slips. Saves you from snapping bits or screw heads off. Should be 1 - 3 speed slide selector, depending on the model. With the torque selection shown on the ring as a series of numbers followed by a drill bit icon, and maybe a hammer icon as well. Numerical slip for installing fasteners(screws), drill icon is for drill bits with max torque and a hammer icon for the hammerdrill setting for concrete or long screws.

Magpie - 1-11-2014 at 05:19

Quote: Originally posted by violet sin

Also magpie, the 17-18 position twist ring is most likely setting the torque before the clutch slips.

Yes, I see. Thanks.

There is quite some information on YouTube about cordless drills and how to disassemble and hack them. Here's an informative one that shows that Milwaukee makes a cordless drill that is brushless:

https://www.youtube.com/watch?v=x-OkkjXVfGw

chemrox - 1-11-2014 at 16:41

I have one I'll sell you. It's cone drive stirring motor for when the material is too viscous for stir bars.

Magpie - 1-11-2014 at 17:09

diddi I think a stepper motor would make a fine stirrer based on what I have read so far. Do you have to buy a separate power supply/control board for these motors, or does that come with the motor? Would an arduino work? What is the user interface with the controller?

diddi - 1-11-2014 at 18:23

I bought 5 of these recently:
http://www.aliexpress.com/snapshot/6208985439.html

the board has direct connection to a range of steppers and offers up to 16x intermediate steps as per my previous post. it will break the budget at nearly $2

the power supply is quite easy. I use old computer power supplies. they work fine and with the number of putas thrown away it wont take long to find one.
the stepper motor connects to the driver board via a standard 4-pin connector. the stepper has an array of coils inside which are wired in 2 "banks" 1 pair of the 4-pin wires drives each bank. the controller board send alternate signals to the banks which advances the stepper 1 step. this "advance" signal is driven by the "clock" input on the controller board. you can use arduino if you like, but by far the cheapest and easiest is just to drive the circuit off the old faithful NE555 and 2 small caps and a resistor (another bank buster at about $1)

you really don't need the high resolution stepping ability of the controller board for a stirrer, but it is simple to invoke, by adjusting the inputs on the board. variable speed stirring is easily accomplished by adding a single variable resister ("pot") to the 555 circuit across pins 7 and 8. if you want to be fancy, you can even use a counter/display chip like ICM7217 to display revs to about +-.01 RPM

any more details I can help with?

Magpie - 1-11-2014 at 19:18

Thanks diddi for providing all that information - it will take me a while to digest it as this is all new to me. Then I'll probably have more questions.

I'm surprised at how little money may be needed to put together a rather nice stirrer. It looks like a fun project.

diddi - 1-11-2014 at 19:21

well I am now inspired to build a demo on a prototyping board, so I can show and label the parts. I have a pair of steppers from a HP scanner and all the other bits lying around, so hopefully I can post a pic in the next day or so.

Magpie - 1-11-2014 at 19:23

Wonderful! That will really help me.

diddi - 1-11-2014 at 21:15

well here is my demo. it runs!
using standard motor
MINEBEA NEMA 17 STEPPER MOTOR 42MM 4-WIRE
as used in lots of printers etc

speed set is really slow (about 20 rpm) but easy to change. the torque was so strong that when I tried to grab the gear and stop it, I cut my finger to bleeding

Magpie - 2-11-2014 at 08:54

That's awesome diddi. I'm going to start scrounging parts right away.

Magpie - 2-11-2014 at 15:29

I had unbelievable luck this morning. I walked into Radio Shack to see what parts they had. While there I mentioned to a young man that I was looking for a junked printer and a junked computer. He just happened to have 5ea in his apartment and offered to give them to me for free. I took 2ea. He works for an internet service co. and offered me more parts and technical consultations also. What a deal! I gave him $5 and felt guilty.

I've already torn apart the small HP Invent printer (2007 model). I salvaged 2 stepper motors and 3 ss shafts, plus some nylon gears. One shaft is 1/4" x 16". The motors have the following numbers:

motor #1: C9000-60005; 1030048; 3H2911 86
motor #2: C9045-60001; 1030151; 3H2263 86

Do these numbers mean anything? Can they be used to find the motor specs? After seeing the stepper motor identified below I think these may not be steppers.

The 2nd "printer" is actually an HP copier. I just pulled off a serious stepper motor:

MINEBA "ASTROSYN" STEPPER, type 17PM-J802-G1VS; NO. T5815-01 A; DWG NO. AX05 0204 A; 3.1V; 1.14A; 1.8 deg

This motor is a cube about 2" on a side w/laminations; there's 6 wires coming off from a plug-in

[Edited on 2-11-2014 by Magpie]

[Edited on 3-11-2014 by Magpie]

diddi - 2-11-2014 at 19:21

MINEBA "ASTROSYN" STEPPER, type 17PM-J802-G1VS; NO. T5815-01 A; DWG NO. AX05 0204 A; 3.1V; 1.14A; 1.8 deg

same brand as mine- the 17PM shows it is same type as well. 1.8deg = 200 steps per revolution. the rest is junk to do with the shape of the gear on the end etc. the only problem is it is the 6-wire type and the controller board I showed is the 4-wire sort, but that is fixable by omitting 2 wires.

this site
http://www.eminebea.com/en/product/rotary/steppingmotor/hybr...

has the data. my interpretation is that 1 pair of wires can be made from pins 1 and 3; the second pair is pins 4 and 6. this converts back to 4-wire model so you can use the controller I used! the capacitors and resistors for the 555 circuit can be ripped out of any computer power supply, and since you now have 2 of those, you should look for values of the capacitors of around 10 - 47uf @ <50V (need 2, same or different). resistor (for non variable speed might be about 2.2K (red, red, red) or if it is to be variable speed, raid an old stereo/radio etc and get the volume control dial. it will have 3 tags/wires attached. I will post pic with variable speed later. if variable speed, you still need a resistor (<47 ohms) eg orange, orange , black or red,red, black or brown, black, black.

if you would like a circuit board design, I can post one to scale and you can make it.

another thought: if a few are interested I can design a board, assemble the whole controller and user just plug in their 4-wire plug, ready to go. it would be fairly lite so postage would be cheap. I am in Australia.

not that I am advertising for work. I have lots to keep me busy, but if electronics scares people off, I don't mind.

the other motors with 90xx numbers are analog motors. (no good for this application)
you can tell steppers by 1) more than 2 wires and 2) if you turn the shaft gently you can feel a sort of internal "clicking". analog motors don't click.

m1tanker78 - 2-11-2014 at 19:48

Stepper motors are great. If for some reason you can't find one or the driver, you might also consider salvaging a synchronous motor from a microwave oven. These run at low RPM and normally connect directly to 120/240 depending on where you live.

Yet another option would be to source a windshield wiper driver motor or even a power window motor from the junk yard. Both offer high torque and low speed. If you have an adjustable 12V power supply, you have your speed control. They do tend to sink quite a bit of current though.

Tank

Magpie - 2-11-2014 at 20:21

Thanks diddi for all that great information. It sounds like I am well on my way to getting a variable speed stirrer. This is not my main hobby interest but I do enjoy learning about it and then making something useful for chemistry.

I was just blown away when I tore into that huge Savin 3515 copier - it looks like an engineering marvel. I almost feel guilty about taking it apart.

I think you are telling me to scavenge a volume dial as a variable resistor. If I can't find one I can always buy a potentiometer from Radio Shack. That would work wouldn't it?

I see that they have those nice little plastic "breadboards" at RS also. I would need something like that too - right?

Are you saying you could post a circuit schematic? I think that would be very helpful to me as well as others.

I will continue my salvage operation tommorrow. I'm expecting to find a real cornacopia.

edit: copier brand name

[Edited on 3-11-2014 by Magpie]

diddi - 2-11-2014 at 20:48

I can post an actual PCB diagram so you can make a circuit board. the plastic prototype board is called a "breadboard" they are available cheap at dx.com

http://www.dx.com/p/solderless-breadboard-white-large-size-1...

they are not good for end users and I would discourage you from using one as your "real" version. great as prototype. they do not provide reliable connections and are not meant to be permanent. you would only need a cheap soldering iron to recover the parts you need from a power supply. don't try to pry them off. and you could solder up the project in no time once you have made a PCB. pics later when I get home.

Magpie - 2-11-2014 at 21:07

I do have a soldering iron, solder, etc. I have assembled a Heathkit volt-ohm meter so do have some experience with electronics assembly. I look forward to your pictures and thank you again.

diddi - 2-11-2014 at 21:18

have you etched your own PCBs? its a bit of chemistry

Magpie - 2-11-2014 at 22:49

Quote: Originally posted by diddi

have you etched your own PCBs? its a bit of chemistry

No. I did make a circuit for controlling my tube furnace as shown here: http://www.sciencemadness.org/talk/viewthread.php?tid=9705&a...

and that's about it.

Magpie - 3-11-2014 at 21:18

hi diddi: I finished tearing down the Savin 3515 copier today (not an HP). I salvaged the big circuit boards and other stuff that looked interesting. My garbage can is nearly full. Now on to the computers.

I looked at the data sheet you linked and tried to identify which motor I have. Mine weighs 298g. So with the amp and resistance values I can sort of determine which motor I have.

I am puzzled by the rating of 3.1v on the motor nameplate then on data sheet frequency-torque graphs it indicates 24.0v. What does this mean? Why the difference?

How do you relate the frequency value to actual shaft rpm?

I have a computer power supply from my old Gateway that I tore down a number of years ago. It will supply both 5vdc and 12vdc. Would this be a suitable power supply?

[Edited on 4-11-2014 by Magpie]

[Edited on 4-11-2014 by Magpie]

diddi - 4-11-2014 at 00:22

5VDC is perfect for logic side of the project (as per my diagram) and depending on the stepper, it may be good to use 12vdc. are there any indentifying numbers on the stepper. it sounds like your motor only has 2 wires? which is not a stepper.

the capacitors you want will look like this:
http://www.tandyonline.co.uk/components/capacitors/electroly...
you need at least 25V and about 10-47uf

Magpie - 4-11-2014 at 07:30

I definitely have a stepper. Nameplate information is as I listed above, ie:

MINEBA "ASTROSYN" STEPPER, type 17PM-J802-G1VS; NO. T5815-01 A; DWG NO. AX05 0204 A; 3.1V; 1.14A; 1.8 deg

This motor is a cube about 2" on a side w/laminations; there's 6 wires coming off from a plug-in.

diddi - 4-11-2014 at 13:34

oh that's the one from the HP copier. the other one you describe does not sound like one tho. all good

Magpie - 4-11-2014 at 14:28

That's right diddi. But I did make a mistake in calling it an HP copier- it was a Savin 3515 - not that that makes any difference.

I just finished tearing down the Dell computer. Not much of value in it - just a couple small heat sinks and a fan. There was no power supply in it - no wonder it was junked.

One more computer to tear down - an "emachines." Then I'm done with my salvaging.

diddi - 5-11-2014 at 01:52

and you trashed the rest of the Dell....
along with the gold on all the connectors and memory modules and on/in CPU
and the tantalum and silver in the SMD capacitors

Magpie - 5-11-2014 at 06:18

Actually I saved the large circuit board in case there might be resistors/capacitors/inductors that I need. I also saved the drives but have no idea why.

I know you are joking, but I won't be attempting to reclaim any precious metals

Edit 1: I finished tearing down the eMachine computer. Again the power supply was gone :mad:

. I did get a large heat sink and a large circuit board w/capacitors/resistors/inductors. Out of all this teardown I only found 1 sizeable stepper motor. But not to worry, RS is nearby and everything is available online.

Edit 2: Apparently I did get a power supply out of the Dell. It looked so different from that from my Gateway that I did not recognize it.

[Edited on 5-11-2014 by Magpie]

[Edited on 5-11-2014 by Magpie]

diddi - 5-11-2014 at 16:02

not joking: I get everyone I know to dump their ewatse with me. I have about 5grams of gold and 20grams of silver from ewaste in maybe 20 hours of leisurely dismantling and a bit of chem.. the hard drive has a very nice NdFeB magnet (or maybe 2) a small stepper and a good amount of gold; and the chassis is solid Al. the screws are stainless steel machine screws top quality.

heatsinks are good quality Al that brings better scrap value. I just fill my tub and cash it in now and then. got about $100 last time

Magpie - 5-11-2014 at 16:49

Nice work on the metal reclaiming diddi. Yes, I did know that there would be a nice Nd magnet in the hard drive as I saved the one from my old Gateway.

I did a little research online for availability and price for the needed components. One thing I learned from my previous component purchases was try to order all of them from one supplier Otherwise postage will kill you. So, I arbitrarily looked at Digi-Key. Here's what I found:

counter: IC OSC UP/DOWN CNTR; Digi-Key No.: ICM7217IPI+-ND; mfg: Maxim Integrated; 2MHz 28-DIP; $9.93

electrolytic capacitor: 47uF, 35V, Nichicon No.: UVRIV479MDD1TA ; aluminum; 20%; radial; $0.27

IC motor driver: Allegro MicroSystems No.: A4988SETTR-T; PAR 28QFN; general purpose; supply voltage:3v-5.5v; voltage-load: 8v-35v; $3.28

As a point of interest, the stepper motor I salvaged goes for at least $50.

Some questions:
1. Would you have to take the counter reading difference over a given time period to determine the rpm? What exactly is being counted?
2. The driver block diagram shown in the link you provided indicates that a "microcontroller" is required. Is this really needed for this application? If so, what is this?
3. You indicate that a resistor is needed. Is this where the pot comes in for variable speed? If so, what would be the resistance value of said pot?

[Edited on 6-11-2014 by Magpie]

diddi - 5-11-2014 at 17:48

ill draw up a quick schematic, but it will be rough...
have not done PCB design yet as I cant find my program I used last time.
I paid about $3 for 7217 and about $1.50 for fully constructed driver module as in my photo

the pot value might be a bit experimental. I would guess about 20k should work about right if you want quite slow speeds. it depends on the caps you use as well.
if you want specs for a particular speed range, let me know

diddi - 5-11-2014 at 18:24

very rough. not at home right now.

the 22 ohm resistor stops the 555 circuit from "locking up". as resistance decreases, the speed increases. 0 resistance results in the 555 freezing.

[Edited on 6-11-2014 by diddi]

Magpie - 5-11-2014 at 21:04

I forgot to identify the IC timer:

IC timer: Texas Instruments No.: NE555DR; IC OSC SGL TIMER; $0.55

Thanks for the schematic. I guess that is +5v on the top.

As I don't have a tachometer it is difficult for me to estimate the proper speed range. But I think 60-600 rpm would be good.

[Edited on 6-11-2014 by Magpie]

[Edited on 6-11-2014 by Magpie]

Varmint - 6-11-2014 at 05:19

A stepper is a good solution when precision positioning is required, but it's loss of torque with increasing speed presents special challenges for the driver circuitry.

Ergo, this is where the wildly divergent "motor rated voltage" and drive circuit "drive votages" come into play. A performance drive will have drive voltages from 4 to 20X the motor "rated" voltage available, and it controls the current and drive waveforms in combination to achieve signals at the motor terminals that do not overheat the motor, yet still have the overdrive required to counteract the motor's inductance with increasing speed.

In this application where you want perhaps a few RPM at the low end, and as much as 600 to 1000 RPM at the high end, you will reach an area whereyou need to make the transition from micro-stepping to full stepping, and unless the driver board is specifically capable of making this crossover on it own, you'll have to have other circuitry make this transition for you.

If you don't, your top speed will be limited by the frequency the driver can handle while micro-stepping, or, you will have to run full stepping at all times, which is going to be subject to some harsh resonance -related vibrations that will be tough to dampen.

A better solution for this wide a range of speeds (and no genuine need for precision positioning) is a DC motor with an external (or internal if you can find one!) optical encoder for shaft speed control.

Use a power Op-Amp to drive the motor, and on the reference input would be a pot to control the motor speed. The other input comes from a F to V converter driven from the encoder pulses. It will present something of a balancing act to get the F to V conversion just right, but the premise is, the amplifier will always strive to match the shaft speed (as represented by the encoder pulse frequency to voltage) to the desired speed as set by the pot.

Some gain in the amp will help too, that way small variations in speed will result in larger variations in drive voltage/current such that the amplifier is ready to react to variations in the load to keep the speed constant.

BTW, the F to V conversion can be done using an actual chip, or it could be accomplished with a couple of resistors and a capacitor doing a simple integration.

The stepper could be made to work, but the speed ranges currently being discussed require a driver of significantly higher complexity than shown till this point.

DAS

diddi - 6-11-2014 at 19:54

valid points... I have actually not invoked any microstepping features available on this driver board (which is 4-bit capable) as I felt that a stirrer did not need to be that smooth. and the driver board is rated to 2A with heatsink (not attached, but provided in the price I paid supplier). I have run the stepper at a few hundred hertz with success but have not finished the display circuit to check exactly (and someone "borrowed" my frequency counter about 3 years ago)

there is certainly merit in using a DC motor and opto sensing to check revs, and would be simpler in some respects as I will need to build a divide 200 module to get rpm. although I would prolly need a division circiut anyway. I would not bother doing F/V method. I think it would be susceptible to error under load?

anyway, hopefully the project works out OK, and it is interesting to see what can be done with junk otherwise being thrown away.

Varmint - 7-11-2014 at 04:34

Didi:

My objection to running full step at all times is the resonances that cause the whole system to vibrate, sometimes scarily so.

I do use a stepper for a non-precision purpose myself, the stepper drives a carboard drum I use to mix flash powder in the most uniform, safest way possible. The driver is controlled by a ATMega328P (basically the u-controller used in an Arduino but stand alone/custom), which offers mixing modes I refect to as "Washing Machine" and others, where the drum rotates one direction, then reverses.

The washing machine cycle is one revolution forward, half revolution back, repeat until stopped. The next mode is 2 revs forward. one rev back, and so on. The default mode is 10 revs forward, 10 revs back, and of course can be changed at any time by recompiling.

With the drum at a 30* angle, the mixing is extremely fast in any mode, I just designed the "Washing Machine" because it's visually interesting and shows off the capabilities of the stepper nicely. In this case, the full step resonances I've mentioned are actually advantageous, they certainly contribute to the mixing action to some degree.

DAS

[Edited on 7-11-2014 by Varmint]

Magpie - 8-11-2014 at 12:55

diddi: I have some resistance data from my stepper motor that may be useful. Consistent with the pin vs phase table shown on the Minebea data sheet you linked, ie:

http://www.eminebea.com/en/product/rotary/steppingmotor/hybr...

my resistance readings are as follows:

pin 1 to pin 2: 18Ω
pin 1 to pin 3: 25Ω
pin 2 to pin 3: 18Ω
pin 4 to pin 5: 18Ω
pin 4 to pin 6: 25Ω
pin 5 to pin 6: 18Ω

All other pin combinations were of infinite resistance. Although I expected the higher readings to be double that of the lower readings I won't swear to the accuracy of my meter either. Does this array indicate a unipolar construction? Also, why are these readings so much higher than the resistance derived from the nameplate 1.14amps and 3.1volts, ie, R=3.1/1.14 =2.7Ω? This calculated value is consistent with those on the Minebea data sheet also.

What is the status of this project from your end? Have you finished or are you still in the design/development stage? Even though varmint has identified a possible weakness of the stepper motor for this application, I am still willing to procure the parts if you think it is worth a try. Maybe just providing a higher voltage, say 24vdc instead of 12vdc, would overcome the vibration issue.

Let me know - and thanks for your work on this project.

Magpie - 21-11-2014 at 16:52

Here's a progress report on my effort to build a stepper motor stirrer. See photo below.

The stepper motor salvaged from a dead copier is mounted on a 1/2" thick slab of aluminum. This was the base of a heat sink also salvaged from one of the dead items described in my above posts. The bolt is a 1/4" x 8" carriage bolt. The shaft attachment is a 5/16" arbor attachment from McMaster-Carr:

http://www.mcmaster.com/#arbor-adapters/=up3sxh

The arbor attachment stud is threaded to accept a chuck, which I have been spending hours trying to find (ref 1), as it has been misplaced here at home.

My reliable but expensive (ref 2) machinist did the machine work. I am now waiting for the electronic components to arrive. These will be used to assemble the motor driver/controller per diddi's schematic. I will have speed control but no rpm readout. That may come later.

References:
1) "And there will come a time when fathers will not be able to find things that were on hand as recently as 6:30PM the previous day." Python, Monty, Life of Brian

2) Cost disclosure is prohibited due to embarrassment.

Magpie - 26-11-2014 at 13:42

Here's another progress report on my stepper motor stirrer project.

The motor driver electronics have been prototyped on a breadboard and tested successfully as shown in the link below. The pulse rate shown is the lowest setting (6v) with the pot turned fully ccw. With the pot turned fully cw (12v) the pulse rate is too rapid to see, ie, the lights are just continuously "on."

With the exception of the added LEDs and and their respective 680Ω dropping resistors, the circuit is that provided by diddi in one of the above posts.

https://www.youtube.com/watch?v=xD-XZukfib0&feature=yout...

[Edited on 26-11-2014 by Magpie]

diddi - 26-11-2014 at 17:12

you will need to alter the capacitor I reckon. it can be a bit hit and miss I am afraid, and I tend to experiment with values.
I will have a look a bit later today and see what might be a good change.

diddi - 26-11-2014 at 17:49

cant access video. could you post a pic plz

Magpie - 26-11-2014 at 22:50

Here's a couple pictures. The ground bus is the top row. The 5v bus is the 2nd row down. The 12v bus is one row up from the bottom row. If these pictures aren't adequate I'll take some more tomorrow when I can get more light.

I hooked it up to the motor this afternoon. The rpm was variable from 9.2 to 46. As varmint predicted it goes through about 3 really rough spots on the way up (high vibration). But this should not be a problem for the planned application. I measured the voltage at the 1st lead from the left at the driver. It was 2.5v at 9.2 rpm and 3v at 46 rpm. The pot position at 9.2 rpm is full ccw and at 46 rpm is about 90% of full cw. Above that the motor stops.

I will post another YouTube video tomorrow showing the mixer in operation. I'm thinking now that it would be useful to be able to reach higher speeds, say at least 200 rpm. The torque is very good, at least at the speeds attained so far.

Can't you get YouTube where you live?

[Edited on 27-11-2014 by Magpie]

diddi - 27-11-2014 at 02:24

what is the value of the capacitor to the right of the 555
the motor stopping is the problem a referred to about the 555 freezing up. the 22 ohm resistor should have stopped that.
oh and the LEDs will appear constantly on because the circuit design does not have the "clock" pulse from pin 3 set at 50%on/50%off (the "Duty cycle") it is more like 99%/1% so LEDs appear on always. (needs more components to get 50% duty cycle

[Edited on 27-11-2014 by diddi]

[Edited on 27-11-2014 by diddi]

Magpie - 27-11-2014 at 08:38

The value of both capacitors is 47µF. All components are per your schematic.

Varmint - 27-11-2014 at 09:27

Magpie:

At the upper speed limit, does the motor continue to whine with pulses, or is this the 555 locking up and failing to provide pulses as /Diddi describes?

If there is whining still present, then the reason for stoppage is the drive not being able to counteract the stepper inductance.

Another source of trouble with steppers is related to their "need" the reach the next step cleanly and quickly. If the load will not allow a step to the next position rapidly, then the motor can get locked up in mid-step so to speak, where the next phase change doesn't happen at the proper time with regard to the angular position, so suffering a loss in torque.

In general, the best approach is to keep the mass to the minimum possible, but beyond that the ideal solution is to use a flexible coupler with elastomeric inserts (rubber or synthetics). This allows the motor to index solidly to the next position, (compressing the insert), and the insert then moves the load. This decoupling of the load dynamic requirements can help quite a bit, but beyond this we are again moving into territory where enhanced motor drives become a requirement.

You mention the costs might be getting a bit high, I'm not sure what high means in context, but industry bought couplers can be very expensive (especially from McMaster-Carr and the like ) and pretty soon you have a setup costing hundreds, yet still nowhere near optimized. For optimal motor drive you might want to look at something like this:

http://www.geckodrive.com/geckodrive-step-motor-drives/g250x...

Coupled with an appropriately selected power supply, this drive (the cheapest Gecko offers) is still full featured enough to drive your motor to its fullest potential. For your purposes, you can set the rotation to fixed CW or CCW, the simply provide step pulses to set the speed.

All the best, and Happy Thanksgiving!

DAS

Magpie - 27-11-2014 at 10:55

Quote: Originally posted by Varmint

Magpie:

At the upper speed limit, does the motor continue to whine with pulses, or is this the 555 locking up and failing to provide pulses as /Diddi describes?

If there is whining still present, then the reason for stoppage is the drive not being able to counteract the stepper inductance.

Thanks Varmint and I will get to your questions as soon as possible. Right now I'm trying to placate my wife as she is being a major grump because it's Thanksgiving and I'm still working on my projects. The above photos show the stepper motor stuff all over the kitchen table. Luckily we have been invited to my son's in-laws for the Thanksgiving meal!

Quote: Originally posted by Varmint

All the best, and Happy Thanksgiving!

DAS

Thanks and the same to you.

Magpie - 27-11-2014 at 15:52

Here's a video of the stepper motor operation through its full range of speed: 9.2 to 46 rpm.

https://www.youtube.com/watch?v=bXObV1q-FzQ&feature=yout...

diddi - 27-11-2014 at 15:55

it says the video is private

Magpie - 28-11-2014 at 14:51

The YouTube videos below should be available to the public now. My error was in not toggling the "publish" button following the uploads. Let me know if you can't view them.

http://youtu.be/xD-XZukfib0

http://youtu.be/bXObV1q-FzQ

If anyone knows how I can increase the top speed (46 rpm) significantly without spending more than $25 please let me know.

Varmint - 28-11-2014 at 20:39

OK, that was a textbook demonstration of the symptoms I tried to describe regarding driver issues.

Where it lost solid direction and stuttered around "hunting" to get back in sync is exactly where the drive voltage became insufficient to counteract the inductance of the windings. What is not immediately clear is if the fully stopped condition at the end was still energized, or if it had in fact locked up the 555 and pulses were no longer being generated. It would be an interesting coincidence that the highest frequency to maintain synchronous stepping just so happened to coincide with the highest frequency before the 555 latched up.

So, the only thing for certain at this point is you need a higher drive voltage to the motor, and perhaps a power supply with a more robust current capability as well. But what I can promise is you won't be getting much higher speeds without very significant driver changes, it's simply the nature of the beast. The motor you are using should be capable of several hundred RPM at a minimum with a good driver (and adequate power supply), so your only real solution is to invest in the driver I mentioned, or abandon the stepper approach entirely.

Please don't be tempted to try an Arduino with a stepper shield or any other approach, you need a quality driver. That is to say, if you were to use an Arduino and a typical low-dollar motor shield, you will still be plagued with an upper RPM limit in the range you are currently seeing, the trick lies in a purpose built motor driver that modifies the pulse duration and modulates the much higher drive voltage (and thereby current) required to achieve high speed operation. Again, for a quality driver you can expect to need a minimum of 4X the motor "rated" voltage, and sometimes up to 20X! All of this is explained well on the Gecko site, so even if you choose not to use their driver, you might want to read up on how steppers need to be driven, if not just for the learning experience, perhaps future applications.

I have two stepper stages that were used to perform final focus of laser diode lens assemblies, they exhibit very fine control (400 steps per revolution driving a 10 turn per inch precision ball screws). The motors are rated at 3.6V and 2.8A per phase, yet their drivers are supplied with 48V from a very stout supply, or 13.33x the rated motor voltage! If you tried to run them of a simple switched 48V they would draw huge amounts of current to the point of destruction. Again, the driver in use is "intelligent" and modifies the step waveforms and dynamically throttles the current to allow the motors to perform well, and remain cooler than if they were driven from a simple h-bridge running at the "rated" current and voltage.

I know a great deal of this seems counter intuitive, but steppers are really quite hard to drive when large variations in speed and torque are required. It all stems from the inductive reactance of the coil windings, and there are no simple solutions unfortunately. I've achieve speeds of 100RPM with a simple H-Bridge, but the torque was woefully inadequate for driving much more than the motor shaft itself.

DAS

Varmint - 28-11-2014 at 21:06

http://www.geckodrive.com/step-motor-basics

Link to Gecko's stepper motor basics.

DAS

Varmint - 28-11-2014 at 21:18

https://www.sparkfun.com/products/11876

This is what I would consider the absolute minimum driver that attempts to address the difficulties of driving stepper motors. The current capability is pretty low, but it does offer some modulation capabilities that might extend your RPM capability. There are similar products from other manufacturers, but none of these cheaper units address ALL the issues encountered when attempting to extract maximum performance from a stepper.

Best of luck.

DAS

Magpie - 29-11-2014 at 08:12

Varmint thanks so much for that very complete and well written analysis. I now have some fundamental decisions to make, ie, do I want to put the money needed into this to make it a truly useful high torque-low speed mixer.

The torque is excellent and this is what is driving me to complete the development work. But I also have another problem to solve not mentioned so far: shaft wobble. But this is not an electronics or motor problem. The stepper motors I salvaged from the copier all have a gear that is press-fitted to the shaft. My machinist tried to remove this with a puller but was unsuccessful - his puller didn't fit right. So we just left it on and secured the collar with a set screw. This does not give the near perfect shaft alignment that is required to prevent wobble. The gear threads are worm configuration and this makes things worse.

I will publish one more video showing the mixer stirring a table salt slurry.

If I purchase the gecko motor driver ($19.95) could I still use the remainder of my existing electronics? Or would I need a new circuit?

Varmint - 29-11-2014 at 11:17

The cheapo $19.95 driver is from Sparkfun. Yes, it should work fine, the clock pulses from the 555 will do nicely.

Keep in mind this doesn't address any of the resonance issues. You would normally run in microstep mode to reduce or eliminate resonance at slow speeds, but as you need to increase speed, circuitry would switch the driver to full step mode. This driver won't do that by itself, which is why I say this is still a sub optimal approach.

In te past I've used several methods to remove stuck pulleys, splitting the side parallel to the shaft with a dremel cutoff wheel then using a screwdriver to pry the slot wider works well. Another for aluminum and plastic pulleys is to crush the pulley with a shop press (the assumption being the motor shaft is far harder than the pulley material). Rotate 90 degrees and crush again, repeat, before long it'll be loose as a goose.

DAS

Magpie - 29-11-2014 at 13:07

Thanks for those suggestions on removing the worm gear. I'm going to first consult with my machinist but I have a Dremel and should be able to remove the gear as you say.

Here's a picture of the salt slurry in a 500 ml RBF. In the movie I'm stirring that slurry easily with the stepper motor.

https://www.youtube.com/watch?v=gHf0w4nliUY

Right now I'm using a 12vdc power source. If I increase this to a higher voltage to get more speed, say 35vdc, will the Sparkfun driver and my remaining electronics still be adequate?

Varmint - 29-11-2014 at 13:17

Frankly I'm surprised it's driving all that mass as well as it is.

I don't really know much about the sparkfun driver other than they are popular in the DIY CNC crowd, being a mid-ground between a bare h-bridge and an advanced drive like the Geckos and others. I notice a current limit pot, and I'm sure you can find info on their site regarding suggested voltage and current control settings.

Seems like a friendly community on their forum, please take the time to ask questions there before diving in.

DAS

Varmint - 29-11-2014 at 15:38

Hold the presses, describe the driver chip you have, I think you can improve it with a little bit of effort.

Magpie - 30-11-2014 at 12:04

Here's the one I installed:

http://www.ebay.com/itm/121427026317?_trksid=p2060778.m2749....

I think I have the shaft wobble problem solved, once I get that gear cut off the 5mm motor shaft. I just ordered a 5mm x 3/8" shaft coupler from 3D Printer Webstore. By using a 3/8"-24 ss partially threaded bolt I should have a good connection. The aluminum coupler is spiral cut to compensate somewhat for misalignment.

My motor is a Minebea 17PM-J type so is a custom motor and there are no published speed-torque curves that I could find (I have written to Minebea to see if they can divulge this data). However, in looking at the data for 17PM-J149U which I feel is likely close in specifications (my motor weighs 300g, is unipolar, and is rated for 1.14 amps). The speed-torque curve for this motor shows a torque of 250 mNm at 0 Hz which does not drop off until 1000Hz.

http://www.eminebea.com/content/html/en/hybrid_list/pdf/17PM...

I calculate the rpm at 1000Hz as follows:

1000Hz = 1000/200 rev/s = 5*60 rev/min = 300 rpm

Even at 600 rpm (2000 Hz) the torque has only fallen off to ~225 mNm.

[Edited on 30-11-2014 by Magpie]

Varmint - 30-11-2014 at 12:31

OK, forget the sparkfun driver, you have an equivalent.

The thing to do is to raise the voltage incrementally to see how far you can take it before heat becomes an issue for the chip or motor.

Did they provide any instructions for setting the current with the small pot?

In any event, you already have the middle-capability driver, I'm sorry for not paying more attention earlier.

Magpie - 30-11-2014 at 13:02

Quote: Originally posted by Varmint

The thing to do is to raise the voltage incrementally to see how far you can take it before heat becomes an issue for the chip or motor.

What do you mean by "raise the voltage?" Ie, do you mean use a higher supply voltage than the current 12vdc, or do you mean turn up the big pot? I have already turned the big pot up until the motor stops at ~90% of its cw travel.

Incidentally I think this big pot is a 2k rather than the 20k I ordered.

Quote: Originally posted by Varmint

Did they provide any instructions for setting the current with the small pot?

No instructions were provided. I notice there is a very small screw on the driver board. Is this the "small pot" you are refferring to? I have not touched it and do not know at what position it is set.

Quote: Originally posted by Varmint

In any event, you already have the middle-capability driver, I'm sorry for not paying more attention earlier.

No problem. I have not ordered any new drivers as yet.

[Edited on 30-11-2014 by Magpie]

[Edited on 30-11-2014 by Magpie]

[Edited on 30-11-2014 by Magpie]

Varmint - 30-11-2014 at 13:30

OK, you should have a power supply providing juice for the 555 and the driver board.

Thje driver board has and onboard regulator so it's logic runs at 3.3 or 5V, and I'm not sure if that is fixed, or a user switchable option. In any even, you want to increase the voltage to the driver board, so it can in turn provide higher voltage to the motor.

Since the motor is an inductive reactance, when you apply a higher voltage, the motor doesn't really "see" this higher voltage (so to speak) until the current stored in the inductor builds up on it's way to saturation, and this is where the current adjust pot comes in.

It works (the tiny pot that does resemble screw I suppose on the driver board) by providing a reference to what current the motor is "seeing" as sensed by the current sense resistors on the driver board. When it reaches the peak allowed current, the driver will modulate the step pulse width so excess current is avoided.

As an experiment, you can leave your supply voltage at 12V, and vary the position of this pot to see if you can reach a higher peak RPM. Note a smooth steady increase in frequency (from the pot controlling the 555) will result in higher attainable speeds, you will have little luck trying to start at high speed.

You will probably find higher driver voltage is required, and you might even want to try tweaking the tiny pot to see if it can improve the speed further with each increment in supplied voltage. At some point vibration naturally disappears since the motor isn't really trying to stop and start with each step, but carried through to the next position by the flywheel effect of the attached mass.

DAS

Magpie - 30-11-2014 at 14:18

I set 555 pot at low speed then turned the pot on the board. At first it seemed to increase in speed. So I slowly turned the 555 pot up to get maximum speed (just before cutout). I measured the speed to be 48 rpm. The previous high was 46 rpm - so no significant increase this way. At present I do not have a higher dc voltage supply than 12v. When I can find one I will run more tests. I see the board is rated up to 35vdc. Any other suggestions at this time?

Varmint - 30-11-2014 at 15:58

Now keep in mind you said the highest speed it attained was near the limit of the pot, meaning the 555 as presently configured can't provide the needed higher frequencies. Try changing the timing cap to 1/2 it's present value, this will double the highest frequency

Beyond that, no other suggestions, you are still in the zone where the applied voltage is unable to "work past" the inductive reactance of the motor.

Magpie - 30-11-2014 at 16:28

Quote: Originally posted by Varmint

Try changing the timing cap to 1/2 it's present value, this will double the highest frequency

OK, I'll try that. Is that the cap across pins 7 & 8?

Varmint - 30-11-2014 at 16:58

Yes, but I'm used to seeing different wiring for astable 555's.

http://home.cogeco.ca/~rpaisley4/LM555.html#3

Magpie - 30-11-2014 at 18:53

Yes! Replacing the 47µF with a 22µF cap at pins 7 & 8 yielded an rpm of 100!

It is not whining so loudly anymore, in fact I can barely hear it.

The span on the big pot has been decreased. Does this mean I could use a smaller pot? It seems it was serendipity that Digi-Key sent me a 2k pot instead of the 20k pot that I ordered.

Quote: Originally posted by Varmint

Yes, but I'm used to seeing different wiring for astable 555's.

Just tell me how to reconfigure to what you recommend.

[Edited on 1-12-2014 by Magpie]

Varmint - 30-11-2014 at 19:53

Usually the cap goes from pin 6 (threshold) + 2 (trigger) to ground (pin 1), using it tied to VCC (pin 8) obviously works, but operates on a different slope than the "traditional configuration". Take a look at the link I provided, you are interested in the astable configuration.

As the frequency rises the whining naturally falls off simply because the motor isn't efficient as an audio transducer (yay!), it has too much mass. Also, the attached mass and the associated flywheel effect tends to smooth things out as well, so the reduction in sound level is entirely expected.

So, you can keep reducing the size of the cap, knowing it also increases the minimum frequency (speed). So far as your frequency control pot you'll want to make the total resistance the same or better yet larger in order that while you reduce the cap for higher frequency, the low end setting still offers a workably slow speed.

There are many websites discussing the 555, some will provide a calculator where you input the minimum and maximum desired frequency, and it will tell you the ideal values for the pot, resistor, and cap in astable operation.

I'm concerned you say the pot range is reduced, but once you configure it for more traditional astable wiring, then it will make more sense to try and troubleshoot.

Magpie - 1-12-2014 at 10:29

More good news: by replacing the 22µF cap with a 10µF cap the maximum speed has been increased from 100 to 200 rpm! The speed range is continuous from 44 to 200 rpm. If it was any faster I would need a tachometer to measure it. Also the 2k pot span is good from full ccw to 90% of full cw.

I will take a look at the link you gave to calculate the resistors and capacitor values for the astable 555 condition. There's also a good description of the 555 timer IC on Wikipedia.

I'm going to work on cutting off the gear on the shaft now. When the new coupler arrives I will make a movie on stirring salt at 200 rpm.

Magpie - 1-12-2014 at 19:56

The gear came right off the motor shaft by making 2 longitudinal cuts with the dremel cut-off wheel. Thanks very much for this tip, Varmint.

I've been playing with the calculator for the astable oscillator circuit for the 555 found here:

http://home.cogeco.ca/~rpaisley4/LM555.html#3

With the cap set at 10µF and R2 set at 22Ω the following frequency and duty cycles result:

R1 = 690Ω
Hz = 197
duty cycle = 97.0%
speed = 59 RPM

R1 = 30Ω
Hz = 1950
duty cycle = 70.3%
speed = 585 RPM

The 59-585 rpm speed range could therefore be achieved by using a pot at R1 covering the range of 30-690Ω.

However, on the calculations page there is this statement:
"R1, R2 -- MINIMUM = 1K."

When values of 1K or greater are used sufficient frequency cannot be achieved. Eg, at R1=R2=1K the frequency is only 48Hz and the RPM 14. It just gets worse as R1 and R2 are increased.

Therefore, I am hesitant to reconfigure to this more "normal" configuration.

Is this right, or am I missing something?

[Edited on 2-12-2014 by Magpie]

Varmint - 1-12-2014 at 20:14

Simply reduce the cap again! You probably needn't concern yourself with duty cycle, I expect the driver input is only looking for a rising or falling edge.

Looks like you are about to nail this, don't forget to fine-tune the driver current reference pot, and higher RPM is waiting with an increase in voltage to the driver when you get the clock input high enough frequency.

Magpie - 2-12-2014 at 13:47

You are correct. The astable oscillator model gives 600 rpm when the cap is around 0.25µF and R1=R2=1000Ω. With R1=7500Ω the speed = 203 rpm.

I am going to reconfigure and try it with R1=R2=1000Ω. The only 0.22µF cap that my local store (RadioShack) has is a polyester film type (50WVDC). Is this type OK? It has no polarity. The caps I have been using are electrolytic with polarity. If not, I will have to get one by mail order.

Varmint - 2-12-2014 at 15:38

Non-polar is perfect. Only reason electrolytics are polarized is the correct polarity creates an ultra-thin insulator between the two plates (foils) which gives the comparatively large capacitance for the size. The art is always advancing, but at one time even the 0.22uF was pretty sizeable. Other than that, a cap is a cap so far as the timing circuit goes.

Don't forget, there is no reason to limit the low speed to something higher than you'd like, you can of course get lower speeds by making the proper resistor larger. There will come a point where capacitor leakage will limit the slowest attainable speed (while still having a respectable high end), it's all a balancing act of sorts, but several decades are easily in reach.

Magpie - 2-12-2014 at 15:46

Great. What I will try then is R1=10k, R2=1k, and C=0.22µF. This should give me 182 rpm.

Varmint - 2-12-2014 at 17:19

Try this:

Capacitor 0.033uF from pins 6+2 to Gnd. (Pin 1)

Fixed resistor 1K from 6+2 to pin 7.

10K from pin 7 to one end of a 1 Meg pot setup as a rheostat (wiper connected to one end), the other end of the pot to Vcc (Pin 8).

The pot minimum setting (max frequency) then should be around 3500Hz or 1050 RPM.

The pot max setting (lowest freq.) should be 35Hz or so, or about 10 RPM.

This gives you a very wide practical range with no more experimenting, and lets you focus on drive voltage and current pot settings to tune the actual useful highest speed.

DAS

IrC - 2-12-2014 at 17:33

Magpie just so you know the 1K is not absolute although I agree with the recent posts by others. The reason for not going too low for this value is easy to see. Pin 7 is an open collector. It's purpose is to discharge the timing capacitor. If the value is too low pin 7 will try to drag the supply voltage down causing the internal transistor to fail. Look at these circuits I found somewhere online, they are useful in understanding both how the IC works as well as how to use it in circuit design.

Astable Multivibrator Using IC 555 Circuit.jpg - 14kB

Reading my post again I should clarify what I mean by 'the 1K is not absolute'. It does not need to be 1K, but it does need to be large enough to limit current flow from Vcc to ground through the internal transistor to a safe maximum. Meaning one also considers what voltage Vcc is. Another idea if duty cycle is important (in circuit above it varies with the ratio of R1/R2 as you vary frequency) is to use a dual pot with the addition of the current limiting resistor between pin 7 and Vcc when the pot is at its lowest value in rotation. A small bias to the ratio is created by this resistor. If it was in a circuit where it is important the value could be halved using two resistors (say a pair of 470 ohm), one in series with R1 and the other with R2.

[Edited on 12-3-2014 by IrC]

Magpie - 2-12-2014 at 18:46

I just finished the reconfigure and a successful test using the components I listed in my last post. I measured the rpm at 177 which compares well to the predicted 182. Actually this is an educated guess as the spin rate is too high for my old eyes to follow with any accuracy.

I'm not planning on increasing the supply voltage from the currently available 12vdc. It is doing the job and I have incurred no cost in getting it as it is salvage from my old Gateway PC.

[Edited on 3-12-2014 by Magpie]

Magpie - 2-12-2014 at 22:08

Here are my assumptions for a final configuration:

Fix R2 at 1000Ω. Fix C at 0.22µF. Provide R1 as a 100k pot. This will provide 21 rpm at the low end. I'm going to assume that the R1 pot will turndown to 1000Ω at the high end for 729 rpm. I don't envision needing a higher rpm than this. To comply with R1 minimum =1000Ω I might have to put a stop on the pot wiper or add a fixed permanent resistance in series. I've been searching the Digi-Key website for pot specifications but they don't seem to list the turndown ratio. I don't believe the pots go to 0 Ω, or do they? Let me know any concerns.

[Edited on 3-12-2014 by Magpie]

Varmint - 3-12-2014 at 05:00

Yes, pots can and do go down to zero (or at least into the single ohms or even less), which is why I suggested a fixed resistor in series in my configuration.

Magpie - 3-12-2014 at 12:23

I installed a 100k linear pot. In testing it with my ohm meter it gave a range of 1k-100k. It ran the stepper from 21 rpm to an rpm that by eye/stopwatch was 218 rpm. By wiper travel (270°) and resistance measurement using the model it was 156 rpm. Beyond that the motor stopped. Full wiper travel is 310°.

Is this limit a function of the supply voltage?

Varmint - 3-12-2014 at 17:42

I'd be tempted to say your 555 might be going flakey, do you have the Reset pin (4) tied to Vcc, and the Control pin (5) tied to Gnd through a 0.01uF cap? If not, please do so, these pins can cause issues, especially in the non-ideal environment of a prototyping board.

The reason I'm not jumping on the supply voltage (being too low) right out of the gate is you are already near 4x the motor rated voltage, and half the mfgrs torque test curve voltage, so I'd look for other issues first. If you can eliminate the 555 from being the source of bad signals, the next option is to try and up the voltage and see what you get.

Magpie - 3-12-2014 at 18:25

Quote: Originally posted by Varmint

I'd be tempted to say your 555 might be going flakey, do you have the Reset pin (4) tied to Vcc, and the Control pin (5) tied to Gnd through a 0.01uF cap? If not, please do so, these pins can cause issues, especially in the non-ideal environment of a prototyping board.

No, these pins are not terminated. Would a 0.022µF suffice?

Varmint - 3-12-2014 at 18:27

Yes, no problem.

Magpie - 3-12-2014 at 19:20

Pins 4 & 5 were terminated and the circuit tested. This did not make any difference. The wiper still came to the same position for peak rpm (by ear) just before motor stoppage.

I don't have any other vdc source.

The shaft coupler arrived today. I will test the mixer on a salt slurry at the new peak rpm tomorrow and post a video.

Magpie - 4-12-2014 at 14:04

The assembly was tested on a salt slurry at peak rpm (~200) and performs well. But I need to reverse the present direction of rotation, ccw, to cw, to prevent unscrewing the chuck. The present wiring is as follows:

Looking at the side of the motor, shaft down:

Left to right: yellow, skip one, red, blue, skip one, orange

Looking down on the driver with the little pot to the right:

pin 11: red
pin 12: yellow
pin 13: blue
pin 14: orange

I could experiment but thought it better to ask: how should I reorder the driver pin colors to reverse the direction?

Varmint - 4-12-2014 at 18:08

No need!

There is a pin on the driver which sets the direction, right now it is either pulled up (most likely by far), or pulled down, you simply need to change that signal to accomplish reverse.

But, if you want to do it via motor leads, move blue and orange to 11 and 12, red and yellow to 13 and 14.

Magpie - 4-12-2014 at 18:51

I can't seem to find that pin. Here's my driver. Please tell me the location of this pin.

http://www.ebay.com/itm/121427026317?_trksid=p2060778.m2749....

Varmint - 4-12-2014 at 19:13

OK, on one row of pins you have the 4 motor wires

On the other row of pins, you have your 555 output going to the 2nd pin of that row, (one pin in from the end). Direction is the first pin.

Magpie - 4-12-2014 at 20:31

I don't think my driver has that switch. I switched the wires and it is rotating cw now. Thanks.

I'll make the video now. If I don't get it posted tonight I'll post it tomorrow morning.

Varmint - 5-12-2014 at 04:20

I went back and looked at the schematic on page 2 of this thread, and Diddi shows the pin to the right of the step pin tied to ground. This is the direction pin.

If we were to number the pins based on that drawing, and treating the pinout just like an IC, pins 1 through 4 are open, 5 and 6 are tied to +5V, 7 is the step input (clock output from 555), and pin 8 is shown as grounded, this is the wire you would remove on your proto board, which would have left it pulled up by the resistor on the board, thereby changing direction.

I know the other way I tried to describe it was confusing, well, there's a reason for that. This hardware is in the public domain, no one has "rights" to it, it can be copied freely, and produced in quantity by anyone who chooses to do so. Well, a lot of these vendors don't much care about accuracy or standards, all they want is a device that will plug into a socket and take the place of a more expensive solution from the original vendor, for much lower cost, and they can do this by providing no support of any kind. This driver happens to be a knockoff of the "Big Easy Driver" I provided a link to, and is produced by a myriad of companies, another being Polulu.

Polulu's page is here, note the schematic at the bottom of the page. http://www.pololu.com/product/2128

DAS

Magpie - 5-12-2014 at 07:18

OK, thanks for that explanation. I wondered how I was able to get this driver so cheaply. When you say "pull" a pin I didn't realize that meant disconnect the pin. Now I know.

The video showing the mixer stirring a salt slurry at ~200 rpm is shown below. The slurry was made up of 3/4 cup of salt and 200 ml of water. Flask size is 500 ml.

I consider this project to be complete now and very successful. I feel that this stirrer would meet 95% of the needs of the home chemist for overhead stirring. I want to thank diddi and varmint for all the help given me. The mixer wouldn't exist without that help.

As always comments, suggestions, and questions are welcomed.

https://www.youtube.com/watch?v=G_A5uT7PpJE

Magpie - 7-12-2014 at 18:13

I recently consolidated the breadboard wiring for my stepper motor. This was done in preparation for transferring it to a perf board to make a permanent soldered assembly. The consolidated wiring is shown in the photo below. When tested the motor did not operate after the consolidation. I knew I had made some wiring mistakes but had corrected them. Assuming I had fried the 555 timer I replaced it with a new one. The motor now operates but the range has been reduced to 48-100 rpm. Before the consolidation the range was 20-200 rpm.

I have checked the wiring many times over. Is there something else I might try to get my old rpm range back?

consolidated & simplified breadboard for stirrer.jpg - 118kB

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