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Author: Subject: Building an open source hot plate stirrer - feature requests!
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[*] posted on 12-12-2016 at 12:29


Quote: Originally posted by careysub  
Quote: Originally posted by zts16  
Yeah ceramic hot plates are superior to aluminum ones for their chemical resistance alone. I would never buy an aluminum hotplate simply because I know that if I had a corrosive mixture boil over it would likely be ruined instantly.


OTOH, with a home-build aluminum top stirrer the aluminum plate could be cheaply replaced after such an incident, about $5.


What is the price for a 300mm square top for an IR hot plate?

BTW, 900 watts. The response time to a change in heat setting on this is FAST compared to the ceramic block units with internal resistance elements- kind of like the difference between cooking stove top with gas range and the slower to react electric ones.

(Can you tell I like these?)

1786-1.jpg - 161kB




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[*] posted on 12-12-2016 at 13:16


mux: Sounds great, you do appear to be the right man for this job.

Let me know if I can help. I can do metal fabrication (lathe, mill, heat treatment), calculations, CAD/blueprints etc.

[Edited on 12-12-16 by Fulmen]




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[*] posted on 12-12-2016 at 14:33


Is this Idiocy in Action or an attempt to build 1 (one) Super hotplate/stirrer ?

Sale Price, Cost, Profit !

If none of these matter, groovy.

If so, dead horse. No way to compete with the mass-producers by making something pretty much the same as they alread make on a vast scale.

In the end, they heat and stir, which is what people want.

Edit:

Definite Lathe and Mill jealousy. Gotta get me those machines.

More edit:

More the Lathe. Can do basic milling with a lathe.

[Edited on 12-12-2016 by aga]




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[*] posted on 12-12-2016 at 19:24


Honestly, I don't understand how people can get by without a decent machine shop.



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[*] posted on 12-12-2016 at 19:34


Quote: Originally posted by Fulmen  
Honestly, I don't understand how people can get by without a decent machine shop.


Creativity, hand tools, light power tools, knowing how to source ready-made dimensioned metal pieces when needed (infrequently, and rarely do more than two dimensions need to be exact) and knowing how to make things out of composites - fiberglass, carbon fiber, wood, epoxy, and doing casting/molding with various materials (polymers, sodium silicate and vermiculite/perlite, etc.).

You'd be surprised what I can do with a metal file.

Being addicted to precision machining can stifle creativity and learning.

Along these lines it is interesting to study the machines made in the early industrial revolution before the availability of precision machining. The early grasshopper steam (or beam) engines for example were made without any precision machined parts (though the piston and cylinder had to be ground to a close fit). All the parts had large tolerances, and were worked to fit when necessary.

The Wikipedia page does not discuss this interesting and important aspect of the designs origin though:
https://en.wikipedia.org/wiki/Grasshopper_beam_engine

[Edited on 13-12-2016 by careysub]




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[*] posted on 12-12-2016 at 19:45


Quote: Originally posted by aga  
Is this Idiocy in Action or an attempt to build 1 (one) Super hotplate/stirrer ?

Sale Price, Cost, Profit !

If none of these matter, groovy.

If so, dead horse. No way to compete with the mass-producers by making something pretty much the same as they alread make on a vast scale.

In the end, they heat and stir, which is what people want.
...


The key is making something does exactly what you want it to do, rather than matching up to the broad demands of a mass market.

I make telescopes because what I make, you cannot buy.

It is possible to make a piece of equipment that meets your specific needs for a fraction of what a commercial offering that would be required to do the same thing (but lots of stuff you don't need) would cost.




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[*] posted on 13-12-2016 at 01:32


Quote: Originally posted by Fulmen  
mux: Sounds great, you do appear to be the right man for this job.

Let me know if I can help. I can do metal fabrication (lathe, mill, heat treatment), calculations, CAD/blueprints etc.

[Edited on 12-12-16 by Fulmen]


There's a decent chance shipping to the US won't be possible (at an acceptable price). If the design works and a kit is designed, US 'customers' (=forum members) will need to be served from within the US, as far as they're not making the units themselves. In that case: yes.

Otherwise, I have plenty of robots to do the work for me. I don't have a lathe, but otherwise I'm fully equipped.

Quote: Originally posted by aga  

Sale Price, Cost, Profit !

If none of these matter, groovy.

If so, dead horse. No way to compete with the mass-producers by making something pretty much the same as they alread make on a vast scale.
[Edited on 12-12-2016 by aga]


This is unfortunately all too often a gross misunderstanding of how to attack a problem. If you don't set a budget, if you don't limit your design space, projects get out of hand quick. Feature creep and delay is the natural state of things.

I don't make a budget and define sale price and margins because I intend to sell, I do this to limit myself and the scope of the project to a degree that makes sense.

For personal projects, nothing matters. You just want a thing that's for you and you alone, and you take full responsibility for whatever happens. But as soon as you build something with the intent to improve the world, you HAVE to take into account the limits of your project scope and you HAVE to systematically attack the problem.

Hopefully that better explains why I'm putting so much emphasis on the design process and not necessarily the implementation details.
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[*] posted on 13-12-2016 at 02:22


I don't have a stirrer hotplate. It is (perpetually) on the list of things to get. If this gets off the ground then I would happily buy a kit. And if the design and quality is good (as seems to be the goal here) then I am fine with paying a bit of shipping.

I would probably never use wifi or bluetooth but good temperature control would be great. And the ideas floated for stirring sound fantastic.




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[*] posted on 13-12-2016 at 04:34


Quote: Originally posted by mux  
There's a decent chance shipping to the US won't be possible (at an acceptable price).

I wasn't really thinking of manufacturing kits, but as I am very interested in the stirrer I could at least build some prototypes for R&D/testing.

In fact I was contacted by an acquaintance who sells brewing supplies regarding the possibility of making stirrers units. If this produces any results I might be able to sell some through him.




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[*] posted on 13-12-2016 at 05:32


The oval stirbars are only for round bottom flasks, they must be a smaller radius than the flask in order to stir well, so that they spin on the center only. That is why most rbfs have a scratched area right on the center bottom. The straight rods ones work fine for most beakers and erlenmeyers, the hexagonal ones simply have a slightly more surface area but there is no real difference. But having a center pivot ring (larger diameter in the center) simply lifts the rod off of the flask, except at the center, creating a bearing of sorts to rotate on, that helps some, mostly when stirring a suspension or slurry.

There are also many various odd ones, crosses, discs, windmills, and such, some of them work well, but many are hard to drive without a good stirrer.

If anyone is looking for a used stirring hotplate, I do have a few that I have finally found and finished testing, almost all are Corning models. I will post some photos soon, when I get a moment of time. I am trying to repair some of the broken ones as well, but also have some that could be parts donors for people who want to play with them. So if you want to play with a broken one, I can sell them for cheap, mostly just the shipping costs. Just send me a u2u if you are interested, but I may be slow to answer, as this is a very busy period for me, so please be patient with me.
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[*] posted on 13-12-2016 at 06:00


Would be nice to have a couple of random stir plates to learn from. I'd be happy to take them off your hands. I'll send a U2U.
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[*] posted on 14-12-2016 at 15:09


I would be interested in buying a used hotplate stirrer. What would you charge?
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[*] posted on 15-12-2016 at 01:34


We're not nearly there yet, first it has to be designed, then it has to work, then we can think about selling :)
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[*] posted on 15-12-2016 at 11:17


I'm assuming he was talking about Dr. Bob's offer, something that should be taken in private.



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[*] posted on 16-12-2016 at 13:12


Well, I guess you can chalk that up to my growing problem of misinterpreting forum posts. Nevermind.

Tiny status update: I've set up a little experiment with an Allegro A4983 stepper board (custom 3d printer control board I built a long time ago) and four 300-winding solenoids. The results so far are... let's just say that this could be an entirely new, exciting product called the Mixture Basher!

https://www.youtube.com/watch?v=6touhF9ISHE

I don't have a proper stir bar handy at the moment, and these hard disk magnets don't really have such well-defined magnetic fields. That really exposes some centering issues. Even if I can get it to properly rotate, it's a bit stop-start.

Also, this is already with ~300 turns per cm. I can maybe pull off twice as much, but that's about the max. Input power is 10W now, and although it's easily strong enough to stir low-viscosity liquids, it's not going to do anything beyond the consistency of cordial.

I mean, you can't expect much progress to be made in a week, but it's already clear that this is going to need a ton more experimenting.
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[*] posted on 16-12-2016 at 13:41


Did you see this post: http://www.sciencemadness.org/talk/viewthread.php?tid=3056&a...




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[*] posted on 16-12-2016 at 13:47


I've been browsing and cataloging various different projects, but hadn't encountered that thread yet. Thanks!
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[*] posted on 16-12-2016 at 15:15


From the looks of it you might need to focus the field more, how were the magnets arranged?



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[*] posted on 17-12-2016 at 03:12


I 'focused the field' of two hard drive magnets by placing two cylindrical magnets on them where I wanted the field to be. They were neo magnets as well.

I expect they will use the field from the flat hard drive magnets to make them stronger. Now the field that gets up past the plate is in two spots and quite strong.

My commericailly made stirrer uses just a normal fan motor, generic sort, like from a microwave oven (easy to get) and it uses a wire wound rheostat to control the revs/speed of it. Does not make sense to me how it works but it does.
The magnets are 1/4 inch dia by 1 inch, mounted vertically in a 1 1/2 inch dia by 2 inch long Aluminium slug/cylinder that's mounted on the fan motors shaft.
It has no hotplate.
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[*] posted on 17-12-2016 at 12:53


Quote: Originally posted by Fulmen  
From the looks of it you might need to focus the field more, how were the magnets arranged?


20mm from the center, no iron core, perpendicular to the surface. No real attempt to focus or direct the field in any way.

I have to stress, again, this thread is now just a little work log of progression on the project. Don't expect good results in every post I make :)

Quote: Originally posted by eesakiwi  
I 'focused the field' of two hard drive magnets by placing two cylindrical magnets on them where I wanted the field to be. They were neo magnets as well.


I'm going to try to use straight inductors first; they have a ferrite core and a decent amount of windings, would save me a lot of manual winding. The only downside would be that the hot plate would be slightly magnetic even when you turn off stirring.


Quote: Originally posted by eesakiwi  

The magnets are 1/4 inch dia by 1 inch, mounted vertically in a 1 1/2 inch dia by 2 inch long Aluminium slug/cylinder that's mounted on the fan motors shaft.
It has no hotplate.


A big reason why this wouldn't fly in my design is the fact that there is a (500C) hot plate on top of the stirrer unit. Any kind of motor would perish pretty quickly in that sort of environment. Unless you seal and cool it, which costs money, adds complexity, etc. etc. yada yada

[Edited on 17-12-2016 by mux]
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[*] posted on 17-12-2016 at 18:14


Quote: Originally posted by mux  
Don't expect good results in every post I make :)


Unacceptable! I DEMAND progress :P

Without an iron core your results are much more understandable, the magnetic permeability of air is far to low to produce an effective magnet.




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[*] posted on 23-12-2016 at 05:58


Alright, another non-update unfortunately.

I ordered various items to test with more than a week ago (from the UK, so I expected quick delivery). Unfortunately, nothing has arrived so far and I'm now entering the holidays and all that. Long story short; probably no updates until halfway through January.

The good news: I have experimented with various ferrite-cored inductors, and those do give me well-defined rotation as well as very good torque. I'm pretty sure that as soon as I have some big stir bars, I'll be able to verify that it works well enough and get going on a proper design.
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[*] posted on 23-12-2016 at 07:25


That's encouraging news, keep up the good work. Have you tried the configuration that kmno4 used or simply 4 separate magnets? If so you can expect a further increase in torque.



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[*] posted on 24-12-2016 at 01:56
Hotplate Stirrer Design Project


I think this is a cool project, however, I think you're probably way low on the actual cost, although I hope you can do it. R&D is expensive!

I'm happy to lend a hand in what I can do. I've designed thermocouples, data loggers, and power supplies. My latest one was on the MAX31856 which is quite honestly one of the chips I'd recommend for your project. It's low cost comparatively, and digital. It also accepts external cold junction sensors which is quite ideal for a project like yours. 0.007*C resolution too! (Yes, that's 0.007!)

I know you're thinking solid state stirrer but you have to think about power consumption as well. Instead of stepper motors check out some brushless motors especially with the advent of camera gimbal systems. They can rotate very slowly, and can carry some torque!

On the WiFi side you also have to consider emissions tests which will add quite a bit to your project. One of my big concerns is the safety with making a mains connected kit. Most "kits" don't consume these levels of power so you have to factor that into your end project. What you might be able to do though is separate the project into modular blocks. This way you can keep the high power side isolated from the others and then you can sell the other half of it without having to require safety testing, emissions, and so forth as long as it's sold in kit form.

I can CAD, program embedded systems, and might be able to assist with some machining as well.

With all that said good luck!!! I'll be keeping an eye on this project and wish you the absolute best. I look forward to seeing your prototypes and how this progresses. Sounds like everyone here including myself is more than willing to help out in any way that we can!




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[*] posted on 24-12-2016 at 02:50


I suppose we have almost perfectly overlapping competences, so that would make for a great schematic/mechanical design/BOM checking buddy. I'll happily use your expertise for this project!

As for the cost side of things; It's pretty simple: that's a requirement, so I won't go over it. I've back-of-the-enveloped it to work and I'll just tweak the details to actually make it work if some kind of cost setback arises. If it doesn't work then the project just crashes, because I honestly don't see good value in a $200+ unproven, random-guy-made-it hotplate stirrer. I'd make one for myself obviously, but that's it.

As for the stirrer: Solid state does significantly up the power requirements, which may be the biggest issue. Unfortunately I don't see this working at all with a moving solution, as
1) I cannot get second suppliers for any motors that would reasonably fit and have suitable voltage requirements, torque and connection schemes. Not having a second supplier is fine for one-offs, but kills a series-produced project.
2) It's a very easy point of failure, and due to the nature of the project I'm pretty sure that some single-supplier motor will not be available by the time your stirrer fails, nor will I be around to help you (I intend to, but from a user perspective this project should be robust enough to allow for me to disappear)
3) How do I guarantee safety in flammable/explosive atmospheres? I can't pot a motor. Brushed motors are immediately disqualified, meaning I need to throw in a frequency drive as well. It's a bit of a rabbit hole. Of course you should buy intrinsically safe equipment if you do this, but let's be honest. People are going to generate H2 near this thing, and that has an explosive mix at like 5-95% concentrations.

For such a small project where I don't have the luxury of ordering specific motors with a reasonably far-out backorder option (e.g. 10 years), it's a much less maintainable option as well as just having mechanical issues. Motors are almost definitely also going to be more expensive. Of course I know that power consumption, consequently heat dissipation as well as magnetic field strength is going to be poorer with solid state, but there are a lot of compelling reasons for me to try solid state first.

Fulmen: I'm still using straight up magnets, now with a ferrite core, no further concentration or field shaping efforts. Ideally I would just use off the shelf inductors as much as possible (because that would mean no custom parts necessary, which is awesome).

Edit: forgot about the wifi emissions thing. Yes, that's definitely the biggest cost. I do power supply design for a living, so I can handle the AC safety issues, but I don't have an anechoic chamber or proper spectrum analyzers/antennae/etc. to do emissions testing. I do have a testing facility I can use, but that would run about €1000 for a full test suite. Maybe I can call in a favor or something, we'll see. Depending on actual cost, I might opt for a pre-certified wi-fi module instead.

[Edited on 24-12-2016 by mux]
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