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Author: Subject: Building an open source hot plate stirrer - feature requests!
JJay
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[*] posted on 9-1-2017 at 07:57


Pay attention to Sulaiman; he's clearly a smart guy who knows what he's talking about.



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mux
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[*] posted on 9-1-2017 at 09:28


Quote: Originally posted by JJay  
Nah, you just think idiots will buy your stirrer if it has WiFi. We both know it would be better if it could be part of an integrated solution that could work in places with heavy electromagnetic interference such as most any heavy industrial environment; even USB would be vastly superior to WiFI. If you want WiFi, you could connect it to a controller that has WiFi. You're incredibly confused here; you're actually suggesting that allowing hackers to control your machinery and industrial processes without authorization is no worse than letting them read your cell phone contacts.

That's not the point though; the point is, WiFi is inferior. I could use a vanilla USB interface connected to a controller that has WiFi if I wanted it.

People, can we really take this guy seriously? I think he's a fraud.


I really don't follow you here anymore. Do you care to elaborate a bit more on this post? What are your exact issues?
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Melgar
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[*] posted on 9-1-2017 at 10:23


Ok, apologies if any of my criticisms weren't particularly constructive, I'll try keep the tone as constructive as possible from now on, if that helps. I'm just happy as long as you've learned some new things about motors, especially if you plan to use a stepper controller to drive it. As far as the possibility of falling back to using a motor, I did a quick search, and there are a lot of brushless DC fan motors being sold for a few bucks on eBay and Alibaba. These are basically the same type of motor as stepper motors, but typically with an average of six steps per rotation, compared to a lot more (usually) for stepper motors. Their controllers also tend to be a lot simpler, at the expense of not being able to fine-tune position as well as with a stepper, but for a stirrer, that'd seem to be an acceptable trade-off. The fan motors usually have the controller built-in, and many can be controlled on a third wire, with either a PWM signal or an analog DC control signal. Fan motors seem ideal, because they're designed to have a long life, and their speed range would be approximately what you'd want at the power that you'd want. For example:

https://www.alibaba.com/product-detail/12V-DC-BLDC-electric-...

Another:

https://www.alibaba.com/product-detail/Dc-Brushless-Fan-Moto...

As far as magnets, I got ten alnico 5 bar magnets (1.5 inches long, 3/8 inch square cross section) for like $11.50 on eBay, and the manufacturer sent me a brochure with my order, stating their manufacturing capabilities, so it wasn't just some underpriced surplus. Considering the size of the magnet in my last stirrer, I was worried these ones would be too small, but they're plenty powerful, and have no trouble turning a stir bar from 1-2 inches away. I also found a 600W hot plate at Family Dollar for $10, that's about 10 inches square, and about an inch and a half deep. It's also teflon-lined aluminum. I figured for baths, I could melt wax in it and use that for my fluid, then I don't have to worry about spilling the bath after it's cooled off. My plan was to basically control and monitor everything with an Arduino, that way the electronics are cheap and I can program in actions for any failure modes I can anticipate.

My project idea was conceived independently of yours, and the stirrer is kind of a minor part of it. Right now I'm just using a motor I pulled out of an inkjet printer and haven't had any problems with it. If it does break, I have three more.
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[*] posted on 9-2-2017 at 02:37


Well, I was meaning to post almost 2 weeks ago with the completed PCB, but I decided to wait until I had a fully assembled unit. Boy, was that a mistake. Anyway, the money shot:



That photo is dark for a reason. My milling machine really doesn't like the 4mm mill bit, so it took me a few tries before I at least halfway succeeded at milling the aluminum parts. Had to file and sand the sides by hand, which doesn't look good.

It works though, and I'll post a more comprehensive update including a video on my youtube probably before the end of the weekend.
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[*] posted on 16-2-2017 at 00:16


Royally late, but here's the video:

https://youtu.be/Kn-eLq7-Fbw
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Sulaiman
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[*] posted on 16-2-2017 at 04:20


Impressive video,
I especially liked the multi-pcb design being testable before cutting.
Most of all, YOU DID IT ! well done.

Although it works better than I expected,
I am certain that your 'electromagnets' are far from optimal,
try a simple experiment;
break the top ferrite ends off of the inductors, keeping the bottom ends and central core intact,
see if the stirring 'strength' increases.
I'm not suggesting this as a working configuration, just a test.
If you have spare inductors :D

Watching your progress with admiration ......

P.S. since the majority of the flux path is air, adding tiny gaps in ferrite makes little difference,
i.e. you can superglue together any ferrite core configuration that you fancy, or just glue together any broken pieces.
(except the core within the coil, best to be continuous rather than contiguous)

[Edited on 16-2-2017 by Sulaiman]




CAUTION : Hobby Chemist, not Professional or even Amateur
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