Magnetic Stirrer Project Reset

[eccerr0r]

Re: Magnetic Stirrer Project Reset

the positioning of your coils are probably not ideal for the pill. The magnetic fields visible to the pill are everywhere, unlike a real stepper where the fields are very compact and close to the magnet.

real stepper motors' steps are usually like 1/100th or 1/200 of one turn. Your step is 1/4 or 1/8 of one turn, this is huge difference that needs to be accounted for. Or you could make your stepper more like a real stepper - you can do this by putting in more coils.

[EasyGoing1]

Re: Magnetic Stirrer Project Reset

Use two STK stereo audio power amplifier modules, chinese clones will work too. This is your "linear amplifier". To make it easier to understand, use the two amplifiers inside each of the modules in "BRIDGE" mode, and you have your H-tree.

Again, this is dumb. What you're building is a stepper motor and we don't care about the "snapping" - at low speeds sure you'll see this happening but as the speed increases, the fluid you're mixing will dampen the snapping and it will go away. You could even put in more electromagnet poles to smoothen the turn and also increase torque due to the poles being closer together.

That being said - you're making a stepper motor - there are plenty of stepper motor drivers out there that you can use that have built-in H-trees. They even have step timing built in so you don't even need to worry about that.

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heck, if you really want to drive sinusoidally, get two class D stereo [subwoofer] audio amplifiers and run each module in bridge mode, Solves the power consumption problem too...

I have different stepper motor drivers, my favorite being the DRV8825, and I did test it many times using different libraries and even direct manipulation of the pulse pin but I could not get the pill to do anything other than jump straight off the platform and I'm not sure why.

I just assumed that it was designed to pulse stepper coils in a way that works for them but for whatever reason, it won't work for this application.

I guess I should look at the output of the stepper driver on a scope and see what it's actually doing ... because using a stepper driver would be ideal.

[EasyGoing1]

Re: Magnetic Stirrer Project Reset

what is wrong with using a motor like one i worked on recently ?

I've already built one with a motor and the strongest neodymium bar magnet I could find and I attached it to the shaft of the motor etc. The problem with that setup is that the magnets are not strong enough to keep the pill tracked to the bar magnet while it's spinning through the solution, which is a thick solution. It worked fine for water or things of that viscosity but as soon as the solution that i was mixing got thicker. the pill would just jump around.

So if I use electromagnetics, I know I can create a magnetic field stronger than an earth magnet which should easily keep the pill pulled down tight while its spinning.

[eccerr0r]

Re: Magnetic Stirrer Project Reset

Use two STK stereo audio power amplifier modules, chinese clones will work too. This is your "linear amplifier". To make it easier to understand, use the two amplifiers inside each of the modules in "BRIDGE" mode, and you have your H-tree.

Again, this is dumb. What you're building is a stepper motor and we don't care about the "snapping" - at low speeds sure you'll see this happening but as the speed increases, the fluid you're mixing will dampen the snapping and it will go away. You could even put in more electromagnet poles to smoothen the turn and also increase torque due to the poles being closer together.

That being said - you're making a stepper motor - there are plenty of stepper motor drivers out there that you can use that have built in H-trees. They even have step timing built in so you don't even need to worry about that.

---

heck, if you really want to drive sinusoidally, get two class D stereo [subwoofer] audio amplifiers and run each module in bridge mode, Solves the power consumption problem too...

[petehall347]

Re: Magnetic Stirrer Project Reset

what is wrong with using a motor like one i worked on recently ?

[EasyGoing1]

So based on some of the comments in my other posts, there seems to be some confusion or maybe some assumptions, I'm not sure exactly, so I wanted to hit the reset button on the entire discussion and make a few things clear that might not have otherwise been obvious.

First of all, the reason I post in this forum is that I simply do not have enough knowledge in electronics to do some things that I would like to do. So I post my questions in here and I try to be as thorough as possible MOST of the time, so that those of you who do take the time to respond, will be as informed as possible so that you can offer your knowledge from an informed position.

I may not always succeed in being thorough enough, or I might make a mistake in a schematic symbol ... but I assure all of you that I have no intentions on making this process difficult, nor should anyone assume that I am locked into anything that I say concerning the parameters of a given project that I'm working on.

I know enough to be what I would consider a trainee technician if my skills were to be placed into the real world where peoples money is on the line. Thankfully, I am far better with network engineering than I am with electronics, and because of that, electronics is something I hobby with and I do not use these skills for any sort of monetary gain.

That being said, I am ALWAYS open to new ideas or different ways of accomplishing what I might be trying to accomplish.

You wont hurt my feelings by telling me that I'm an idiot for trying to do something a certain way because if I weren't an idiot in a lot of this stuff, I wouldn't be here in the first place. Fortunately, ignorance can be corrected, and I am often ignorant on many things but always willing to learn in order to correct it.

OK, now that that's out of the way. I took some time to make an animated GIF that should clearly show what it is I'm trying to do with this project, and I included in the animation, the way that I envision how the magnetic energy should be distributed in order to attain the results I need. That doesn't mean that this is the only way I intend to do this, it just means that this is the only method that I can think of in order to get the results I need. I am always open to someone showing me a better way - on all levels of this project.

However, if I didn't describe to you the method that I think would work, then you would not have a clear picture of what it is I'm trying to do. So I offer the method that I think will work with an open mind to be taught better methods whenever that would apply.

SO, the way that I envision making this magnetic pill spin inside a viscous solution, can be seen in this animated GIF where I show the lines of magnetic flux as it needs to change over time and I indicate the reverse polarty being applied to the coils by the color changes in the north and south letters.

There are four coils in this project, but I wired them in a similar fashion to how coils are wired in a stepper motor. Two sets of two coils per set and they are wired in series so that there are only two leads per coil set. When I energize the leads, one coil will light up with magnetic north polarization while the coil opposite of it will light up with magnetic south polarization. Then if I reverse the polarity on the leads they will flip (obviously).

Here is how I envision making this happen using four phases wherein each phase I will gradually increase the voltage in one coil pair while decreasing it in the other coil pair ... then reverse polarity as indicated and repeat the graduating voltage, etc. And the reason why I believe it is necessary to gradually increase in one set while simultaneously decreasing in the other set is to keep the swing of the pill as fluid as possible so that it doesn't snap around ... picture an ocean wave gradually reaching up to the shore then gradually receding back into the ocean ... its a timed event with consistent fluid motion with no significant jumps in voltage happening anywhere along the travel path of the magnetic pill.

It should make sense by looking at the animation



Here is what the coils look like in terms of the leads coming off of each coil pair:



Now, since I'm thinking that the best way to accomplish what I'm wanting to do here would be through the utilization of an Arduino, I am thinking that I need essentially two H-bridges where I can sweep the input voltage at each input of the bridge from 0 to 5 volts and at the output, I would get a 1 to 1 linear amplification of the voltage that will drive the coils so that when I code the driving of the H-bridges, I can use some consistent sweeping of voltage values using consistent timing. And I don't know how to design the H-bridge so that I can get that kind of consistency between input to output voltage with a solid linear relationship between them at every step of the way from 0 to 5 volts.

I'm looking for advice, or someone to point me in the right direction so that I can learn what I need to learn to accomplish what I'm trying to accomplish. If there is an IC package with H-bridges that will do this, that would be amazing because I'm not looking forward to building two H-bridges by hand. It would be messy on the breadboards and prone to error in too many ways, but if an IC like that does not exist then I have to do what I have to do ...

Also, if my approach to solving these problems is lacking, then please help me correct that.

Thank you for your time,