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So I run an engineering class even though I mostly just do theory myself, so when it comes to actually building stuff I miss some basic ideas I should know.

I am having them make a DC motor out of a battery, magnet wire, a magnet of some sort, and however they want to finish the circuit.

My biggest concerns are what kind of batteries and magnets to buy for them. Going off of F=IlxB, V=IR, and P=V^2/R I am assuming a higher voltage batter would be better, so I was thinking of doing something like a 9 or 12 V.

I want their motors to be able to move a light cardboard car (it can run with 2 motors as well) Would those work? Should I be looking for anything else? I am also thinking about just getting some neodynium fridge magnets for them but I have no idea what the value for B is on them so I am not sure if they would work well enough.

I will link https://www.amazon.com/TRYMAG-Different-Neodymium-Refrigerator-Whiteboard/dp/B09WZTSQ9Y/ref=sr_1_3?crid=1QKVZM42UG3XQ&keywords=neodymium+magnets&qid=1663178402&sprefix=neodymium+magnet%2Caps%2C145&sr=8-3 the magnets there. Would those work well enough or should I look for something else?

It is also worth noting I am working with kids between 13-17 so it can't be anything that could cause any real harm of course! Thank you for any help!

Solar Mike
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Patrick Flint
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  • I would just go with the cheapest batteries and the cheapest magnets, which probably means not rare earth magnets. DC motors tend to require commutators or brushes though there are other kinds (homopolar motors, but you won't really find them in applications). What do you plan to do about that? – DKNguyen Sep 14 '22 at 20:18
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    if they are building their own motor please use low power batteries. A short in a car battery circuit can be catastrophic – Tiger Guy Sep 14 '22 at 22:32
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    Making a motor from scratch is not easy. How are you going to made the mechanical pieces? I would try to find some kind of off-the-shelf kit. – Mattman944 Sep 15 '22 at 00:37
  • One thing you have not mentioned at all is fuses. – Solar Mike Sep 15 '22 at 05:42
  • Google diy cardboard motor, there are two detailed videos on Youtube. Unfortunately, the average kid in that age group will have no chance at success, the skill level required is too high. But if you could 3D print most of the parts and only have the kids wind the coils and assemble it, then this could work. Your next problem, the motor will have a high speed and low torque, the car may not have enough torque to get started without gears. – Mattman944 Sep 15 '22 at 07:12
  • @Mattman944 Yeah. You definitely want them to almost blindly follow canned instructions step-by-step instructions. I mentored maybe 150 students a while back where they had to target something that people needed and make a mock-up, a model, for display purposes. Not necessarily even a half-working prototype. The only ones who were even remotely successful were the groups that had been frequently nudged throughout their project in particular directions by adults. They just didn't know what to do with the level of freedom and decision making that was afforded to them. – DKNguyen Sep 15 '22 at 15:05
  • and however they want to finish the circuit. That's going to end well. The question I have is: Have you done it yourself?. No. And I realize Engineering is all about throwing you into the deep end and finding a solution. But I picture the saying that got me through Engineering. When you are up to your neck in aligators, it's difficult to remember the goal was to drain the swamp!. Thank god they have the internet. – StainlessSteelRat Sep 15 '22 at 16:41
  • How do you plan to commutate the DC motors? – Drew Sep 18 '22 at 09:11
  • @DKNguyen Following step by step instructions doesn't teach anything except how to follow orders. I've given challenges to middle schoolers with zero instruction and had great results. I think the problem you gave them was just too difficult to solve unaided at their skill level. I had the kids design projectiles which we fired out of a cannon to maximize distance if you're curious. – Drew Sep 18 '22 at 09:15
  • @Drew And you don't think "having them make a DC motor out of a battery, magnet wire, a magnet of some sort, and however they want to finish the circuit." is not too difficult a problem for them to solve? And not just a motor that keeps itself spinning for the sake of spinning, but one that can move a little car? – DKNguyen Sep 18 '22 at 14:46
  • @DKNguyen I agree it's too difficult. I suspect many adults would not be able to do it. – Drew Sep 19 '22 at 02:30

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