Electricity merit badge motor woes and others too

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Electricity merit badge motor woes and others too

Postby danmc91 » Wed Jul 31, 2013 12:00 pm

This is in reference to the "you can build a motor...." stuff on page 34 and 35 of the 2010 electricity merit badge book. I'm more than a little disturbed that these pages made it into publication as I'd bet money that it doesn't work. Anyone know if there is a way to submit corrections/improvements online now or is a paper letter to the address in the front of the book still the only way?

In the mean time, if anyone wants to build a motor and make it actually work, here are some important bits.

1) Friction is your enemy. A dowel through a jagged hole in some sheet metal will present *way* more friction than a small motor of this type can tolerate. There are multiple ways around this but a simple one is to take some sewing straight pins. The ones with the round plastic head work reasonably well. Stick those into the ends of the dowel and use those to support the dowel with. Much less friction than the wood.

2) Friction is still your enemy. You can try bending a paperclip into a shape which starts attached to the board. It goes up, bends over and comes back down a little and then has a smooth "U" shape going back up. Try that instead of the hole punched in the sheet metal.

3) Wobbly things and obstacles are bad like friction ;) (we have a theme here....). Try putting a strip of metalic duct tape (the sort actually used on ducts, not the silver stuff we all call duct tape) on the dowel for the wires in figure 5 to brush against. That is better than the bump, bump, bump, bump you'd get going over the wire in Figure 4.

4) Last, but most certainly not least (in fact, this should be first), the axis of the coil should be perpendicular and *not* parallel to the axis of rotation of the motor as drawn. As showing in figures 3, 5, and 6, the setup will not generate torque. No torque means no spinning even with beating down the friction. It is this point which really was surprising to see in the pictures.


For an even simpler way.... just make a coil of wire approximately 1/2-1" in diameter. Use a bunch of turns. Use enamel insulated wire not plastic insulated. Secure the turns of the coil with some tape or even by a couple of turns of the wire or use some thread. Make the two ends of the coil exit opposite sides of the coil. Those 2 ends are the ones which form the shaft of the motor. Picture a quarter lying on the table with a wire leaving to the left and one to the right. That is about what this looks like. Now remove the insulation fully around one end of the wire and partially on the other end. Use the paperclip supports as in #2 above. Connect the battery to the other ends of the paperclips.

On motors like this (single coil instead of multiple coil, and relatively few turns), you will likely need to give the motor a bit of a push start. So.... orient the coil correctly, beat down friction, and balance things as much as possible and it isn't that hard to get something which will spin.

For the more interested reader, the reason the coil orientation in the book won't work is because if you keep the coil energized and rotate the motor, the magnetic field doesn't change. If there is no change, then there is nothing in the system which would cause it to want to turn. If you have the axis of the coil be perpendicular to the axis of rotation, then a rotation around the shaft will indeed cause a very significant change in magnetic field. Now all you need to do is only energize the coil part of the time so that the motor spins instead of just turning part way and stopping in place.

An unrelated error I noticed in the book is the figure at the top of page 41. The middle parts of the two figures are swapped. In other words:
/
----o o------
on the left part of the inset should be swapped with the

[xxxx]
o o o

on the right part of the inset. This is an easy enough typo sort of error to make when publishing anything.

And... one more. On page 19, making a buzzer. Anyone using aluminum as that thin strip as suggested will be disappointed. If a small bit of iron or steel with enough iron content or a permanent magnet is glued on top of the strip, it should work much better. Any doubts? Just try sticking a magnet to an aluminum drink can. Doesn't stick. An electromagnet will not have any better luck.

The worrisome part is this is what I saw on only a few minutes of flipping through the book. Makes me think that the BSA would do well to put out a call for volunteers to do some pretty careful review of a lot of the literature as I've found other examples in other areas (wilderness survival, BSA handbook) where clearly what was being suggested hadn't really been tried out.

-Dan
danmc91
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