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How to build a simple electric motor, plus how it works.





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Published on Feb 24, 2007

The Tabletop Explainer is an intermittent educational vlog presenting answers to viewer questions, brief science lessons, and ideas for teachers and students. It is a feature of my blog "Tilts at Windmils" which can be found at

Download the background music, Time to Funk by Trafic de Blues:


First, it's important to understand the context of the "Build Your Own Motor..." video. It's a demonstration aimed at solidifying the ideas presented in two earlier videos. If you haven't already, you should watch the whole set:

1) What is the magnetic field?

2) Electricity & Magnetism Hand Rules (part one)

3) How to build a simple electric motor, plus how it works.

The main idea here is that charges moving through a magnetic field experience a "push" perpendicular to the direction of their motion. This force is also dependent upon the direction of the magnetic field. The fact that the wire is stripped on only one side alternates the current from "on" to "off" every half rotation. So halfway through the spin, the ring coasts through until it gets current again receiving a "kick." It's a poor man's commutator. The particulars of this kick/force are discussed in the second video. Armed with the knowledge from the above videos, you should be able to troubleshoot most of the problems that arise. The key is to make sure you understand the concepts first.

That being said, here are the most common issues I've seen my students have when working on their motors:

1) They strip the wrong part of the coil.

1.a) Most often they forget that they are supposed to strip only the underside of the wire on the arms of the coil. They mistakenly strip the whole wire. This could cause the coil not to spin properly and also in some cases to over heat.

1.b) They strip the bottom of the wire when the coil is lying down. Make sure you are stripping the underside of the coil when it is oriented as an upstanding "O." Ask yourself, will the charges flowing through this wire get a push in the right direction according to the rules set out in the second video?

2) The coil isn't symmetrical. Before you connect up the power, the coil should spin quite well with just a little push. If the arms are off center this can be a problem.

3) The coil isn't wound tightly enough. The coil should be very tight and neat.

Also you could be using the wrong type of wire. It needs to be thin, but also insulated. I've had good luck with this wire.

If something isn't working ask yourself "why?" You should have enough information to figure out the answer. After all, that's half the fun. I hope that helps.


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