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trouble -shooting Simple DC Motors assembly

by jeffrey1evesque / March 5, 2005 9:37 AM PST

In my physics class (highschool) we constructed a simply DC motor, or was our objective. However only 2 groups completed motors that actually worked. I am one of the many frustrutated students among my class that doens't understand why my motor didn't work. Our objective was to make a motor using concepts of electromagnetism using ferromagnetics (not actual magnets). This process using the right hand rules provided us means to create a motor with a core and armature. The Core i used was constructed out of an Iron can i folded few times then bent it into a blocky U shape. I then wrapped 24 gauge wires around it three times. The core im assuming is great, i can pick up a nail with just one AA battery hooked up with it. However my armature is another story.. I used a coat hanger as the axle (its approximately 4.5 inches long). I made two armatures, one with antique iron nails, and another with nails from the hardware store (its not galvenized so its good im guessing). However the one with antique nails is that after i wrap wires around the nails (connected perpendicularly with the axle going thru both the nails) is that when i test its balance, it always balances perfectly one way. i'm guessing the nails always balance a fixed way because one nail is heavier than the other? Anyhow when i connect the entire circuitry, the armature only twitches, then it doesn't do anything. And same thing happens with the nails i got from hardware shop. The nails i used in the armature is the same as in core.

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(NT) (NT) this forums for problems with the forums
by Mark5019 / March 5, 2005 11:00 AM PST
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Interesting question in a forum such as this
by Steven Haninger / March 5, 2005 11:03 AM PST

so I have no idea how you found your way here. I'm no electrical engineer but I remember making such motors in my youth (about age 12) with instructions from what might have been a Boy Scout project book. I cannot envision your configuration but remember a couple of things that might help. One is that 3 wraps of wire will not produce much of a magnetic field. These fields need to be quite robust. Another is that an even number of armature windings is a problem. You must envision what you are trying to do but in a linear fashion. You are trying to push an armature pole away from a fixed magnet while pulling it toward the other. As the moving "pole" arrives at the next magnetic peak, it switches polarity but must have enough inertia to overrun the pole. Now, it's the same polarity as the point it just passed so repels it and goes onto the next point, switches again...etc...etc. This requires good strong magnetic fields and well defined poles. Critical is the switching. This is done with your brushes. Your positive and negative battery poles must be positioned at exactly 180 degrees apart and the armature contacts precisely placed on the armature spindle to switch at just the right time. Your armature windings needs to be done in one continuous wrapping with the same number of turns on each segment. You bring a lead to one contact point on the spindle and back to the next armature segment continuing the wrapping in the same direction until you are back to the start. Each armature contact will have the trailing lead of one armature segment wrap and the beginning lead of the next. You can make these armature contacts on a concentric insulator of the armature spindle that can twist a little to find the sweet spot for the best efficiency. Now, as I recall, motors with an even number of poles may run but tend to not self start. Odd numbers work better. I know I don't have the right terminology here but hope this offers some clues. Good luck.

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Addendum
by Steven Haninger / March 5, 2005 10:14 PM PST

Electric motor primer...Here

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Try howtoons.
by R. Proffitt Forum moderator / March 6, 2005 2:42 AM PST
http://www.howtoons.com/ and just a few items down is one of those build it yourself motors. If one doesn't do the shellac proper it may indeed just twitch, but some may not know that such motors do not self start.

Bob
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