pimpsmurf wrote:Dude. you are missing the point on the silver motor wire.
I don't think so. The point is to get more current through the motor.
a Amp turn is 1 amp run through 1 turn on a coil. 1 amp isn't that much, until you look at having 27 more ATs of EMF on a 27 turn motor. That is a good bit more power.
Its a linear relationship, 10% more current, 10% more torque.
If you have a 21 turn, 22ga copper motor, and a motor with 19 turns of silver, 22 gauge, you will have slightly higher current draw with the same amount of torque, BUT you will have a higher top speed because of less double rotating mass. Correct?
When you change the number of turns you'll be reducing the torque constant of the motor, but at the same time you'll be increasing the current by changing the resistance of the coil. Going from 21 turns to 19 turns would reduce the motor torque by about 10%. To compensate for this loss you must push more current through the motor to get the same torque. You can do this either by raising the voltage supplied to the motor by 10%, or by increasing the conductivity of the coil by 10%. Switching to silver increases conductivity by 8.7%, which puts you pretty close to the original output torque.
The top speed of the motor is determined by the voltage constant of the the motor, which is essentially the reciprocal of the torque constant. Decrease the torque constant by removing windings, and you also reduce the back EMF generated by the motor, which means the motor runs faster. Not because of the weight of the armature, but because you've changed the back EMF constant by removing windings.
Since sliver is about 20% denser than copper, and you are removing only about 10% of the winding length, you will actually be increasing the weight of the armature. Depending on how that weight is distributed, you might end up with a moment of inertia that is the same or greater than the copper armature with more turns. With the same gauge and turns the silver armature will always have a greater moment of inertia.
The only thing the armature mass will effect is how quickly the motor can change velocity (or the torque required to genereate a given change in velocity).
If you compare the difference in moment of inertia between a silver coil motor and a copper coil motor to what you've got in wheels, you'd probably find that the difference it is completely swamped. To get a feel for this, disconnect the motor from the transmission and time how long it takes it to get from stop to top speed, or top speed to stop. Its probably nearly instant. The motors rotational inertia is usually swamped by that of the meats hanging off the transmission. Varies by motor though.
I'm not sure how many inches of wire this is per turn, so I'll ball-park it and say that we're averaging about 2 inches of wire per turn.
22AWG copper is about 0.071grams and 0.00135 ohms per inch.
22AWG silver is about 0.086 grams and 0.00124 ohms per inch.
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Length Mass Resistance
21t Copper 42" 2.98g 0.0567 (baseline)
19t Copper 38" 2.70g 0.0513 (11% improvement)
19t Silver 38" 3.27g 0.0471 (20% improvement)
Silver motor wire is definately better.
Looks that way. Basicly, if you do it right, by using silver wire you can maintain the torque of the motor while increasing top speed by something under 10%. Or you could keep the same top speed and increase motor torque. Or you could keep the same performance parameters and reduce your input voltage.
