**FIRST EMAIL**/Fisher-Price Motor Information

[Alex1072]

Originally Posted by HPA_Robotics_13

Teams such as 254 (the Cheesy Poofs) used the FPs to power their arms last year. How did they make their setup work? I am very confused because I have heard many people, like Alex, say that it would be bad to use these motors for an arm mechanism, yet others talk about how it could work and how their team has done it.

The Cheesy Poofs beat my team in the quarterfinals at the Sacramento Regional last year, and I happen to know (I was the driver last year) that their arm worked phenomenally well.

Sometimes it's hard to tell who really knows what their talking about around here. No offense to you, Alex, I'm just confused.

None taken. I didn't mean to say that you can't use a FP motor to power an arm, I was just saying that it in general would be a bad idea to servo an arm with it (although I'm sure there is some clever ways to do this safely). We're using 2 FP motors this year to power our elevator, but we are making sure that they will never stall.

There are two factors that cause overheating when motors stall. First, the higher torque the motor provides, the more current it draws. This increases the heat output of motor's wiring. Second, motors usually cool themselves by spinning, so by stalling a motor you are also taking away the major form of heat dissapation.


Now, the FP motor given to us by FIRST was designed to run as 6V. When you double the voltage to 12V and stall it, you are actually more then doubling the heat output: Power = Voltage*Current. Stalling at 12V will draw twice as much current as stalling at 6V, so the current doubles as well. This means that the Power is actually increased by a factor of 4. Since the motor shaft is not spinning, no Work is being done on anything by the motor. That means all that 4xPower has to go directly into heat. *sizzle*, *melt*.


I don't know about stalling it when running at half (effective) voltage, but from what i'm understanding these motors are not of the highest quality, so even that tends to burn them out after a couple of seconds.

There is nothing wrong (I think) with stalling them at a low voltage, so maybe if you gear them down enough it would work (not sure about this)?

Hope that helps.