Re: Advices on FP Motor
 

David,
Mike refers to the current trip point in the breaker but we also must add into the variable mix the fact that your speed controller is not at full up all the time. That means that there are current pulses being fed to the motor that could be at full stall current but the average is actually less. What makes the situation worse is the fast rise times at the switch points do produce some significant back EMF when the motor is heavily loaded. These add to the heat in the motor due to eddy currents and arcing brushes that the circuit breaker will not react to. As to the circuit breakers, they are usually out in the open getting cooled off by moving air and the large diamter wire will draw heat away from the breakers as well. However, when these self resetting breakers start to trip under heavy loads they do get extremely hot and reset times can be under a second, so fast that the breakers actually buzz. When this occurs, do not allow anyone to get near the breaker panels until they have had time to cool. The temperatures are beyond the point of producing second cegree burns.
Other things that are beyond our control that affect whether a motor winding burns are the uniformity of the varnish coating and bending and nicking of the wire as it is wound on the armature. A wire that is bent and/or pulled tightly around a sharp corner will become the weak point in the winding, having the highest resistance and therefore the highest heat. Add these variables to the mix and winding failure is inevitable at the weak point(s).
Again, running this motor at normal design speeds will let the fan move air through the motor minimizing the heating factors.

Re: Advices on FP Motor
 

F P Caution

We have used the FP motor and gearbox every year since it has been in the KOP. Not the most efficient, but easy and economical to use.

Our gear mod will not work on the newer FP gearboxes. The final gear set is much heavier than before. The weakest link now appears to be the gear cases. Don't have a fix for it yet, but if we come up with something, we will post it.

Re: Advices on FP Motor
 

The BeachBots have used the Fisher Price motors with great success ever since they were introduced. But we have never used them as a drive motor. when combined with the supplied gearbox, they make a pretty good winch. You can even use the supplied wheel adapter for your winch drum. Two plates with a hole in the right spot and a couple of scraps of aluminum angle and you have a really powerful winch. Our winch for pulling us on the bar last year was one of the fastest around, and we had enough pull to lift a second robot, in case somebody should have accidentally gotten hooked on us. It used two FP motors and gearboxes with a custom drum. The only problem we have had was a failed limit switch. It allowed the winch keep pulling beyond its normal travel and bend our lift. Fortunately it was during a demo and not the competition season

As Al S mentioned earlier, it is important to keep them operating at the correct speed. We always design our systems so that the motors are running at 75% of free speed and 25% max torque under a normal load. Those rules pretty much apply to all motors. Follow them and your motors will live long and you will prosper.

ChrisH

Re: Advices on FP Motor
 

Chris,
I saw a few similar setups to yours, but I wonder if you'd be willing to share any pics/drawings? We've never been really good at using the FP Gearbox, I'd be VERY interested in seeing how 330 does it.

Thanks,
John

Re: Advices on FP Motor
 

In 2003 we used the FP's and their transmissions (with addition 5:1 reduction) to operate a very heavy 7 ' arm (~40 pounds) and we're fairly successful, but when practicing we kept smelling something awful - our FP's were smoking but not tripping the breakers - we put two muffin fans on each motor - and never smelled again!!!

Re: Advices on FP Motor
 

Beware of the plastic gear boxes.. they dont like changing directions much.. if you keep going in one direction, i believe you will be fine.. if you change directions (like in skid steer or similar drives) the plastic gear boxes will strip out very easily
JP
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