FisherPrice Problems

We are using two fisher price motors into 5:1 Banebot transmissions. When we run the motors at any speed they shut off after a variable amount of time it decreases with each time we do it. The motor seem to be getting hotter but nothing like they should be turning off. They are only slightly warm. We don’t know what is causing this at all. We have monitored the current in the motors and they are steady at about 20 amps till right before they shut off and they ideally with out going through any other value go to zero. The breakers are not popping because it also does it when it is connected directly to a 12v battery. If anyone has any experience with a problem like this I would really like any advice. Does anyone know if the fisher price motors have any thermal shut offs or anything like that. Also we have the 9012 motors.

I don’t think it has a thermal shut off (that I know of), but there is a fan in the back which sometimes gets covered by the metal covering. Make sure it is able to get air in. :slight_smile:

The 9012 are the ones with thermal protection. It could very well be that the motor has a somewhat different opinion of what’s too hot. Remember that the motor can be a lot warmer on the inside than casing would seem to indicate. All the heat is generated in the coils, that aren’t actually touching the casing much at all. Particularly, the fact that it shuts off quicker the longer you run it indicates that it’s probably the thermal protection.

If you really want to check, run the motors till they shut off, then blast them
with cooling spray till they’re cold to the touch. Run them again and see if they run longer.

If our motors are the thermal protected motors then what do you suggest we do to solve the problem? Also what is the part number for the non thermal protected motors? We would like to trade for some.

No, you don’t. In this case, “non-thermal protected” would mean “future paper weights.” I think your real answer is to either provide better cooling for your motors, or don’t run them so hard.

Per Rick, the motors are thermally protected for a reason. The motor engineers decided operating past that point was bad for the motors. You’re shortening their life if you’re running them that hard. It is, of course, up to you to decide if it will still survive the competition season despite this. Extra cooling is certainly a good idea. If you could modify the banebot trannies to get some airflow through the front vents of the FP, then it’d help. You could also consider changing your gearing slightly to push the motors less.

If you choose to ignore all this advice and get an unprotected motor, this 2005 thread has information about ordering the motors. I’d order a some spares if you go this route.

We are going to change the gear reduction to 25 to 1 which I know will help but I am just wondering what should be a normal load that will not allow the motors to over heat we are only running them at a 1/3 or stall current which I guess is quit a bit but I don’t think it is enough to turn off the motor but I guess I am wrong.

If you blast it with cold spray, don’t do it where the brushes are (near the cutouts in the back of the motor). You could crack them.

Anyway, here is the solution http://team696.org/images/fpcooling.jpg

And buy that exact heat sink here http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXTG84&P=7
But there is a cheaper one here that looks like it will actually fit better http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXJCZ9&P=7

I recommend these to anyone using a Fisher Price motor in any application (other than in a Dewalt transmission, it will not fit).

We used these every year since 2003 and have not had a drill or Fisher Price motor get too hot since.

We are using the 5:1 banebots gearbox on an FP to power our shooter (8" skyway wheels from KOP). The first pinion gear we tried on the FP cracked… you might want to order some extras.

As for current, it draws about 10 amps and seems pretty happy… we’ve run it for a couple of minutes and while it heats up, it never gets hot, stops, smokes or smells “hot”. We’re going to run it downside of a 20amp breaker so we can use some lighter gauge wire as that makes it easier to feed up to the turret.

Jason

P.S. Of course saying all this is a violation of Murphy’s law and I stand to be punished. We have four spare FP’s waiting to go… so that means Murphy will blow out the transmission on us.

It that powering some mechanism or is that just the motor and gearbox running free. If the latter, that is not good.

Thermal protection is nice to keep you out of a problem, but they are almost certainly more protective than you need.

20 Amps is a little higher than what I’d like to see for continous use, but it is not outrageous. My rule of thumb is to load the motors to 1/4 the stall load, you are running at 1/3.

I think you will be okay by switching to the non-thermal protected motors.

But then again, I am a run 'em as hot as you like, just don’t burn 'em up kind of a guy.

FYI, teams I am associated with typically buy Freeze-It by the case :wink:

Joe J

I’d even add a little thermal paste (like what you buy to slap between the heatsink and processor for your computer) in between the heatsink and the motor.

You can get it any online computer modding site, like www.xoxide.com or www.frozencpu.com

yes. I would recommend thermal paste (heat sink compound). You can eeven get it at radio shack.

Allen,
I question what you are using for current monitoring. If you are at anything less than full power, most current meters will not be able to accurately measure the changes in current from a PWM output. If that is the case you are running more closer to stall (64 amps) then you think. Even at 34 amps (max power) you are asking the motor to dissipate over 360 watts, at about 41% efficiency you are dumping over 200 watts in heat inside the motor. That is a lot of heat. You also may have loose connections on the motors (FP motors are very difficult to terminate properly). Heat generated at the connection migrates inside the motor and raise the temp on the thermal cutout.

Hi-
Different member from the same team. We were using a clip on amp meter and were taking the readings on the wire leads coming off the victor. We agree that the thermal protection was probably put into place for a reason and are going to be taking steps to reduce heat and current draw. We are definitely going to be using a higher reduction gearbox (we don’t need the speed, and that should help reduce the stress on the motor) and are considering the heat sinks.
The problem of overheating the Fischer-Price motors was one we were aware of from the beginning. We had considered building custom heat sinks but decided that wasn’t feasible with the machining capabilities we had. Thanks for pointing us to the pre-fab ones. It’s sure going to help us out. We are still wanting to find a way to obtain non-thermally protected motors. Although we don’t think the thermal protection will trip after we’ve made the changes, it was decided that we’d rather not have that limitation pop up on us in the middle of a match. Thanks for all the help, this would have stopped our robot dead in it’s tracks without your help.

-Will

Al - We’re using a Fluke 336 clamp on ammeter to measure our DC motor currents. Am I correct in believing that it should read the average DC current in the pulsed waveform out of the Victor? Is there something better we should be using?

Bruce

Bruce,
The 336, as with most clamp on ammeters and VOMs are only good to 400 HZ. The output of the speed controller is a 2 kHz rep rate so the pulses are even shorter than that. That allows for a lot of error to build up at less than full throttle. I am guessing that you might be reading 50-60% of what is actually taking place. It is a good tool to check between motors and will give accurate results when the controller is producing full throttle. It is a tool many teams don’t have in their tool box but should.

Heat sinks most likely will not solve your problem. Take a look at the gear box motor mounting. Did you block any vent holes? If so see if there is a way to reestablish the motor venting. The small can motors rely on the integral fan to move air and provide cooling. If the motors are venting then the load must be reduced.

Al - Thanks. I knew the output of the Victor was pulsed, but didn’t realize the rep rate was that high (Note to self: Read the nice manual.) I was also thinking the meter would read the average current under the pulses, regardless of width, a holdover from my old “analog thinking.”(<sigh> I miss the days of the old Simpson 260.) :slight_smile:

Check the IFI specs. The 883 was about 2k output feq. The output feq of the 884 is low about 120. This was done to give control below 10%. Using a UEI digital clamp on amp meter VS an old Amprobe analog clamp on I’m getting less than 10% variation in current readings.