FisherPrice Problems

[CyberWolf_22]

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.

[DarkJedi613]

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.

[Kevin Sevcik]

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.

[CyberWolf_22]

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.

[Rick TYler]

Originally Posted by CyberWolf_22

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.

[Kevin Sevcik]

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.

[CyberWolf_22]

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.

[sanddrag]

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...?&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...?&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.

[dtengineering]

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.

[sanddrag]

Originally Posted by dtengineering

As for current, it draws about 10 amps and seems pretty happy....

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

[Joe Johnson]

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 ;-)

Joe J

[Not2B]

Originally Posted by Joe Johnson

FYI, teams I am associated with typically buy Freeze-It by the case ;-)

This stuff is legally "non-flamable". But that doesn't mean you can't make a 5 foot fire ball in your kitchen when your wife isn't home. Nevermind.... (Don't worry - you really need to try to make it burn like that - your robot won't make it go whoosh. It's OK... really it is.)

Has anyone ever thought of making aluminum blocks to mount to the motor, and storing them in a cooler of dry ice between matches? Actually... you may loose most of the cooling by the time the match gets started... just a thought...

[Joe Johnson]

Originally Posted by Not2B

This stuff is legally "non-flamable". But that doesn't mean you can't make a 5 foot fire ball in your kitchen when your wife isn't home. Nevermind.... (Don't worry - you really need to try to make it burn like that - your robot won't make it go whoosh. It's OK... really it is.)

Has anyone ever thought of making aluminum blocks to mount to the motor, and storing them in a cooler of dry ice between matches? Actually... you may loose most of the cooling by the time the match gets started... just a thought...

This is not going to help. Actually, even starting the match with ice cold motors doesn't help much either.

The problem is that the Cp of metal is just not that high -- meaning you can't store that much heat energy in them unless a phase change is involved (i.e. melting the metal).

In my opinion, even heat sinks on the outside of the motor can are of only marginal usefulness. Yes, heat sinks will make your motors able to runs somewhat higher current in steady state, but FIRST is not really steady state. Our uses come in bursts. Heat transfer takes time (especially conducting heat out of the windings of the armature, through the air or the shaft to the outer can to the thermal grease to the cooling fins). By that time, your windings are toast.

Air blowing across the armature -- now THAT is cooling. Keep your current down and your armature speed up (1/4 of stall torque) and you'll be fine.

...you mileage may vary...

Joe J.

[Tom Bottiglieri]

Originally Posted by sanddrag

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

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

[sanddrag]

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