FisherPrice Problems

Technical Motors
#6

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.

#7

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.

#8

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.

#9

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.

#10

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

#11

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

#12

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

#13

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

#14

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.

#15

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.

[RIGHT]-Will[/RIGHT]

#16

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

#17

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.

#18

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.

#19

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:

#20

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.

#21

I looked through the specs on the 884 on the IFI site and don’t see the output pulse rep rate. have you got a link to where it might be? I’d like to demo this to the students with a scope (if I can get near the robot this last week.) Thanks.

Bruce

#22

I looked on the IFI website for both the 883 and 884. Last fall there was a post in the IFI forum looking at the differences between the 2. IFI detail the differences in the switching feq. Seams they have cleaned the posts up for the 2006 season and it’s not there. Would have to be re asked or give IFI a call to confirm. There where some threads where this topic was discussed on Chief Delphi. Again check the motor mounting blocking the vent slots. There was another post concerning this.

#23

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…

#24

I’d just like to re-iterate this. It is probably too late for you to do anything about it, but the vent holes in the front of the FP motor are critical to its cooling.

Matt

#25

Try reading the current after the breaker, going into the victor.