FPs Gone Exothermic

Well we weren’t planning on giving our robot the ability to roast marshmallows :ahh: :eek:
…just kidding. :smiley:

Our biggest problem in building our robot has been procrastination… As such, the robot was built yesterday, in time to discover that FP motors like to overheat. Our “leadership” called me to see if I as a programmer could slow them down to avoid a bonfire. I’m not too knowledgeable with the motors and such, but as I have read and understand it, slowing down the FPs would only cause more overheating, but maybe I’m wrong. If anyone has any advice, I’d love to see it. If we should change to a different motor, suggestions as to which ones would be greatly appreciated, as any other advice.
Thanks in advance.

OK… so, I guess you were to busy procrastinating and then building your robot to search before you posted. The FP’s in the kit are rated at 6v.

Search for the rest of the answer… I forget what you are supposed to do. Sorry.

The rest of the answer would be to run the FPs with a speed controller. Speed controllers send 12V pulses to the motor, and through software, you control how long the pulse is on vs. how long it’s off. As I recall, 128 or 127 is software is zero duty cycle, or off. 255 or 0 is full on in one direction or another. Soo… in programming, if you limit yourself to a range of 64-192 it’s similar to limiting the voltage of the motor to 6V. It’s not exactly the same, and the motor will be slower and less powerful and more likely to stall… but if it does stall, you’re only pulsing 12V to it 50% of the time, so it’s less likely to overheat.

the best answer is to order motor from 2004 as laid out in one of the updates.

first sent you the wrong motor, you need to acquire the older 12v motor and gearbox…things should work better once the appropriate motor is installed.

Ah, I see, I had seen that they are rated for 6V and I had never fully understood the PWMs (it’s my noob year after all, too bad it’s my last).
Thank you Thank you Thank you!!!

Hmm, so you are saying I should read those updates…now I really feel noobish, definitely applies to the first quote in my signature. At this point, it’s pretty much too late to order the old motors…oh well, maybe this information will help the future of our team.

You should have one last chance to aquire 12V motors as a drop in relaplacement when you arrive at your regional, so long as FIRST doesn’t run out (which is very possible). Read the updates closely for the details.

In response to your original querry over applied voltages and heat: It sounds like you’ve done some reading, and have heard people say over and over again to keep fisher price motors away from stall, and run them at high rpm so the cooling fan can do some good. When you half the voltage to 6 volts, obviously the cooling fan slows down, but much more importantly you have reduced the power (heat/time) that needs to be dissipated by 1/4. So running at lower pwm values should prolong the life of your 6V motors.

as far as i’m concerned fisher price motors are cots items…order them, make any neccessary preps for their use and install them at your fisrt regional. this is well within the rules and many other same in your same boat.

all is not lost. put the correct motors in there, now or later, it won’t matter to the rules but it will make your bot more successful in the end.

One should note that even the older, 12 volt rated, motors are also prone to failure.

Basically it doesn’t matter what FP motor you use if you don’t design with it’s limitations in mind. If you stall it, it will smoke and die. If it is under load, it will heat up. Who doesn’t know the smell of fried FP motors?

100 watts is a lot for that little can. 400 is sadistic. 12 volt motors will last a little longer, but if you beat on them, they’ll give up to.

All that said, we are going to try to run with the kit motors. The extra speed and torque are worth the risk to us. If/when they toast, we’ll switch over to the 12 volt motors. We think with attention we’ve paid to keeping vents open and careful current monitoring, we can pull it off.

Theres no such thing as a safe FP motor.

-Andy A.

We figured that with caution, we could successfully use the 6 volt FP motors. We had one motor emit that magic white smoke this evening during very minimal testing. If you have the option of switching to 12 volt motors, give it serious consideration…

Alright, maybe we can order/reserve some for the competition. Sounds like we’ve got some phone calls to make. Thanks a lot for the information.

It depends on what the “neccessary preps” are.

Buying them later and bringing them unmodified is legal. Buying them now, and making the necessary modifications is legal within the fix-it window (2 days after ship), as long as the modifications make them exactly the same as the ones you shipped. They would also have to count in the 25lb limit of spare parts you can bring. Doing any work, after ship, is illegal if it isn’t making an exact spare.

Our 2005 FPs have not gotten even the slightest bit warm. Even with no fan, even over a three hour testing period. Perhaps this is due to the fact that each one is being helped along by two Chiaphuas. :yikes: Fear the HexaMax R2.

Actually today at the Chatsworth Scrimmage, I believe I did see one or two of the FPs on a single robot beginning to smoke.

If your motors are overheating the answer is NOT to slow them down. It is to speed them up! If a motor is getting too hot then it is turning too slowly. FPs of all years like to run around 15,000 rpm. If you are not running that fast then too much energy is being turned into heat.

More gear reduction is the proper answer. Getting it is the problem.

BTW we managed to blow up an FP tranny early this morning. Apparently our arm blew through an electronic stop and hit the hard stop. Fragments of the output stage wound up all over. But the motor did not fry. At least our gear ratios are right!

Don’t let the FP’s run at stall for too long…unless that is you get a kick from watching the magic white smoke get released as the insides fry, and short out. 2 years ago we had a robot that used a scissor lift to lift up the bins, and we used the FP’s to turn a lead screw to operate the mechanism…well, it turns out a lot of force is required in a mechanical system with as many inefficiencies as a scissor lift design…when all the dimensions are critical, and you have kids drilling the holds on a drill press…(measure it with calipers, mark it with chalk, cut it with an Axe)…I mean you are gonna have some problems…well the system did work, but the stress on the FP’s where too much, and we had to replace them often. The system would bind up and stall the motors, and it wouldn’t take long for those motors to overheat. Personally I’m a globe motor guy.