Curious... Anyone smoked a motor with Tetrix ptc

[vamfun]

I remember seeing in a post somewhere that some are still burning motors out with the Tetrix PTC fuse. Anyone experienced that?

[Captaindan]

those motors arent great keep extras the motors burnout like nobodys business if stalled et. magical blue smoke and burning electric smell

[Team 1574]

hahah sure we smoked some tetrix motors...
those motors are really really bad..

[Trent B]

He is referencing motors hooked up through the Protective Thermal Cable (that effectively acts as a fuse to cut power before they fry ideally.

[Teched3]

Originally Posted by Trent B

He is referencing motors hooked up through the Protective Thermal Cable (that effectively acts as a fuse to cut power before they fry ideally.

Even with the PTC, motors can burn out under stall conditions. They do not react quickly enough.The Game Development Committee will not allow individual fuses to protect EACH motor. (it's been asked on Q&A). When prototyping, we used fuses to protect our motors, and it worked well. We were able to design the minibot drive to minimize stall potential. Analogous to the Hostbot electrical system, circuits are fully protected with a main breaker and an individual fuse or circuit breaker to EACH motor. The minibot should follow the same wiring protocol as the Hostbot for many reasons, but proper electrical design and consistency across the board are major concerns that have not been addressed.

[thefro526]

For preliminary testing we were running a 5amp fuse on our Minibot and since then we haven't had any issues with burning out motors. More often than not, you'll burn out the 5amp fuse before you can draw enough current to do any damage.

[Teched3]

Originally Posted by thefro526

For preliminary testing we were running a 5amp fuse on our Minibot and since then we haven't had any issues with burning out motors. More often than not, you'll burn out the 5amp fuse before you can draw enough current to do any damage.

Then you're minibot is not operating at max power at 5 amps current draw for two motors. There is a large difference between what these motors were designed for and what we are doing with them. The question still remains why not fuse each motor? It doesn't enhance performance, and, in fact, will add some resistance to the circuit, lowering performance. Are there any electrical engineers that would design a circuit like this without proper component protection? I hope FIRST will have a lot of replacement units at the Regionals and Championships. You're depending on both motors to split the 5 amps. what happens if one motor quits during a climb, and the other takes the full load?

[PAR_WIG1350]

Originally Posted by Teched3

Then you're minibot is not operating at max power at 5 amps current draw for two motors. There is a large difference between what these motors were designed for and what we are doing with them. The question still remains why not fuse each motor? It doesn't enhance performance, and, in fact, will add some resistance to the circuit, lowering performance. Are there any electrical engineers that would design a circuit like this without proper component protection? I hope FIRST will have a lot of replacement units at the Regionals and Championships. You're depending on both motors to split the 5 amps. what happens if one motor quits during a climb, and the other takes the full load?

This is exactly why you DON'T fuse the motors individually, by using a common fuse they both quit at the same time.

[Teched3]

I didn't say the main fuse from the minibot battery should be replaced with individual fuses to the motors. The thermally-protected motor feeds, repair of damaged motors, and main fuse reduction were allowed by the GDC in team updates to help protect these motors. Every other motor circuit on the robot requires power be delivered to a motor trough a main circuit breaker and then through an individual fuse or circuit breaker. The minibot should be no different just to maintain consistency, if for no other reason. I guess I can agree to disagree.

[philso]

Hello Teched3

What rating and type (slow or fast-blow) of fuse did you put in series with each motor?

I was going to put one fuse in series with each motor to protect the motors during testing. If one fuse blows, there is no expectation that our Minibot continues to operate correctly (a fuse is not a current regulation device, it is a safety device). The extra fuses would be removed before the competition.

Thanks.

Phil

[Teched3]

We used 2.5 amp fuses for testing. The power lead disconnected (one motor) on one of our test runs, and the fuse saved the other motor as the fuse blew when all the transferred to the operating motor. I believe they were standard fuses, not slow-blow. We are currently using the thermal protection leads on our current design for competition.

[vamfun]

Originally Posted by Teched3

Even with the PTC, motors can burn out under stall conditions. They do not react quickly enough. ....

Did you actually experience this with the Tetrix motors or is this a more general statement based upon your experience?

Perhaps more people would have responded if I had asked if anyone had stalled the Tetrix motors and were saved by PTC's.

I ran an informal PTC test and posted the results on my blog. Our minibot ran ok with the PTC's and was slower than predicted because of the power loss. A little friction in the drive train and the minibot tripped about half way up.

I'd like to remove the PTC's but we are driving the motors on separate axles and I'm not sure that the 5 amp fuse would do any good. I expect that if one motor blows, the other will also. So, I am in agreement that the GDC should have allowed separated fusing.

[Teched3]

Yes, in testing, the PTC feeds offer more protection, but if you're working the motors on the edge, it's a slippery slope to failure. Our only failure with the PTC occurred when one motor lead disconnected, and all the current transferred to the functional motor. Weight reduction, proper speed selection, consistent deployment on the pole, are the keys to speed and dependability. Why the GDC doesn't allow individual fusing of motors along with a main fuse still evades me.