Fixing Burnt Motors

[komeiji_koishi]

Hey,
We kinda sorta burned out two of our motors for the minibot earlier this week, and we can't get any more of them because they're currently stuck in the Iowa snowstorm.
Could we open up our motors and fix them, and still compete with them?

[Team 2035]

[joek]

Originally Posted by komeiji_koishi

Hey,
We kinda sorta burned out two of our motors for the minibot earlier this week, and we can't get any more of them because they're currently stuck in the Iowa snowstorm.
Could we open up our motors and fix them, and still compete with them?

[Team 2035]

I don't think you could fix them,even if it was legal

[EricH]

For future reference, Team Update #5 specifically allowed teams to replace the 20A fuse that the Tetrix motors come with with an equivalent type of lower amperage. I guess there's a part that likes to fry at about 20A, so they're allowing that to be protected.

[Chris is me]

Originally Posted by EricH

For future reference, Team Update #5 specifically allowed teams to replace the 20A fuse that the Tetrix motors come with with an equivalent type of lower amperage.

The Tetrix motors don't have a fuse - what are you talking about?

[EricH]

Originally Posted by Chris is me

The Tetrix motors don't have a fuse - what are you talking about?

Originally Posted by <R92-C>, as amended by TU#5

no more than one 12V rechargeable NiMH battery pack identical to those supplied in the FTC kit of parts (PN W739057) except the 20A fuse may be replaced with an equivalent type of lower amperage,

OK, so it's the battery. But it's the motor part that is the problem, as noted in this sentence from the same Update: "Additionally, it has come to our attention that teams have burned out their Tetrix motors by stalling them while directly connected to the battery."

The motor has a part that lets the smoke out at about 20A. As such, teams are encouraged to replace the fuse on the battery pack or use the thermal protection wiring (allowed later in the rule as updated in TU#5).

[ouellet348]

He means the fuse that is on the battery, it comes with a 20Amp fuse but by lowering it you can fix the issue with the motors burning out, in response to the fixing question the issue is a 3.9 ohm resistor that burns out at about 20amps. The resistor can be replaced but it is illegal to compete with in such a state, also to remove it it cause significant damage to the motor housing in the form of destroying the tabs bent to hold in the actual components. However if you can solder a bridge in and solder in a replacement resistor to outside of the motor for easy access, the motor will perform identically to a normal one for testing, so that you don't risk new ones. I'd advise using those for testing and running at most 15Amp fuses to fix the issue. good luck !

[Chris is me]

Originally Posted by EricH

The motor has a part that lets the smoke out at about 20A. As such, teams are encouraged to replace the fuse on the battery pack or use the thermal protection wiring (allowed later in the rule as updated in TU#5).

Doesn't really solve the poster's problem or answer their question, though. Their motors are burnt out.

Anyway - burnt out motors can't be repaired and remain competition legal, sorry.

[AlexH]

If burnt motor means the "magic smoke left it" then I don't think its fixable.

[BEEKMAN]

Originally Posted by AlexH

If burnt motor means the "magic smoke left it" then I don't think its fixable.

It's easy, just get some magic red smoke, and put it back in!

[Andy A.]

A little clarification-

No, you can't modify the motors and still compete with them.

Additionally, you can't really fix a fried motor, at least not in the traditional sense. Whats burning is the insulating enamel on the wire coils of the armature. Once that coating is burnt off the wire starts to short against its self, decreasing the effective strength of the magnetic field it can generate. Torque decreases accordingly. The only way to 'fix' the motor is to either rewrap the coils with new wire (nigh impossible to do by hand) or replace the armature. For a small DC motor like this neither option makes any sense.

Mark the fried motor and use it for R&D purposes that don't require full power, or toss it.

You can buy new motors from Lego and Pitsco. $30 each and make sure you get the same part number!

[PAR_WIG1350]

Originally Posted by BEEKMAN

It's easy, just get some magic red smoke, and put it back in!

RED????? Since when does magic smoke, or at least the type found inside electronics, come in such a color? Also, once the magic smoke is let out, it cannot be put back in, so even if you can get some, it is useless.

[BEEKMAN]

Originally Posted by PAR_WIG1350

RED????? Since when does magic smoke, or at least the type found inside electronics, come in such a color? Also, once the magic smoke is let out, it cannot be put back in, so even if you can get some, it is useless.

Well, if the magic blue smoke comes out....it only makes sense to put the red stuff back in.......

[AndyH]

The rules basicly say no modifications. Repair therefore should be legal. I think if you realize what the spirit of the rule is and do not push these limits you will be OK. You can absolutely repair it for your developement and testing and you can hope your new ones show up before the regional. You may carry in your minibot.

[Justin Montois]

We fixed our burnt out motors only for use in prototyping, the fix we used would not allow the motor to be legal in competition.

This thread shows what we did.

http://www.chiefdelphi.com/forums/sh...ad.php?t=89848

[Al Skierkiewicz]

komeiji,
***Note: Under current rules, this is not a legal modification of this motor!***

The method you would use to open these motors is first remove the transmission and adapter plate. Then I use a wire cutter to pull back the outer case at each point it has been crimped over the end plate. Using a long, slender tool, i.e. screwdriver, push gently on the gear and shaft to push the end plate and armature out of the case and magnet assy. Once you have The armature and brush assy open, you can gently move the brushes to release the armature. Inspect the armature to see if the wires are burned or are dark in color. If so, dispose of the motor it is not repairable. If everything looks normal, set the armature where it will not roll off the table. Look at the endplate with the brush assy. (The picture in the linked thread will help.)
You will note an axial leaded component that resembles a coated resistor. This is an inductor that is likely burned open. If you carefully unsolder this component, replace it with a short wire. Assemble the endplate and armature being careful to avoid damage to the brush assy. Then using a long slender tool, reinsert the endplate/armature assy back into the case. Try connecting a battery to the motor and see if it spins. If it appears to be working correctly, then using a hammer and some other tool, recrimp the case to hold the endplate in place. This will give you a working motor that is not legal for competiton.

***Note: Under current rules, this is not a legal modification of this motor!***