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
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.
The Tetrix motors don’t have a fuse - what are you talking about?
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).
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 !
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.
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!
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!
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…
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.
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.
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!
My surgery on one of our two dead motors was done in a similar fashion. A wire replaces the inductor now. Incidentally, the burned hulk must have iron in it somewhere because it was attracted to the motor’s permanent magnet as I cut it loose. When you reinsert the armature and brush-bearing end plate, you have to be careful that the magnets don’t just snatch the armature away from you. It will separate the two pieces quickly. I devised an alternate re-assembly method, but that’s another story.
After reassembly, a power test had the motor spinning for about 10 seconds before it blew a 5A fuse. Current measurement with another fuse in place showed over 7A current for the free-running motor. The armature coil wires looked OK or I wouldn’t have attempted reassembly. My theory is that wires on the armature deep inside have cooked off their insulation making this motor useless for testing even in its “repaired” condition. siiiiigh. :eek: Maybe the other motor will be repairable while I await replacements from pitsco.
At least I now have gears to play with. 
Bill,
We have smoked 3 motors, but they all have partial power still. I measured one with a 4.5 volt input and measured the torque. It scales to about a 45% torque of a new motor. So I suspect that we cooked some windings.
Will a burnt inductor possibly allow partial torque or is the motor a brick with this condition?
If we do have partial torque, then is is likely any repair can be effected?
Burned out motors can be fixed, as of team update 11.
See this thread. they are discussing the resistor value, which is most likely what you burned out.
I’m pretty sure the internal part of the coil has shorted by burned insulation there. This is based on the high current observed by running my one attempt to repair a drive. I thought burned insulation would be more obvious by discoloration. My nose tells me something serious has happened to that motor.
I think overcurrent in the inductor has made its coating break down and might have been the source of the first noticed smoke. My current theory {pun noted} is that the motor failed in stages as more internal coil heating caused more insulation failure leading to more overcurrent in a vicious circle that eventually killed the inductor into open circuit failure. The circle ended but repairing with a new inductor, or a new wire in my case, will not restore the motor to original condition. It won’t make it usable for practice either due to the suspected armature damage.
The partial torque you noted throws off the gearing calculations so any experiments you are trying mechanically will be skewed for a fresh motor. That is, you get your robot working well with a “repaired” motor, but changing to a new one inserts a different energy profile that effectively negates all your mechanical tweaking. In our earliest testing, I think we might have fallen prey to changing characteristics of partially disabled motors. That is, the first smoke only wounded the motor so we adjusted pole grabbing tension, for instance. As the motor became less and less capable, we thought there was fault in whatever adjustment we just made.
Bottom line {hate that term} I’ll be playing with the gears from these motors, and maybe I’ll try to compare the burned coils with a good armature, but the motors will never make it into even a testing robot.
Thanks… I think I’m in full agreement with your reasoning.
It doesn’t make sense to under design the choke unless you are using it as a protective component.
So lets assume two cases:
The choke is properly designed to take the 7.5 amps. The temporary stall condition then smokes the windings first. This shorts the armature and leads to higher currents. The higher current eventually smokes more winding and eventually smokes the choke. The motor will have residual degraded torque if the choke didn’t self destruct open but the motor will not be usable for a minibot design.
The choke is undersigned and opens before the motor windings smoke. Then it protects the motor windings and can be replaced to restore the motor to original specs. But… the motor will not have residual torque after this event. So… This doesn’t fit any of my motors.
Maybe something in between where either the choke or winding smoke first. If the choke just smokes and doesn’t open , then its resistance will lower and the motor current will increase and probably lead to more power in the motor. This is probably a good thing unless the stall persists… then the extra power will smoke the motor faster.
4)???
Bottom line, smoke a motor and if it still operates… use it for mini fan motor and not a minibot.
I hope someone can post a counter to this reasoning:)