Broken/slow buggy motor

[JoshsTechnicWorkshop]

Hi, i've got 2 buggy motors which i got from the 8376 Hot Flame buggy set. 

This morning i decided to test the motors which are in a moc im working on but it only ran a few times then slowed down drastically, slower than the xl motor i mean. Does anyone got this issue? The motor is discontinued and it is relatively expensive so i can't replace them anytime soon nor contact lego's customer support. I've tried to power it with Lipo batteries, the lego rc hub from the set, the AA battery box, the rechargeable battery box and even a custom 9v battery but none of them worked at all.

Thanks

 

[TechnicRCRacer]

Strange, it seems like the overheating issue that happens with PF battery boxes, but you mentioned you tested with the RC hub... Have you tried different cables? Are you comfortable taking it apart to look for faults or resistance?

[JoshsTechnicWorkshop]

8 hours ago, TechnicRCRacer said:

Strange, it seems like the overheating issue that happens with PF battery boxes, but you mentioned you tested with the RC hub... Have you tried different cables? Are you comfortable taking it apart to look for faults or resistance?

I ordered 2 new cables, hope it'll work. Then i'll take it apart as a last resort. 

[Thierry-GearsManiac]

If we can exclude a mechanical problem at a first glance (something broken, dry grease... blocking the internal gear train), then my first guess for an electrical problem would be that the motor windings got partially shorted : they perhaps endured stalls in their past life, making the enameled wires more fragile through repeated overheating. Then, even after some tests under normal conditions, the enamel broke down and got shorted somewhere.

In order to check this hypothesis, I would measure the resistance of the motor and compare it to the resistance of known good motors (I don't own such ones ==> someone else's measurement reasults would be useful). If yours is much smaller, then the hypothesis is unfortunately true, and the only solution to bring them back to life would look like a non obvious hack (finding a somehow equivalent motor part, transferring the metal pinion from the broken one to the new one, mounting the new one in place) : nothing found about such a hardcore repair after a quick Web search.

 

If a dismantling of the unit is eventuelly needed, then look at @Philo's picture in the following topic (which shows a fully dismantled unit, where we can see that the motor's shape is rather common),

... and at this short video (which only shows the gearbox).

Edited June 4, 2020 by Thierry-GearsManiac