**Disclaimer - Repaired motors may not be competition legal.
**
Like many teams, we have a box of motors marked “BAD”. I decided to see what was salvageable from these at the weekend and found there were four common causes.
Missing pins on the end of the cable.
Solution - Replace pins or entire cable. We have discussed this before.
Frayed wire and/or damaged cable strain relief.
We’ve all seen this before.
Solution - Replace cable with one from an unused 269 motor or a 393 motor with a good cable but different problem.
Intermittent operation.
I found a couple of motors that had either a cold solder joint or had managed to damage the trace on the motor PCB. Here is an example.
This seems more likely to happen to the connection on the black wire after the rubber strain relief has also been damaged.
Solution - Re-solder the connection or repair the damaged trace.
Dead motor
This is usually due to worn out motor brushes.
There is no solution for this, use the parts from this motor to repair one of the above problems.
I decided to use parts from some of the now unused 269 motors we had. Just for fun here is a photo of the motors from 393 and 269 side by side.
I agree that fixing old motors is not only smart thing budgetwise, but will let roboteers gain valuable insights into motor internals.
Last year we built all our prototypes and run in a scrimmage using only recycled motors. It saved us several new motors, as we were grinding the old ones really bad, before getting our lift right.
I would assume that getting launchers or catapults debugged and calibrated will burn through at least one set of motors.
Sometimes the wires are shorted inside but appear normal outside. When trying to turn such motors manually you will feel as if it is in a serious need of lubrication. Then you move the wire a bit and motor seem to rotate freely again.
Stripped or broken motor gears. You usually hear it by the abnormal sound the motor will make, instead of the smooth running. Hopefully, yours won’t be as bad as this:
If there is no additional damage to axles or housing, you should be able to repair it with a new set of gears (393 Motor Refub Kit).
Finally, the need of lubrication. There are several good threads on this subject: 60430, 72601, 82573.
Regardless of lubricant you choose, the most important rule is: DO NOT MIX LUBRICANTS. You never know how they may interact. Thoroughly clean gears and motor housing before applying new grease. If you are using Motor Refub Kit, it is better to squeeze whatever little oil came in the packet than using your own.
The second rule is not to add too much lubricant. It is better to lubricate motors twice a season, than have oil leaking from it or flooding motor brushes (you will smell smoke if you do that).
Last year we put white lithium grease in all recycled motors. It doesn’t have the low viscosity as some of the high speed motor oils like SAE 5 or 10 have, but works well overall and seem to be a good choice for torque oriented tasks of Skyrise.
Be aware that lithium grease separates from its oil substrate over time. The can or tube needs to be shaken well before the application and you want to relubricate the motors if they were sitting idle for more than a few month.
For this year’s NbN launcher motors I am considering using something other than white grease, but not sure what would work best. Does anyone have any suggestion or good experience beside what is mentioned in this post?
This is the bane of my existence. I really wish VEX would improve on this. All it would take is a better rubber strain relief. It is so cheap it just rips within weeks of use.
That’s easy compared to some of the things our sister teams do, sometimes they will put on zip-ties too tight and when they try to cut them off they cut the wire in half. I see tons of motors and motor controllers like this. At least were able to fix a few of them with electrical tape.
This is annoying, but at least easy to fix, as you are allowed to repair external wires, for example by soldering it back together or snipping off the end and soldering on a new one. But when it’s right at the edge of the motor housing it has got to be really hard to fix, you would have to solder a new one onto the board but I’m not too sure if this would be considered legal.
Hmm true, I did not think of the plastic being so close to the wire melting… perhaps they have some sort of crimp/cringer that solders where it contacts the wire of sorts?
