Motors Motor maintenance

[Eggy 71]

I had a weird issue today. I'm throwing it out there to see if anyone else has had a similar experience. After starting up my Trex 550e it started acting funny after about 1:30. It seemed to loose power slightly and then totally causing an auto rotation. Battery was/ is fully charged. I started up again and was testing the throttle on the ground. It was laboring occasionally and then all of a sudden it seemed the main gear locked up and took a couple chunks out of the main gear.
The one way bearing and tail gears are great. The blades slowed down very gradually and there was no drag or binding. The issue is either the motor, ESC or main gear.
After the lock up the gear messing seemed fine. I hadn't adjusted it in at least 20 flights and the motor was tight in position, it hadn't moved. That made me think it's either the motor or ESC. After realizing I've never serviced the motor and there is at least 2 hrs on it since I've owned it and who knows if it was ever looked at in the last 5 yrs, I took the motor apart and cleaned/ lubed it. All seems good, not much grit and the bearings are sealed so not much to really lube. After cleaning the resistance seems to be gone but I havent tried flying yet.
Do ESCs ever go bad and could stop the motor that fast or would something mechanical (grit or something) that could have caused the motor to bog down and then stop suddenly?

 

[Tony]

Are you saying it stripped the gears just under normal power? If so, I'm thinking main shaft bearings are gone. Regardless, you need to remove the head and motor and check every bearing in the drivetrain.

 

[Eggy 71]

It was running at around 60% throttle and just locked up torqueing the heli a bit. I took the head off and then removed the main gear and the motor. I have another main gear ( got a ton of spare parts with the heli) and replaced it. Everything seems to move smoothly. There is no binding what so ever. That is what made me start looking at the motor. It had a little grit but nothing much to worry about and nothing that would have caused it to lockup. Now I'm thinking ESC , it's most likely the original from 6 yrs ago but not sure, no markings on it.

 

[Smoggie]

The motor stopping quickly wouldn't be expected to strip a gear, the freewheel looks after that. The motor and main gear can stop suddenly but the rotor can keep spinning so no reason for the gear to strip, there is nothing driving it.

So I'm thinking of a couple of things... maybe you have the brake set in your ESC, does the motor stop very suddenly when shut off power?.. And possibly the one-way bearing is sticky?

 

[Tony]

Something has to have stopped the head. As Steve stated, if the motor has brake turned on or the motor locks up (should have mentioned this earlier), the head will just freewheel since it has a OWB. The head just stopping cold in its tracks tells me there is a bind somewhere in the head or tail. Or something like a linkage came off the head.

 

[Eggy 71]

I wouldn't have thought a quick stop would affect the main gear either but I'm scratching my head on this one. The heli lost power and ultimately made me land to start all this. Either something added a lot of resistance if it was mechanical or the battery which was fully charged or the ESC had an issue. I keep looking at the OWB and it's smooth as butter. I cleaned up the OWB a few weeks ago as it was showing a quicker stop and some resistances. All the drive gear spins very freely, it will probably take 30-45 sec for the blades to slow and stop after shut down.
First I thought the pinion/main gear mesh was too tight from when I put it back together after cleaning the OWB but it was tight and seemed good. That's when I started to look at the motor. It's a pretty simple part and the motor shaft bearings are sealed so there really isn't much to do. That was my original intention for this thread but got side tracked, SQUIRREL.
1) How long are motor shaft bearings usually good for? 50 hrs, 500 hrs ? Could they be wearing out? The bearings still moves freely and seem tight with the shaft.
2) Can anyone confirm which ESC is on this bird? There is no markings on it and I'm not to familiar with older components.

 

[Tony]

Live expetancy of motor bearings depends on a number of factors including how often you clean the bearings and lube them. And that looks like either an older Align ESC or maybe a hobbywing.

 

[Smoggie]

There is no way that the motor bearings, even if they were worn out, could cause the main gear to strip. Like said already, if the motor did lock up that would not cause the main gear to strip because the OWB cant drive in reverse. The main gear would simply stop turning along with the motor.

I think you are barking up the wrong tree on this one. Is it maybe possible that the gear was already stripped due to some previous mishap and what you just experienced was the dive skipping as it passed the missing teeth?

 

[Eggy 71]

I agree with you on that. That's why I'm stumped. There is no added resistance in the OWB or the drive train. The main gear was perfect prior. The only thing I can think of is the OWB had something that added resistance, caught, and then completely cleared itself.