Winfred
07-08-2010, 08:52 AM
I made posts a while ago about a snapped scorpion motor shaft, that had not seen that much of run time. And broken tail push rod guides.
http://helifreak.com/showthread.php?t=224688
http://helifreak.com/showthread.php?t=219363
Here is how it all went down.
It all started with small tail kicks that I could not get rid of. I was thinking vibrations, so I changed main shaft, feathering shaft, flybar and flybar paddles. I balanced and re-balanced tail blades and main blades, but nothing helped. New set of main and tail baldes.. nothing. Played around with different lenght on the tail servo horn, nope, not that either. One day the vibrations went so bad that the tail servo just snapped the tail rod guides. The tail must have been doing back and forth kicks so hard that it did not show on the tail. Instead of moving the tail, the energy went into flexing the push rod, and then snapping the guides. A while after, when it was time to re-check the gear mesh, I noticed that the shaft support bearing had come loose. Did not think so much about it and pushed it back with some green loctite. A few flights after that and the motor shaft snapped. At that point I really wondered how this could have happened.
Now when knowing what the cause is, looking at the remains of the shaft shows that the bearing was having a party and oscillating around the shaft big time. Well, that would probably be the source of the hf vibration. Even though I re-attached the bearing the shaft was probably already much weakened by the vibrations, and the heat generated by metal vs metal contact. The pinion spacer was a bit blueish indicating around 500F. And the side loading from running a loose bearing would have stressed the shaft quite a bit.
Now after the shaft change I also noticed that I have gained +600mah in flight time, so it was robbing the system from a considerable amount of power. Just check the two graphs. The first from when the bearing was loose, and the second after the fix.
So if you have a weird vibe, remember to check the support bearing.
http://helifreak.com/showthread.php?t=224688
http://helifreak.com/showthread.php?t=219363
Here is how it all went down.
It all started with small tail kicks that I could not get rid of. I was thinking vibrations, so I changed main shaft, feathering shaft, flybar and flybar paddles. I balanced and re-balanced tail blades and main blades, but nothing helped. New set of main and tail baldes.. nothing. Played around with different lenght on the tail servo horn, nope, not that either. One day the vibrations went so bad that the tail servo just snapped the tail rod guides. The tail must have been doing back and forth kicks so hard that it did not show on the tail. Instead of moving the tail, the energy went into flexing the push rod, and then snapping the guides. A while after, when it was time to re-check the gear mesh, I noticed that the shaft support bearing had come loose. Did not think so much about it and pushed it back with some green loctite. A few flights after that and the motor shaft snapped. At that point I really wondered how this could have happened.
Now when knowing what the cause is, looking at the remains of the shaft shows that the bearing was having a party and oscillating around the shaft big time. Well, that would probably be the source of the hf vibration. Even though I re-attached the bearing the shaft was probably already much weakened by the vibrations, and the heat generated by metal vs metal contact. The pinion spacer was a bit blueish indicating around 500F. And the side loading from running a loose bearing would have stressed the shaft quite a bit.
Now after the shaft change I also noticed that I have gained +600mah in flight time, so it was robbing the system from a considerable amount of power. Just check the two graphs. The first from when the bearing was loose, and the second after the fix.
So if you have a weird vibe, remember to check the support bearing.