camra88

OK, so i tap a wall with the main rotor with my esky. The rotor head busts (SK004). I buy a new one from hobby-lobby.com. I get it, install it, and had no problems installing it at all. I take it on its first flight, and it vibrates so bad, that the main rotor and tail rotor hit each other. Its progressive, though. It will start to shake a little bit... i have little control... then it starts to shake more violently, untill the rotors are hitting each other and it crashes before i can land it. I quadruple-checked all my work, and cant see anything wrong. I can only get the problem to go away (I think so... the problem is on and off) by tightening down the rotors as hard as i can. When i did that, i didnt seem to have a problem. But I never had to tighten it down so much before... Why is this happening? Is thore more to it then just that, or is the problem really that simple?

racemiata

It's most likely the main shaft got bent in the crash. It happened to mine before.

Remove the main gear/shaft from the heli. Clean the shaft (any dirt can skew the result) and roll the shaft on a perfectly flat surface (e.g. marble or mirror) to check for warppage. With the "pin" hole in the middle, the main shaft can easily get bent. Just try your best to bend it straight and it should be all good.

camra88

From what i can tell, i can't see any damage to the main shaft. I did what you said, but since the big gear was glued to it, i had to have the gear on the edge of the taple, while i moved the shaft around the table. I didnt see anything bent...
The pin that holds the rotor head to the main shaft is kinda bent, could that be the problem? Also, the problem is off and on... like it has a mind of its own...

racemiata

It's ok if the pin is bent. That shouldn't affect the balance.

However, to bend the mainshaft, you don't really need to hit it onto something during a crash. At normal operating head speed, a big sudden halt on the rotor (like in a serious crash) could bend the main shaft. A bent small enough to be barely noticeable on a perfectly flat surface can bring the rotor head out of balance. What happens is that the pin hole weakens the shaft at that point such that the mainshaft is more likely to bend in the direction of the flybar (i.e. perpendicular to main rotor). When this happens, centrifugal force "unfolds" the blades off-parallel to each other and creates uneven lift (like when blades are not tracked). This in turn shifts the blades even more off-parallel and the vicious cycle comes in. That's why sometimes it gets small vibration at first and then progressively gets worse and eventually shakes like crazy when the heli is lifting off. And that's why a temporary solution is to manually unfold the blades to perfectly parallel to each other and tighten them to prevent going off-parallel.

If you just roll the shaft (and gear) on the edge of a table by itself (especially at a higher speed), you may or may not be able to notice the small warpage enough to initiate the drastic vibration. To check for warpage on the mainshaft, I clean it from any dirt and then file off any protrudings around the pin hole created by the torque and/or crash. Then I put the shaft on the edge of a marble table (gear hanging off the edge) such that I can see light thru' potential slit between shaft and the table. That means I have to almost lay my head on the edge of the table and use only the one eye that's closer to the table. Then I use 2 fingers to press on the extreme ends of the shaft and slowly roll the gear thru' one revolution with another hand.

If you indeed can't find any slight bend on the mainshaft, next thing to check is the main gear. Of all the main gears I've seen, there's always some kind of out-of-round. Many times having set up from the factory, gear lash at one point was OK but not on another point of each revolution. In those cases, I set the gear lash at the point the 2 gears are closest together to make sure there's always enough (but not too much) gear lash.

If those check/fix won't do it, maybe check for the obvious (you should've done those at first really). Is there any binding on the new centre hub? Is the flybar balanced on either side? Are the flybar paddles parallel to the rectangular frame the flybar mounts to? Do the blades still track OK? Is any balljoint popped out (or in)?

camra88

after i put it back together, i flew it in my living room, and had no problems. And yes, i did check all the obvous things first. Dunno... If i have the problem again... i will take it apart and do what you said with the main shaft on the table, using 2 fingers on both ends, etc.

Thanks for that help, its appreciated!

Kalocals

i have a honeybee and i apologize for my typing..i have abroken hand...my esky ccpm honeybee had vibration from the pitch adjustment being off...

[email protected]

Sam