Broken belt, sticky rotor

[SurfCity]

My belt broke yesterday, and getting a new one installed turned out to be quite an undertaking. Removed the side panel from the tail, ran fishing line through the tube to pull the belt through, removed the main shaft, and worked REALLY HARD to get the main gear and mast collar out. The tolerances are so tight that there is just zero wiggle room. I must have fussed with it for two hours.

I reassembled things and tightened the mast collar grub screw, and my rotor no longer spins freely. It runs and flies fine, but now when I cut the power, the motor and rotor run down together. Before, the motor would stop and the rotor would freely spin. If I remove the mast-collar grub screw, the rotor spins freely as before. But then, of course, the mast falls through to the floor.

I know everything was installed correctly as before. I've wiggled and jimmied and fiddled. I spent two more hours and disassembled the whole thing to replace the old collar with a fresh one, which is slightly different. No change. Nothing frees the rotor. Like I said, it runs fine. I know this issue has come up before. Any clue?

[Buzzkill]

No idea on the reason the main rotors are stopping so soon unless its the oneway bearing.

As far as getting the gear out, I take out the two bolts at the back and swing the upper frame up. It makes it a lot easier in the long run npt to mention saves time.

[mrivers]

Maybe the tail belt is too tight. I loosened mine recently, and the main rotor will spin freely longer now.

[crabfu]

I've had this happen before... rotor stops quick, but flew fine, and I lived with that for quite a while. The fix, is going to sound a bit mickey moused, but it worked... I had an unrelated vibration issue, and decided to mark the center of the rotor on top, spin it to see if that center mark is perfectly one dot, or making a circle & a slight wobbling caused the vibration (which turned out not to be the case). To do this, I decided to give it a little push on the top with a phillips screw driver, sort of center punch lightly on the soft aluminum to mark the center. I pushed LIGHTLY and it made a tiny mark, then I spun the rotor to check if it is centered.... to my surprise it spun completely free... and not wobbling what so ever. The vibration issue turned out to be the cf plate / bearings in the tail.

Anyway, my best guess is that the shaft collars or bearings weren't seated perfectly, and a light push fixed it. I too spent hours trying to figure out why it wasn't spinning freely, took so many things apart many, many, many times. If you loosen the boss screw on the collar on top of the main gear, it will probably spin freely, but with it tight, it drags. Try a very light push, it'll probably fix it :)

hope that helps.

-Crabfu

[Jetleaf]

I had the same thing and discovered I had to much pre-load on the main bearings. Loosen the mast collar that sits above the main gear and give it a spin and see if she is free, if so tighten the grub screw and be careful not to pull up on the rotorhead. The belt can be to tight and make sure the boom is parallel to the surface the heli is sitting on.

[SurfCity]

Well, guys, thanks for the suggestions. I spent several hours today trying them all, and none worked. Put it back together and did some hovering. It's very smooth, but the collective is pretty frenetic; without that freewheel effect, the rotor speed rises and falls exactly with the motor speed. This makes for super-quick altitude changes -- which actually is pretty fun. It began loosening up, too; the motor would stop, and the rotor would continue to freewheel, although much less than before. So we'll see; maybe it'll get looser still.

During the disassembly-reassembly session(s), I noticed a fair amount of side-to-side vibration -- a buzz -- in the carbon-fiber tail piece, although none in the shaft or control rod (both aluminum). I removed the tail blades and spun it up again and saw zero vibration. So those tiny blades have a big effect. Balance them carefully, and get them tracking as well as you can (with hot water and a little twist).

When this little bird is together and tuned and balanced and trimmed and everything's humming, it's a thing of beauty. Really. I was making pillow-soft, spot landings in my living room beneath a tiny rotor spinning probably 150 mph. Zowie.