When flying chopper, flew good, had a crash and now after repair of obvious problems, flight to about 6 inches off the ground the chopper goes into a wobble and has to be shut down before it crashes. It doesn't do it when you hold onto the chopper only when it's flying independently. Maybe 4 into 1 mixer or gyro. Any ideas?

Bent main shaft
Bent feathering spindle
Blades out of track
Something on the head not balanced

Thank you for fast reply.
Are you replying to the shaft that hold main blades.

main shaft = vertical shaft with main drive gear near the bottom and rotor head assymbly on the top

feathering shaft = horizontal shaft with blade holders on each end (blades pivot on bearings that ride on the feathering shaft)

tracking = a way of determining if both blades are creating an equal amount of lift. If you have the helicopter rotor blades spinning near or at flying speed and you look at the blades from the side and at the same level (wear eye protection!) you can see if the blades are tracking correctly. if the blade tips are at the same height and look as if they are following the same path then they are tracking correctly. if you see one blade higher than the other then the high blade is making more lift. normally you would either decrease the pitch of the high blade or if desired, increase the pitch of the low blade one turn at a time until they track correctly. If you are having trouble getting the blades to track correctly, that can be an indication of a bent feathering shaft.

balancing is pretty obvious. I found the other day that one of my flybar paddles weighed considerably more than the other. I drilled little holes in it until enough weight was removed to make the two equal. you have to do that with the main blades also but use some tape on the light blade to increase its weight to match the heavy blade. You could also use tape on the light flybar paddle to make them equal weight.

Sounds like a bent main shaft....the shaft that goes through the main gear, swashplate and head that holds the main blades. You can try to straighten it but its cost is only $6 to replace.

These main shafts bend easily so buy a spare or two while your at it.

a test you can do is....

remove the main blades and disconnect the tail motor from the 4 in 1 (note the way the wiring is connected prior to removal to insure proper reconnection)

Carefully check/measure to be sure the paddles are equal distance from the center hub and that both are aligned horizontal to the swashplate, when turned/aligned both side to side and front to back.

Spin up the main motor and look at the top center of the main rotor head. If the main shaft is bent, you can detect the "wobble". If your heli is wobbling enough to almost fall over, this should be very obvious visually with this test.