HELP Heli spinning problem

[AGM]

I have a silverlit RTF helicopter. Had loads of fun with it until recently the heli started spinning. Due to this spin that heli can't even take off anymore. Can any bro give me some advice on fixing it? Will appreciate any advise cause this heli is of sentimental value to me. I fly planes but know nuts about the mechanisms of a Heli

[yhchoong]

My best guess is that 1 of the main motors has burnt out - I have a Syma S107 which did the same spinning thing after one of the main motors started to die.

A co-axial heli like yours has 2 main rotors which are counter-rotating. One rotor spins clockwise, and from physics of action-reaction forces this rotor will exert a counter-clockwise torque on the heli, making the heli itself want to spin counter-clockwise.

The other rotor spins in the opposite direction - counter-clockwise. Similarly, it exerts a clockwise torque onto the heli itself, making the heli want to spin clockwise.

When both motors are working fine, they exert the same amount of torque but in opposite directions, so essentially the clockwise and counter-clockwise torque cancels out. Thus the heli will not have a tendency to spin in any direction.

The spinning problem arises when after many, many flights or a few bad crashes, one of the main motors start to burn out. So it becomes weaker and will not produce as strong a torque as the other main motor.

What happens next is that the stronger main motor will then cause the heli to spin in the direction of its applied torque, since the weaker motor no longer has the ability to counter this fully.

The other possibility is that if your heli has a gyro - it died or isn't working properly anymore.

[SpinOff]

check the gear drive for both rotor,

most likely a gear pinion had slips off.

my little nephew had one that after some knock one of the gear pinion will slips off.

just push it back and u r good to fly.

[AGM]

Thanks guys for replies.

Have opened up the heli, all looks ok except for the gear of the rear motor. The small gear that connects to the motor shaft does not have a clip to secure it, hence it can slide up and down. But when the motor is running it seems to rotate fine. Perhaps I will find a way to secure it and hope it helps. Or else, then could be motor burned.

But i realised that when i cut throttle, the top rotor spins to a stop gradually. The bottom rotor stops rather abruptly like there's some fricition.

[yhchoong]

Touch the motor that controls the bottom rotor after you run the heli for awhile. Is it very hot to the touch?

[xuen7]

Just guessing here, but i wonder if you are able to tilt the tail rotor horizontally down to point its thrust against the direction of the spinning heli to cancel out the piro? hehe