I have an odd thing happening to my helimax axe cp. I have never used the idle up switch so this only happens in the fixed pitch setting. When I kill the power the heli spin violently to the right or clockwise until the the blades stop the spinning. the tail motor doesn't keep running after the head stop or anything like that. Any ideas?

Sounds like your tail motor is not functioning properly. If it is about to go it might not get up to speed and hence you get the spin.

Thanks for the response. The problem is it is spinning the opposite way of the torque of the main blades. It other words unless I am mixed up. The heli shouldn't "want" to spin clockwise it should want to spin to the left of couter clockwise due to the spinning of the main blades. This suggest it isn't the tail motor because if it was the tail motor failing to spin fast enough it would would spin the other way. I'm still lost on any ideas.

GravityTester,

I'm not sure what you mean by "kill the power". I'll assume you mean a rapid movement of the
throttle stick to the full down position.

And as you didn't mention otherwise, I'll assume your heli flies normally.

There is only one thing that can provide a force to yaw the heli to the starboard, or clockwise -
that is the tail motor.

So what is happening is - you chop the power but the tail motor does not reduce the force that was
necessary to keep the nose straight against the port or counterclockwise yaw force from the main rotors.

The nose turns clockwise due to the force from the tail rotor.

If you are using the stock 3 in 1 board, I can think of a couple "maybe" causes. One the tail motor esc circuit is defective. Two the gyro gain is set too high. And last, the left right bias adjustment is set to extreme right tail bias.

The Axe manual says: Left/Right Bias – Is used to obtain a balanced feel between
left and right tail rotor inputs. The adjustment is very
sensitive so only make small changes. Turn clockwise to
increase the left tail rotor bias.

I've never really understood what the "bias" is, but turning the potentiometer can make the tail motor start turning.

Here are some things to try:

Reduce the power very slowly and be sure you are not putting in any right rudder, does the problem still occur?

Reduce the power enough so the heli is not light on the skids, then put in full left rudder and kill the power.

Turn the bias adjustment on the 3 in 1 maybe 1/8 turn clockwise and see what happens. If the problem is worse, turn it 1/4 turns counterclockwise.

Turn the gyro gain all the way down and then up maybe 1/8 of a turn.

I'd like to know what you find out.

Good luck!

Thanks for the response. It does seem to suggest that I have an over active tail rotor. However this isn't the case because as it spins the tail motor is not on. you can see it as it spins that the tail rotor isn't on and also I have brought the throttle up slowly not enough to even come close to taking off and brought the stick down fast and it still spins to the right all with the tail motor never coming on.

GravityTester,

OK, this is getting interesting.

Imagine a servo actuated clamp, with the body attached to the heli frame and the jaws positioned over the main gear so that when the clamp is activated, the jaws grab the main gear and instantly stop its rotation and the magic clamp also cuts power to the main motor.

Now with the rotors and main gear turning, activate the clamp, what is the body of the heli going to do?

All the energy in the angular momentum of the main gear, shaft, head and rotor, all of which the clamp "froze", is going to be transferred to the body of the heli and it is going to turn clockwise.

In reality, the clamp could be the main motor body-shaft interface, the pinion gear-main gear interface or the main bearing-main shaft interface. For the main motor, the motor body is the body of the clamp and the shaft/pinion gear represents the jaws. If the main motor suddenly froze up so the motor shaft could not turn, the pinion gear would stop the main gear from turning, and the heli would rotate clockwise until the rotors, etc. stopped turning. Just the situation you describe. This might also happen if the pinion and main gear are set way too tight or if there is damage to the pinion or main gear, i.e. when the motor is running it overcomes the excessive friction. When the power is cut, instead of rotating relatively freely, the main gear might be "binding" with the pinion.

Similarly, if the main bearings "froze" and stopped the main shaft from turning, and provided the main
motor was not running, the heli would turn clockwise.

When you cut the power, the main motor stops driving the main gear so the force that yaws the heli counterclockwise also stops. Either the main motor shaft or pinion/main gear or the main shaft is "freezing" and transferring the rotational energy to the body of the heli.

The main gear and pinion should mesh with a slight amount of "play" between the gear teeth. Because the main gears on the Axe are not especially true, you need to check the play all around the main gear.

If you loosen the motor mount bolts and disengage the pinion from the main gear and spin the rotor it should be obvious if there is too much drag. The rotor should turn with almost no friction.

If the rotor turns freely with the pinion disengaged, and the gears were meshed correctly, then the my guess is the main motor is defective.

Please post what you find out.