I'm assemblying a Hangar 9 Twist 40. I have procurred some long servo arms (1.25", I think) for use on the rudder and elevator servos. I have standard Futaba 3001 servos.

When do I need to be concerned that the servos don't have enough umph for the job. As they are set now, the servos will only travel from about the 4 o'clock to the 8 o'clock positions to provide maximum control surface deflection (set by ATV).

Should I bring the push-rods in on the servo arms so they rotate more?

What will be an indication that the servos aren't strong enough? Seems it will be difficult to determine when the plane is flying.

Thanks for any enlightenment.

I have 3001's in my Twist with normal length servo arms. They don't have any problem. To gain more conntrol movement move the pushrod further out on the servo arm, and further in on the control horn. My movements on high rates are as far as the controls will move.

Thanks for the reply but I know how to maximize the throw, that's not the question.

With long servo arms and ATV I can set up to where the servo moves a minimal amount to get maximum control surface movement (i.e. faster) , but this requires more servo torque. Question is how does one determine that servo doesn't have enough torque?

Why are you aiming for your servos to move as little as that? You wont really notice servo speed when you're flying unless you've got 150% ATV on ail and you go from, say, full left then instantly full right. Even then, you would only notice with a medium/slow speed servo.

Go for max servo deflection and then alter your output arm and horn after that to get the desired movement. With the output closer to the centre of the servo you will get more torque. Same out at the surface (further away = more leverage).

Once you've done this you can then check you've got enough torque by flying full speed and doing a rates off roll. Then go to idle and if the roll rate speeds up as the airspeed comes down you've most likely got insufficient torque. You can do the same thing on rudder.

Basically you want to set your ATV as high as possible.

Hope this helps,
Angus

Angus,

Thanks.

>>Why are you aiming for your servos to move as little as that?<<

Just seemed to be more efficient for the servo arm to rotate from say 4 o'clock to 8 o'clock than like 3 to 9.

>>Once you've done this you can then check you've got enough torque by flying full speed and doing a rates off roll. Then go to idle and if the roll rate speeds up as the airspeed comes down you've most likely got insufficient torque. You can do the same thing on rudder.<<

OK. Good thought.

>>Basically you want to set your ATV as high as possible.<<

Why? To maximize torque?

It maximises the leverage/torque of the servo as you can put the pushrod outlet closer to the centre of the servo plus you get better servo resolution and any slop in the gear train will show up less.

I tried what you were going to try on a modified Alliance and couple of years ago. Basically huge output arms and 100% ATV. At full speed it was like you were just doing a normal roll and well you chopped the power it would immediately start rolling faster. That was with hi-torque servos and 6V. I then put on smaller arms, upt the ATV and lived with the slower surface movement and it was cured.

Angus

Thank Angus. I'll shorten the servo arm a bit.