Gyros Explained

[Steve]

Rob

Here you go mate.



My push rod was actually touching the main gear at one extreme of its travel when I put the servo in its intended position, which is why I moved it.

[robgt]

Nice and clear

Your throttle linkage looks pretty close to the tank?
Cheers,
Rob

[Steve]

Nice and clear

Your throttle linkage looks pretty close to the tank?
Cheers,
Rob

It isn't. It's just the photo making it look that way. There's loads of room for it.

[robgt]

Cool - that's ok then
Do you have any info on the required program mixes for the Tx to allow the use of 140° ccpm mixing on the Vibe?
Cheers,
Rob

[Britflyer]

The tail offset thing is a common improvement to the mechanical setup of alot of models. I've been doing it for years on some of my models. You have to offset the tail servo horn in the right direction, relative to the tail............ I could try to explain but here it is from the experts !!!

Quote:

Servo Arm Neutral Position

Very few model helicopters have truly corrected tail rotor geometry and this creates a natural flaw in the tail rotor’s ability to stop at equal speeds form left and right hand pirouettes. When hovering a right-hand rotation model helicopter, we need about 8 degrees of tail rotor pitch to hold the tail stationary. If we then make a demand for full right tail rotor, the tail pitch changes from 8 to about 40 degrees. This equates to a change of 32 degrees of tail pitch from neutral to full right tail rotor. If we now return the tail linkage to neutral and then apply full left tail rotor, the ideal change in tail rotor pitch would be from 8 degrees of right tail to 40 degrees of left tail rotor, which equates to an overall change of 48 degrees of tail rotor pitch. So the tail rotor linkage will obviously take longer to move from neutral to full left in comparison to neutral to full right. So when stopping from a right hand pirouette, the servo will reach full left tail linkage travel slower than when stopping from a left-hand pirouette where right tail is activated. In real terms, this means that the gyro gain is in effect higher for the right hand direction and lower for the left direction. This has the effect of producing a slower stop from a right-hand pirouette and a swifter stop from a left pirouette. This is why the CSM SL 560 has an interface function called ‘dual gain tracking’ to help balance out incorrect tail rotor geometry.

However, there is a natural limit to any gyro's ability to compensate for incorrect tail rotor geomettry. So it does help to introduce a mechanical differential on the servo arm to assist the gyro in this respect. This is best thought of as a mechanical offset and in the case of a right-hand rotation machine, the servo arm is offset in the right direction of tail rotor. This has the desired effect of reducing the servos mechanical effectiveness for the right direction of travel and enhancing it for the left. By offsetting the servo arm and using the ‘dual gain-tracking feature’, it is very easy to achieve an equal speed to the stops for each direction.


End Quote:

http://www.rcmodels.org/csm/getting_...your_csm_s.htm

Cheers

Paul

[Stuart]

Very informative and top class thread...As asked I've copied it into the beginners section and make it sticky too.

[robgt]

Thanks for posting that Paul - thats helped my understanding of why I've done that on my Vibe
I know it works - I now know why!

Cheers,
Rob

[kevinh]

usefull information on the gyro

i certantly benfit from it.

[Rotorhead]

The Manager, sorry but there are special cases where you have to use trim or subtrim with HH.

The most common one is where you are using an older HH gyro or a cheap one, and especially when you are using different manufacturers equipment.

For example I had a few years back a JR G550T and was using it with futaba gear, the thing was that because its an older design it had a hardwired figure for what it regarded as the centre stick pulse length, a figure of 1500 microseconds, unfortunatly futaba and JR use different values (futaba 1520, JR 1500) this means that the futaba reciever was sending a slightly longer pulse at centre stick than what the gyro uses, the difference was interpreted as a command by the reciever to the gyro to slowly yaw.

This was not drift, I checked at the time with JR and they said it was because the gyro always used 1500, and it meant that with futaba recievers you have to add some subtrim in to bring the pulse length down to the 1500 microseconds that the gyro uses for centre stick, basically confirming what I had thought it was.

Once I added the subtrim in, it held the tail straight as an arrow, and I never had to touch it again.

More modern gyros calibrate the centre stick pulse length upon start up to avoid these brand incompatibilitys, but some cheap HH gyros also suffer from this as they have gone for the simpler and cheaper option of hardwiring it rather than making it able to self calibrate.

If you want, you can add this exception to the rule to that document