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

[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

[Kwickkwack]

Thanks for a great article, it has explained why my both my raptor and my Mini Titan are very slow to turn, i have the gyro set to 100% movement, and have set the travel via the transmitter. I had a feeling it was a setup problem, as both are using a 401, and my other two helis turn much much quicker.
If I set the movement up on the governor, what setting would you recommend on the TX. I assume i do the basic set up with it at 100%

[Steve]

Thanks for a great article, it has explained why my both my raptor and my Mini Titan are very slow to turn, i have the gyro set to 100% movement, and have set the travel via the transmitter. I had a feeling it was a setup problem, as both are using a 401, and my other two helis turn much much quicker.
If I set the movement up on the governor, what setting would you recommend on the TX. I assume i do the basic set up with it at 100%

If you want a faster pirouette rate, just increase the rudder end points on your Tx. You can go over 100% if you want to. I have 110% one way and 120% the other wat on one of my helis that has a 401 gyro. I've set the end points to give approximately the same piro speed in each direction, by trial and error at the field.

[Steve]

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

Thanks, and very useful info, but the aim of the document is to explain generically how gyros and tail control systems work, rather than get bogged down into specific moddels and manufacturers.

Personally, I've only ever had experiences of CSM, Futaba and one other cheapy that was my very first gyro, and I can't remember the name of it (something 2000 I think). Anyway, the theory that I've tried to put across works for all the gyros that I've used. Like I said, it's written from my own understanding of the devices, and attempts to explain what the average club flyer actually needs to know in order to get the most out of, and setup their gyro acurately.

[Rotorhead]

No probs, just thought it was worth mentioning, since some people have looked like they had seen a ghost when I have told them that, and some just refuse to believe it until it cures their problem with the tail.

[kevinh]

would that have been a vision 2000 heading hold gyro

[Rotorhead]

would that have been a vision 2000 heading hold gyro

It can affect many gyros, but mainly the older/cheaper ones.

I hav'nt had a vision 2000 and by the talk at the time I feel good that I didn't get one, from what I heard about it, it may be that it suffered from the problem.

[Steve]

That's the one I can't remember the name of - the Vision 2000.

My very first gyro in my very first heli, a Hirobo Shuttle. It worked ok for my early hovering days with a JR 811 tail servo, but I soon upgraded it to a CSM 560, just because I was a bit flush that week!

I think the Vision 2000 only cost about £40 back then, so you pays your money....

[moyesboy]

Great stuff manager!

It amy be worth mentioning that although the best performance is avaiable when you have set the mechanics up to fly hands off with zero trim in rate mode, it is possible to do a quick setup as long as the heli is close to holding in rate mode - it is quite fiddly to get it precisely right and it does vary a bit with head speed too.
With both futaba and CSM, after you have it nearly mechanically trimmed out in rate mode you just hover nose into wind in HH and then flick into rate and back five or six times slowly. now the gyro memorises the neutral position its using in HH and uses that for rudder stick centre when you go into rate mode.

I just did this thisevening flying a 401 in place of the normal CSM560 on my raptor50. The mechanical setup was so close and even the gain from the 560 was close with the 401 - I just had to reverse the gain channel so the switch worked the same way. I was amazed that I got great performance out of the 401 after only about 1 minute of fiddling about!

Also, I',m not sure you paragraph about pirouette speed in FF flight/strong wind is correct. If the gyro was in rate mode then it would wip with the tail slow into wind and fast down wind, but unless you travel fast enough to overpower the tail rotor the pyro speed should be constant in FFF while in HH mode.

[Steve]

Great stuff manager!

It amy be worth mentioning that although the best performance is avaiable when you have set the mechanics up to fly hands off with zero trim in rate mode, it is possible to do a quick setup as long as the heli is close to holding in rate mode - it is quite fiddly to get it precisely right and it does vary a bit with head speed too.
With both futaba and CSM, after you have it nearly mechanically trimmed out in rate mode you just hover nose into wind in HH and then flick into rate and back five or six times slowly. now the gyro memorises the neutral position its using in HH and uses that for rudder stick centre when you go into rate mode.

I just did this thisevening flying a 401 in place of the normal CSM560 on my raptor50. The mechanical setup was so close and even the gain from the 560 was close with the 401 - I just had to reverse the gain channel so the switch worked the same way. I was amazed that I got great performance out of the 401 after only about 1 minute of fiddling about!

Also, I',m not sure you paragraph about pirouette speed in FF flight/strong wind is correct. If the gyro was in rate mode then it would wip with the tail slow into wind and fast down wind, but unless you travel fast enough to overpower the tail rotor the pyro speed should be constant in FFF while in HH mode.

You're right about doing the mechanical setup on gyros - it really doesn't take very long to do, just a few minutes. But, that assumes you understand what it is you are trying to achieve, and how to do it. It's like everything in life - practice makes perfect.

As for the piro speed in fast forward flight - you're right again, but have you tried it in HH mode while travelling fast? Unless you've got bags and bags of tail authority, it will be slower during the first have than the second half, because the gyor will send the servo to its full travel position in an attempt to attain the desired piro speed, but of course once the servo gets to its end-stop, it can't go any further (limited by the gyro of course), so the gyro can do no more at this point, so the heli will piro at whatever rate the tail geometry allows it to.

Even with my Vibe 90, fitted with a Futaba 611/9256 combo, which is arguably one of the finest heli/gyro combinations available, the piro rate is noticeably uneven for its first and second halves during fast flight.