Rudder Control Rate or HH Setup

[waveydavey]

This started in another thread and I didn't want to carry it on in there, sorry for meandering.

So, why does a HH gyro need to be setup in rate mode for it to work better, or some need to be setup like this.

Now it may be my inability but I can't tell any difference whether I do this or not. Accelerations, stop gains etc surely make up for the requirement for the heli to hover without weather vaning in rate mode.

I conned myself on earlier helis that this worked but you know what it didn't, placebo effect I think

[scallybert]

I think it might have been the case with old, slow servos; etc. With fast, modern ones, you can run high enough gains that the P & I gains can take care of pretty much everything.

Ideally, the 'default' tail pitch would prevent yaw; via a mechanical set-up. Similarly collective pre-comp would roughly take care of collective input; without rate damping getting involved.

So, a good mechanical set-up, would help; as would collective pre-comp on FBL. You hardly seem to need bothering now, with more than a rough set-up. [?]

[myxiplx]

Heya Wavey,

Well with you flying Vortex you might be interested to know that it's one of the FBL units where a rate mode setup is recommended to get the best performance out of the tail. Angelos himself advises to set the tail in rate mode.

The current Vortex firmware assumes that the central position for the servo is the neutral position on the tail, and it uses that assumption for stops. I know the 3GX is similar, and there are other FBL systems like it too. Vbar however uses a different approach and so you wouldn't see any benefit at all there.

On the Vortex, without setting rate mode it's hard to get CW and CCW stops equal, you will end up with either a soft stop one side, or a bounce back on the other. You can work around it by tuning the gains and deceleration setting, but all you're really doing there is making your stops more gentle and giving the Vortex more time to react. It works, but really it's masking the issue.

To get the absolute best out of the tail you should set it up in rate mode, or use the trim flight function to optimize the tail pushrod. Once that's done the stops on each side should be much more even and you should be able to run higher stop gains and get much crisper stops.

Then once the gains are as good as you can if you see a single bounce back on stops a small decrease in the deceleration setting can be used to tune that out.

I believe it also helps even out your CW and CCW piro rates, but I haven't really tested the behaviour there without doing the rate mode setup so I can't be sure.

[waveydavey]

I use Vortex on both a 700n and e700 and no matter what I try results in good stops in both directions. They're not bad but no where close to the V bar. I haven't tried the rate mode setup as I don't and haven't seen the point but as part of a setup following a crash I'll give it a go. I'll report back in this thread what I find, it'll be on the e700. With all due respect to Angelos and after repeated criticism of the tail on the Vortex even he is doing something about it, reference the videos at a secret location in the South and the thread on here where some respected pilots can't get the tail right, whipping, uneven stops, etc So I'm not convinced the old set it up in rate mode will do anything but take up my flying time at the weekend. But, seeing as I started it I'll give it a go

[myxiplx]

To be honest, given the new firmware is meant to be out in a matter of weeks, it's probably easier to wait for that, but if you're doing it anyway I'd be interested to hear what you think :-)

[coolice]

Hey buddy.

There has never been a true reason given for why the rate mode setup works to my knowledge, but it does. Most probably Colin Mill from CSM could give an in depth explanation.
However from myself I have a theory that seems plausible.

Imagine you're hovering, the tail rotor is at its rate mode neutral position that has a small amount of pitch input to counteract the torque reaction. Then we command a piro from the model and release the stick for a quick stop, the tail rotor then returns to this neutral position with the small amount of pitch to counteract the torque which is the required amount, so the gyro has to make minimal tail pitch adjustments to hold the new heading.
Now let's visualise a tail with zero pitch at the neutral position and add in the same yaw command. On release of the rudder stick the tail rotor returns to the neutral position but with zero pitch to counteract the torque it then has to quickly compensate for the torque on the fuselage and throw in tail pitch and still then adjust with small changes to compensate for wind/conditions etc. So now we can see where the potential for wooly stops following a hard yaw stop can come from.

A helicopter naturally needs some tail rotor pitch to compensate for the torque reaction of the main rotors on the fuselage, so our models are no different to full size, but have electronic ( or mechanical :-) ) gyros to provide additional stability.
For many years it's been advised to setup in rate mode and that has stayed pretty constant throughout.
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[gazmk2]

Got to be honest I've never once done that! I fly vortex and all I do is put the tail blades to centre when the tail servo is neutral. I get perfect stops in both directions and no drift at all.

[Granpappy]

Hey buddy.

There has never been a true reason given for why the rate mode setup works to my knowledge, but it does. Most probably Colin Mill from CSM could give an in depth explanation.
However from myself I have a theory that seems plausible.

Imagine you're hovering, the tail rotor is at its rate mode neutral position that has a small amount of pitch input to counteract the torque reaction. Then we command a piro from the model and release the stick for a quick stop, the tail rotor then returns to this neutral position with the small amount of pitch to counteract the torque which is the required amount, so the gyro has to make minimal tail pitch adjustments to hold the new heading.
Now let's visualise a tail with zero pitch at the neutral position and add in the same yaw command. On release of the rudder stick the tail rotor returns to the neutral position but with zero pitch to counteract the torque it then has to quickly compensate for the torque on the fuselage and throw in tail pitch and still then adjust with small changes to compensate for wind/conditions etc. So now we can see where the potential for wooly stops following a hard yaw stop can come from.

A helicopter naturally needs some tail rotor pitch to compensate for the torque reaction of the main rotors on the fuselage, so our models are no different to full size, but have electronic ( or mechanical :-) ) gyros to provide additional stability.
For many years it's been advised to setup in rate mode and that has stayed pretty constant throughout.
.

This would be okay as long as you do hard stops in the hover. As soon as you change the collective load ie, climb whilst pirouetting, then your mechanical tail rotor pitch compensation is wrong. So you might as well let the gyro do all the work in the first place.

[Peteski]

Setting it up in rate mode simply takes some load off the gyro control loop as coolice explained. I use BeastX and the user manual states that it is not usually required to set up in rate mode if you are flying in HH mode. But it does say that it can help if your mechanical setup is "unfavourable". The tail on my heli is designed with a 3.5 deg counter-pitch when the bellcrank is at 90 deg. So I just set it up like that and fly. Tail stops are crisp in both directions and piro rates consistent CW and CCW, so I don't see that I would get any benefit from a rate mode setup.

[coolice]

This would be okay as long as you do hard stops in the hover. As soon as you change the collective load ie, climb whilst pirouetting, then your mechanical tail rotor pitch compensation is wrong. So you might as well let the gyro do all the work in the first place.

Hey Buddy.

Ah no, not necassarily, as you then move onto another form of tail control which can in it's simplistest term be called "revolution mixing".
On the Vbar for example, if you input collective pitch (or cyclic for that matter) tail rotor pitch changes are introduced to counteract the impact of these controls on the models ariframe, so on collective pitch inputs as you describe, a throttle to tail rotor mix is introduced to help keep the tail in check. Simply put tail rotor pitch is altered by the FBL controller with collective inputs.

Those who have not been in the hobby long, will probably not know what "revolution mixing" is, but may have seen it in their transmitter menus. Basically this is a mixing parameter that can be fine tuned to automatically input yaw/tail commands alongside collective pitch inputs made by the pilot, thus keeping a better hold of the tail during aggressive pitch changes as the tail rotor is automatically adjusted to compensate. Of course along came heading hold gyros and this feature wasn't really needed, but that is because it's built in already.
The last time I used Revo Mixing in the transmitter was when I flew for CenturyUK and we had fun with the FP Hummingbirds, as we could tame the tail even more with finely tuned Revo Mixing.

We then move onto other gains available within most FBL units, P Gain, I gain etc etc to help smooth out any other tendancys.

The bottomline is that there is benefits for most tail gyro's/FBL units out there when setup in rate mode, whether the pilot is at the point in his flying skill to notice the improvement makes this setup procedure a do or don't do affair, but if you're at a level that can benefit from it I'd say do it, as it takes minimal time.
What I have found in my training is that most people are frightened to fly in rate mode for fear of what will happen, experience helps one to set a pretty close neutral pitch position off the build bench, thus minimising any tail swing in rate mode. As Peteski has said above, some models even have this neutral tail pitch position designed into the controlling arms, making it even easier for the builder to set.
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[waveydavey]

Got to be honest I've never once done that! I fly vortex and all I do is put the tail blades to centre when the tail servo is neutral. I get perfect stops in both directions and no drift at all.

Perfect in both directions. I'll do this then tomorrow, I'll set my tail up as I do, same as you Gaz and without fannying around with other stuff I'll video the piro stops. Then I'll do a rate mode setup and video the result. Then I'll give up because neither method will work and I'll start fiddling with gains etc

Ian thanks, get your thoughts but these days with the sort of processing ability and programming available the unit should be able to predict the stop condition and there should be no bounce, soft stop etc The V bar doesn't do this, or not that I've experienced and doesn't need a rate mode setup, set in the middle, go do a trim flight and Bob's your sisters mother equal speed and stops. This isn't a comparison of the Vortex and V bar by the way, I use Vortex, nuff said. So I'll give the above a go and see what occurs

[GIXERMAN]

you never no Dave, up and coming update may help your issues with the vortex.

[waveydavey]

you never no Dave, up and coming update may help your issues with the vortex.

Hey Brian, I haven't got any really and I wasn't bashing my choice of FBL. My question was based around why bother with a rate mode setup, never understood why it's necessary. What I'm doing is a trial to see what effect a rate mode setup has and I'll record it for posterity Or, proof it makes no discernible difference whatsoever

[Peteski]

Should be an interesting test. I wonder how much trimming it will actually need when you go to rate mode. I guess the more you need to trim it the more chance of seeing some kind of improvement in HH mode.

[coolice]

Perfect in both directions. I'll do this then tomorrow, I'll set my tail up as I do, same as you Gaz and without fannying around with other stuff I'll video the piro stops. Then I'll do a rate mode setup and video the result. Then I'll give up because neither method will work and I'll start fiddling with gains etc

Ian thanks, get your thoughts but these days with the sort of processing ability and programming available the unit should be able to predict the stop condition and there should be no bounce, soft stop etc The V bar doesn't do this, or not that I've experienced and doesn't need a rate mode setup, set in the middle, go do a trim flight and Bob's your sisters mother equal speed and stops. This isn't a comparison of the Vortex and V bar by the way, I use Vortex, nuff said. So I'll give the above a go and see what occurs

Hey buddy.

Be good to see the results and I think you'll see a stop improvement.

No, you're right the Vbar doesn't require an actual rate mode trim flight, but asks the user to set 3 degrees tail rotor pitch against the torque on the tail setup stage/tab. So this is doing the rate model setup of adding pitch at the neutral stick position, but on the bench with a value known to be enough to work effectively, rather than an actual trim flight where you adjust the pushrod length.
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