Vbar Collective and Cyclic Ranges on Specter V2 700 machine question

Hello,

I have noticed now seeing some folks using Vbar NEO and on the XL Power Specter 700 machine using the inner holes of grip arms to get 1:1 ratio, with stock 19mm servo horn.

Anyhow on bench with outside holes on this setup I see for 13/13 pitch and 8 degrees cyclic in setup I see collective of 98/94 and for cyclic 92

On inside holes of grip arm which many seem to suggest I find numbers for same ranges in setup of 13/13 pitch and 8 deg cyclic to be 84/80 for pitch and 77 cyclic.

This seems really low when going to what pilots are saying the optimum ball position on grip arms is it not?

Also have heard pilots saying they going and using 9-10 degrees cyclic, so therefore their setup numbers surely be higher, is that a problem to run such high cyclic in setup for Vbar? I mean sure maybe it does not have swash hitting main shaft, maybe not even binding but I want to understand for certain if there is any bad effect to running 9-10 deg cyclic?

Hi,

as a general rule , the servo's specs are best used if they are not limited or overdriven, hence 100 % servo travel is the recommendation.
Limiting is OK to some degree, while overdriving can make things worse disproportionately, because of unfolding linkages. Lever rules ... period.

With today's powerful digital servos, there's more wiggle room, and of course you can play with it, to see what works best for you, e.g. get a tad more torque from a shorter servo arm, or a tad more speed, but on the other hand you might loose some precision.
It's a bit like tuning a race car to your liking, habits, driving style.

Increasing cyclic (cyclic gain, more precisely) > 8° will make the model more aggressive, more responsive. Since it's at the end of the calculation, right before the servos, it also affects gyro response. What can happen is that if you cross the threshold between OK and too much, the model may start fierce oscillation when triggered, and this can escalate until self-destruction if you don't react, switch to a bank with lower head speed, lower main rotor gain, or autorotate.
Unlike maxing out parameters e.g. on a simulator, any model out in the real world has it's mechanical limitations, there is no unlimited stop gain, roll, yaw or tumble rate etc, and even though gains set too high can maybe even be checked by the blades (stop with a bang), but this can also overstress the weakest mechanical link, and ... we've all seen it.

In fact, the VBar (legacy and NEO) has huge reserves when it comes to control outputs, but it's sensible to go with the recommendation and work with the control loop parameters designed for it, namely main rotor agility and main rotor gain.
If you exceed the recommended range of values, be aware that anything can happen, so don't just copy what others do, but think.
There's not one model like the next, even two equally equipped models of the same type (re-)act somewhat differently (A machine is not B machine, any competition pilot will second that), and if you were using different servos, different blades, running different head speeds etc., it will also be different.

If you do some math, you can e.g. set cyclic gain to 8.8° (+10 %) and reduce the main rotor parameters by 10 %, then you are more or less where you were before _but_ the fact that the control loop outputs (stabilization) _can_ be increased by another 10 %.
This is e.g. what F3C pilots can do, to set up a bank with more hovering stabilization.

But we do not recommend exceeding the parameters, because ... anything can happen, e.g if you do it, do a particular maneuver and your model just explodes because it can not/no longer take the strain ... we can only shrug. Same as if you would overpower your model, way above the recommendation, and then complain that the gear trains strip ...

—Eddi

Born to fly ...
forced to work.

Ok thanks for very detailed understanding. From what I get from this say 8.5 degrees is still very safe as close enough to 8 degrees which is the recomended yes?

Also from my table setup experiment on the inside holes getting value for pitch range of 13/13 and having the numbers of 84/80 for collective travel in setup and 75-79 range for cyclic @ 8 degrees also is perfectly fine?


Just want to understand 100% what the optimal #s range for collective and also that optimum range for cyclic in Vbar is..

Is 90-105 on collective optimum for both collective and cyclic in setup or is there a min max like if you are below 70 for either this is bad kinda thing? Something I guess I never have fully known and would like to here.

Hi again,

I would guess that you can run 8.5° easily, if everything else is within sensible limits, and if the geometry of the linkages has no ratio, multiplying the servo output to the swash plate, like on earlier T-Rex 1:1.6.
Imagine someone has maxed out e.g. main rotor gain to the limit already where the main rotor disk would start to oscillate, in hards stops (like a tail maxed out, in FFF), adding the proverbial final straw can cause a catastrophic result.

So if you were to experiment here, start over with a more conservative setup or reduce the main rotor parameters gyro gain, agility, I gain by the percentage you increase the cyclic gain in setup, then approach cautiously again. Leave a safe bank, and/or be prepared to auto. Mind that maxing out will also max out the mechanical stress on all components, and also the power consumption of the servos, back voltages, too.

Once you have acquired a feeling for it, on a particular machine/machine size, you know what's possible to start with.
If you change other parameters (like head speed) or if you replace items (like blades) be aware.
Again, same as if you have maxed out your tail rotor gyro gain, and up the head speed considerably, or use longer or more profiled tail blades or such.

80...100 is our ballpark figure recommendation. Less will work, more will work, but you might not get the VBar grin from it, and blame it on the VBar ...

Much more can result in servo pulses becoming too long, in the end exceeding what a servo can accept as 100 % throw, and that can result in servos becoming limp in end positions if they are not programmed properly themselves. The control loop simply adds cyclic + collective + trims and multiplies with the cyclic gain (very simplified). If a standard servo say accepts 1.1...1.5...1.9 ms pulse, and 120 cyclic plus 120 collective plus 100 trim * 9° cyclic gain exceed 1.9 ... it's up to the servo how to deal with it.

Much less can result in strange effects, e.g. if collective is below 66-ish, the full-positive-enable-trim-flight thing will no longer catch (with legacy radios).

In the end, the equations are open in a very wide range, at least that's my understanding. There's no hard limiting which could result in other strange effects, like one of three swash plate servos stopping while the other two still have reserves, resulting in the heli to sidestep.
The limiting actually lies in the proper setup (which still has a very wide range of values to work with), and checking that nothing binds or folds out too far.
Only the cyclic limiter ring limits, but it would be a weird idea to max out everything and then limit it again, with the CR, and the results would be not very optimal.
Same as some pilots think opening the CR would help with increasing agility ... ostensibly it might feel that way, but it's the wrong set screw, and you risk binding or folding out too far, in end positions, because the CR is designed as a double truncated cone, limiting particularly towards the end positions, high collective, limited cyclic, while it's more than fully open at 85 (default) already, around center to hovering collective-ish.

Kind regards

Eddi

Born to fly ...
forced to work.

So on bench I made the change to inner ball holes. I ended up with 88/82 for 13/13 pitch and 77 as a number for cyclic to get 8.1 degrees. That is a lower number then I’m used to for cyclic number but should work fine?

Actually sorry was wrong on cyclic number it’s 74 for 8 degrees seems super low?

A friend of mine (XLPower distributor) tested the Specter with Neo on inner and outer holes.
His recommendation is 100% to go with the outer holes. For other FBL-systems it's different but Neo wotks better with the outer holes (i also fly like this).



1 mal bearbeitet. Zuletzt am 23.01.2022 19:47 von Memphis.

Hi again,

74 would still be OK, but I would expect lesser performance, just by the numbers.

Then, there's theory and practice: if it feels better this or that way, and if you don't run into other (maybe related) troubles with the mechanics, like risk of swash plate or linkages binding for example, and if you don't have to limit elsewhere just to get into the range of values, go with it.

In the end, don't worry too much but still remain vigilant: the mechanics are the limiting factor, and e.g. if you overdo the cyclic gain considerably (8° setting) the results can be somewhat sobering ^^

—Eddi

Born to fly ...
forced to work.