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Is there a way to edit gimbal in a VTOL tilting engine aircraft?


salaminho
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It's been a while I’m designing some VTOL aircraft. I usually use tilting engines with the BG servos, the biggest challenge is attitude control. Using engines gimbal would help a lot here.

Gimballing is automatic and works just fine when the engines are pointing backwards on level flight, but when I tilt the engines downwards for VTOL flight the gimballing gets all messy and doesn’t work the way it should. I know it can work pointing down if I set control to point up, like If I click “control from here” in a dorsal docking port, but then I loose situational awareness and it get’s really hard to fly as yaw and roll control switches place.

Is there a way to manually edit gimballing to point the way I want?

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1 hour ago, salaminho said:

the biggest challenge is attitude control. Using engines gimbal would help a lot here.

For my VTOLs, gimbal does not help with attitude control, because the gimballing engines tend to be close to the centre of mass.  Even when the engines are spread out, mine tend to be spread horizontally, at the same vertical height as the centre of mass, so that even if an engine rotates on its gimbal it still provides the same torque trying to turn the craft.  Threads on VTOLs (link link) tend to suggest other ways to control attitude, like RCS or the mod throttle-controlled avionics.

The more recent versions of KSP let you connect the 'thrust limit' of an engine to 'Axis Groups' including the steering axes. (The SAS control, however, only steers with the hardwired steering controls, not the ones you connect using the axis-group feature.)

That being said, if some engines gimbal opposite the way you want, you can set Pause Menu => Settings => Advanced Tweakables : Enabled
and then manually edit under the right-click menus for each engine to selectively disable whichever of the pitch/yaw/roll responses are not what you want.

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Not sure if this will help you or not-  Your flight controls may be working against you sometimes too.

I ran into this while trying to build a vertical-landing spaceship, I'll link that thread below.  The flight surfaces worked fine while going UP, but actually worked against me while the rocket was descending (going backwards) to land.  My solution was to deactivate the flight surfaces while going backwards.

@camacju had a better solution, which was to set the flight control surfaces authority limiter to -20, so they effectively work in reverse.

As @OHara mentioned, I imagine (a screenshot would help) that your engines are mounted too close to the COM to be very effective during gimbaling.  I do suggest turning off the pitch/roll/yaw gimbals one at a time to see what effect they have.  I'd start with the roll axis.

 

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Thanks for the reply you guys.

3 hours ago, OHara said:

gimbal does not help with attitude control

Gimbal does not help because the engines are not gimballing the right direction for vtol flight.

I’ve created my own set of gimbals using the servo motors to test if gimballing would work.

For yaw control, gimbaling works flawlessly. For pitch and roll it works, but the vectoring range in most of the engines wouldn’t give much torque, so using differential thrust is more effective.

Pitch: https://imgur.com/ugQpIyT

Yaw: https://imgur.com/EakFTHM

Roll: https://imgur.com/OaDuT7C (by the way, I don't know how to use the "insert image from URL" button :blush:)

 

This vtol aircraft is working very well, but there are still some points to improve:

1-      Setting target angle of the rotors and thrust limit to kal-1000 and hardwire it to control axis doesn’t work with SAS, only manual input.

2-      Differential thrust is less responsive when using airbreathing engines since they are slow to throttle up and down, so using gimballing could work better.

 

RCS and reaction wheels works fine for small and medium size ships, but are not effective in bigger craft, this is why I’m looking for alternatives. 

5 hours ago, 18Watt said:

As @OHara mentioned, I imagine (a screenshot would help) that your engines are mounted too close to the COM to be very effective during gimbaling.  I do suggest turning off the pitch/roll/yaw gimbals one at a time to see what effect they have.  I'd start with the roll axis.

I tried doing this, but there should be a way to not just turn them off, but to set where it should point when I hit an axis input. This seems to be impossible.

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