RcV

  • *
  • 7
Re: My LibrePilot VTOL TiltRotor FixedWing
« Reply #165 on: May 18, 2018, 07:12:38 am »
...For quads, if you don't have enough "I" term the most obvious symptom is that the quad won't hold correct pitch angle when flying forward fast...
Thanks for the info. I thought it was strange that it worked with no I and D also. As soon as I put in some I it would just drift all over the place. Don't really care to mess with that old code after experiencing what can be achieved these days.

...One of the main things that VTOL needs is a smooth transition from nose up mode to nose forward mode...
I did one tail sitter VTOL flying wing model. Don't think I got any video but it did the entire transition. Was using the same FC though, so just gyro with the P PID. Really want a good accel to add into the mix. I'm working on another Osprey type bicopter VTOL so I don't need to rotate the assumed "level" angle on this build.

...the LibrePilot code as is, has plenty possibilities to be configured for a multitude of VTOL uses though...
Sounds good. I'll take a look at the custom tab some more.

Thanks for letting me interrupt your thread karla. You have both been very helpful in answering these questions for me and providing great suggestions. I'll keep an eye on this project.


« Last Edit: May 18, 2018, 07:17:56 am by RcV »

karla

  • *****
  • 505
Re: My LibrePilot VTOL TiltRotor FixedWing
« Reply #166 on: May 20, 2018, 01:49:04 am »
Thanks for letting me interrupt your thread karla. You have both been very helpful in answering these questions for me and providing great suggestions. I'll keep an eye on this project.

Haha, no worries, not interrupting, visitors welcomed!
Provides inspiration to this very slow project. I lack suitable flying fields to test it. Its easier to find a spots for quads and helis.
Good luck  :)

karla

  • *****
  • 505
Re: My LibrePilot VTOL TiltRotor FixedWing
« Reply #167 on: December 27, 2018, 11:08:27 am »
Hello all and Merry Christmas :)

Just arrived to a place where flying is legal.
It looks like this VTOL has gone to the dark side after so long with no opportunities to stretch out from hover to straight forward flight :) just look at his eye brows.



Here is a very short video of transition.
I changed the transition from hover to forward from a on-off switch to an accessory turnable nob, in order to have some better control of how much the tilt rotors should tilt.



I turned it some 50% from vertical towards horizontal and it took off just fine.
Will need to do a lot more testing about this.
At least I have some time here to fly.

Re: My LibrePilot VTOL TiltRotor FixedWing
« Reply #168 on: December 27, 2018, 08:02:33 pm »
How do you handle the difference between tilted forward thrust and tilted vertical thrust?  Do you switch to manual (disabled) stabilization for forward flight?

karla

  • *****
  • 505
Re: My LibrePilot VTOL TiltRotor FixedWing
« Reply #169 on: December 28, 2018, 06:53:50 am »
At the moment, I use Basic Attitude Estimation Algorithm with stabilization mode for Thrust, kept at Manual.
That is both for hover and forward flights.
Actually, the only difference in stabilization from hover to forward, is that the yaw axis is at AxisLock in hover and at Manual in forward flight.



The reason for this Yaw stab settings is that in Hover mode it really helps not have to think about the yaw direction. And in Forward mode, I don't use the yaw stick at all (rolling with the elevons makes the wing turn), plus the fact that, if the FC would try to stabilize the yaw, then it would mess up the flight completely since it would now affect the roll axis.

This sounds like I know what I am doing, but I am really just experimenting :)
But it make some sense to me at least.
The flying behavior will be the judge.
Too windy today to fly.
Hoping for tomorrow.

« Last Edit: December 28, 2018, 12:30:09 pm by karla »

Re: My LibrePilot VTOL TiltRotor FixedWing
« Reply #170 on: December 28, 2018, 06:38:07 pm »
So it sounds like you have elevon servos set up for roll (/pitch), but you also have left-right motor differential set up for roll (and differential motor tilt for yaw) and all of this (except motor tilt in switch position #2) is always active?  Are the elevon servos stabilized or just manually connected to the RC aileron channel somehow?

So in forward flight, you probably get yaw effect when you use the roll stick and don't even need elevator for turns?  So even if you used Rate instead of ATtitude, it would be hard to do a roll?

I like flying fixed wing in Rate or Manual mode (to allow loops and rolls) more than ATtitude mode.  And because I have flown unstabilized fixed wing for many years.  :)

An interesting coding project might be to automate all this:
- in hover flight mode, differential motor thrust gives roll, so it is connected to roll stick and roll stabilization, also differential motor tilt gives yaw so it is connected to yaw stick and yaw stabilization
- in forward flight mode, differential motor thrust gives yaw, so it is connected to yaw stick and yaw stabilization, also differential motor tilt could give roll, so it could be connected to roll stick and roll stabilization; it could also be locked pointing straight forward.
- these act like two flight mode switch positions but don't use the flight mode switch, they use a transmitter knob to control the transition from one mode to the other: tilts motors proportionally and also effectively proportionally mixes everything between hover mode and forward flight mode
- different PIDs for the different flight modes, just like when using the flight mode switch, PIDs mixed by the knob too
- options for elevon or elevator/aileron setups, maybe even V tail


Also: I see that you have what looks like a 433mhz antenna mounted horizontally on the wing.  I guess you understand that your range will not be good to the front or back (antenna nulls) and that the ground antenna should also be horizontal (for polarization issues) (also bad).  It is OK at high power and close range, but both ground and air antennas should really be mounted vertically.  :)
« Last Edit: December 28, 2018, 06:44:10 pm by TheOtherCliff »

karla

  • *****
  • 505
Re: My LibrePilot VTOL TiltRotor FixedWing
« Reply #171 on: December 29, 2018, 07:19:42 am »
Cool idea Cliff,

Quote
So it sounds like you have elevon servos set up for roll (/pitch), but you also have left-right motor differential set up for roll (and differential motor tilt for yaw) and all of this (except motor tilt in switch position #2) is always all active?  Are the elevon servos stabilized or just manually connected to the RC aileron channel somehow?
All above correct!
Always active, and yes, elevon servos mixed in with stabilization.

Quote
So in forward flight, you probably get yaw effect when you use the roll stick and don't even need elevator for turns?  So even if you used Rate instead of ATtitude, it would be hard to do a roll?
I like flying fixed wing in Rate or Manual mode (to allow loops and rolls) more than ATtitude mode.  And because I have flown unstabilized fixed wing for many years.  :)
Yes, should get yaw effect since turning left (roll/elevons left) will increase right motor and decrease left motor speed, resulting in left yaw motion. A roll could be twisted, but I really do not know. For loopings, they might be quicker and tighter due to the tail rotor pitch (could also configure it as a reversible motor to facilitate that).

Quote
An interesting coding project might be to automate all this:
- in hover flight mode, differential motor thrust gives roll, so it is connected to roll stick and roll stabilization, also differential motor tilt gives yaw so it is connected to yaw stick and yaw stabilization
- in forward flight mode, differential motor thrust gives yaw, so it is connected to yaw stick and yaw stabilization, also differential motor tilt could give roll, so it could be connected to roll stick and roll stabilization; it could also be locked pointing straight forward.
- these act like two flight mode switch positions but don't use the flight mode switch, they use a transmitter knob to control the transition from one mode to the other: tilts motors proportionally and also effectively proportionally mixes everything between hover mode and forward flight mode
- different PIDs for the different flight modes, just like when using the flight mode switch, PIDs mixed by the knob too
- options for elevon or elevator/aileron setups, maybe even V tail

I think I know what you mean...
The current Mixer table (actuator mixer matrix?) looks like this and delivers all that you pointed out.
Ch 1 and 2 - left and right front motors
Ch 3 and 4 - left and right motor tilt servos 
Ch 5 and 6 - left and right elevon servos
Ch 7 - tail motor



Now, you suggest to simplify this table to take care of only Hover flight and then create an additional table simplified to take care of only Forward flight. Call them mix matrix A and B. Then to create a function that will transition Ch 1 to 7 from 100% A to 100% B proportionally by turning of a transmitter nob.
You mean something like that?


Sure! the interest for VTOLs is there and the available FCs to handle it are not many.
The KK2 board that most VTOL vehicle projects on the internet seems to use, are getting more and more difficult to get hold of? Someone did his own FC to fix this, but anyway, seems easier to add on to a mature fully gps enabled sw like Librepilot, than build from scratch.

Quote
Also: I see that you have what looks like a 433mhz antenna mounted horizontally on the wing.  I guess you understand that your range will not be good to the front or back (antenna nulls) and that the ground antenna should also be horizontal (for polarization issues) (also bad).  It is OK at high power and close range, but both ground and air antennas should really be mounted vertically.  :)
I know. Thank you. Its just a very convenient and robust mounting during testing.
« Last Edit: December 29, 2018, 07:29:06 am by karla »

Re: My LibrePilot VTOL TiltRotor FixedWing
« Reply #172 on: December 29, 2018, 08:53:47 am »
I haven't tried to figure out everything that would need to be changed.

I believe it would need two read only mixing tables (the two endpoints) plus the current mixing table which would be some linear combination of the two fixed tables.  It would also need to mix everything from two switch positions, including the PIDs.

The mixing table takes care of outputs.  On your aircraft, the FC is at the same attitude when hovering as when in forward flight, so that may be most of everything you need (plus PIDs if you want them too).

It would be nice to allow for a hovering airplane that does not have tilt rotors.  It would hover with nose pointing up but fly with nose pointing forward.  I imagine it would be nice for this to allow the roll stick to do a hovering airplane rudder yaw in hover mode and a flying airplane aileron roll in flight mode.  That would require remapping the inputs and stabilization as well.

Of course, the easy way to do this (non-tilting motor) doesn't require any code changes.  Attitude or rate mode in hover and rate mode in forward flight.  The pilot would have to use the correct sticks.  Yaw in hover becomes roll in forward flight, etc.

Finally, the transition knob could be replaced with a knobless timed transition that is activated when you use the normal flight mode switch to switch from hover to forward flight mode.

This would allow other such mixings as well:
- X to + quadcopter
- flying a quad backwards or sideways like it was flying forward (we already have CourseLock)
- (auto leveling) fixed wing knife edge or inverted flight
- attitude mode in either hover or forward flight