• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

VTOL controllability

#1
Wanted to run this idea/question by the community, but perhaps it's already been covered elsewhere. Regardless.....

I've been running some designs on paper for a 3 motor VTOL design. Yes, I know it's nothing new but wanted to give it a shot anyway. My design will have two motors in the front and one in the rear, all in a pusher configuration. I plan on having all three motors pivot 90 degrees downward to act as a tricopter for vertical flight. I think I can work out the mechanics fairly easily but the electronics side of it has me scratching my head.

What I don't like about current models I've seen is that during forward flight the multi rotor flight controller seems to still be commanding individual motor rpm as roll, pitch and yaw inputs are introduced. Of course, during forward flight, all I want is control surface throw to achieve the desired movement about the three axis. I know that I can split each roll, pitch and yaw control to both the flight controller and the control surface servo but I want to 'shut off' the command to the flight controller during forward flight. I plan on using a high torque servo (1) to move the three motors through their 90 degrees of tilt travel via an aux channel on my transmitter. I was wondering if there are any electronics out there that I could connect to an additional channel in my receiver and, by programming a mix in the transmitter following the servo that is controlling motor tilt, have this aux channel shut off the signal to the flight controller while the motors are in the forward flight angle. Perhaps there is an easy answer to my problem but again, electronics are not my thing.
 

earthsciteach

Moderator
Moderator
#2
This is a great question. I've also wondered about this. And, like you, electronics are not my thing.

I'm guessing the best way to go about this would be programming. Have the "mode" of the flight controller toggled by a switch on the tx. FC operates as a tri when in "normal" mode and turns off the motor rpm control when in "fixed wing" mode. Sounds easy. :p

Of course, I have NO idea how to go about this!
 

engineer

Senior Member
#3
It may be brute-force method, but with kk2 (or any fc with acro switch) and 9XR and 8 channels, I think its doable.
Basically there's all 4 inputs to fc, switch to acro to disable the auto leveling/automatic attitude corrections and split to run the flight mode servo, and 3 for control surfaces.
On switch to acro/forward flight, program radio to disable fc ail/rud/ele. Maybe set a slow timer for acro switch, the fc flight mode shouldn't switch until the voltage drops to almost 0. There is a device that does slow and delay in the signal, I think.

With more complex mixing, you could do differential thrust also or instead of rudder surface.

Hmm.. Any issues I missed?
 

TEAJR66

Flite is good
Mentor
#4
you can check out the VTOL thread on RC Groups. Lots of discussion and FC Programming development going on there.

I think Peter has worked out some simpler combinations, but i am not sure. I did here Mr. Bixler mention that Peter was working on VTOL for the masses. What that entails, I am not sure.

I think the amount/type of control that you want to have during Vertical, Slow Forward Flight (SFF or the transition), and Fast Forward Flight (FFS) will be the determining factor for how you set up your aircraft.
 
#5
It may be brute-force method, but with kk2 (or any fc with acro switch) and 9XR and 8 channels, I think its doable.
Basically there's all 4 inputs to fc, switch to acro to disable the auto leveling/automatic attitude corrections and split to run the flight mode servo, and 3 for control surfaces.
On switch to acro/forward flight, program radio to disable fc ail/rud/ele. Maybe set a slow timer for acro switch, the fc flight mode shouldn't switch until the voltage drops to almost 0. There is a device that does slow and delay in the signal, I think.

With more complex mixing, you could do differential thrust also or instead of rudder surface.

Hmm.. Any issues I missed?
The problem isn't auto-level. It's that when the craft is configured for forward flight, the motors are still acting like they are pointing up. Roll results in yaw because the front motors shift thrust.
 

engineer

Senior Member
#6
The problem isn't auto-level. It's that when the craft is configured for forward flight, the motors are still acting like they are pointing up. Roll results in yaw because the front motors shift thrust.
Yup, that's right. If I'm not mistaken, acro mode doesn't provide any motor input that isn't signaled. So if you turn acro on, and turn off roll/pitch/yaw input, only throttle will be used, which is what you want for toward flight, naturally. Control surfaces need to be on separate channels or course also.
 
#7
The problem isn't auto-level. It's that when the craft is configured for forward flight, the motors are still acting like they are pointing up. Roll results in yaw because the front motors shift thrust.
Bill I do believe TomStanton has done a VTOL aircraft and he talked about a 'flashing' sort of upgrade for the KK2 board that has the mixing necessary for VTOL flight. I believe it has the compatibility of doing quad tri etc. but I'm unsure.
Here's his article link: http://www.flitetest.com/articles/vtol-tilt-rotor

You can ignore most of the tilt-arm stuff but the rest is still useful.
Hope this helped

Safe Flying!
 
#8
@engineer:

Not sure if I follow you. Are you describing a setup where you put roll, pitch and yaw on three channels and then roll, pitch and yaw to the multi rotor flight controller on three (more) separate channels.... for a total of six channels? I guess I could do it that way but I have other things I need those spare channels for. I did run a test with a quad I have and, after powering up the quad, I disconnected to roll, pitch and yaw inputs and still have throttle control which is exactly what I need. Until I want to connect a pixhawk for forward flight control, but that may be a topic for another thread!

I have thought of an idea. If I used a rc switch similar to one used to turn on and off lights remotely, I should be able to to shut off the roll, pitch and yaw controls to the flight controller. Basically these devices are a remotely controlled relay, allowing the positive and negative leads of a battery to flow past the switch to the positive and negative leads of the device you want to control. Because I need to shut off three signals, I could just use one and a half remote switches (positive and negative of one and just the negative lead of the second) both sharing the same signal from the receiver channel (spliced). I could program a mix in the transmitter such that when the tilt servo for the motors reaches a programmed position, the switch is activated shutting off the roll, pitch and yaw to the flight controller. Since these three are already spliced to the standard control surface servos, I should always have them on the ready. I put a picture below to better illustrate what I am talking about. Am I missing something? Seems pretty straight forward. Why hasn't anyone tried this? Or maybe they have and I just haven't noticed.

VTOL Wiring Diagram.jpg
 

engineer

Senior Member
#9
Yup, you got it. I had not considered a remote switch, thus separate channels to switch.
I think you can put tilt servo on the same channel as remote switch.
I guess a big part of the mix design is: how many channels do you have, and how many do you need to keep open (or what the open channels will be used for)?