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Old May 03, 2006, 01:04 PM
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H.R. Colorado
Joined May 2006
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What kind of on-board stabilization are you using?

I'm a new member but I have been building a 4 motor tilt wing VTOL (think Osprey with 2 tilt shafts) for the last several months. It will hover at 50% throttle but is still not very pitch or roll stable. I have roll and pitch gyros (GWS PG-03) augmenting the throttle input for some of the motors but they tend to drift and once the VTOL drops one end or the other, the gyros don't recover completely.

So...I am wondering if anyone has corrected a similar stability problem using other gyros, accelerometers, or onboard microprocessors. Any advice / recomendations will be appreciated.
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Old May 03, 2006, 06:33 PM
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United States, IN, Granger
Joined Jan 2003
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You aren't doing the future Bell Quad rotor are you ????
Vtolman has used arcamax gyro's (two ,one on pitch ,one on roll ) and it worked good for a normal two prop VTOL
I am guessing here ,, that you need two more gyro's for the other motors.
You might do well to consider a TH-2 GP that Tech Model Products is making for VTOL projects.We have not had the beta version long enough to be able to tell you it would solve your problems .. but I think you could introduce the gyro before the mixer and it would take care of both motors but you would still need four gyro's I think.The Rosswell flyer (4 prop VTOL . but in at + configuration ) only uses two gyro's but has an onboard mixer.
Hopefully Joe will see this post and jump in and be able to tell you more on the mixer unit.

Or you could email him
Welcome to the board and Good luck and keep us posted on your progress and get us some pix too ,,please
Larry
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Old May 03, 2006, 08:29 PM
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Joined Oct 2005
387 Posts
Just wanted to chime in hear. I have been doing a lot with 4 rotor tilt wing. Check out my project.

I have tried the TH-2 and it can work for what you are doing it just needs some code modifcations that I hope to be able to do without rewriting things but Joe has not expressed interest in letting somone else modify his code but he has expressed interest in helping me make my own code from scratch.

Its exciting and scary to see somone else doing this.

http://www.rcgroups.com/forums/showthread.php?t=436841

I will telll you what this design once built right could yeild an entirely new flying experience IMHO.

Im curious to see you design!
Scott
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Old May 04, 2006, 12:00 AM
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H.R. Colorado
Joined May 2006
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Good stuff. I think we all run into the same design issues eventually. I would like to hear more about the TH-2. I will post some pictures when I can. My design is not based on any existing design. My goal was to build an entirely new and simple to fly VTOL based on off-the-shelf components with a fairly low end radio. In other words, something that would hover autonomously and that a kid could fly. While it was more complex than I expected, I think I've achieved phase 1, so I'm working on phase 2 which is to integrate some on-board controls to handle stability, transition to forward flight and motor failures. I can do some channel mixing on the Spektrum radio, but the VTOL really needs to hover without the radio.

My first prototype was a 16oz plywood airframe using 4 articulating ducted fans, but I couldn't get even half the published 8 oz thrust out of them, so it wouldn't get off the ground. My second prototype used the same GWS EDF-75 fans in a foam delta wing (F27 Stryker) which was much lighter but the fans still couldn't lift it.

My third prototype uses 4 SK400XT (cheap and plentiful at HobbyLobby) and 10x4.5 CR props which crank out over 20oz of thrust each!. I was using 4 eFlite S75 servos rotating 4 tilt shafts / wings, but it only took a few hard landings to strip out the servos and bend the shafts.
So currently I'm using 2 ball bearing mounted shafts for strength, 1 JR retract servo for tilting both shafts, and 4 Hitec HS65HB (carbonite) servos for elevons on each wing. I'd ultimately like to go back to 4 shafts and vector the thrust instead of using aerodynamic controls, but that will require even beefier shafts and more ball bearings (i.e. more weight) so that will have to be down the road.

Currently, I have 3 gyros; 2 roll and 1 pitch. The pitch gyro is inserted in the two rear motor circuits and I have 1 roll gyro on each of the front motors. This is the most stable configuration I've come up with yet, but these inexpensive gyros tend to creep pretty quickly. Rather than throw mor gyros at it, I'd like to make it more intelligent, so I was thinking about the Parallax Javalin chip controlling the PWM to the motors and servos based on x/y/z axis data from the gyros or an accelerometer. Anyway, I'm committed to making this work, but I hope to learn from the mistakes of others, since because it's too expensive to make them all myself.
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Old May 04, 2006, 01:11 AM
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H.R. Colorado
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Diagram update

Here is an updated diagram. The gyros were changed since that old diagram was made and there is no more Vtail mixer. That experiment did not work at all.
Jim
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Old May 04, 2006, 06:32 AM
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Israel
Joined May 2004
130 Posts
Hi,
Gyros are not stabilizers as you would expect. A gyro will keep the last angle but will not level your aircraft.
The best solution I'm using for the last two years with my huge tandem heli is the FMA Co-Pilot FS8 (this includes a very good 8CH receiver) for roll and pitch axis and a standard gyro for the yaw axis.
The GWS PG-03 were tested with my helicopter and found to be very low quality and unstabilized especially with vibrating platform as in the case of nitro or gasolin engines. I use the Futaba 240 gyro for the yaw.

Using the Co-Pilot makes flying very easy and once you take your hand off the stick the aircraft immediattly levels in all axis in about 0.2 second, a child can fly it (with the attention of an adult as these toys can be dangerous...).

This setup works great with the TH-2, I'm using the TH-2 from it's begining (one of the first users) and it would be a very good solution for simple to use and sophisticated mixing you would dream of.
Regards,
Eyal.
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Old May 04, 2006, 08:24 AM
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H.R. Colorado
Joined May 2006
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Thanks Eyal, that is exactly what I am finding with my gyros. I recently looked into the FMA Co-Pilot and it looks like for $100 US it costs about the same as a decent gyro (or 2 simple gyros). How do you have it hooked up in your tandem? Does it control servos as the description seems to imply? Or are you handling pitch and roll with differential thrust as I am trying to do?

I don't think a lot of solutions are meant to be used in the motor control circuit, which is a little "unconventional". To complicate things further, all of this stabilization must go away after transitioning to forward flight since the roll axis becomes the yaw axis and the pitch axis is controlled by direction of thrust (or servo position) as opposed to the amount of thrust. So I need a way to reduce or disable the stabilizing device after transition. Again, thanks for your feedback.
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Old May 04, 2006, 09:29 AM
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Lewist's Avatar
High Wycombe, Great Britain (UK)
Joined Jul 2004
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Indeed as stated above, gyros will only make it easier to fly, they can't provide hands off hover.

The way i intend to get arround the problem of the gyros (or copilot) messing with normal flight is to have a set of relays that just totaly bypasses the (in my case) gyros.

when the transition to fff is complete the relays will bypass the gyros and switch arround any of the control systems that you need.
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Old May 04, 2006, 10:43 AM
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H.R. Colorado
Joined May 2006
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VTOL Pictures

I don't have any in-flight pictures since I need both hands to control this thing, but here are a couple of shots to show what it looks like. It's built out of 1/4" plywood, which is easy to work with but heavy and brittle. After stabilizing this prototype, I will be building a fuselage out of depron and carbon fiber rods for flexibility and light weight. The wings will probably be depron over balsa ribs.
Thrust is phenomenal on the test stand using the SK400XT brushless motors and Todds Models 10x4.5 counter-rotating props. On the static thrust stand they generated over 20 oz of thrust each, so I just have to keep this aircraft under 4 lbs to hover. Its about 3 lbs ready to fly, right now.
In the vertical mode picture you can see the four wings on two shafts rotated up by the retract servo. Unfortunately the retract servo has only two positions so I can't do partial transistions. But that sucker holds those shafts in position tightly, which is all I need right now. All low current controls are on top of the fuselage, and high current controls are on the bottom, including retract servo and batteries for a lower CG. Most of the fuselage will hang below the tilt shafts. The CG is the big X on the blue tape, which is roughly in the middle but depends on battery placement.
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Old May 04, 2006, 10:55 AM
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High Wycombe, Great Britain (UK)
Joined Jul 2004
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looking good!
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Old May 04, 2006, 11:18 AM
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H.R. Colorado
Joined May 2006
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Thanks. Most of the design was by trial and error since I don't have any modelling / design software. I have had a couple of flashes of insight that have made a big difference but mostly it goes like this:
step 1: think up something
step 2: build it
step 3: realize you made a critical thought error
step 4: rebuild it
step 5: test it / crash it
step 6: go back to step 1

By the way, how would you mount your relays? On the tilt shaft? And how would they bypass the signal around the gyros / devices?
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Old May 04, 2006, 03:31 PM
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Israel
Joined May 2004
130 Posts
I see no problem for the Co-Pilot to handle you design in any mode. Don't throw away good idea and practice...
In any case the relay idea is not the right way to do it, if you want to change the gain of a gyro or the Co-Pilot you do it by changing the gain using the Tx and a spare channel. The channel can be assigned to a switch that controls the gain in each mode or to a variable value channel. Anyway, I'm sure the Co-Pilot will do the job in any mode, just place it at the right location - on the fuse as the fuse should be level and not the wings.
Eyal.
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Old May 04, 2006, 04:43 PM
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Joined Aug 2004
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Note that very soon the vtol software for the TH-2 will be available. It will switch your aileron and rudder inputs for you when you tilt. The point it switches at is user defined, Also the rate can be different for heli and airplane mode.
Rudy
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Old May 04, 2006, 04:47 PM
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Joined Oct 2005
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FMA Co Pilot is a good basic solution.

Heading Lock gyro's should help I dont know are those GWS heading lock?

My favorite servo but a heavy one is the 59995TG. 400oz of torque titanium gears but at $130 its not cheap. If you see my design the wings are directly attached to the servo shaft. I thought for sure I would ruin these servo. Nothing yet. It seems the wing will break before the servo.

See another desing is so nice. Make me feel all warm and happy that Im not doing somthing ludacris. I will put more effort in freeing time to get programming the TH-2 for a 4 rotor tiltwing now as I am sure you can understand how complicated it can be to mix 4 motors and 4-8 servos for this.

I have worked out the mixing in my head now I just need to get it in code.
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Old May 04, 2006, 05:15 PM
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H.R. Colorado
Joined May 2006
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Quote:
Originally Posted by Eyal M.
I see no problem for the Co-Pilot to handle you design in any mode. Don't throw away good idea and practice...Eyal.
No I won't overlook this as an option. I just don't have any experience with it. The experience I have with the gyros requires a couple of minutes of setup to get everything balanced at the beginning of every flight. And usually that only works for one throttle setting. I'm just guessing but I don't think the were designed to augment ESC / motor control. But if FMA says that the Co-pilot can control ESC inputs, it will be worth a try.

So which way are you using the Co-Pilot?
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Last edited by Unconventional; May 04, 2006 at 05:23 PM.
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