Anyone who has been involved in aeromodelling for a while dreams of having one of those days when everything works right. It doesn't happen often, but when it does it sure is nice!
CanberraUAV had one of those days yesterday. It was a wonderful sunny winters day at our local flying field and we were test flying our latest creations.
First up was the "Vampire Mark 2", a combined plane quadcopter built by Jack Pittar. It consists of a senior telemaster with a 15cc petrol engine, but with the addition of 4 quadcopter motors. It was the maiden flight yesterday, and it was setup with a Pixhawk controlling the quad engines and the rest controlled manually as a normal RC model. We flew with two pilots (Justin Galbraith and Jack Pittar). The takeoff was vertical as a quadcopter, and it then transitioned to fixed wing flight using the extremely simple method of advancing the throttle on the plane while lowering the throttle on the telemaster. Transition was very easy and the plane reached 31m/s in forward flight at full throttle. The landing transition was equally easy. Jack lowered the throttle on the plane while Justin raised the throttle on the quadcopter. No problems!
Given this was the first flight of a highly experimental aircraft we were pretty pleased with the result! Jack is thinking of building an even bigger version soon that will be able to complete the 2016 OBC mission with plenty of room for equipment.
Next up was our JS90 helicopter, originally built by Ryan Pope and adapted for autonomous flight.
This is the flybar version of the JS90-v2 heli from Hobbyking, with a OS GT15HZ petrol engine fitted, along with a Pixhawk2 and a new "Blue Label" Lidar from pulsedlight. We've been flying (and crashing!) this heli for a while now, but yesterday was finally the day when we got to try high speed autonomous flight.
apart from a small gap where we lost telemetry in the north west corner you can see the tracking in the auto mission was great. Once we learned how to tune a flybar heli (which turns out to be extremely simple!) it flies really well. We did have some issues getting it to fly as fast as we want. Above about 17m/s it occasionally pulled back and stopped for a second before continuing. We knew it could do more as it happily flew at over 27m/s in ALT_HOLD mode. With some help from Randy and a small code change to help with tuning we think we've tracked down the cause of that issue and expect to be doing 27m/s AUTO missions next weekend.
Next up was another quad plane, this one quite different from the big telemaster build!
We had been trying to track down a problem with loiter on the Parrot Bebop when running ArduPilot. We suspected there may have been a GPS lag issue, so we wanted to get some flight data that would allow us to compare the performance of a uBlox GPS with the GPS in the Bebop for dynamic flight. We thought a good way to do that would be to strap the Bebop to a plane and take it for a fly. The results were very interesting! For this flight we saw a lag on the Bebop GPS of over 5 seconds, which must be some sort of buffering issue. We'll chat to Julien from Parrot to see if we can track down the issue.
Next we thought it would be fun to see if something else could lift the tiny Bebop. Peter had his Solo there, so we strapped the Bebop to it and went for a fast fly in drift mode. Great fun!
Overall it was a fantastic day! Next week we're really looking forward to trying the Trex700 petrol conversion that Greg has built which you can see in the background in this photo of our build day on Saturday. The build looks really good and we expect it to perform even better than the JS90, as Greg has managed to fit a Pixhawk while still being able to install the canopy. That should reduce drag quite a lot.
The switch of focus for CanberraUAV to VTOL aircraft has been a lot of work, but the results are really paying off and we're having a lot of fun in the process. We hope that we'll have a lot more weekends like this one in the future.
Comments
@Tridge - with the transition - I noticed that you had very little wind on the day. If it is at all windy the quad part will be pitching down to maintain a hover into the wind. If you advance the throttle on the plane in this attitude the aircraft could lose a lot of height before recovering. If you don't try to maintain a stable hover then the quad will take off down wind at a rate of knots.
Try it on a windy gusty day and see how it goes.
Congrats!!. lot of fun there :D; don't you need someone for "cebar mate"? :) (Argentine common infusion used specially on friends meetings)
That's hybrid looks very interesting for farmers, sometimes you don't have enougth area to land an airplane.
Here is a video of the VTOL takeoff of the Telemaster:
unfortunately our normal photographer (Darrell Burkey) was away on the weekend, and the video taken from the pilots box by a visitor didn't work. It does show the takeoff and transition to forward flight though. Thanks to Stephen for this video.
CanberraUAV at CMAC....Sure, we started off small. Now, we have installed solar powered electrics with a security system, webcam of the field (see weathercam on http://www.cmac.org.au/default.htm ), clubhouse lighting, and a LiPo battery charging facility. On a Sunday morning, a good proportion of the members are involved in CanberraUAV activities. We get alot of assistance from the members, and we provide alot of assistance.
Jason - The reason we are using flybarless helis is so that we can flip quickly between manual control and Pixhawk control while in flight. This allows us to incrementally find the right parameters for tuning the helicopter without it returning to earth. We are also developing with flybarless.
Andrew - Everything we do is totally legal. We have dozens of coffee drinking armchair club member critics watching everything we do. We tried waiting around until they all went home before we started our more experimental activities, but now they wont go home till we perform.
Jack.
@tridge, That is some very good points, I didn't think too much about it like that as with FBL unit's these days they are very reliable and stable. Even if tuning is set very high it generally does not result in a crash, but, they are not doing complex EKF algorithims and are not relying on accels. I look forward to hearing more about your tests with heli's and am very excited to see the development for VTOL planes with the pixhawk!
@JB, I was interested to see the VTOL code from the PX4 native dev team. It is a great piece of work! I doubt we'll use it though. Integrating that with ArduPilot would be a lot harder than just implementing transitioning in ArduPilot I think.
What we discovered on Sunday is the transition for this type of aircraft is trivial. The quadcopter code does a normal takeoff and then just hovers. The throttle for the plane is then increased and the plane starts moving forward smoothly. The throttle on the quadcopter is lowered and the transition is over. We were really not expecting it to be that easy! The transition back to quadcopter is just as easy. The throttle on the plane is lowered and the plane starts slowing down. The throttle on the quadcopter is raised and it takes over stability control. That is it.
@Jason, we started with a flybarless Trex500 but had a very nasty crash. The crash happened when we were trying to improve the pitch tracking by raising the P gain on the pitch controller. The gain went too high and the helicopter started oscillating, causing the accelerometers to saturate. The EKF completely lost its solution. The gain was lowered within 2 seconds of it being too high but by that stage the EKF could not recover. The heli went completely out of control in a quite dangerous fashion.
We wanted to find a way of continuing heli development without risking a repeat of that scenario. The problem is that there is no way to know in advance how much gain on the rate controllers is too much. It is very airframe dependent. So if you want good tuning you need to push it higher, and when you do you risk an oscillation and a breakdown just like we had.
With a flybar heli that doesn't happen for two reasons. First of all, you set both the P and D gains in the rate controllers to zero. Tuning consists of setting one number (the feed forward) and it is quite insensitive to the exact value of that number. Tuning is downright trivial as a result yet you end up with something that tracks desired roll and pitch far better in 1 minute of tuning than what we managed in a dozen tuning flights with the flybarless heli.Basically a flybar heli comes "factory tuned" by the flybar.
The second reason the oscillation doesn't happen is the ability to change to a stable flight mode that is entirely independent of the IMUs on the Pixhawk. You can flick to ACRO at any time and be certain that no matter what the EKF is up to and now matter how bad your rate controller settings are you can fly the heli. The Pixhawk could have detached entirely and be hanging off the side of the heli and you could still fly it fine. That gives a big safety advantage.
You do lose some efficiency however. We don't know exactly how much. We are considering going back to flybarless now we've learnt a bit more about tradheli in ArduPilot just to gain that efficiency, but first we are trying another flybar heli with a canopy and better setup to see if that suits us.
Note that in some ways using a flybar heli is like flying a fixed wing with ArduPilot. With a plane you always have the option of changing to manual mode. You know that in manual mode you can always fly the plane if it is still mechanically sound. I'm used to having that safety net with the aircraft I normally fly, and I enjoy being confident that the pilot is in full control of the aircraft.
On a flybar heli you still do rely on the tail gyro, and if that fails (which happened to us once when it fell off!) then you lose control, but that is a much easier to contain risk than the risk of testing experimental code on a flybarless heli.
Cheers, Tridge
All of ours are flybarless as well. Thought it was weird to see those foreign objects in todays day and age haha
Telemaster was always a great plane, really like your "Quadmaster" version.
Looks like you guys are all having a great time.
And the Space Shuttle type piggy back for BeBop testing is a great idea.
I also second what Thomas says above, I wish our club was even close to yours, they think I'm just a weirdo with all this new fangled stuff and banish me to the edge of the field where I won't get in the way of the real RC.
Best Regards,
Gary
Hi Tridge,
Nice flying!
I wish that my flying club was a progressive as yours. All they do is fly the same or newer planes day after day with a little multicopter FPV thrown in.
Regards,
TCIII AVD
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