I've got a Cyclops EPO that I'm setting up with a view to attempting a 200km flight (lovely plane, I'm sure it's capable of it), but I've crashed it twice out of three outings, and I've got no idea what's going wrong.
The maiden flight in manual mode was a success (it came back in one piece), but the test pilot said it was pretty lively and had trouble trimming it.
The second flight was in manual mode too, it flew a circuit or two before it banked hard right and spiralled into the ground. The speed was about 90 km/hr so it wasn't a stall. The pilot said it just stopped responding to his input, we switched to Stabilize after he realized he'd lost it, but it made no difference.
The telemetry logs show a large right aileron input (green trace, see the white asterisk on the graph, high=right) to level it after a left turn, but it kept rolling right and didn't respond to the subsequent left input. The trace also shows some big right inputs, I don't know if that is panicked pilot input or a dodgy radio/connection. You can see the aileron trace go low when I switched to Stabilize, but it didn’t make any difference to the roll (red).
I repaired it and tested everything I could think of and found nothing unusual, so I flew again, this time in FBW A mode. It took off and flew very smoothly, but I didn't have much authority. Up elevator input barely made a difference, and it only turned very gently when I gave it right aileron and rudder. Then it never really levelled out. The right roll kept increasing (red trace below). I gave it some left aileron (I'm not sure that I gave it full left as indicated on the trace), which didn’t do much, and then it banked right and hit the deck.
In both cases it rolled to the right. In the first case it was like it kept rolling after a large right input, and didn’t react to the left input corrections. In the second case it flew the whole flight with too much right roll and didn’t react to the correction from the APM or from me. It feels to me like an aileron servo problem (failure, loose connection, brownout, jam, insufficient power).
Any insight or expert log analysis would be very much appreciated.
After two weeks of late nights building then repairing and analysing logs, I’m a bit burnt out and it seems hopeless rebuilding it if I haven’t found the problem.
Some of the tests I did:
- Removed the power module, replaced JP4 and powered the whole thing from the UBEC. I monitored VCC while I moved and loaded the servos to see if the was any problem with the UBEC voltage/connection. It stayed at 5.0 V +/- 0.2V.
- Moving servos through their full range, and jiggling all the power/servo connections to see if they would fail, loading the wing to simulate the load in flight.
Things I haven’t tested:
- Anything at high power. Perhaps the ESC or motor caused interference. They both sit about 4 inches above the APM.
- I don’t know if there is any telemetry record of the servo rail voltage if JP1 is removed?
Materials and specs:
- Most gear used successfully in my Maja up until now.
- DX8 radio, Orange DSM2 receiver with one satellite (range tested to 30m before flight)
- APM 2.5, firmware 2.78, 3DRpower module (JP1 removed)
- Turnigy 3A low noise UBEC powering servo rail
- Turnigy D-Lux 30A ESC with red BEC wire disconnected
- Hacker A30-52 motor
- Vtail – mixing done in APM, RC is setup as T tail (according to instructions here)
- Hobbyking telemetry module
- Hitec HS-65HB servos x 6 (ailerons, flaps, v-tail)
Considerations/Complications
- I have combined the power supply wiring for the flaps and aileron servos in each wing, and in the v-tail. Both get their power supply from the same red and one black wire, each have their own signal wire. Is one 26g wire enough to supply two HS-65HB 11g servos?
- When I first connected everything I plugged the UBEC the wrong way around on the servo rail for 30 seconds or so. Could that have fried something? It "appeared" to work fine after I corrected that. Is there a way to check?
- There is a large amplitude v-tail servo twitch that I get when I have the flaps switch in position 2 (50% flaps, no Elevator) if I have the elevator trim switch at 2 or 3 clicks of up elevator. Bizzare, it doesn’t happen at any other time. I still have normal manual control via the sticks; it goes away as soon as I move them more than a few mm.
Three log files attached from the three flights.
Replies
IT FLIES!!! I've solved my gremlin.
Thank you to everybody that offered help on this issue.
I started with a couple of hand launches without the motor to see how it glided, and it was perfect. Then I did one at 50% throttle just cruising a few metres above the runway in Manual mode and it was perfect. I didn't even have to touch the aileron stick.
Then I flew it properly and it was effortless. Manual needed a little up elevator trim, but I didn't have to touch the aileron trim at all. I couldn't believe the difference.
I didn't fly it fast though. I kept at 50-65% throttle. In auto mode I flew a few circuits and it handled well at all the speeds I tested from 11 up to 18ms. (40 to 65 km/hr)
I probably had over an hour in the air, two battery packs. Cruising amperage is very low, as low as 2.5amps (on a 3S Lipo).
So thanks again to everybody that helped.
Now I've got a bit of tuning to do before I know if I'm ready for a 200km attempt.
Yes I straightened it, I twisted it by hand in the direction I wanted, then ironed it top and bottom and left it to cool. I had to do that twice and then it was perfect. That was last night, I checked it again and it was still perfect. Thanks for your help
By way of an update, I haven't had much time to work on my plane lately. I've got it fully repaired so I could fly again, but I'm a bit nervous as I haven't found a smoking gun. There have been lots of good suggestions, but no smoking gun has been discovered. One crash each in a Manual and FBWA flight. The first one was quite aggressive flying (fast, steep turns) and the other was very gentle. In both cases the log shows the correct inputs and outputs were given to the ailerons and in both cases it rolled steeply to the right and hit the deck. Although the FBWA flight it pitched down and lost height BEFORE it rolled right.
One thing I don't think I mentioned above was that the aileron trim was about 1/2 way to the left so there wouldn't have been as much authority to the left as to the right. I've adjusted the pushrods and brought the trim tab back to the centre.
In addition I've:
I've got three keychain cameras that I'm going to mount to look at the aileron and tail control surfaces. That will tell me whether they are working properly in flight. I think I'll do a few hand launches and short glides first to see if there is anything funny to see before attempting a proper powered flight.
I'm thinking about disconnecting the flap servo cables and just taping the flaps stationary, and switching to a T-tail in the interests of simplicity. I don't have any spare servos, or control horns on hand, so I'll have to order them in, and have the patience to wait.
Hi jg
I placed my wings on blocks to give the servos and control horns some clearance and measured the distance from the middle of the leading edge to the block, and did the same for the trailing edge. Here are the results.
The left wing is within a few mm, but the right wing has a down turned leading edge at the outside relative to the rest of the wing, and the opposite wing. I don't know if it was like that before I applied the laminate. If it was then it would explain why I need to trim the ailerons to the left.
Any suggestions how I could try to straighten it. I've put a 10mm stack of business cards under the leading edge at the outside, and placed a 5000mah battery on the trailing edge, and leading edge of the inside. I'll leave it for a few hours to see if it makes any difference. I've got a feeling I probably need to apply some fiber tape on the diagonal to keep it there.
The weight definitely isn't the problem. It's a very light plane, and I have just the battery I need to balance C of G on the spar.
A little judicious application of heat from a heat gun can help fix a bit of wing twist. I put a weight on and then blow a little heat and let the whole thing cool down. Check and re-do if needed.
The ailerons weren't level after trimming, the right was about 1-2mm down, and the left 1-2mm up.
The Vtail wasn't perfectly straight, the tip of the left side was about 2cm higher. That would give some unwanted yaw to the right when I give up elevator (but 2cm isn't much, I don't think it would have been a big effect, but it was an effect in the direction that it crashed in). I have fixed that now, but I'm thinking about switching to the T-tail because it seems much simpler.
I'll have a look at your other suggestions tonight when I have some time. Thanks for your ideas.
Did you have any Rudder-Aileron mixing? (APM or Tx)
Yes in APM only.
The APM setup for a V tail said don't change Tx settings. All the V tail mixing happens in the APM.
In Manual mode there is no Rudder-Aileron mixing, but in FBW modes there is. There is rudder and elevator. I used the default settings for both. In Stabilize and FBW modes if you give aileron input (or if the plane banks) then the ailerons move, as do the rudder and elevator. Rudder is to give coordinated turns, elevator is to pitch up to compensate the loss of lift due to the roll.
Parameter info pasted from http://plane.ardupilot.com/wiki/arduplane-parameters
Rudder Mix (ArduPlane:KFF_RDDRMIX)
The amount of rudder mix to apply during aileron movement 0 = 0 %, 1 = 100%
Roll compensation (PTCH2SRV_RLL)
This is the gain term that is applied to the pitch rate offset calculated as required to keep the nose level during turns. The default value is 1 which will work for all models. Advanced users can use it to correct for height variation in turns. If height is lost initially in turns this can be increased in small increments of 0.05 to compensate. If height is gained initially in turns then it can be decreased.
One thing I would definitely do as well is to disable rudder completely until you're sure the plane is flying correctly. Rudder in this plane and 90% of model planes is really not needed as the need to keep "the ball in the center" or coordinate the turn is negligible.
Hi Moglos,
Sorry to hear of your troubles. It's been quiet, so I thought I might add my amateur opinion.
1st Flight:
-Though hard to tell because of the short flight, it looks like your altitude is inversely related to your roll attitude. What seems odd (to me) is you gain altitude when you roll left and lose altitude when you level out. Could this be an indicator of a v-tail mix issue?
-You mention the speed was 90 kph so no stall, but I see your airspeed was about 16m/s at the last sharp left bank followed by the right bank. Your bank angle was ~75 deg. This would equate to a doubling of your stall speed. Your airspeed also dips with the increase in altitude - as expected - so please recheck to be sure it did not stall at the end.
-Lastly, just out of curiosity, are you flying the entire flight at 100% throttle?
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