Hello to all you X8'ers,
I'm opening this discussion to find all of the optimal flight parameters for an X8. The parameters I'm trying to pin down to make an X8 fly as optimally as possible are listed below in order of importance. The current parameters are listed below, though they have obviously not been optimized yet. This should help anybody with an X8 to get in the air ASAP.
- CoG. Updated: 1-2 inches in front of the stock CG seems to prevent stalls from constantly happening.
- PID settings. Most say that default PIDs are optimal.
- Maximum/minimum pitch/roll angles to avoid stalls. Pitch: -20*, 15*. Roll: 35* maximum bank.
- Wing and aileron reflex to reduce stalls. 3* reflex at the wingtip trailing edge is suggested by some.
- Wing pitch calibration for level cruise flight. I usually place the hatch cover under the nose when booting the APM, for approximately a 5* upwards inclination.
- Maximum AUW/TOW. Maximum is thought to be at 3-4kg (6-8lb) but there are reports of heavier ones.
- Elevon throws. 2cm movement in either direction with dual rates on, less when they are off.
- Maximum motor size and pitch offsets. Below 2000W is suggested by some. 1.8kW has been tested.
- Camera placement. Around the rear spar bulkhead is optimal for vibration reduction.
- Whether or not the camera bump on the bottom of the wing should be removed. Experts (Daemon) have removed it, but most people (including me) have left it intact for various reasons.
This thread has been started partly for my benefit (so I stop crashing) and for the benefit of anyone with an X8 who keeps crashing.
I have attached a .tlog and mission file from a flight today in which I crashed the X8 into a 120' tree due to a stall and spin. The stall was likely caused by the observation of what appeared to be a flyaway, and my failed intervention. If anybody can help me understand if this was actually a flyaway caused by a hardware or software failure, or was just the result of bad parameters, I would be infinitely grateful. I have also included a photograph of the damage incurred by the crash, as Ning issues are preventing me from inserting an image into the text.
Everybody on the X8 forum: Please post any and all of your crash stories, .tlogs from them, photos of the damage, and parameters that I have listed above so we can finally figure out this airframe.
Many thanks,
Paul
Replies
Hi,
How about adding wortex generators through the whole wing to avoid stall and spin?
Would that help?
IMO no, the reynolds numbers are too low
That's bad.
I saw on anotherd build that someone using slats on 1/3rd area of the leading edge, counted from the wingtip.
Thought I'd share a spin-recovery from my X8. I've been meaning to post to this thread for a while, so, sorry for the delay. I've technically had two spins, and both are since adding a second battery (4s 5000mah 45/90C - its what I had..)
The first spin was while tuning FBW-A and unintentionally going too slow, somewhere in the 8m/s range with light winds, and when it started, I was just too low to flip to manual, max the throttle, and pitch-forward out of the spin. I got to "flip to manual, then shit self" by the time the X8 kissed the deck. Only minor damage thankfully, but CG was still at the back of the forward finger holes.
The second spin was higher, and while flying either FBWA or STAB under the hood; I don't remember the mode I was in anymore, and accidentally had loaded Copter firmware on the MinimOSD so the mode appears to be AltHold the whole time. I'm happy to go back and find the tlog if anyone would see any value in reviewing it. I was meeting up with an X7 that had just launched when things just went weird. Luckily I was high enough that I had enough time to max the throttle (which was limited by the APM to 75%), pitch down, and recover. Here is the youtube link: https://www.youtube.com/watch?v=zsqUghGhi2A
Overall it was weird. My speed was fine, and it was a pretty windy day so possibly I caught a gust or something during that last turn that contributed, but I just wanted to share with this thread as I think the intent of the thread is helpful for people to learn from. I didn't start getting spins until I added the second battery, so naturally I am questioning myself on measurement of CG and will continue to pay closer and more careful attention to this item.
Any questions, please let me know! :)
Specs:
Skywalker X8 AUW 3444.4G
Power: Hyperion HS3026-1210 with Atlas 90A ESC, APC 13x5.5E
Flight Controller: APM2.5, 2.74b, RDF900 Telemetry
FPV: 600tvl CCD with 1.3GHz 800mw, IBCrazy Cloverleaf, MinimOSD-Extra
FPV2: (via switch) Hero3 on ReadyMadeRC PanTilt Pod
RC Link: EzUHF 8ch Diversity
Battery: 2 x Nanotech 4S 5000 (Parallel) with 12v ubec for Video and 5v ubec for output rail on APM
Hi all,
Had a pretty annoying crash on Friday with my X8, not a CoG issue but some dodgy electronics or software I think. Happened when I switched from RTL to FBW-A. Randomly flicked into manual for some reason (shouldn't have done) and the aircraft banked sharply.
My initial suspicion was that my rx browned out, but it is on the same 5v rail as APM, and the datalog for the 5v line looks reasonable.
If anyone is free, and bored, and fancies having a look at my data for a diagnosis I would be forever grateful!
http://upload.droneshare.com/view/bvjl2vy
Cheers,
Si
Had a cracker yesterday...
Finished building my third X8 for chuck launch (also working on a 4th which has wheels). Decided to push the CoG back a bit to where lots have people have said is safe (rear end of the front finger holes). How it didn't crash is beyond me, highly unstable and managed to miraculously get out of two spins in one short circuit.
Did nothing bar push the CoG forwards exactly 1" and now she flies like a beauty with no sign of wanting to spin.
I got into a spin when trying to fly my x-8 without the GoPro in the nose.... the cg moved back a little but was still within limit (i taught...)
I managed to recover before hitting the ground by applying full throttle and elev down.
I Have a 510kv 52mm motor on 6s so now i found a use for all of the power...
Just to throw my tuppence in:
Currently flying at 3kg AUW with a 1800W motor with 12x7 folding prop with lots of success.
The grand plan is to have this up to 6-6.5kg AUW.
More info on my DIYD Page.
Hello Paul and all X8 operators!
We have picked the X8 wing as our long range aerial survey machine. We currently perform commercial photogrammetry for Western Canadian energy companies using our MK multi rotors, But mapping more than 500m x 500m in a day is a challenge. We decided the X8 and APM 2.5 should be the platform to go with.
With about 50 flights on the system we have had zero incidents. I have 25 years of RC experience and I would have to say that improper C of G has probably led to the majority of scary moments. We have tried to stall it, but the wing just gets the mushy feel and keeps going straight ahead.
1. So we started with the balance far forward of the point suggested in the X8 instruction manual. Usually 1.5-2" ahead of the rear finger hole. Fast (6-8m/s landing speed)
2. PID's are basically stock. We can never seem to get FBW to achieve 45* of roll even though it works great in all other modes.
3.-25*, +25* and 45* of roll has been good so far
4. built as stock. trimmed elevons up a couple mm.
5. Ours in manual leveled using a bubble level glued to the bottom of the plane. I would say 0* inclination and flys great.
6. Weighs 8.5lbs. Flys like it could handle 10lbs though I would make reinforcements such as fibreglass tape at that point.
7. at least 2cm of throw either way.
8. Motor is OS 25 - OSMG9530
OMA-3825-750 (.30 Size)
Rotor Diameter (mm): 38
Magnet Length (mm): 25
kV: 750
Watts: 590
Weight (oz/g): 6.7 (190)
Spins a 12x8 APC fixed for 7-9 amps at 15m/s. Folding props drew 15-20amps typically.
9. Camera mount is around the C of G
10. Left the hump. (it will wear off eventually)
Curious to hear others experiences!
Robert
Robert,
Thanks for share your setup, have you any picture of your x8?
If you use a fixed propeller, how are you avoid that the prop touch the floor?
thank you
Sergio
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