First run with my APM - help balancing needed (Bixler)
Went for my first APM fixed wing flight this morning. It wasn't a great success, though through no fault of the APM.
I had the APM, RX and GPS sitting in the Bixler electronics chasis. I had a Gopro gaffer taped to the spine just in front of the engine "intake". To balance it I placed the 2200mAh battery as far back as I could (the front was roughly in line with the rear of the cockpit).
I thought I had it balanced right on the wingspan, but clearly I was wrong. The plane kept trying to pitch down. I should have landed right away but I instead attempted to fix it with trim (it never occurred to me to put it in stabilise). 60 seconds later we were parked in a tree.
Now to my questions:
How do you properly balance the Bixler with all this extra stuff in it? I don't think I could put the battery any further back. I removed the ballast from the nose long ago. The only way I see is to add a little ballast to the tail, but this seems quite inefficient to me.
I've since read that "level" for this aircraft is in fact when the rudder/elevator pushrods are level, and balanced 70mm from the leading edge. Is this correct?
Finally, if I'd had the presence of mind, could Stabilise have saved the day here?
Thanks for reading through this, I'd appreciate any advice you can offer.
For this interested I've attached the video of this flight below. Lots of near misses before the final blow. It took me over an hour to get it out of the tree (no helicopter rescue for me!). It turned out to be too high to throw things at, and I couldn't climb the tree. I ended up gaffer taping a bunch of long branches together and poking it out.
Replies to This Discussion
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Permalink Reply by Eagle on
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Hi Christopher,
I balance my Bixler using the ballast removed from the nose.
A picture worth a thousand words...
If you are wondering what the heck this servo is doing there... I'm a big fan of removing the push rods for the elevator and the rudder and installed them at the tail...
Like you did I balance the Bixler at the wing spare. I'm not sure but maybe mounting the Gopro on top of the wings can create "lever effect" that might produce the plane to rolls further when banking. Again i'm not sure about that...
Maybe more knowledge community members can comment on this.
Good luck on your project and thanks for the videos. Glad you were able to retrieve your plane from that tree.
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Permalink Reply by Christopher Cooper on -
Thanks for that Eagle. I guess I'll add some weight to the tail then. This will allow me to mount my Gopro further forward in the cockpit and reduce drag a bit.
I see you've replaced the hinges on the elevator, what's the reason fort this?
Turns out there was no real damage from the crash, though I did have to return yesterday to search for my Xbee which fell off without me noticing.
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Christopher, I did not replace the hinges. This is a Bixler II and elevator and rudder have hinges.
Flaps are also great.
Did you find your Xbee? Hope you did.
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DeveloperPermalink Reply by Randy on -
I've been thinking of getting a bixler. looks like fun. love your video.
wow..you came really close to some other trees before you finally hit "the one". Cool!!
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Hi Randy, IMHO, Bixler is a great platform for APM. Well done and cheap.
The chassis available is also a plus. Fits well on Bixler I but need some carving to adjust on the Bixler II.
My only deception is the stock motor on Bixler II. Suck big time.
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Permalink Reply by Christopher Cooper on
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Public holiday in Melbourne today so I was able to head out this morning for another try. I had relocated to GoPro to the cockpit and adjusted the balance as necessary by adding weights to the tail. It was perfectly balancing at 65-70mm from the leading edge. I'd also rearranged the electronics a little, placing the ESC on the outside of the fuselage just under the starboard wing.
Anyway, today was not my day. I normally have no problems launching, but for some reason I could not get it right today. Either I wasn't giving enough throttle or wasn't throwing it hard enough, but it took several attempts to get it in the air. Even then I struggled to gain any altitude.
When finally launched it kept trying to roll right, despite my efforts to keep it level. Yes, I did check that the control surfaces were responding appropriately. On its final flight even with the stick full left and ailerons fully (and correctly) deflected it was still rolling right. Then this:
This all happened in manual mode, so I can only blame myself. However I'm trying to look through the logs to see what was going on. Does anyone know where I can find the values for Airspeed and Barometer Altitude?
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Christopher since I am now using Bixler II, I have a Bixler 1 Kit that just take space in my appartment and I don't know what to do with it... I can give it to you. The only question mark is that I'm not sure what would be the cost to send the box from Canada to Melbourne. I can check with my local post office. Anyway PM me if you are interested. Sorry about your crash. Let say It is part of the hobbie. :)
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Permalink Reply by Christopher Cooper on
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Hi Eagle. That's very generous of you. However I fear shipping on a package of that size would be prohibitive.
I'm not giving up on this plane yet, I think the photo makes the damage look a whole lot worse. The nose broke off at the weak point, and the tailplane snapped in half. I've already superglued it back together, reinforcing the tail with skewers and I'll buy some carbon fibre rod for the belly. Wrap it all up in gaffer tape and I think we'll be good to go for Saturday morning.
I have a feeling the poor performance can be put down to me forgetting to charge the battery fully. I thought I had, but the voltage level after the crash was 11.4V, which doesn't seem right for ~2mins of flight.
Thanks again Eagle for the offer!
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Permalink Reply by Christopher Cooper on
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Well it's dead.
After launch It seemed to be responding appropriately to my control inputs, staying relatively level on its own. Then I flicked it into stabilise and it suddenly rolled over. Flicked it back into manual mode but it was too late to save it. It hit the ground so hard the GPS module broke off its circuit board. I don't think any amount of gaffer tape and super glue can fix this guy.
See the GPS plot below (.kmz also attached). Blue and pink are Manual, purple is stabilise. The APM seems to think it went on some kind of adventure after the GPS module broke off!
I've also attached the log file. I would much appreciate it if someone could take a look and let me know where I went wrong. - Attachments:
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Log & KMZ.zip, 1.6 MB
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Permalink Reply by Lloyd Breckenridge on
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Have not had a look at your logs yet.
However you should make sure with a ground test in stabilize that the ailerons and rudder are doing what there supposed to do when in stabilize.
That is if you put the nose down the elevator should go up and vice versa.
I know I always have to reverse the pitch in mission planner.
Unless I do that then the elevator goes in the wrong direction when I push the nose down.
It does not affect the stick control only the stabilize actions.
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+1 with Lloyd, I lost my first airframe because I did not test stabilize on the ground... find out later that aileron should have been reversed. To bad, that Switch was good looking. And I also found out that it was not cheap to replace parts. Thats is why I decided to go for a Bixler.
Sorry about your lost Christopher.
-Eric
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Permalink Reply by Christopher Cooper on
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Thanks for the responses. I was sure I checked this many times before I flew but I'll triple check when I get home. I kind of hope this was the problem as its an easy fix!
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