Once upon an idea...

okay, okay, you all know the great idea about building a convertible tri - to planecopter. Oh yes Avatar like, old story no news. However, I started to work on one. I am still far away from anything that is convertible, but it might be soon a flying tri.

I'm using APM v1 with the 2560atmega the oilpan, gps, sonar EZxx. The frame is made out of CFRB, re-enforced with honeycomb. The arms, about 36cm each, are made from titanium, with a cold coated wolfram-aluminum coating. The three motors, 750kV; NTM 2836; about 250W each on 4S 2200mA LiPo. The props are 12"4.5; CCW/CCW/CW. I use a digital servo to rotate one of the motors, but I've already the setup to turn each motor 90° fwd/aft. All together, including a bunch of stainless steel A4 grade bolts and sel flocking nuts, the tri is on 1.7kg. Heavy beast. If I replace the titanium arms with carbon fibre, I could save about 150g. My body is more or less two round carbon sheets, 20cm diameter. Way to much material, but - who cares. I use as ESC the HK Blue Series 30A. 


The pictures shows a partly disassembled tricopter. Troubleshooting... 


 The Firmware is now 2.2.6b. To reverse the yaw servo I had to change the fiftyHz loop in Arducopter.pde

 APM_RC.OutputCh(CH_TRI_YAW, ( (-1 * (g.rc_4.radio_out - g.rc_4.radio_trim) ) + g.rc_4.radio_trim ) );


Time for takeoff...soon. I've to find the best CoG - but I'm not completely sure on how exact the CoG must be - clearly, as good as possible,...but maybe a few mm off? Fine too? Who knows.


I had some troubles, most are solved:

*) Vibration due to loose turn table mechanic. Some preload on the bearings and the problems was solved

*) Vibrations caused by unbalanced blades. The CW blade (from Arducopter Store) had a nice inbalance. Trimming was necessary

*) Yaw servo reversed in auto trim. Solved it with entering the update line, see above.

*)  Took me a few minutes to figure out on how to load AC through Arduino. But finally easy.

*) Then was the little software updates when suddenly the YAW servo wasn't supported anymore (2.2b-2.2b5).

*) Too heavy, first I had two 2200Ah LiPoFe A123 6.6V in series. I've now one single LiPo 4S 2200Ah; reduced the weight about 150g.

*) Some flips because I connected the esc left/right reverse....STUPID I AM

*) Some flips because one ESC did not provide the same output power as the other one.....solved new ESC; I hope

*) Last but not least...working on the CoG.



I use a 6 Channel TX/RX Skytech Ts6i. 


I hope I can lift of at about 60-70% throttle max. The next days will proof it. Then next step: full conversion. Mechanic is easy, but coding will take time.


Thanks for Igor and Don for support. 



Views: 1452

Comment by Don Brooks on February 1, 2012 at 1:49pm

Hrmm... convertible... that would effectively be the complete marriage of Arduplane to Arducopter.... A very intriguing idea! 1.7Kgs though wow, you're almost 1 full Kg heavier than mine. She's a beast, but looks good!

Comment by Randy on February 1, 2012 at 6:27pm


     I think you shouldn't need to make the code change to reverse the yaw servo direction so you should be able to use the code directly out of the mission planner.

     It's slightly inconvenient but I think you can accomplisht he same thing by changing a parameter in the Config screen of the APMission planner.  Sorry, I don't have my notes with me but I think it's RC_7_REV parameter.

Comment by Martin Szymanski on February 1, 2012 at 6:34pm

The Gyro's and IMU's are not center cored to this frame based on the photo. Putting them in the middle will help.

Comment by Don Brooks on February 1, 2012 at 8:58pm

@Randy: I never paid much attention to the channel 7 reversing, but I just checked it for fun, and -1 in RC_7_REV doesn't reverse the output to channel 7. It may need to be reported as an issue.

Comment by Martin Szymanski on February 1, 2012 at 9:21pm

Ch 7 is experimental and may be do nothing at a given version build.

Comment by Don Brooks on February 1, 2012 at 9:24pm

Channel 7 output on a tricopter is the yaw servo. Hardly experimental.

Comment by Martin Szymanski on February 1, 2012 at 9:32pm

ok you win. I'm going on.

PS: I was talking about the input.

Comment by Tobias Krieger on February 2, 2012 at 4:54am


Dammit, I should have thought about this by myself. Definitly, this offset of IMU/Gyro to center point can cause an inbalanced control condition and leads automatically to a different motor speed. The easy way is to change the position mechanically, the hard way, to enter the offset in the code.


Comment by Tobias Krieger on February 3, 2012 at 5:10pm

 Found finally a way to determine the ideal CoG of my little tri!


Comment by Don Brooks on February 3, 2012 at 9:10pm

hahaha nice!

Beer fixes everything :)


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