Flip, the tri


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. 



E-mail me when people leave their comments –

You need to be a member of diydrones to add comments!

Join diydrones


  •  Update: after some fine tuning everthing works fine. Updated to 2.4. and no big issues. Except...I lost a prop mount during flight. Lucky as I am I had no damage on the equipment, first, I landed in snow, second, I landed on the legs, third, titanium and carbon fibre can take the load of a four meter drop. 


    But since it looks promising, I think I will advance to the next version soon. Some minor tests with this frame, but I've some ideas....



  • Update: (still version 2.2.6b); still fwd/aft revered, but I mentally changed it ;-) 


    Went flying today. 5m above ground. Easy takeoff, hard to land softly :-) Big issue is that the tricopter heads forward without RC input. Possible reasons: 

    1) tail motor is not mounted straight

    2) esc's are not properly trimmed/aligned - but I doubt it since the aircraft is stable

    3) PID's tuning (which....Pitch...?) 

    4) CoG ? I actually don't think so, since see 2) the aircraft is stable 

    5)...good ideas?

    I lost a prop mount at my last T/O, but I was so close to ground that nothing happens...now I need for the NTM motors a new prop mount... 

  • @Randy, nice hint, thanks, easy to solve.


    @Don, okay it is/was installed the right way - I just had a brain lock yesterday night and thought I installed it wrong way...for whatever reason. 

  • Developer

    My guess is the pitch channel in your radio needs to be reversed. 

    When you did the radio set-up using the APMissionPlanner did you see the green bar for the pitch moved in the opposite direction from the physical stick on the radio?  That's what it should do! :-)  Not too intuitive..but if you actually look at the raw signals coming out of the radio it makes sense.


  • RC pins point to the back. If you look closely at the IMU up near the I2C port and SW1 (the other button that isn't reset) you should see FRONT and a little arrow.

  • Gosh dammit. APM reversed. Pins should point away from the tail (fwd!).

  • The beer trimming function (in short BTF) from last night works. First take off and a few touch and go. Stable, but always a slight fwd heading without control input. Moreover I've the feeling that when I push the EL control stick aft, the tail motor increases rpm, while when I move the stick fwd, the two fwd motors increase the rpm. Shouldn't it be revered?    

    Sorry for the poor video quality.



  • hahaha nice!

    Beer fixes everything :)

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



This reply was deleted.