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Right side motors are consistently producing less thrust in home grown quad...

Posted by Marc Dantonio on July 15, 2011 at 2:24pm

Hi folks...

The situation is that I am using Phoenix ICE 75 motor controllers and Rimfire .60 motors. Its a 51" diameter quad in an X configuration.

 

The ICE ESCs log data well. I download the logs after doing bench testing. One set of tests were simply throttle tests. The motors on the left (motor 3 forward, motor 2 rear left) are consistently showing higher throttle output than motor 1 in the right forward location and motor 4, at the rear right. I thought, coming from RC Airplanes, that perhaps this is simply a trim problem. Add some aileron trim and the throttles should match up. I did that and the problem is exactly the same. I used a -3 [to the left] and then a -8 setting on the Futaba transmitter trim tab for aileron. There was no difference. The right side motors still show LESS thrust by several thousand RPM each.

Yet, when I do stick tests and log which way the motors try to thrust the craft on the bench (no props!) the control movements produce exactly the right results in the logs.. It is as if the vehicle would require extraordinary LEFTward aileron trim to balance the throttle input on all four motors. 

 

The problem with this approach however is that in Stabilize or Simple mode I imagine this will be ok. But what happens when I go to Loiter? Auto? The radio trims are not IN the picture at that point...

 

The bottom line is that when I put the throttles at any setting with the control sticks neutralized or when in any other non manual related mode, I should see the motors turning very similar RPMs when sitting on the ground prior to liftoff... Currently I do not. If I take off in this current condition, the vehicle will flip over to the right I am sure ....

Any ideas??

Thanks,

Marc

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Replies

  • Marc Dantonio July 16, 2011 at 1:06pm

    @Don

    I now have a bubble level to put on the vehicle at which point I will 'level' it and see what happens. I will zero trims...

    @Roger

    I will balance the craft but this test was done with no props and with no liftoff possible. This was simply a 1/3 throttle test and the right side motors show less thrust. This is without props as I said... It is POSSIBLE dont you think that if the gyro doesnt think its level that it might automatically call for more left side thrust? In other words, it was leveled at a non-level setting and therefore now thinks it must compensate by adding some right bank to the craft?

    @Sanjaya

    Thanks for answering... If I was testing with props I would say this was a possibility. Plus the craft is in no way getting airborne yet. It is simply sitting on a table and spinning up motors only to 1/3 throttle. With props installed, we require approximately 40% throttle to lift off perhaps 45% it appears.

     

    I think I will try to re-level the craft using the CLI mode AFTER using the bubble level to level the APM... I will let everyone know what happens...

     

    Thank you very much so far...

    Marc

  • Sanjaya Kumar July 16, 2011 at 12:56pm

    Make sure that the motors are exactly vertical. If one or more rotors have a non-zero thrust in the x-y plane, then two of the motors have to work extra hard to compensate for that.

    I had the same problem -- I noticed on the raw-sensor radio output that two motors were consistently drawing more power and it was because my frame has booms with a round cross-section and one of the motors was tilted as a result. Correcting the tilt solved the problem.

  • roger July 15, 2011 at 8:06pm
    On Don's note, a simple balancing your ardu on your fingers will do the trick at least in my case. What I did was put one finger approximately in the middle of the ardu arm on the left and do the same on the right. Then lift it a bit. If the ardu tilts towards you then the back part is lighter than the front part so you have to re arrange some of the item on the ardu like push back the batteries so the copter will balance out. If its the other way around, then do the appropriate shift in weight. Once you are satisfied, do the same procedure for the remaining arm pair ... hope it helps.
  • Don Cramer July 15, 2011 at 7:27pm
    Could it be that the craft is tilted slightly? If so then the lower side should generate higher rpm than the other (trying to level itself). Also, dont use trims. Reset them to zero.
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