Is there anything (barring motor thrust axes being misaligned) that would cause an opposing pair of motors to overheat?  I'm guessing my quad is fighting yaw because of opposing pair part.  Navigation looks fine so I don't think its a gyro or compass drift or something like that.

Potentially related:

I've done auto APM 2.5 ESC calibration (https://code.google.com/p/arducopter/wiki/AC2_ESC) and the only deviation from the procedure was I had to drop the throttle in order to get the 2 beeps in step 5 (as opposed to waiting for 2 beeps to drop the throttle).  I waited for 2 minutes and they never beeped twice unless I drop the throttle first.  Am I misunderstanding the procedure?

Any ideas?

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If you enable motor logging and do a hover, do two motors show higher motor inputs?

That's a good way of diagnosing imbalances in the system, you can see if any motors are working harder than others, eg if CG is way out or you have some twist causing the CW or CCW motors to have to work harder.

In a normal, balanced copter with calibrated ESCs, all motors should show basically the same MOTOR value in the dataflash logs.

Are the hot motors rotating CW (from top)? And, what type of motors are they? Some motors build a fan into the bell casing which is rotating the wrong direction for the reverse pitch pair, thus those motors do not cool as well as the others. Same goes for coaxial motor pairs in which the bottom motor will run hot.

Thanks, I'll try to log it tomorrow. That will rule out bad motors I suppose if their commands are higher.
They're rctimer HP 2212s. They're the front left and rear right ones which are CW from the top. If I remember correctly I believe that would mean it's fighting a CW net yaw..

I tried logging with the motors command enabled.. however, I dont get a log of much.  Looks like its just saving setup values (below).  Am I supposed to enable something?  I've read the manual and cant find any switches to set to enable recording more data..

2

ArduCopter V2.9.1
Free RAM: 1461
APM 2


FW Ver: 120
----------------------------------------


Radio
----------------------------------------
CH1: 986 | 2008
CH2: 982 | 2008
CH3: 986 | 1940
CH4: 986 | 2008
CH5: 982 | 1875
CH6: 1496 | 1498
CH7: 1497 | 1498


Frame
----------------------------------------
Quad frame
V mode

Batt Mon:
----------------------------------------
volts and cur

Sonar
----------------------------------------
disabled
Type: 0 (0=XL, 1=LV, 2=XLL, 3=HRLV)

Flight modes
----------------------------------------
Pos 0: STABILIZE, Simple: OFF
Pos 1: STABILIZE, Simple: OFF
Pos 2: LOITER, Simple: OFF
Pos 3: STABILIZE, Simple: OFF
Pos 4: STABILIZE, Simple: OFF
Pos 5: RTL, Simple: OFF


INS
----------------------------------------
G_off: 0.02, -0.06, -0.03
A_off: -0.13, 0.39, 1.27 A_scale: 1.00, 1.00, 0.98


Compass
----------------------------------------
enabled
Mag Dec: 0.0000
Mag off: -75.5666, -60.0049, -245.4465

OptFlow
----------------------------------------
disabled


SYSID_SW_MREV: 120
SYSID_SW_TYPE: 10
SYSID_THISMAV: 1
SYSID_MYGCS: 255
SERIAL3_BAUD: 57
TELEM_DELAY: 0
RTL_ALT: 1500
SONAR_ENABLE: 0

Any update on this issue? 

I'm experiencing the same symptoms - diagonal (opposing) motors get really hot (cant touch them after 5 min flight) while other ones are cold as ice. 

Quad is stable, flies ok (there is some drift but still have to tweak PIDs), but I don't think this overheating is normal. 

Setup  - H-quad (X config)

APM 2.5.

FW 3.0.1

Thnx for any info!

I've started flying FPV which actually helps.. because I fly more aggressively, the airflow helps out.  Not a solution, but surprised it helped out so much considering I push the throttle a lot more.

I think it's from me mounting them with their shaft axes not exactly facing in the same direction (I made a custom frame).  The quad then had to fight a yaw induced by the asymmetry because they were both turned so that they would yaw the quad in the same direction.  The problem is if throttle is increased to them to control that yaw with angular momentum, they increase the yaw that was the problem in the first place.  So it basically becomes change in angular momentum vs thrust torque, causing them to overheat every time.  I used some plastic shims under the motors to turn them into the right direction and that helped until I made a new frame.

Check if your motors are all mounted properly and your shafts are in the same direction.  Or fly crazy :)

But I'd start there, it's the easiest one to rule out.  Hover the quad at eye level and walk around it to make sure the blades look like they're spinning in the same plane.

Thank You for the reply!

My frame is custom as well, and even though I tried to align everything perfect along all axes - we all know that didn't happen :) So yeah, I had some Yaw issue (now I've crashed, so have to rebuild it before I can test it) so that could be true... just frame imperfection... but could it be that much?

Anyway - Your reply makes sense - I'll test and get back to You.. Thnx again!

Ha yeah :)

Mine were off about 5 degrees which actually should make a big difference:  

sin(5 degrees) * ~400 g thrust per motor * 2 motors = about 70 g of yaw-inducing thrust at about 10".  That alone is a problem.  As far as overheating I think the issue is that it spools up to provide counter change in momentum which in turn causes more yaw in the wrong direction, which it must now fight.

Let me know how it goes!

Did you ever find a solution for the overheating?  I'm experience the same symptoms.

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