S500 has propellers spinning but doesn't take off

Flight Testing & Log Analysis
1

Hi there,

I have built an almost exact replica of an S500 drone I already have, which is flying fine.
The specs are:

  • PixracerPro (This is the only different component to the existing drone, which has a Pixracer)
  • 4S battery
  • Brother Hobby 900 KV Avenger V3 motors
  • TMotor F45A ESCs (interfaced with Dshot600 on channels Main 1-4)

The Problem:

  • The main problem is that after arming, I can increase the rotor speed by putting more throttle, but it never reaches as high RPM as the other drone and doesn’t take off.
    • One sub-problem is that there is a lot of drift in the state estimation, I don’t really care about odometry but the pitch and roll don’t look stable in the logs. See this log file, where I used Manual mode, so the pitch and roll estimates are used for control.
      In the motor outputs section, you can clearly see that right after boot, the motors spin at the same speed, but as the drift accumulates, the drone tries to counteract by throttling some motors down.
    • In this other log file I have switched on Acro mode, so the estimator is not used for control. Here, we see that the motor outputs are nicely going up to 1.0 in synchrony. But still, the drone doesn’t take off, even though it’s close at full throttle. Also, after roughly 70 % throttle, the rpm don’t audibly increase. I would like to first get this problem sorted, as I see it more problematic.

What I’ve tried (nothing helped):

  • Switching to PWM communication between ESC and PixracerPro, and calibrating it.
  • Measured resistances to rule out that the motors don’t get enough current. Everyting is at roughl 0.1 Ohm, so should be fine
  • Tightened the lock nuts, from the impression on the props, it looks like the motors are not free spinning.
  • Throtteling without props. Audibly it sounds like the motors stop spinning faster at the same 70 % throttle.
  • Made a slow-mo of the props while spinning, they go the right way around.

Some general things comparing the new drone to the old one:

  • the pitch of the ESC bootup sequence seems lower.
  • the bootup sequence does not go 123 1 3(1 is low pitch, 3 is high pitch) but only 123. So according to the doc the esc does not detect the 0 throttle position and does not signal readiness, even though afterwards it allows spinning the props. But this should not be a problem because I’m using Dshot, should it?
  • For comparison, this flight log is from the the other functioning drone. The odometry also drifts during throttle-up but after takeoff, pitch and roll become stable.

I kind of ran out of ideas, so would appreciate ideas a lot for things I could try or I should fix.
Thanks already!

lordreas

2

Hey @TOTON95 can you please take a look here?

3

@rroche Thank you for tagging me

Welcome, @lordreas. I’ll take a look and see how I can help you. :raising_hands:

1 Like
4

Kindly send a picture of the drone including the propellers .

5

Thanks for helping out! This is a picture of the quad:

17485161456741879496871164204923
174851614567418794968711642049231920×2550 880 KB

17485161819847735501279322973359
174851618198477355012793229733591920×2550 187 KB

6

Hi,

Your propellers are installed upside down !! :slightly_smiling_face:… you cannot turn the propellers upside to make it clockwise or vice versa …!!

propellers
propellers564×750 276 KB

7

I see the lighting and propeller texture is misleading and makes it look odd. But I can reassure they are mounted correctly. See attached picture:

17485202058646745560930111708179
174852020586467455609301117081791920×1446 441 KB

8

Can you advice what is the brand and the size of the propeller. Normally these are sold for fixed wing push configuration models. Did you buy them in pairs like CCW and CW ?

Also note that for creating lift , we do not require Px4 or Ardupilot firmware for the Quadcopter. These firmwares along with PID tuning are for balancing the body frame.

9

@sibujacob I bought these propellers in CW and CCW configuration, identically to the drone, that is working. They are 9 x 4.5 inch propellers.

10

You may need to increase the size of the props to 11" for an S500 drone. 9" may be small to create the lift .

11

Hi @sibujacob,
I already thought about that, but I don’t think this solves the actual problem. The other drone flies just fine with 9-inch props. With 10-inch props, we had clearance problems with the cables under some circumstances. (The drone on the picture is not yet the full build)

12

@lordreas These are indeed abnormal readings for the state estimator. I will look into that with more detail, I would need some time to study it properly. For the throttle output, have you already tried to swap the Pixracer with the Pixracer Pro into the current setup and see if the issue is still there? Also, the Pixracer Pro may be unable to communicate with the ESC. I’m wondering if you could please share the output of dshot status. In the meantime, I will try to schedule a space to use my measurement tools to see if the current firmware/configuration is causing this issue.

13

Hi @TOTON95

thanks for taking the time! I will try to swap the boards on Thursday and see what happens.
The ouput of dshot status is the following:

nsh> dshot status
INFO [dshot] Outputs initialized: yes
INFO [dshot] Outputs used: 0xf
INFO [dshot] Outputs on: yes
dshot: cycle: 16669 events, 230988us elapsed, 13.86us avg, min 12us max 67us 1.201us rms
INFO [mixer_module] Param prefix: PWM_MAIN
control latency: 16672 events, 4870184us elapsed, 292.12us avg, min 264us max 534us 52.808us rms
INFO [mixer_module] Switched to rate_ctrl work queue
Channel Configuration:
Channel 0: func: 101, value: 0, failsafe: 0, disarmed: 0, min: 109, max: 1999
Channel 1: func: 102, value: 0, failsafe: 0, disarmed: 0, min: 109, max: 1999
Channel 2: func: 103, value: 0, failsafe: 0, disarmed: 0, min: 109, max: 1999
Channel 3: func: 104, value: 0, failsafe: 0, disarmed: 0, min: 109, max: 1999
Channel 4: func: 0, value: 0, failsafe: 0, disarmed: 0, min: 109, max: 1999
Channel 5: func: 0, value: 0, failsafe: 0, disarmed: 0, min: 109, max: 1999
Channel 6: func: 0, value: 0, failsafe: 0, disarmed: 0, min: 109, max: 1999
Channel 7: func: 0, value: 0, failsafe: 0, disarmed: 0, min: 109, max: 1999
14

Hi all,

I have now had access to an oscilloscope and can confirm that the DSHOT values on the pins correspond to full throttle. So the PX4 is working fine and the problem must be at the ESCs or the motors. I will replace both of them and see what happens.
Thanks anyway for your time and ideas.

Cheers,
lordreas

15

@lordreas Thanks for sharing your findings, I am keeping the task to find what’s is happening with the state estimation for the Pixracer Pro.

Best Regards.