Severe glitching at idle when moving cyclic

[Hogster]

Hi all

I've got a strange problem with my hexacopter setup which concerns me a little. When the motors are running at idle and I give full forward pitch on the cyclic stick, the rear three motors twitch up to 1500 to 1600µs and back to idle (1300) rapidly and randomly. If I give full backward pitch, the front three motors twitch. If I give full right roll, the left three motors twitch. If I give nearly full left roll (not to the point where the motors stop), the right three motors twitch.

My main questions are:

- Is this a known bug?
- Is it something to worry about?
- If so, how do I fix it?

Many thanks for any advice you can give!


David

PS. I'm running a MultiWii 1.7 dev version at the moment ....

[Hogster]

Just as a note, this also happens on 1.8 as well. It seems to be generated by the the MultiWii end rather than the ESCs, as the GUI shows the glitches even without the ESCs powered up.

Does anyone have any ideas?

Many thanks


David

[mr.rc-cam]

It might be best to list all your IMU components so that someone with the same installation can advise if they have experienced it.

[Hogster]

Hi Thomas

Thanks for your reply - I should have provided that information earlier.

I'm using a Flyduino V1, FFIMUv2, Futaba R617FS 7-channel receiver, Turnigy Plush 25A ESCs, and am powering all the avionics from a 5V UBEC. I2C is set to 400kHz.

Cheers


David

PS. As soon as I raise the throttle above idle this particular problem disappears.

[mr.rc-cam]

The FFIMUv2 has all the same sensors I am using and I don't see the dramatic twitch you are reporting. But I have a hunch; temporarily install an old school FM PPM Rx (not PCM) and see if the problem goes away or changes in any way.

[Hogster]

Ooh gosh I will have to have a hunt around for one of those! I might have one kicking around at my parent's house where most of my old R/C stuff still resides ... Interestingly I'm using the same receiver on my tricopter with no such problems ... but then the sensors are different (WMP and NK) ...

As a side note, a chap on RCGroups pointed out that it's not the UBEC as I'm seeing the problem without the UBEC being powered up ...

Cheers


David

[Hogster]

Here's a video clip showing the problem in the GUI ...

http://vimeo.com/27569510

Cheers


David

[PatrikE]

Make sure you have common ground for reciver and Flyduinoboard.
I´we seen the issue before.

Test 100kHz.

[mr.rc-cam]

I didn't see anything unusual with the R/C pulse data, so my hunch was wrong. So there is nothing to be gained by trying the PPM Rx.

You didn't "Read" the settings so none of the PID's are shown in the video. Might be best to include a screenshot of them in case the experts need to see it.

Test 100kHz.

Good idea. Also try disabling all sensors except the Gyro.

[ziss_dm]

Hi Hogster,

Could you also drop all PID's to 0 and repeat the test?

regards,
ziss_dm

[Alexinparis]

@David:
Your throttle value is very close to the MINCHECK value (1100).
=> when the throttle is higher than this value, the stabilization loop is activated. full pitch => full flip => 3 rear motors at full speed
when the throttle is lower than this value, the stabilization loop is deactivated => every motor goes at MINTHROTTLE

What you are seeing is an oscillation of your throttle around 1100.
Just decrease it a little, and the problem will be solved.

Note: to operate correctly a multiwii, ALL RC channels MUST range [1000;2000] including the RC throttle channel.

[Hogster]

Hi guys

Sorry for the delay in replying, I haven't had access to the hexacopter for a few days.

Alex you were spot on! I have reduced the MINCHECK value to 1000 and the glitches have gone! I have also adjusted the throws on the transmitter to ensure all channels now go from 1000 to 2000, with centre stick giving 1500.

Many thanks for everyone's input - onwards and upwards from here ... hopefully!


David