X-Racer Multi-Shot issue

[Paul01]

Hi Guys,

Got a strange issue with the following setup

X-Racer 303 3.1 flight controller running Betaflight 3.0.1
FVT LittleBee 20a running Multi-shot 14.85
Gyro set to 8k
Looptime set to 2k

When I power the board everything starts up as expected, however if I plug the flight controller into the computer and connect to it with betaflight (lipo still plugged in), all of the motors randomly twitch or spin a little, usually individually.

All this goes away if I set the looptime to 4k.

Anyone know the reason for this?

Cheers,

Paul.

[Cheredanine]

Most likely:
Are you sure it is a 3.1 and not a 2.1? 2.1 and earlier use i2c gyro, that can';t go at 8khz, the 3.1 has SPI like most other boards and can do 8khz gyro

Also check processor load

[Paul01]

Most likely:
Are you sure it is a 3.1 and not a 2.1? 2.1 and earlier use i2c gyro, that can';t go at 8khz, the 3.1 has SPI like most other boards and can do 8khz gyro

Also check processor load

Hi Cheredanine

Yeah its defiantly the 3.1, and I am running the SPI version of the firmware. CPU is around 8% when I last checked I think with with 8k 4k enabled and no issues apparent, only happens when I set looptime to 2k.

[Cheredanine]

Ok mate, just rereading.

What is happening is potentially a slight difference in timing.
Have you calibrated your escs (this may or may not help)

Multishot uses 5 to 25 millionths of a second to indicate 1000 to 2000 throttle.

The difference between min command (which is what the FC sends when the thing should be still) and the point where the motors twitch is relatively small, potentially impacted by signal rise and fall
(This is one of the reasons for the new dshot protocol)

You could try cutting 20 points off min command but TBH if it only happens when you have a lipo plugged in and you connect configurator I wouldn';t worry about it, you shouldn';t be doing that often

[Paul01]

You could try cutting 20 points off min command but TBH if it only happens when you have a lipo plugged in and you connect configurator I wouldn';t worry about it, you shouldn';t be doing that often

I did try setting min command to 900 to make sure that wasn';t the issue and it made no different, minimum throttle is confirm at 1040 with minimum command set to 1000.

Just been uber cautious, but was think the same myself. I might just test it a little bit more first though 

[Cheredanine]

it shouldn';t be doing it, sounds like you are getting spurious spikes on the signal line, if it was doing anything then a cap may help, as it is check soldering? Have you used ground and signal wires to esc?

[Paul01]

it shouldn';t be doing it, sounds like you are getting spurious spikes on the signal line, if it was doing anything then a cap may help, as it is check soldering? Have you used ground and signal wires to esc?

Yeah used ground and signal on all ESC. What I did notice was that the FC';s voltage is 5.1v with the lipo connected, but jumps to 5.3v when the usb cable is also connected. I';ll check soldering tonight, and I think i';ll connect a Bluetooth module to it and see what happens when I connect to it with Betaflight configuration without the USB cable.

Thanks for your help, i';ll let you know how I get on