Flight Controller Soft Mount – is it worth it?

Is it worth to soft mount flight controller? Are gyro pads I recommended here better than rubber stand offs? I feel that they are better, but I do not have any solid data to prove it. So I can only tell, that I find them better and that is all. But, I can answer the question is it worth to soft mount flight controller at all. The answer is YES and here is a proof…

The problem of twitching motors

After I updated my 5″ racer to stronger motors (EMAX RS2205S 2300KV over RS2205 2300KV) I noticed something very very irritating: twitching motors. When throttle was in more less middle position or after rapid throttle change, twitching from motors was very audible. Quad was flyable, but performance was very low. I had to reduce yaw P gain by more than 50% not to see those twitches in FPV footage!

Blackbox log revealed the truth: from time to time, strong vibration was getting into yaw gyro traces. I also localized the source of those twitches: stronger motors with more torque and higher radial acceleration were able to shake whole machine when frequency was close to the resonance frequency of the frame.

hard mount twitch example

This was happening only on YAW axis. ROLL and PITCH were fine. Nothing bad was happening over there.

The only solutions I could think of were: fly with low yaw P gain, go back to old motors or damp those nasty shakes! I’ve chosen to damp those shakes of course!

Yaw traces on hard mounted flight controller

RAW gyro signal

Hard mount yaw raw

Filtered gyro signal

hard mount yaw filtered

As you can see above, yaw gyro traces, both raw and filtered, are showing some noise on all frequency ranges. Even filtered yaw shows noise up to above 200Hz. Those twitches I was fighting with were located somewhere there at around 105Hz. I knew the twitch frequency, because I measured it using this method.

Yaw traces on soft mounted flight controller

RAW gyro signal

Soft Mount yaw raw

Filtered gyro signal

Soft mount yaw filtered

When happened after I soft mounted? Magic! Not only filtered signal shows no signs of twitching frequencies (around 105Hz), but even raw signal is very close to zero at around 100Hz. It is very close to zero everywhere above 20Hz! There is less noise on raw traces with soft mount than on filtered traces on hard mount! This is the proof that soft mount really really works!

No more twitching motors on soft mounted flight controller!

Soft mount no twitches

But what’s more important, all those nasty twitches were gone as soon as I soft mounted. Immediately. No filter tuning, no PID gains adjustments. I soft mounted and that was all. Twitches are history!

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