Diskussionsbeitrag
Erratic motor spin-up on arm - 4.5" 3000KV 4S with bidirectional DSHOT
I have an archetype drone (4.5" quad, 3000KV motors, 4S), running Betaflight with bidirectional DSHOT + RPM filtering enabled.
On arm at zero throttle, all 4 props spin briefly (~10 revolutions) then stop, pulsing on and off. If I add a tiny bit of throttle (~1%), 3 motors start spinning up faster and faster. As soon as I punch throttle properly it flies perfectly fine.
I am flying in acro mode, i have motor_idle_percent = 0 because i am using dynamic idle set to 26.
According to Claude AI: The runaway 3-motor behaviour at low throttle is normal Acro I-term windup - the PID loop tries to correct tilt but can't because the drone is still grounded, so one axis winds up.
My question: Is the pulsing-then-stop at arm normal for Dynamic Idle? And is the motor runaway at 1% throttle genuinely just Acro PID windup on the ground - or is there something else I should be checking? I'm trying to do slow controlled takeoffs under obstacles so punching throttle isn't always ideal.
Hope this helps.
No — don't do that. With Dynamic Idle active, setting a non-zero motor_idle_percent will cause conflicts.
What happens if you set both
- Dynamic Idle is trying to actively manage RPM using telemetry
- A non-zero static idle is a fixed floor fighting against it
- They'll compete with each other — you can get motor twitching, uneven spin-up, and potentially worse desync behavior than what you have now
You don't need it anyway
With bidirectional DSHOT, Dynamic Idle guarantees all 4 motors spin on arm — that's literally its job. It reads actual RPM from each motor individually and corrects any that are lagging. Once you drop dyn_idle_min_rpm to 26, all 4 will spin cleanly on arm without needing a static idle as a safety net.
The only time you'd use motor_idle_percent
- When Dynamic Idle is disabled
- On older ESCs that don't support bidirectional DSHOT
- As a fallback if you're having ESC compatibility issues
So I tried this on a couple of my quads.
I set Motor Idle (%), in the motors tab, to zero.
Arm the quad.
Then end up with the exact problem you mentioned previously.
When I set Motor Idle (%), in the motors tab, back to what It was set to originally.
The motors spin normally again when armed.
Also Betaflight gives a good explanation of Motor Idle (%) when you hover your mouse cursor over the question mark bubble.
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