Quadcopter severe oscillations and overheating of motor

Hi all, I cannot figure this one out and I truly appreciate your help!

My setup
Frame: ZMR 250
Motor Emax RS2306 2400kv
ESC: T-Motor F45 V2.0 4 in 1
Prop: Gemfan hurricane 5.1 x 4.99 x 3
Battery: 4S 1550mah 100C lipo
FC: modalai flightcore
FW: V.1.11.3 generic 250 quad

The above setup works perfectly when i fly it with a 3s lipo, but when i shifted to a 4s the quad would oscillate really fast. It can maintain altitude but the oscillations are really quick in the roll axis. The motors get really hot within few seconds of flight, hot enough to burn your hands!!
I am not able to figure out why this is happening! I havent changed any parameters on the FC, using the stock parameter and havent done any tuning! The escs are also using the FW that came from the factory. I tried using the PWM protocol and Dshot 1200 as that is supported with my esc while flying on 4s and the results are still the same!
I will upload the Ulog tomorrow and if possible the flight video as well.

Thanks & Regards,
Mohammed Naveed

Hi @Mohammednaveed ,

The drone oscillates probably because the rate loop gain is too high. To reduce it, you can try to lower MC_ROLLRATE_K until the oscillation stops (see Multicopter PID Tuning Guide (Manual/Basic) | PX4 User Guide)

Good luck!

Hi @bresch
Thank you for your input i will try that out!

Thanks & Regards,
Mohammed Naveed

Please have a look at the Ulogs
3s Flight Ulog
4s flight Ulog

Is there anything else i should a keep an eye for?

Thanks & Regards,
Mohammed Naveed

You need to reduce the rate controller gain even more if you want to fly with a 4s battery. That’s normal, it’s be cause the gain on the motors is then higher due to the higher voltage, so to keep the same tuning, you need to compensate in the controller for that gain increase.

In the 3S flight log, it seems fine and the hover thrust is already quite low, so I think you should really fly with a 3S battery

Understood! I will change the gains.
Thanks, I will stick to 3s!

Thanks & Regards,
Mohammed Naveed