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Strange motor runaway issue with kk2


Junior Member
I have a strange issue that just cropped up. I have a 450 quad with a kk2.0 board with 1350KV motors that was completely rock solid stable, one of the motors M3 started with bearing issues so I swapped out all the motors with some 900KV motors because I didn't have a replacement 1350KV. I went flying, couldn't get off the ground because it would yaw really bad. So, calibrated the ESCs, several times, checked their programming all to no avail. On the bench, the M1 motor will start out at the same speed as the other motors then after 5-10 seconds it will start to drift up in speed, probably about a 25% speed increase. I also have a Turnigy 9XR TX. Here's what I've done to try to isolate the issue:

- factory reset kk2, calibrated ACC, set motor layout
- swapped out the yaw input cable
- swapped M1 and M2 wires at FC, it follows to M2 so seems to be isolated on M1 output of kk2
- swapped out KK2 board, factory reset, calibrated ACC, set motor layout
- swapped RX
- moved RX inputs around seems to follow yaw input
- rebooted TX(pulled battery)
- did receiver test to see if strange values are coming from TX, rock solid
- Moved the cables from the RX to see if it is the throttle pot on the TX, it followed to a different pot.

Conclusion...I'm stumped, it seems to follow yaw input, but the TX isn't doing anything strange and the RX has been swapped out. The only thing I've not done yet is put the old motors back on. I'm out of ideas and very frustrated...I just got some FPV goggles and was hoping to get in some practice today...argh!

Link to video: http://youtu.be/gKRWL5ih4Eg

This has got to be something really stupid, I'm just not seeing it...come on guys, throw me a bone here. :)

Last edited:


Faster than a speeding faceplant!
I hear something grinding. How are the motors mounted? Is it possible your mounting screws are too long by 1mm?

That said, the KK2 will always start low and pick up speed. It doesn't mean anything on the bench so long as the low side motor(s) always spin faster than the up side motors. Do you have video of the 'yaw really bad'?

When you went from 1350kv motors to 900kv motors did you also change rotors? If so, what rotors did you go to?