Yaw (spinning) cw then anti cw randomly after each take off

Not sure if I’m in the right place or asking the obvious but I have set up the apm 2.6 as per the guide and and everything arms and seems to work ok. I take off gently and the quadcopter starts yawing faster and faster either clockwise or anti clockwise. If I then “land” and take off again straight away (either waiting to disarm and rearm or continue straight away) the quad may then yaw the other way or the same way again. I have recalibrated everything and bought an extra motor trying each position in turn.Please don’t ask about logs as I havn’t a clue how to do these yet. I have flown upto BMFA B certificate years ago but planes were simple then this is driving me nuts! Any help or to be pointed in the right direction, would be most appreciated. Cheers, Rob.

Thanks for your quick response. It must be irritating when when people new to these machines ask basic questions, so thankyou. I am trying to find which version I am on. From the web it says I can find it on the CLI or command line interface. I assume this is the DOS looking screen which comes up when loading Mission Planner? If so I will check when I get Home. Cheers. Rob.

I think I have found the firmware version in messages on Mission Planner. V 3.2.1 (36b405fb)

Also found firmware version 120???

Just spotted that if I take off let the spin build, put in opposite rudder briefly then centre, it then spins faster and faster in the direction I have put rudder on, even if I only blip it??