motors run on arm

Hi all,
I am a new member to this forum and this is my first post.
I am building a F450 quadcopter. Using an apm 2.6 FC .
I set it up as per painless360 YouTube videos . Using mission planner.

I did have it setup correct at one stage, where I was able to arm the board and throttle the motors from zero up to max speed.
The next time I did it I must have done something wrong because when I armed the board the motors started running right away, and when I increased the throttle to max the motor speed only increased a small amount, no were near max speed.
I have gone through the whole process again, and I still have this problem.
Can anyone suggest a remedy?

Try calibrating the radio and escs.

Thank you for your reply,
I thought I did that, I calibrated the esc's manually one at a time and when they run they sound like they are all running at the same speed. I am not sure about the flight controller, I re calibrated that with mission planner, going through each stage.
I will try and recalibrate the FC again. Do I need to re calibrate the esc's again?
Do I need to factory reset the FC?

Once should be enough for the escs.

Maybe your controller needs calibrating. Thats my guess.something changed. Did you mess with it at all?

It seems that APM 2.6 is no longer supported by copter, or is it. what can we make of this???

APM 2.5
Warning

The APM2.6 board is no longer supported for Copter. From Copter 3.3 firmware (and later) no longer fits on APM boards. The last firmware builds that can be installed (AC v3.2.1) can be downloaded from here: APM2.x and AMP1.x

Warning

The APM2.6 board is no longer supported for Plane. The last firmware build that fits on the APM is Plane 3.3.0.

My take is that it's like Microsoft Windows - Microsoft no longer supports XP, but you can still use it. I just downloaded firmware on a new APM 2.6 clone that I bought on Amazon. I used the latest revision of Misson Planner - the download was successful. As long as you're happy with V3.2.1 you're okay; just don't expect any bug fixes or enhancements.

I might have to migrate to Pixhawk sometime however, as soon as there's a compelling reason to do so. In the meantime, my demands are pretty modest and I'm happy with existing functionality.

Thanks for your reply, when I go to download V3.2.1. I get a message, that version is retired.
I will try and download again .

I found V3.2.1 and downloaded and installed it. Set up the board again.
I calibrated the esc's one at a time with the receiver, they run great as expected via receiver.
Connect the esc's to the APM and run the motors. They run as described in my first post.
When I armed the board the motors started running right away, and when I increased the throttle to max the motor speed only increased a small amount, no were near max speed.
Maybe I have stuffed the APM board
Can I do a factory reset on the board and start again?

I read that it's normal for the motors to run slow when armed with V3.2.1
So there was nothing wrong. Seems like a good idea.