I'm gutting a treadmill to use the motor on my lathe. Using the directions found in this YouTube video:

I am able to get the motor to start, but after a few seconds I hear the relay click and the motor turns off. I don't want to replace the controller when a fix is possible, but can anyone give me an idea as to where to start?

I can also connect a lower horsepower motor to the same controller and it will not cut off until the smaller motor is about 3/4 speed.

 

If you used the motor and controller off the same T.M. then motor size should not be an issue, use a incandescent lamp to detect whether it is a time or current issue.
Those are the SCR bridge versions and are generally the easier one to get going.
Max.