Generating PWM signal

[Mr V]

The quick and easy way to do it would to use servos and a servo tester. That eliminates the need for the limit switches and a motor controller.

This one from AndyMark can also be used to control a motor controller. http://www.andymark.com/product-p/am-2503.htm Of course you won't be able to use a joystick with it whether you are using servos or motors. The plus side is that it has dedicated buttons to cause it to re-center or sweep through the range.

[DonRotolo]

I posted a schematic for a servo tester you can build, definiteky in a thread and maybe also as a whitepaper. Several years ago. Go search.

It uses cheap and readily available parts and is easy to build.