I'm having some trouble wiring up a camera slider where a motor moves the camera to one end of a slider and hits an NC/NO/C 3-pin switch which triggers a 12V 8-Pin DPDT relay to reverse the motor polarity and move to the other end of the slider and trigger another switch. The camera keeps "ping-ponging" back and forth as it should. I'm basically following this example: http://cheesycam.com/cheesycam-diy-auto-reverse-polarity-motorized-video-slider-update/
Here is the wiring diagram from the cheesycam post:
The trouble is that I need to be able to control the speed of the camera, so I added a speed controller to the motor. The speed controller reduces the voltage to slow down the motor - which causes the relay to stop working once the speed/voltage is low enough.
Is there a way to retain the speed controller without reducing the voltage (and thus making the relay stop working)? Does it make sense to use a lower voltage relay (6V DC, for example) so it will work for a wider range of speeds?
I thought I could move the speed controller directly between the motor and the relay (basically use the relay's output as the input to the speed controller, and then use the speed controller output directly to the motor), but couldn't make it work.
Here is a related post regarding the same circuit I'm trying to build, but the answer uses a 3PDT relay (and plus I'm not able to read the wiring diagram there unfortunately): Adding Speed Control for a DC Motor
I not at all experienced with wiring circuits, so any help or ideas are greatly appreciated.
**UPDATE WITH FINAL SOLUTION: @Charlie provided the solution after some back and forth. Here is the final working solution:
Ideally, this would be wired with a 3PDT relay, but all I had on hand was a 4PDT, so the last of the 4 relay switches was not used. This is working great, and the speed controller is now independent of the relay voltage, so the relay continues to work and reverse the polarity/direction of the motor even at low speeds.