To complete the project, I got:
1 - 6v DC 6rpm motor
1 - 1/4" x 36" piece of all-thread rod
1 - 1/4" coupling nut
1 - 1/4" bronze bushing
1 - 3/8" rubber bushed wire clamp
1 - 3/8" grounding coupler
Step 1: Mockup and Assembly
The bronze bushing is held by the rubber bushed wire clamp. I had to use a 1/4" shim to put it out so the rod would be parallel to the dolly. You have to be sure you have the coupling nut (which pushes/pulls the dolly) also mocked up into it's final position as well so binding is eliminated.
Once these two were where I wanted them, I then positioned the motor to be sure it could be mounted in the necessary location. It fit perfectly, so I then drilled SHALLOW holes through the outer wall of the square tubing (Remember- on my slider design there is an all-thread running through it - severing it would ruin the slider) only, just enough for a short sheet metal screw to go in.
At this point I mixed a batch of epoxy and liberally covered the connections at the bushing and the motor to lock them into place. I am attempting to use a strong magnet to connect the coupling nut to the dolly, but ther is not enough friction/stiction to use the dolly at angles other than level, so that needs to be addressed.
Step 2: Wiring and Power
I took an old extension cord and cut the ends off to make a quick connect for the motor. I did this instead of wiring the motor direct to the USB plug because the motor is reversible and when setting up shots I want the flexibility to run the dolly from either end, or in either direction, and by merely flipping the plug I can reverse the polarity - and the direction of the motor.
The other end of the plug is wired to the USB plug that goes into a USB hub so the battery can power the motor and add to the camera's battery capacity to last for 2+ hours.
Step 3: Final Notes and Thoughts
1] The coupler to the motor needs to be set where the ends aren't touching, by doing so there is no binding and it turns smoothly.
2] I need a stronger magnet to attach the coupler nut to the dolly, it just isn't quite strong enough to pull the dolly vertically without slipping off. I may bite the bullet and just epoxy the nut to it, as when the motor coupler is loosened, you can still quickly turn the rod to reset the dolly or remove it.
This is the first test video, just under two hours and a bit rushed in my eagerness to see the results.
Hopefully you find something useful in this build that may be able to use in your own way. As always, comments, suggestions, and critiques are always welcome.