A short while back I shared a simple way of wiring up a motorized slider to move back and forth continuously (original article found here). No fancy software or programming, just a basic electro-mechanical system. There are many benefits to having this 'auto-looping' feature. One benefit is that a 'B' camera can continuously slide back and forth without the need for an additional operator, and another benefit is for TimeLapse projects that can continue to capture footage without stopping at the end of a rail.
Throw a few of these around an event and you'll have some great Dynamic Camera Movement footage to cut to without hiring additional crew.
I decided to update the project because some people couldn't quite figure out the circuit. With these new instructions using a numbered socket block, anyone should be able to follow this build, even without understanding the circuit. Hopefully this clears things up for some of you out there, and for those who may have been initially intimidated by the wiring.
Color coded wiring diagram - Click for larger view
I would set this up in a test scenario (loose parts on a table), and once you have it figured out, you can start attaching things to your actual motorized slider. Remember that this is all based on a very specific DPDT Relay + Socket Base Kit (found here).
Step by step Check List for you to follow on building an 'Auto Reverse Polarity Circuit'.
#1 Wire connects to 'NC' on Switch A
#2 Wire connects to one side of the Motor
#2 Wire (also) LOOPS back to Terminal #3
#3 Wire LOOPS back to Terminal #2
#4 Wire LOOPS back to Terminal #7
#5 Wire connects to 'NC' of Switch B
#5 Wire (also) connects to NEGATIVE on Battery
#6 Wire connects to POSITIVE on Battery
#6 Wire (also) connects to 'NO' on Switch A
#7 Wire LOOPS back to Terminal #4
#7 Wire connects to 'C' on Switch A
#7 Wire connects to one side of the Motor
#8 Wire connects to 'C' on Switch B
Remember to start this build by having parts loose on a table. You should know exactly what side your switches should be (left/right) so that the Slider is bouncing back and forth properly. If it's still not working correctly, try swapping the wires on your motor. If you have it swapped it will turn in the opposite direction. This circuit is designed specifically for the motor to turn a certain way.
Hopefully this has been helpful for those struggling with this project...