DIY Slow motion zoom/follow focus - Servocity / eMotimo TB3

Part I:  The Build

Although I've had this idea for a long time, I never could figure out ho to accomplish it. Recently, I saw a video post from photographer Mike Ver Sprill, (@MikeVerSprill) on his DIY slow motion zoom rig using servocity actobotic parts.  His build was the inspiration behind mine, and I hope that it works as well as the one that he created.  The main difference between my build is using stepper motor versus a gear motor.  I actually have the same motor controller that he used, but is currently being used on my servocity cable cam rig, but I'm not sure if that would work with the eMotimo TB3 as the controller.  Since I already had the TB3, the simplest method was to purchase a geared stepper motor to use on this rig. Since the zoom, doesn't have more than a couple inches of travel, I needed a motor that would turn very slowly.  I chose the 51:1 Planetary gearbox NEMA 17 stepper motor.  I already have a 27:1 that I use on a 6 foot rail, and didn't think that was slow enough.  I probably could have gotten away with the 71:1 or 100:1 to really slow it down.

To wire the motor to work with the eMotimo TB3, you need a Molex Jumper 4 Wire Assembly that is available from sparkfun.com.

The remainder of the parts, except for the 1/4" bolt to attach the camera to the rig, the lens gear, and the shaft coupler came from ServoCity.com. The follow focus microLensGear was from RedRock, and used a 32P Pitch, which aligns with the Actobotics gears perfectly.

FYI:  The Actobotics planetary gear mount does not align with the screw holes.  I'm not sure if all of the motors that I have are metric and the servocity mounts are imperial, but I needed to drill some additional space to get it to work.  There is always the NEMA 17 mount that I used on my rover build, but this way is much more seamless, and gives you additional shaft length to clamp onto.

Here is a quick demonstration showing the rig moving and zooming.  In a real world example, the rig will zoom over a long period of time, probably hours.

I will use this rig mostly for star trail photography, and adding the motorized zoom will give my pictures a vortex effect.  I'll post images as soon as it's warm enough to go out the test the new rig!  Thanks again to Mike Ver Sprill for the inspiration.