Phil 3:8 Tank Drive Units

This tank drive system is a WORK IN PROGRESS. Each drive unit is powered by a standard 540-sized RC motor paired with a gear-reduction transmission (33.33:1 ratio). These drive units functions well on smooth surfaces (like tile or wood floors) but need a tensioner system for improved reliability on high-grip surfaces such as carpet.

I developed this system for my DIY R2-D2 inspired Droid, Phil 3:8. I built him for a Star Wars inspired Kids’ Camp at my Church, but the system should be adaptable to a number of tracked vehicles. The drive system mounted to Phil 3:8’s legs by screwing directly through the included yokes, but the track frames could also be mounted directly to a vehicle chassis via mounting holes modeled into the side of the frame or with a custom mount. The tracks are joined together with ~3-inch segments of piano wire.

I printed all parts out of Inland PLA+ with 0.2mm layer height and 100% infill. I’m sure I could have used a lower infill setting, but I did not have the time to experiment with different values for this build.

A full parts list is included below along with basic build instructions. I have included a “Left” and “Right” drive system, which are simply mirror images of each other. Each drive system will need the following parts printed.

Printed Items:
1 x Yoke
2 x Frame (Left or Right)
4 x Cogs
1 x Gear Spacer
1 x Blank Spacer
1 x Motor-Side Reduction Gear
1 x Output-Side Reduction Gear
1 x Output Gear
1 x Redux Spacer

Hardware & Materials List:
2 x 540-sized RC Car motors (brushed or brushless)
2 x motor mounting screws per motor (consult motor for proper size)
4 x 3”-ish long 1/8” rods (axle rods)
8 1/8” cap screws (to hold the axle rods in place
8 5x11x4mm ball bearing
16 x M5x15 screws (to mount yoke to track frame)
2 x M3x15 screws (for 20/60 tooth reduction gear shafts)
2x M3x25 screws (for 15/50 tooth reduction gear shafts)
2 15 Tooth 32-pitch (Mod 0.8) pinion gears
70 3”-ish lengths of piano wire (35 per drive unit)

CA glue or epoxy
Silicone Grease (or equivalent)
Blue Loctite (or equivalent)

Build Instructions
- After printing all parts, clear all 3mm mounting holes with a 7/64” (2.65mm) drill bit to insure proper hole size.
- Glue one output gear to one cog to form output drive gear. Use 4 screws though reference holes to align cog & gear to insure proper concentricity
- Screw Motor-Side reduction Gear and Rudux Spacer to frame using M3x25 frame as shown in picture applying grease between moving and stationary surfaces.
- Screw Output-Side Reduction Gear to frame using M3x15 frame as shown in picture applying grease between moving and stationary surfaces.
- Install one 5x11x4mm bearings into each Cog
- Use 1 Axle Shaft to assemble 2 Cogs, Gear Spacer, and Output Gear as shown in pictures.
- Secure Drive Axle Assembly with 2 Cap Nuts
- Use 1 Axle Shaft to assemble 2 Cogs and one Blank Spacer as shown in pictures.
- Secure Idler Axle Assembly with 2 Cap Nuts
- Use 8 M3x15 Screws to secure Yok to Frame

And in case you are curious, the name Phil 3:8 is short for Philippians 3:8 which says “Everything else is worthless when compared with the infinite value of knowing Christ Jesus my Lord.” (NLT Translation)