This is small fpv tank, inspired by https://www.thingiverse.com/thing:2896083 and https://www.thingiverse.com/thing:3013262. I created this mainly to practice at fusion 360.

The tank uses lego x939 treads, 9g servos, a 4ch frsky receiver, and a typical small all-in-one fpv camera. It's powered by a 600mah 1s lipo stepped up to 6v with a boost converter. There is also an arduino pro mini that reads in the receiver signals and controls the servos. While not entirely necessary since you can directly hook up the receiver and servos, it does let me control an rgb led, add a deadzone to avoid servo jittering when idle (by just floating the pins), and monitor the battery voltage.

The drive wheels have cutouts for gluing in cut-down servo horns. The idler wheels attach to the chassis with ball bearings and M3 bolts. The body cover directly snaps on to the chassis, and the turret attaches to the body cover via M2 nylon bolts (or just superglue). The lipo battery stays in place with a friction fit.

Parts

• TG9e servos - https://hobbyking.com/en_us/turnigytm-tg9e-eco-micro-servo-1-5kg-0-10sec-9g.html (modified for continuous rotation)
• 4ch frsky receiver - https://www.banggood.com/2_4G-4CH-Mini-Frsky-D8-Compatible-Receiver-With-PWM-Output-p-1143300.html
• MT3608 boost converter - https://www.amazon.com/gp/product/B07RNBJK5F
• FPV camera - https://www.amazon.com/gp/product/B07F62M5Z7
• Lego x939 treads
• Arduino Pro Mini
• RGB LED + resistors (I used two 100ohm and a 220ohm)
• M3x19mm bolts, M3 nuts
• 3x8x4mm ball bearings
• M2 nylon bolts

Software

https://github.com/kevinbchen/fpvtank/blob/main/fpvtank.ino

Wiring

Lipo (~3.7V) -> MT3608, FPV camera
MT3608 (5V) -> Arduino, Receiver, Servos

Arduino pins:
A0 <- Lipo voltage
D2, D3, D4, D7 <- Receiver Ch 1-4 PWM
D5, D6, D11 -> LED green, blue, red, respectively
D9 -> Left servo PWM
D10 -> Right servo PWM

Notes/learnings

• I initially designed the wheels with notches in the middle to match the treads. Unfortunately, I think the circumference and notch spacing were slightly off, causing the tracks to ride off the wheel eventually. Just having a smooth inner ring worked fine.
• The snap fit between the chassis and body cover is both very tight yet very fragile due to the print direction of the cantilever joints. Take care when attaching - I also use a screwdriver to pry them apart when needed.
• I ran into an issue where one servo randomly stuttered, but only in one direction. Unfortunately was not able to figure out why, and ended up just swapping the servo. One servo also moves a bit faster than the other.