This is a small pull-back car, fully 3D printed and just under 50 mm in size. I made it to learn more about how gears work and to see how accurately my printer could handle moving parts. Everything is printed; gears, axles, even the spring. The model fits together without any extra hardware. This project shows how a pull-back mechanism works from start to finish. Important Note: This project requires a 0.2 mm nozzle. A standard 0.4 mm nozzle will not print the smaller parts accurately enough.

Supplies

Materials

PLA filament (any basic brand)
Elastic bands for tyre grip – buy pre-sized ones or cut a larger band to fit
Super glue – optional, use sparingly where noted

Tools

3D printer (I used a Bambu A1)

Glue tip: use the lightest possible smear; too much can lock the gears.

Step 1: Print the Parts

0.2 mm nozzle only.

Print the small gears and small axles one at a time to avoid print failures; orient them vertically to avoid layer-shift failures.
Housings and wheels (remember to print "Wheel and axel" and "Wheels" files twice) can be batched together.
If a different orientation works better on your 3D-printer, please feel free to note it in the comments to help others.

Step 2: Prepare the Tires

Wrap each printed wheel with an elastic band for traction. If you’re cutting your own band, trim it size, then glue it around the tire .

Step 3: Assemble Gear 1

Press-fit the Large Gear and Medium Gear together.
Add a tiny drop of glue on the outer edge of the spring and on its hub (Indicated in green).
Insert the spiral spring into the back of the Large Gear.
Push the Gear 1 connector axle through the assembly allowing for the axle to poke out around 1/0.5 mm each side, expect a snug fit through the spring.

Step 4: Assemble Gears 2 & 3

Slide each gear onto its matching connector. The axles are thin, so press gently but firmly until axles is visually equal either side of gears.

Step 5: Assemble Gear 4

Slide Gear 4 onto its axle. This pair has loose tolerances, so it should spin freely without force or glue.

Step 6: Build the Chassis

Lightly glue the ends of the Gear 1 connector and the Gear 4 connector (Indicated in green), then insert them into chassis 1 & 3.
Then connect Chassis 2 to Chassis 1, Handle Chassis 2 carefully, it’s thin. If it snaps/cracks at its ends, a bit of super-glue should fix it.
Slide Gears 2 and 3 into place between Chassis.

Step 7: Gear 5 & Wheel Assembly

Insert the wheels connected to the axle in between chassis 1 & 3.
Slide Gear 5 onto the rear axle; add a bit of glue inside the bore (Indicated in green).
Push the axles through all chassis and press on the other wheels.

Thanks for reading, I hope you like it.

Introduction: 3D Printed Pull Back Toy Car