3D Printed Wind-Up Car Kit: Swappable Gears

This is a 3D printed wind-up car with gears that can be swapped out to create different gear trains. This page includes two versions of the gear train, one with a 1:9 gear ratio and the other with a 4:3 gear ratio. The first is maximized for speed and distance while the second is better for high torque.

Supplies

3D printer (Prusa MK 4 was used for this version)
PLA filament
8 O-rings (see below for specifications)

Create the Spring Motor

Pawl Gear

Use the spur gear add-in to create a 24-tooth gear. Project the profile onto a new sketch and add the axis hub and holes. Create a single tooth of the pawl and use the circular pattern command to repeat it. Extrude the gear 4 mm. For the alternate gear use a 16-tooth gear instead.

Pawl

Project a single tooth from the Pawl Gear onto a new sketch. Create the axis hole and connect it to the projected tooth. To connect it create a larger circle around the hole and use the line tool to connect the hole to the circle. Offset the line on both sides and then connect the ends of each to the tooth using the 3-point arch tool. Use the circular pattern tool to duplicate it 3 times.

Spring

Create a coil and project the profile onto a new sketch. Add the axis hole and the connector at the end. Extrude the spring 4 mm.

Knob

On a new sketch create an axis hole. Offset the plane to create a rectangle and connect the rectangle to the axis hole using two splines. Loft the axis hole to the rectangle using the splines as rails. Fillet the edges.

Create the Gears

Compound Gear

Use the spur gear add-in to create a 24-tooth gear and an 8-tooth gear. Project both profiles onto a new sketch, making sure they are concentric. Add a circle around the base of the 8-tooth gear. Add holes. Extrude the larger gear profile 4mm and the smaller one 10 mm. For the alternate gear train use a 14-tooth and 12-tooth gear instead.

Pinion Gear

Project the 8-tooth gear profile onto a new sketch. Add a hole for the pinion axle. Extrude 4 mm. For the alternate train use a 14-tooth gear.

Axle Gear

Project the 8-tooth gear profile onto a new sketch. Add a hole for the axle. Extrude 4 mm. For the alternate train use a 16-tooth gear.

Create the Frame

Frame

To create the frame align all the gears along with the spring motor. Project the axle holes onto a new sketch and offset them for tolerance. Create circles around each hole and join them using splines. Extrude the frame 4 mm.

Create the Axles

Axle

Project an axle hole from a previous part (such as the spring) onto a new sketch. Offset for tolerance and then extrude it 35 mm on both sides (70 mm total)

Axle Stopper

Project the axle profile and offset it for tolerance. Offset it again by 2 mm. Extrude the outer profile by 8 mm.

Create the Wheels

Wheel

Project the axle profile onto a new sketch. Create a circle around it and another larger circle for the face of the wheel. For the alternate gear train the axles hole is higher, so a larger wheel is necessary. Either way, ensure the center of the wheel is aligned with the axle hole on the frame and the bottom of the wheel extends below the bottom of the frame. Extrude the smaller circle 1.4 mm and the larger circle -8.3 mm. Use the torus command to create two rings that intersect the wheel. These represent the O-rings in the model; when printing hide them.

Print and Assemble

Most of the parts are printed at 50% infill with a 0.15 layer height. The spring, pawl, and knob were printed at 100% infill. The only parts that require supports are the knob and the alternate compound gear. O rings are needed for the tires. You will need 8 rings with an OD of 45 mm and 3.5 mm cross section. For the alternate gear train with larger wheels, you will need 4 rings with on OD of about 75-80 mm and a 3.5 mm cross section.

Once all the parts are printed assemble it based on the CAD model.

For more information on some parts including the spring, wheels, axles, and some gears check out gzumwalt's wind up car which includes tutorial videos for these parts.