Remote Controlled HotWheels

Ever since I was a kid, I’ve been fascinated by cars, and naturally, Hot Wheels have always been one of my favorite toys. Recently, as I've begun to teach myself electronics, I wanted to take this interest to the next level and transform a classic HotWheels into a remote-controlled car. This project involved custom 3D modelling, some simple circuitry, and a lot of tedious soldering. I chose to use a 2014 Lamborghini Urus as the platform for this project.

I spent a lot of time through this project consulting this guide from MaxImagination, and this video from Aaron Sabu!

Parts:

1. x1 Matchbox Car
2. x1 9G Servo
3. x1 Linear Servo
4. x1 RC Receiver (FS2A)
5. x1 FS2A Compatible Controller (FS-16X)
6. x1 3.7V LiPo
7. x1 JST Female Connector
8. x3 Paperclips
9. x1 22 Gauge Wire (I used excess from the servo's signal cable)
10. x2 2.2K Ohm Resistors (Optional, can be replaced with servo's potentiometer)
11. x1 1.2 mm ID Pipe (Optional, can be omitted w/ minor adjustments to the 3D model)
12. x4 2mm x .5mm x 5mm Screws (Can also use glue to mount the linear servo)

Total Cost: ~$70

Tools:

1. 3D Printer
2. Hot Glue Gun
3. Pliers
4. Dremel
5. Flush Cutters
6. Soldering Iron

To prepare the car, first drill out the two rivets on the bottom that hold it together. With the individual pieces isolated, carefully remove the two axles from their clips on the car's bottom plate. HotWheels will normally have two pillars running from their main shell. Drill those out too. I added a small piece of foam to cover the drilled-out bumps to protect the battery that will eventually sit there.

The car will be powered by the motor found inside a 9g servo. As the car doesn't have space for an electronic speed controller (ESC), we can make one from the board inside the servo, and 2 resistors.

Taking the 4 screws out of the servo, the motor will split into 3 pieces - a gearbox, a central housing with the motor, board, and a potentiometer, and a back cover. Save a screw to use for the steering assembly.

From the gearbox, save the gear linking directly to the motor.

Free the motor and board from the central housing. depending on the servo you have, this might require breaking the case, or wires. That's okay - the only pieces we need from the servo are the motor and board. Try to protect the input wires to save yourself from needing to resolder them later.

Tip - Add a dab of hot glue to the solder connection to physically reinforce them.

As the car doesn't have space for its own dedicated ESC, we can trick the servo's board with 2 resistors equivalent to the potentiometer in a neutral position to add speed control. I used two 2.2k Ohm resistors to make my voltage divider.

Note: If you don't have any resistors on hand, you can also use the potentiometer from the servo, hot glued in a neutral position. To test this, connect the servo to the RC receiver and power, and fix it in place where the motor doesn't spin when the controller is in its neutral position.

Wire the resistors to the board's potentiometer connection points. Ensure the resistor's shared branch connects to the board's center hole. Solder as close to the resistor bodies as possible, clipping the excess off the legs once done.

If needed, resolder the motor to the board.

Cut the wheels off the back axle of the car, replacing the axle with a straight length of paper clip, around 3.2cm long. You will need to drill out the wheels

Snip the knub off the gear saved from step 3, and glue flush with the wheel on the axle.

As I had some extra pipe, I glued that to the 3D printed base to reduce friction. If you don't have any, you can just as easily reduce that hole's diameter to ~1.2mm in the 3D model.

Fix the other wheel onto the axle, ensuring they both spin with the axle.

Glue the motor in place, so that it locks with the gear fixed on the axle.

Glue the servo board onto the base in-front of the motor and the resistors on top of the motor. Pictured above is the final (messily glued) assembly should look like.

The paper clips will be used to make the steering rods. This was the hardest step for me and required quite a few tries before I got an assembly that was aligned well enough to steer straight.

With your needle nose pliers, bend the paper clips into the left and right rods shown above. Begin with the coil at the center, ensuring it will be able to spin freely around a length of paperclip. After 3.5 loops, add a vertical bend .4 mm from the coil.

Attach the steering rods to the body, pinning a length of paper clip, ~9 mm long, through the base, coil, and base. Ensure the rod is still able to rotate freely and glue the pin in place.

Connect the rods with the steering bracket, ensuring the rods are straight when the bracket is centered.

Screw the linear servo into place, connecting the lowest mounting hold to the steering bracket with the screw saved from step 2. Clip the top two holes off the linear servo arm.

Once the steering assembly is working, trim the steering rods to and test again under the shell.

Bind the FS2A (RC receiver) to the FS-16X (RC Transmitter). Before soldering, test the circuitry on the FS2A's included JR pins, ensuring steering and speed control work, and everything is properly connected.

Solder the linear servo to Channel 1, the drive motor to Channel 2, and the battery connector to Channel 3.

Tip: Tin the wires first, before pushing them through the holes, then solder once all three wires are set in place. You can use a clothes pin to hold the board in place while you solder.

Glue the board into place in its slot on the base.

Drill out the front wheels and attach to the steering assembly with 3D printed washers and glue. Ensure they can spin freely across the entire range of the assembly's motion. Trim the rest of the front axles to size.

After initial fitting of the base onto the car's shell, you can use a Dremel to glue the car's front and back bumper to the 3D printed base for a more polished final look.

Overall, this project was a super fun beginner project for me to get into electronics, staying relatively simple, while allowing me to practice my soldering, 3D modelling, and challenge myself with the miniature scale. With the battery I chose, the car has a pretty impressive runtime of ~12 minutes on a full charge.

Steering can be a little finicky, and along with a more secure method of attachment to the outer shell, is something I'll look to improve in future designs. I've had a lot of fun drifting this car around my desk, and if you choose to build it, I hope you will too!

Thanks for reading!