Mini RC Car

I go through how to make a mini RC car in this tutorial. I've included my challenges, so hopefully, they will help you do better than I did! Moreover, I try to be environmentally conscious in my material usage, reduce, reuse, and recycle. I use materials that I had lying around with no real use, and most is recycled (apart from the electronics, although the switch and battery is salvaged from old electronics). Enjoy and do your part for the environment!

Electronics:

3.7V, 500mAh Li-Po battery x2

TP4056 micro-USB charging board x2

Coreless drone motors x2

4-channel 27MHz RC receiver and transmitter module x1

SPDT 3pin switch 0.3A x2 

0.5mm Red LED

Parts:

Spur gears x1SET

PVC Pipe (or sheet if you can access it) 

Safety pins to use as axels, any metal rod works, (eg. paperclips)

Superglue/hot glue

5-min hardening epoxy resin (this is optional, I used it on all PVC parts but you can use superglue. I used it as it is more durable in the long run than superglue)

Wheels repurposed from an old toy (you can make yours from scratch too!)

Sticks (BBQ Sticks recommended)

Double-sided tape 

I designed a basic chassis with the measurements I wanted for the length of the car. Ensure it is large enough to allow your larger spur gear; 's diameter and a 2cm (approximately) steering system to fit. Along with this, account for your motors, one will be vertically placed towards the front wheel on the plane of your chassis. 

Here are my measurements, although depending on the availability of material and microelectronics, you can make yours smaller and cram a few parts.

Here I used an extra PVC sheet to cut out the chassis. I used an iron set to its maximum temperature and parchment paper to flatten a PVC pipe into a sheet. The pipe will warp as it heats up, use a heavy block/book to keep it flat as it cools. Cut according to the template above or your own. 

Front Steering:

Cut two identical long rectangles of plastic, sized to the width of your chassis.

Make holes equidistant from both ends and the centre.

Cut two shorter and thinner pieces with the same holes.

Straighten a paper clip and cut four small metal wire pieces.

Attach two short pieces perpendicular to a long piece, locking them with a bung (avoid glue to allow rotation). I used hot glue to make makeshift bungs.

Cut a hole in the centre of the top long piece. Insert wire through the short pieces, placing a slice of eraser at the height where the motor top will sit. Attach the final long piece horizontally.

Next, cut a medium-sized piece (enough to exceed the plastic height) and glue it to the motor's rod. No rotation is needed here since the motor rotates. Use an eraser to lift the motor so the plastic is 80% into the top piece's hole. Bend and connect the front bottom piece's excess metal to wheels with spokes, closing them with bungs. Glue the motor and eraser setup to the base and insert the motor extension into the top piece. Bend the bottom wire of the top pieces with pliers or scissors (don’t glue as it must rotate), and glue the excess wire to the top piece.

Steering should now look like the top, bottom, and side views shown. Both the bare steering and its attachment to the base are pictured.

Note: Ignore the soot from using a direct flame to melt plastic. To avoid this, heat a metal tool like a screwdriver before cutting to reduce melted plastic and ensure smooth movement.

The front steering's performance is affected by friction. If it's too high, add tape to contact surfaces to reduce friction. This is likely the hardest part of the build.

Rear-Wheel Drive:

Take another piece of metal, measuring 3.1 cm (based on the back of the base template), and glue a wheel to one end. No rotation is needed, so glueing is fine. Cut a small piece from an empty ballpoint pen refill and place it on the axle. Slide the gear onto the axle and measure the distance from the gear’s centre to the top of the refill. Subtract the radius of the small gear on the motor, then cut a piece of eraser to match this height. Glue the eraser, refill, and motor in a straight line, perpendicular to the axle.

Slide the contraption onto the axle, making sure to glue the mini gear onto the motor (so it doesn’t rotate freely). Measure the distance from the wheel to the slit in the base of the gear and mark this point on the axle. Glue the large gear firmly to the axle at that point. The gear must be attached to the axle to rotate it.

Do a dry run, then finalize the motor and gear positions. Mark the spot on the axle where you need to glue the refill. Once everything is working, glue the second wheel in place. Below are images of the axle and how it was attached to the base, along with the front steering.

Important: Only glue the refill part to the base—never glue the axle to the base, or the car won’t move.

Top and side views are provided.

Let’s start by understanding the ports. B+ and B- are the positive and negative inputs for the receiver. FM stands for front, BM for back, and LM and RM for left and right, respectively. The ANT wire connects to an antenna, but it’s unused in this tutorial.

The transmitter, the longer horizontal board, is easier to understand. Each button corresponds to FM, BM, LM, or RM. On my board, these weren’t labelled, so I tested the buttons with 2 motors and the receiver before soldering it to the mini model. The white wells with the screw control the range—unscrewing increases the range and vice-versa.

Note: Do not unscrew too much. These wells can crumble with even slight resistance.

(Let's just say, I learnt from experience ._.)

Creating the Circuit:

Connect BM and FM to either end of your gearbox motor. The motor pin connection doesn’t matter as the module reverses the current direction. Connect LM and RM to your steering motor. Then, connect the +ve and -ve wires to the corresponding terminals on a 3.7V 500mAh battery. A higher mAh will overheat and damage the module.

Before soldering the battery to the receiver board, solder a TP-4056 charging module to the battery. Solder wires to the inner B+ and B- ports (input) and the outer ones (output). Carefully solder the input wires to the battery, avoiding overheating the battery. Solder the output wires to the +ve and -ve wires of the receiver module. Add a switch to one of the output wires before connecting it to the corresponding wire on the board.

For a light element, you can connect a single LED in series with the switch. Be sure to include a resistor in series with the LED, as a 5V supply is too much for a 3V commercial LED. A 10 Ohm resistor is recommended, calculated using Ohm's Law.

Once complete, check for loose solder joints, ensure no two joints touch, and verify all connections are correct. Make sure the battery and controller terminals are properly soldered. Switch on your circuit—if the LED lights up, the circuit is working.

To place the circuit, I created a table-like structure from sticks to hoist the receive and stuck it on top of the gearbox. It looked rather fat and ugly, so I ended up creating a buggy-style body to go with it! You can add pieces of cardboard to make a custom livery atop your car!

This was my final model and I loved this tiny thing. I hope you had fun making the model (and controlling it :D).