Building RC Toy with Clojure

Bored and have free time? Lets build something. Lets build RC Toy. Hm, and lets use Clojure (because clojure is pure fun to use).

First of all we need some parts.

  • Tamiya Universal Plate Set (TAM70157) (better to order 2 pcs)
  • Tamiya Track and Wheel Set (TAM70100)
  • Tamiya Twin Motor Gearbox (TAM70097)
  • Arduino (I have UNO and Leonardo, UNO was choosen since I don’t need to make modifications in Firmata code for it (except baudrate))
  • HBridge IC L293 (L293B was used)
  • Bluetooth module (you can buy Arduino ready module, I will be using cheapest possible module)
  • Bluetooth in PC
  • Wires
  • Batteries or Accumulator (I have 9v batteries so I will use them)
  • Gamepad (Logitech Rumble Gemapad F510 was used)

Putting things together


First lets build gearbox. You can use it in few different modes of gear ratio. I selected 114.7:1 gear ratio (lucky guess). Read instructions, take your time. I had 2 9v motors, so since I will be using 9v batteries I decided to replace default motors with 9v ones.

Next assemble tracks. Pretty easy, right? Next is time to put it all together. Since I had only 1 plate I made second one from peace of plexiglass. I made something like 2 floored chassis. First floor is for motor and wheels (and maybe batteries) and second is for Arduino (and maybe batterries).


We need to do 2 thing with our cheap bluetooth module:

Solder legs to it Soldered bluetooth module

Use voltage divider (bluetooth module is working on 3.3v, Arduino is working on 5v) Voltage devider

Gearbox and HBridge Driver

To control motors I decided to use HBridge. You can use bunch of transistors if you want, but I’m afraid it would be messy. To understand how HBridge works you should read Adafruit post.

HBridge -> Arduino Schematics: Schematics

Final version


rc-toy-001 rc-toy-002 rc-toy-003 rc-toy-004 rc-toy-005 rc-toy-006 rc-toy-007 rc-toy-008 rc-toy-009 rc-toy-010 rc-toy-011 rc-toy-012 rc-toy-014 rc-toy-016 rc-toy-017 rc-toy-018 rc-toy-019 rc-toy-020 rc-toy-021



Writing some code

Bluetooth as Serial port

I used blueman on my Arch Laptop. Gui is straightforward and easy to use.

Gamepad and kernel

You need to find kernel module for your gamepad. For my gamepad module joydev was required. After module is loaded you should see new device in /dev/input.

Clojure code

I used Clojure as main language for controlling Arduino. I took Clodiuno library. It is Firmata protocol implementation for Clojure. Why Firmata? Because it’s easy, fast and provides great way to extend your project in future.

So I wrote some code, uploaded Firmata to Arduino. And… it’s not working.

After some digging in Firmata and Clodiuno code I wrote 2 pull request to Clodiuno.

First issue was that bluetooth uses 9600 baudrate for communications. Fix? pull.

  • Update standart Firmata example code in Arduino IDE. Change baudrate to 9600.
  • Change Clodiuno baudrate to 9600.

Second was that Clodiuno waits for version response from Firmata on startup. It’s ok for wired UNO since it will be restarted when serial connection is established. But boards like Leonardo or if you are using bluetooth miss that behavior.

Fix? pull. Manually ask firmware version on Clodiuno initialization.

Most of controller related logic was extracted from awesome library overtone-jinput. I just replaced overtone related events handling with my own code based on Clodiuno.

Final version of code is on GitHub

You can run it with ./

Raspberry Pi

Currently work in progress on moving Clojure code to Rapberry Pi.

Fixed Issues

Native dependencies issue

Seems like jvm tries to load linux64 native dependencies for Raspberry Pi. Fix:

#INFO: Failed to load library: no jinput-linux64 in java.library.path
sudo ln -s /usr/lib/jni/ /usr/lib/jni/`

Gamepad configuration

Add joydev to /etc/modules to see gamepad in /etc/input. Also you need to switch gamepad to direct input mode (X -> D switch on the back of gamepad).

Unfixed Issues

Bluetooth as Serial port

To scan for devices from command line use hcitool scan.

To bind bluetooth to serial port on startup use following code (untested yet):


rfcomm0 {
        bind yes;
        device mac-adress-of-bluetooth-on-arduino;
        channel 1;
        comment "Arduino";

JInput permissions

For now I have no idea how to fix that issue. Looks like something is wrong with permissions.

Failed to open device (/dev/input/js0): Failed to open device /dev/input/js0