How to Convert (almost) Any 27 or 49 MHz RC Car Into a Robotic Car




I am teaching a robotics course in my kids high school (Rambam Mesivta in Lawrence, NY). I was looking for a cost effective way to teach them about the priciples of robotics without spending an arm and a leg, and getting them excited about the prospects of hacking hardware and teach them how to interface to the arduino platform. We studied H-Bridges made using  trasistors and switches, but there was something missing.

After reading this article:

It suddenly occurred to me that almost any toy RC car might be using this or almost similar architecture. I opened up 4 RC cars that were donated to the project and indeed they all use more or less the same configuration: All these cars have 2 H-Bridges on a small board mounted inside. Almost all the cars these days use a variation on the RX2C toy car chip (link) (i.e. pins 6,7,10,11 are the drivers for H-Bridge) and these boards can accept  logic voltage levels regardless of the battery voltages. The boards that do not use the chip will usually have an equivalent daughter board that fills the same function.  Furthermore- the boards are optimized to drive the motors of the cars optimally. Contrary to the article  they are safe to turn on both sides of the H-Bridge at the same time by mistake - all they do is turn on braking mode.

Almost all RC cars are configures so the rear wheels are running of a power H-Bridge for the forward/reverse motion and one H-Bridge is used to run a servo or servo-like mechanism in the front wheel. There is another configuration in which the right two wheels are connected to one motor and the left two wheels connected to another and this configuration can do some interesting stunts such as turning on the spot and other tricks.

The chip specifies an additional output - "turbo mode" however I am yet to see a car with this function implemented.

If you open you car and do not find the standard configuration - do not despair - figuring out the H-Bridge inputs are easy - and usually are the pins connected to 2.2k resistor.

The steps involved in making this work:
1) remove the RC chip - more on this later.
2) solder 4 wires to the H-Bridge Terminals
3) solder a wire to the negative terminal of battery - to power the arduino
4) solder a wire to the positive side of the switch - to power the arduino..

Here is a video of this mod after we completed the mod in 25 minutes.

Once reassembled, you can control the car from the arduino - and viola! you have a robotic car!
After doing a few cars - i find that the process of conversion of a car takes about 30-40 minutes.s a
Note the cars are sensorless!

* RX2C microchip based controller/receiver
* Daughter bvoard based controller/receiver
* Analog (transistor based) H-Bridge - can be used with analogWrite and PWM to control the power
* Relay based H-Bridge for the bigger devices. This can only be turned on and off - if you want to use PWM on there - you will have to turn to a custom H-Bridge design and ditch the board.

NOTE: This mod cancels the RC functionality. I have had thought to hack the RC part to allow two arduinos (or more) to communicate via hacking the transmitter and then connecting the (disconnected) signals lines as an arduino input. thus one would kill a few birds in one stroke: a dual H-Bridge, robotic car, and half duplex RC communications between arduinos. maybe I will tacle this in the future :)

WARNING: Make sure that the switch is off while programming your fully charged vehicle -or you will have  a robotic missile flying off the table at maximum speed and power. Also you can expect some weak movement of the wheels due to the H-Bridge being powered by the USB cable - even when switch is off.

Here is a video of the kids programming their own cars by themselves, and also note the cars are sensorlesss

Step 1: Modifying a Car From A-Z

During class I brought a brand new giant monster car I purchased at radio shack and I wanted to show how easy it is to perform this surgery on the car.

These pictures show the beginning of the dismantleation.

Step 2: A Closer Look at a Hacked Board

Here you can see chip was removed and that wires were installed instead 

Note - some boards do not use a variant of the TC RX2C  chip instead they will have a daughter board (the last picture in the set)
Also some boards do not use transistors for the H-Bridge but rather use micro relays.

Interfacing to through hole dips is easier than soldering carefully to surface mount pads. Also care must be taken not to strip the pads by pulling and wires should be secured to board using hot glue or by some other means.

Step 3: The Disembowelment of the Car

Here the controller board is gently pried out in order not to destroy anything. The H-Bridge is now visible, it uses relays for the switching.

Step 4: The RC Module Has Been Removed

This board uses an RC daughter-board  to control the H-Bridge. By removing it and soldering sires to the control pins the mod is complete.

Step 5: Adding the H-Bridge Wire Hack

Note the non-standard configuration using a (now removed) daughter board. The H-Bridghe lines are self evident.

Step 6: Final Result

Here are the two RC cars - the smaller one is actually carrying an arduino microcontroller on its back.  

Step 7: More Videos

The kids are presenting the robots they programmed themselves. The next step will be adding sensors to the boards.

Step 8: Some Videos

The kids are presenting the robots they programmed themselves.

Step 9: Arduino Code Example

#define FWR 3
#define BACK 5
#define RIT 7
#define LEFT 9

void setup() {
  // put your setup code here, to run once:

void loop() {
  // put your main code here, to run repeatedly:



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    30 Discussions


    Reply 2 years ago

    Just by reading that I assume that it is to prevent short-circuit between the arduino and the chip


    2 years ago

    Geat instructable was wondering if anyone knew if the taiyo 93r is similar to the rx2c chip have serval older tycos id love to ressurect with this


    3 years ago

    Instead of modifying the control board of the R/C car, it's simpler to replace the whole board with an L298N Dual H-Bridge Motor Controller. The board in the latest R/C car I bought is to small to modify.


    3 years ago

    Isn't it possible to keep the RC-Chip in place so you keep RC funktionality?

    You could for example just add anti-collision functionality...

    1 reply

    Reply 3 years ago

    Yup that would be a great idea. The idea was to just show the kids how it works internally.


    4 years ago on Step 9

    Why not hack the remote using an arduino to control the inputs? Would be cool if you could hook that to computer with webcam and computer could navigate car in its field of vision. Just throwing out crazy ideas. Nice work!


    4 years ago on Introduction

    I am trying to convert a New Bright RC car (MonteCarlo).

    The thing is that it have a weird chip (see picture). Can't find any data of this chip. Has any one ever has this chip and convert it's pin settings to use with a Arduino?. I want to remove the chip and connect an Arduino Pro Mini atmega328 5V and a Bluetooth module. Found out on the weird IC pin 12 = right, pin 13 = left, pin 14 = back and pin 15 = forward but the car has a speaker and some led lights and can't find out how to let that work.

    hope that any one can help me (forgive my bad English because it's not my native language).

    wire_diagram.jpgparts_view.jpgrx_ clone_chip.jpgrx_clone_chip(connect_diagram).jpg

    5 years ago on Introduction

    i want to learn complete boards repairing so please give me a guide line


    5 years ago on Introduction

    I do not understand what you are asking :)


    5 years ago

    Hi, is it possible to simply is the RX2 board directly with the arduino? still a newbie at this and don't quite understand how the circuit should be assembled if we want to use only the chip.



    5 years ago on Introduction

    Thanks for sharing such a nice information. It offer a variety of information about RC auto and ery useful for me and also for others to convert their first rc car.


    7 years ago on Introduction

    I did this for an upward bound class. I bought 9 identical cars... and found 4 varients of the board. It was pretty impressive.

    If you are unsure on the chip.. take a logic probe to one pin. Then activate each function on the remote control. Keep notes. You will find 4 pins are doing all the work. Solder to those chips.

    Nice work!

    4 replies

    Reply 7 years ago on Introduction

    I came up with a simpler method - connect a wire to battery plus and then just touch the pins with it and see what moves. obviously this is inferior to a logical analyzer - but my goal was simplicity.


    Reply 5 years ago on Introduction

    This might not always be a good idea. My decoder chip is rated at 3.3V max while the power supply on my car is 4 AA cells ... 6volts. Instead, jumping from the decoder's Vdd to the pins being tested might cause the chip to live longer.


    Reply 7 years ago on Introduction

    Not a logic analyser.. logic probe. Led + resistor + transistor. A little bit safer if you want to ensure you don't damage the chip.

    You can even use the arduino as the logic probe (use d13) or write a simple sketch.

    I'm doing something simular with a newer (digital controlled) "NEW BRIGHT" rc subaru impreza I picked up on clearance from my local Walmart.

    I simply removed the existing radio link and signal decoder, and drove the H-bridges Directly from the digital I/O pins of my arduino duemilanove. I had to remove the RF-link because it acted as an energy parasite. once this was done, I got much better function outta my "RcCarduino"
    Thats what this type of project is being nick named. ( I take no credit for its inception. )

    in a way, the digitally driven cars are easier to work on then the old analog type, and you thought modding your 27Mhz. version was easy. the difference is the digital cars are all surface mount instead of through hole type, so you have to be more careful when soldering.

    2 replies

    Reply 7 years ago on Introduction

    Thanks for sharing. What do you mean by digital? Almost all RC cars use an RX2C variant. There are surface mount versions and some are through hole versions. I am confused, because my article describes exactly this - connecting the digital outs of the arduino directly to the control line of the H-Bridge. Disabling the radio as a way to prolong battery life is interesting. However I like Doug Paradis's idea about taking out the 2.2k resistor and leaving the chip in place allowing to use the radio to signal the arduino for on-off and synch operations. Doug's system also allows bit banging of information to the robot.


    Reply 5 years ago on Introduction

    Please give me a reference to Doug Paradis' idea ... which 2.2K resistor ... there are at least 2?