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Topic: modding an RC car (Read 38924 times) previous topic - next topic


Thank you :) This was much easier and less messy than the cheap cars :) Works good now.

The ESC came programmed. The manual makes no mention of it at all (perhaps because it was the cheapest 1/8 crawler I could find which had ESC and a servo).

I just have a couple of minor issues  (like working out how to read an integer into arduino rather than the character).

I have noticed I only have 60 degrees of motion each way on the wheels because the chassis gets in the way.

I will change the scale, all suggestions are very welcome. This is the first time for me so I am trying to learn.

I know you advised against using the battery to power the Arduino, but I would really like a one battery solution if you have an suggestions. The arduino will be a mega, have about 8 sensors and a wifi shield.

I also ordered http://littlebirdelectronics.com/products/acs712-breakout which I hope to measure the battery level with. I assumed it would be a simple matter of putting it into VCC and GND, but since you have given me a more intelligent way of doing things I am now not sure how to measure it.


Feb 16, 2012, 10:04 am Last Edit: Feb 16, 2012, 10:06 am by DuaneB Reason: 1
   For the servo movement, thats one advantage of thinking in milliseconds, you can use my monitoring code to read the servo input, output the same value and record how far you can take the servo in each direction using milliseconds. You can then use the same milliseconds values to set software limits in your own code.

As for the battery and charger, I assume that for the money you paid you will have a 7.2 volt nimh battery and the charger is most likely a trickle charger similar to the wall wart power supplies that some use for their Arduino projects.

If this is the case the battery output is not high enough for the Arduino regulator to reliably generate 5V - I am far from expert here and will no doubt soon be corrected if wrong.

You should also be aware that your nimh batteries should never be fully discharged (something tells me this might not be in your instruction manual ?), if this happens the battery chemistry can change so that one or more cells will no longer accept a charge - through negligence I have had this happen to all of my nimh packs. I now use more powerful LIPO Batteries, they can also fail after a full discharge however I have only had this happen once. The down side to LIPOs is that you will need to invest in a different, more expensive charger to use them.

Duane B.
Read this
then watch this



Indeed the battery is as you describe.

Is upgrading to lipo hard?

Is there anyway to tell how much juice is left in the battery?

I am really not keen on needing an extra battery for the Arduino.


Okay I have a weird problem.

The arming sequence isn't working much. However if i disconnect the ground it works but i need to reconnect the ground to get back control properly. Clearly this isn't how I shoould be doing things.

I am totally confused as to why it is doing it.


Posting this here for others - on another thread, another user () has managed to directly interface to the signal input pin on the RX2 chip - so no more hacking of the h-bridge connections and such are needed (if you can live without needed PWM):


It's a pretty neat hack, actually. I think someone needs to take the code and make a library with it!

Also - another note: In my various wanderings on the internet, I found a couple of other cheapo RC chipsets out there. One's the TX5/RX5, the other is the TX7/RX7. Something to grab the datasheets for - I'm sure they can be found in cheap RC toys.

I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.


Wanted to update this thread with a link to this one:


Not TX#/RX# related - but does show an interesting relay/mosfet (at least, I suspect this) based "hybrid" h-bridge setup for the drive motor.

Also, I recently purchased a couple of toy RC cars, that were made closer to a hobby RC car than other. 4wd, full independent suspension - but likely "bang-bang" steering, though there does seem to be some kind of feedback (probably limit switches - I haven't delved in deep enough).

Anyhow - the cars are called "Extreme Machines Thunder XX" by Xin Yu Arts Toys Co., Ltd. - there is a 49 MHz and 27 MHz (standard toy RC pair) versions; they look to be 1/10 scale. They use a TX2/RX2 pair - and the h-bridge for the drive motor is a pair of SPST relays (while the steering is done via a discrete transistor or mosfet h-bridge). 9.6 volt NiMH battery, Tamiya connector. Not sure on motor size, but brushed (not brushless).

Cheap, but seemingly effective. All plastic construction, except for drive shafts and such; it must have some good torque, though, because the drive shafts on one of the vehicles I have are twisted slightly. Fairly easy to take apart, re-lube, repair, etc - but as with anything plastic, things tend to easily break or strip out (JB Weld to the rescue!).

Just another vehicle to keep in mind!
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.


to the original poster. 
I have a similar project that can be found here : http://alibe.codeplex.com/. I am happy to share my learnings.  But, keep your hot-glue sticks and the hot-glue-gun handy.  it really saved me a ton of fabrication workload.


May 23, 2015, 10:27 pm Last Edit: May 23, 2015, 10:36 pm by Isaac96
Do not PM me for help. I will delete immediately.

After Tuesday, even the calendar goes W T F


Do not PM me for help. I will delete immediately.

After Tuesday, even the calendar goes W T F


I am adding a link onto this thread - I know it is old, but all of you know that I kinda "maintain" and refer others to it.

At the following link, I give a small "tutorial" on how to hack the RX2 board in a (somewhat) typical toy RC car:


There is a small album of pictures on imgur (the originals were supplied by the OP of that thread):


...showing the components, etc of the RX2 board in the car, and the car itself. Hopefully it can help others.

Cheers. :D
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.


Hello Guys

Thank you cr0sh for this mega thread in which i have spend the last 9 hours reading! with its external links.  I have a RC car i bought for my son for his birthday and i would like to add some lighting leds for eq. turning lights reverse. etc.

I have actually mounted all leds i want :d and i wrote an arduino program for operate those function but i need something to trigger the lightning events for e.g. indicate left upon turning left. I have thought of two options to achieve this as follows:

1. taking reading from the RX-2B IC from legs (Forward,LEFT, RIGHT and Reverse) and input those into arduino to take voltage measurement in order to trigger appropriate events.

2. Taking PWM measurement from the correct RX-2B IC PIN ( I don't know until now which, Please name it) and then running PWM code finding via serial to record PWM for each movements. Then this pin only will be attached permenantly to the arduino to detect movement and arduino will trigger lighting events accordingly.

Would you please cr0sh and other guide me which would be the best option? I personally prefer No. 2 hence i will only have to attach one pin to the arduino but i do not know what pin i should connect and how to take those reading.

Any help is appreciated.

here are some photos


Option #1 is probably easier to achieve; the RX2 protocol has not been cracked AFAIK. Just make sure to put resistors in line to prevent burning out the Arduino.
Do not PM me for help. I will delete immediately.

After Tuesday, even the calendar goes W T F


Thanks a lot Isaac96, I have attempt that now, i got 3.5V from right and left pin, but only a few fluctulating  milivolts on the backward pin! any idea why?

Right left voltage seem fine with arduino, but i am not sure about the current, do i need current limiting resistor? and i am sorry for the question but i do not know if the current limiting restores is normal one that we use with leds or is it a special one?

How i could achieve reading from backward pin?


The current limiting resistor is just to be extra safe. Any resistor is fine; one you use with LEDs is good.
No idea about the backward pin. Maybe you could use analog inputs instead of digital?
Do not PM me for help. I will delete immediately.

After Tuesday, even the calendar goes W T F


Thanks Isaac for your advice about reaistors. I found a way for reverse light. I will not be taking cable from reverse leg as the car came with backlight which turns on when the car is reversing, I tested the led voltage from its leg it gives 2.95V, as such I will be reading this to trigger my new white leds for reverse light. I am using arduino pro mini Chinese one 5V 16MHZ which I will throw in and connect with the car batteries. I read somewhere that I use analog pin to put led high normally as I would do that with digital pin. Hence promini has 13 digital and 7 analog I am running out of pins. I have around 16 LEDs to connect plus 3 pins for triggering events. I used 5 leds for each read indicator to emulate the new Audi style indicators as my son requested that :D. But no warriors about current as i am planning to program that only 5 maximum leds will be high at any point of time.

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