Hack an RC Car's Unused 3rd Channel!

So, as we all know most remote control (RC) cars use only 2 channels on their remote control: one for forward and backward, another for left and right. What you may not know is that there is an unused third channel on most RC cars! Cheap cars such as the New Bright line found at places like WalMart and Target use a standard chipset (RX-2/TX-2) found in many many remote control vehicles.  Today we will be hacking that third, unused channel.  On the RX-2/TX-2 datasheet, that third channel is called the "Turbo Mode".

This Instructable showcases a couple of example projects I made to test out if I could take advantage of this unused "Turbo Mode" and operate a gun turret remotely. I built two vehicles - one using a fully automatic battery powered Nerf gun and another using a battery powered squirt gun with an electric pump.

EDIT: I originally titled this "Hack an RC car's unused 5th channel!" but I've since been informed that it's actually just three channels.  The forward/backward and left/right controls are just two channels!  If you see me refer to a 5th channel, just imagine I said three, okay?

EDIT #2: (5/28/13) I recently made another project and Instructable very similar to this one. I mounted an Airsoft machine gun on the top of an RC car! Here's the link to see a full video tutorial to make it: https://www.instructables.com/id/Airsoft-Gun-on-an-RC-Car-Hack/

Helpful Guides:

• I was helped greatly by this Instructable by techbitar: "Use Arduino with TIP120 transistor to control motors and high power devices"
• I also found some great information from this tutorial: "Using a transistor to control high current loads with an Arduino"

I was amazed to find that between your local Walmart, Target, and RadioShack one can find all the parts necessary for this project!  In fact, this project is so quick and easy that you can do it in mere minutes if you know what you're doing.

You will need:

From Target, WalMart, Toys 'R Us, or wherever:

• RC car - try to get one big and powerful enough to carry a couple of extra pounds on its back. I used this H3 Hummer from Target.  It was on sale!
• Battery operated Nerf gun, squirt gun, or anything else with a little DC motor in it you want to trigger remotely. I managed to snag this beauty (the Nerf Swarmfire) on sale as well for just $15!  I also found this gun (the Super Soaker Thunder Storm) for $15 as well.

From RadioShack:

• TIP120 transistor  Catalog #: 276-2068
• 1N4004 diode Catalog #: 276-1103
• 1kOhm resistor Catalog #: 271-1321
• While you're at it, you might as well get a bigger capacity battery because we KNOW the one that comes with whatever cheap RC car you're using ain't going to last.  I used this one - Catalog #: 23-1272
• I found these battery connector clips useful too - Catalog #: 23-444
• Some sort of extra button or switch to put into your remote control

Okay, so check out page 6 of the datasheet I included.  You can see that if you put in a button or switch in the controller that shorts pin 6 to ground you will activate the third "Turbo" channel.  This causes the receiving chip to output 3v on its pin number 12.

Now, we can't just power a DC motor directly from that RX chip.  First of all, the voltage probably isn't high enough.  Second of all, the amount of current needed to power the motor is absolutely not going to be provided by that little chip (I measured 1 Amp for the Nerf gun!).  We need something else to take that 3v signal from the chip and use it to turn the DC motor in whatever toy you're hacking on and off and power it directly from the battery.  That something is the TIP120 transistor.

The two tutorials I listed in the introduction of this Instructable pretty much spell it all out.  I made up a drawing of the circuit, but basically it is just a circuit that takes the 3v signal from the RX-2 chip and switches the battery power on and off for the motor.  The diode, pointing AWAY from ground toward the transistor, is to help prevent back voltage from the motor frying the RX-2 chip.

Now for the really fun part - go make some stuff!  The motor in the previous step's diagram is just whatever motor you find in some toy.  In my case, it was a Nerf gun and a squirt gun.  Included are some pictures and stuff of what I made, just check out the captions for each picture for more info.

I put in a beefier battery to give myself some more playtime and the car some extra "oomph".  Original battery was 6v and lasted a measly 15 minutes.  This one is 7.2v NiMH and is 2800mAh.  Just solder a connector to the battery terminals of the car, hook in your new battery, and you're good to go!  So far as I know the little DC motors in both the car and the toys I used can handle the extra voltage without any issues.  If someone out there is more knowledgeable about this topic then I'm all ears!