Please note, the RC car described in this document no longer exists. This
document remains only for historical purposes. There have been 4 different
controllable vehicles over the years. The first two were converted RC Cars,
the third was a converted RC tank, and the current incarnation is a robotic
critter which I have built from scratch. Please visit the main page and
inquire about playing with it. Thank you.
When I interfaced the first RC Car I didn't post detailed instructions
or even take pictures. This time I'm doing things in a much more detailed
and professional way, and allowing others a chance to see the project step
by step.
There are two stages to this project. Modding the remote, and modding the
car. Although both are necessary for the full effect, they can be done
separately and still end up with a useful end result. We will start with the
remote.
The Remote
First a little info about how the remote operates. Each of the toggles is
a double pole, triple throw switch. When you push the drive lever up to make
the car go forward, two small conductors connect two pairs of contacts on the
circuit board. Moving the lever in the opposite direction makes two separate
contacts, although one of those contacts is common between all four of
the lever positions. When the levers are in their center state, no contact
is made.
Unscrew the four screws on the back of the remote and remove the cover and
you'll see something similar to this:
Inside the Remote. AKA: Voiding your warranty
Remove the screw attaching the wire to the antenna, then you should be able
to lift the circuit board over the levers and look at the back side.
The other side of the circuit board
The back of the remote. Levers and Sliders
Circuit Board up close
Labeled Circuit Board
If you look at the board, there are two sets of 6 contacts on the board. This
is where the sliders make contact. All contacts labeled Common 2
are electrically common, as are all the Common 1 contacts.
To move the car forward, a connection will be made between the contact labeled
forward and common 1, and another connection will be made between common 1 and
common 2. The same method is used for the other three possible actions.
How you wire this up depends on if you want the remote to be useable as
a manual remote after modding. If there is no concern about manual use
afterwards, wires can be soldered directly to the large contacts. To maintain
the use afterwards, the contacts need to maintain clear and wires need to stay
out of the way. Therefore, its best to find contacts on the component side
that electrically match the control contacts. The 6 wires needed then need
to run to the relay board.
Relay board
The Relay board is composed of 5 relay circuits, the same I have controlling
the office lamp. Since I don't need much power, I can get by with smaller
relays. I will include a schematic for the board in the future, bit
its not too tough. Basically, each of the 5 relays is controlled via
one of the data pins from a parallel port.
The Car
Now on to the second stage. The car itself.
The Car
As you can see I have the cam mounted to the hood of the truck. I've
later decided to remove the entire frame and just use the flat platform,
as you'll see later. However, I didn't consider this possibility until
after I disassembled it. And what a chore THAT turned out to be. It was
a very well put together little bugger.
40 screws later, the frame and platform is off.
Not much to see here, but the bottom of the truck is where the battery
would normally be placed, and there's a power cable under there for it.
Well, since we will have a rather LARGE battery on top already, there's
no sense in adding a second battery. The car can just use power from the
gelcell. To do this, we need to cut the connector off the plug under
the car and pull the wires through the bottom. Then take the platform
of the car that you've removed and drill a hole wide enough for the two
power wires (or just widen one of the screw-holes you won't be using
any longer). Run those wires through the hole and replace the platform.
You should now have something like this:
It's Starting to Look Like Something.
Notice the two wires sticking up from the base, those are the power
wires. Now we need to get the battery hooked up.
The Battery
The Charger
A Power Cable
The Battery is a 12 Volt, 4.5 Amp Hour Gel-Cell. It will run the camera
and transmitter for 21 hours and recharge fully in about an hour. I suspect
I will have two batteries that I will swap out every 12 hours. This will
allow me to also run Infrared headlights and perhaps some other features.
The battery is charged using a special battery charger for lead acid batteries.
Normal wallwarts won't work, as they'll overcharge the battery. So get
a real charger.
To wire the battery to the car, first take one of the cables with the
plugs on the ends, and cut it in half. Take the female end and wire it
to the battery. This will allow you to plug either the car or the
charger into it. Take the two tabs and use them to seal the wires to
the battery. Pay attention to polarity. The wire colors will match up.
You might want to solder the wire onto the battery to be
extra secure. You won't need to remove it before the battery dies, so
there's no concerns of permanancy here.
Take the male end and wire it to the power wires for the car. Like the
battery, the wire colors will match up (assuming the car's colors were
Red/Black). You can now plug the car's power plug into the battery and
the car will have power. Turn it on and grab the remote and see if it
works. Of course, as soon as it moves, the battery will fly off the car.
For testing purposes, I'm just taping the battery to the car's platform.
Speed
The next important issue is speed. The RC car is probably quite capable of achieving adaquate speed to cause damage if it hits a solid surface (a wall for instance). While the car itself can probably handle it, remember, we are also mounting a camera on top of the car and the camera is far more delicate. Therefore, you want to force the car to not go faster than a certain velocity. The easiest way to do this (and its already in the code) is to simply put a delay between the time you make the contact and the time you stop it. A delay of 500 ms is a nice speed. Of course you may want different speeds. That is completely up to you.
Camera
The camera part itself was much easier, although more expensive. First, you'll
need a capture card or a Snappy or some video input device that will take an
RCA jack as input. Then you will need to purchase a transmitter/receiver kit
that can send/recieve video and a small, low powered camera. I purchased both
these items from MatCo. The model numbers there are CNL-100 and ASK-2000TR. I
also purchased the enclosure for the camera, model number A-300. You may have
to browse the pages a bit to find the actual model numbers. They don't all
appear on top. Please note that I am in no way affiliated with MatCo, I simply
found that their products were the least expensive for what I needed to do and
so far I have had no problems with the products.
The receiver has a female RCA jack for video out. Take any RCA cable and hook that puppy up to your capture card. Take the camera, which has 4 wires. READ THE INSTRUCTIONS THAT COME WITH THE CAMERA. They are vague, but they tell you which wires do what. Two of the wires are for power, and the other two are for the video signal. The video wires can be directly wired to an RCA plug, which can then be plugged into the transmitter. Then go to radio shack and find yourself a power adapter plug which fits the transmitter.
Wire the camera's power wires to this plug as well as another set of wires
which will then go to your power source. Plug it into the transmitter and now you have power to the camera and transmitter.
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