PC Controlled Car
Submitted by Gordon M, Birmingham, UK
Introduction
In this article I will describe how to take an inexpensive radio
controlled model car, commonly available almost everywhere, and turn it
into a computer controlled car following pre-programmed sequences of
actions. This will include how to modify the car handset to allow it to
be "driven" from a standard USB port and the software to run on the PC
to create and run the action sequences. Before continuing I have to say
that the end result of this small project proved to be a lot more fun
than I could have anticipated, leading to challenges as to whose program
could get the car round an improvised course on the floor the quickest
and who could create the best stunts. If you've ever tried some computer
racing games where using the handbrake causes a controlled slide into a
fast corner you should try instantly setting the rear wheels into
reverse and seeing the effects on the car on a smooth floor...
Hardware
Although I will be describing how to modify a particular remote
controlled car handset I have found that almost all radio controlled
cars of this class have a virtually identical system. (This is from
modifying quite a few now for friends and friends of friends). The only
type to avoid are the "high end" proportional control racers that use
analogue signals to give precise speed control and steering. Cheap and
cheerful is best, although make sure the car does have separate steering
and forward/reverse controls.
The first step is to attach some wire connections to the inside of the
remote control handset, so we need to open it up. Fortunately there are
not too many problems here, just four screws on the base. There were no
tiny bits that spring out when you open the case or bits that could be
difficult to re-assemble but it is worth taking time to make sure you
understand how the bits inside work.
With the cover off, the controls for forward, reverse and steering need
to be removed. These are just held on by two screws on the base of the
handset. The levers have an internal spring to make them return to
centre when released but otherwise there only function is to move the
two slide switches mounted on the base. These simply move a piece of
metal over a pair of solder pads on the pcb shorting them together to
produce the desired effect.
The PCB can now be removed. There are four small screws, one on
each corner, to be removed. It is not necessary to completely disconnect
it from the handset. Just turning it over will give access to the
required solder points.
You can see from the photo that there are small rectangular pads
designed to be "shorted" by the slide switches. It is necessary to make
a connection to each of these. Although it is possible to solder wires
directly onto these pads it is better to find another connection point
for the pad somewhere on the pcb. This will allow the pads to be used
exactly as before with the handset when not being computer driven. I
just traced a pcb track from each pad to a suitable solder point and
attached a wire to each. For this purpose you can use almost any small
gauge wire but I found a small section of ribbon cable was best and gave
a neat finish.
Although each of the pads will have a different function (forward/
reverse, left/right etc..) it is not absolutely necessary at this point
to distinguish which is which. The programming is flexible enough to
adapt this later. It is however necessary to identify the "common" or 0v
connection to which all of the pads get connected to by the slide
switches. In this case it was easy to identify by the black wire coming
from the battery compartment. I made this the first wire on the ribbon
and noted that it was the brown wire.
It is not necessary to make separate connections to all of the visible
pads since you will notice that all of the "middle ones" are connected
together and these are connected to the 0v track going to the battery.
In
the
end I had six wires: five signal connections and one to the 0v. In this
particular car the signal connections were forward, reverse, left, right
and turbo. The turbo was just a higher speed forward. On some cars I
have modified additional connections allowed turning the lights on and
of and even a horn.
With the wires connected I fed the ribbon through a gap in the battery
compartment part of the case and re-assembled the pcb taking care not to
impede the operation of the levers. I made sure the car still worked ok
before continuing to the next phase of connecting the wires to the pc
adaptor.
The USB adaptor that I used was the PC-BEE from PC-User
(now replaced by MiniBee, available from this
link, Ed).
MiniBee
It is inexpensive and simple to use. One end connects to a free USB
port and the other is a set of screw terminals for connecting the wires.
It is important to connect the 0v wire, (in this case the brown one) to
the common connection on the pc-bee (terminal 8). The others were simply
connected in sequence to the first 5 terminals, leaving the software to
sort out which output to activate for each function.
Job done. All that's needed now is to create a control sequence and
start some "road trials".....
Software
Fortunately this part is quite easy since the PC-Bee device comes with a
software package (Bee-Step) that allows control sequences to be created,
stored and run. It is basically setting on/off patterns for
particular durations executed according to your step sequence.
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