Experiment 32: A Little Robot Cart
268 Chapter 5
Experiment 32: A Little Robot Cart
Robotics is another application of electronics that deserves a book in itself—
or several books. So, once again, I’m going to give you an introduction fol-
lowed by some points that you can follow if you want to go further. As always,
I will start with the simplest possible device, which in the world of robotics is a
cart that finds its way around your living room.
You will need:- SPST or SPDT microswitches requiring minimal pressure to activate them.
A force between 0.02 and 0.1 newtons would be ideal. Quantity: 2. See
Figure 5-74. - DC gear-motor, rated for any voltage between 5 and 12, drawing a maxi-
mum of 100mA in its free-running state, output shaft turning between 30
and 60 RPM. Quantity: 1. A motor is shown in Figure 5-75. - Disc or arm that fits securely onto your motor shaft. Quantity: 1.
- 555 timer. Quantity: 1.
- DPDT nonlatching relay rated for the same voltage as your motor.
Quantity: 1. - 1/4-inch plywood or plastic, one piece about 2 feet square.
- #4 sheet-metal screws, 5/8 inch or 3/4 inch long. Quantity: 2 dozen.
- #6 bolts, 3/4 inch long, with nylon-insert lock nuts. Quantity: 2 dozen.
- 1/4-inch bolts, 1 inch long, with nuts, to mount the wheels. Quantity: 4.
I’m not specifying one particular motor, because if I did, it might not be avail-
able by the time you read this. Motors aren’t like logic chips, which have re-
tained their basic function throughout various improvements over a period
of several decades. Motors come and go, and many that you may run across
will be surplus parts that will never been seen again. Search online for “gear-
motor” or “gearhead motor” and find one as close as possible to the specifica-
tion that I have provided. The mechanical power output of the motor shouldn’t
be important, because we won’t be requiring it to do much work.
The important consideration when you buy your motor is that you should also
obtain something that fits onto its output shaft. Typically, this will be a disk or
arm that can be screwed into place. To this you can then add a larger wheel of
your own, which you can cut with a hole saw or make from the screw-on lid of
a jar, or anything else circular that you may find in the house.
A larger wheel will make your cart move faster than a smaller wheel, but will
reduce its torque, thus limiting its power to overcome obstacles.
This brings me to my next topic: fabrication. Although this is an electronics
book, motors are electromechanical devices, and you have to be able to install
them in some kind of a machine to get any interesting results. You can use
Figure 5-74. A microswitch has a small
button (at the front, righthand side in this
picture) that is often actuated by a pivoted
metal lever. The switch can respond to a
very light pressure, but can handle rela-
tively high currents.
Figure 5-75. For the Little Robot Cart, I
found this 5-volt motor, which is supplied
with a disc that fits its output shaft. The
combination cost less than $10.