You have several options for the base material.
1. Wood Depending on the size of your robot plywood may be a good
choice it is inexpensive or free and easy to work with simple tools.
You can get 1/4" and 3/8" plywood at Hardware, Home Improvement, Craft,
or Hobby stores. A good place to look for free material is at a Cabinet
shop they have lots of scrap too small for their use but perfect for a
small robot.
2. Aluminum Light weight and moderately easy to work can also be found
at Hardware, Home Improvement, Craft, or Hobby stores. You should
always be very cautious when working with aluminum as edges can be very
sharp and should be sanded or filed to round the edges.
3. Plastics Acrylic or Plexiglas are both easy to work and can also be
found at Hardware, Home Improvement, Craft, or Hobby stores. High-speed
tools should not be used, as they will melt the plastic. When cutting
or drilling use low speeds.
4. Old CD’s These can be easy to find most people get them in the mail
from AOL or Earthlink instead of throwing them away you can use them to
make a robot. They can be a little on the brittle side so go easy when
you do any cutting or drilling.
Motor Selection
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You can use servos for easy to get gear
motors. Hobby shops will usually carry several sizes and brands. You
will need to modify them for use there are many sites on the net with
different methods; the one I like is detailed at the PARTS website at http://www.portlandrobotics.org/.
Servos already have all of the control circuitry built in and are easy
to control they have 3 wires signal, +, and ground by pulsing the
signal line you can go forward, stop, or backward. Servos are probably
the easiest and cheapest way to go but may not be the best for you.
2.Gear motors
These are available from surplus stores or hobby shops
some people modify servos and remove the electronics to use them as
gear motors. Gear motors will require control circuitry normally an
H-bridge to allow forward and reverse motion and in some cases braking.
Gear motors can give the greatest flexibility but at a higher cost
compared to servos. Another source for gear motors is the toy section
of your locale department store. What you want are the radio control
toys that have differential steering, meaning they have a separate
motor for each side. To turn left they go forward on the right motor
and turn off the left motor and do the opposite to turn right. The
really good cars will turn right by going backward on the right motor
and forward on the left this will allow a vehicle to almost turn on a
dime. If you use gear motors you will need to devise a method to mount
the wheels I will be using a toy for my example.
Wheel Selection
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they have pneumatic or foam wheels for model aircraft that are very
easy to use.
Power System
Batteries You will need to decide what type of batteries to
use. It can quickly become very expensive replacing batteries.
Rechargeable batteries are best; there are a number of different types
to choose from. Electronic supply stores or Hobby shops are good places
to look, you will need batteries and a charger to charge them with.
Power supply We will need a voltage regulator to drop the
voltage from the battery to the 5 volts needed by the Microcontroller
and other parts of the Brain for the robot.
I will cover using two different voltage regulators both are
available FREE from National Semiconductor as samples. Each part has
its good and bad points.
LM2825 Integrated Power Supply 1A DC-DC Converter is a
complete switching power supply on a 24 pin DIP although a little large
it requires no other components and has an efficiency of 80%. It does
require at least 7 volts on the input but your batteries will last much
longer than with a linear regulator.
LM2940 1A Low Dropout Regulator is a linear regulator in a TO
220 package it requires a couple of filter capacitors it is not as
efficient as the LM2825 the big up point is it only requires 5.5 volts
input to give a regulated 5 volts out.