by Michael Simpson
WARNING!
Before you read any further, I feel it only fair to warn you that this
series is going to be akin to a very fast roller coaster ride.
Over the years, I have built several robots of various
shapes and sizes. Most of them were controlled by a
microcontroller of one form or another. I have even built a
few that were tethered to a desktop computer. It’s time to
build a robust robot with an on-board PC computer. This
will not be a toy.
In this series, I am going to build two robots around
the RS- 64 actuator: a six-wheeled robot utilizing six and a
three-wheeled robot utilizing only two of them.
The code I use to control these motors will be isolated
into a set of subroutines so that you may utilize other types
of drivetrains. For instance, you could use a brushless motor
controller and motors as long as the routines to control the
speed and direction of the motors are named the same.
This will allow you to plug them into this system without
modification. The same applies to most of the sensors that
I am going to use. While I will be using Maxbotix sonar
sensors, you should be able to make your own substitutions
as long as you work out the interface and return the
distance to your objects in inches.
The reason I am going to build these two types of
robots is simple. The cost of six RS- 64 actuators is over
$1,700. The cost for two is $570. The cost difference is the
same if you are using some other motor/controller system.
The cool thing is that you should be able to build the three-wheeled robot, then later upgrade to the six-wheeled bot.
Unlike other projects that I built well in advance before
publishing, this is going to be a work in progress. I will
provide you with step-by-step instructions, as well as a
source for all the components that I use, and even some
that I haven’t. I will show you various techniques and
options along the way, so even if you don’t build the
exact same robot, you should be able to use much of the
information that I will provide. Let’s start by writing down a
few requirements for the project.
Payload
The first requirement is payload. It is important that
you look at this requirement early on in the design process.
My robot will need to carry the following items:
• Main Controller — 5 lbs
• Battery — 8 lbs
• Robot Arm and Accessories — 3 lbs
• Miscellaneous Extras — 1 lb
As you can see, based on my estimates I will need a
robot that can carry 17 lbs in addition to the base, wheels,
and actuators. You may have noticed that I set the main
controller payload to 5 lbs. If you use a Pocket PC, then you
will only need to allocate 0.5 lbs. For a WinCE device, about
1.5 lbs will be needed. What I am trying to say here is there
will be a large disparity in weights of various controllers.
Keep this in mind.
Size
The type of controller you use will determine the size
of your robot. If you are going to use a 17” laptop, you will
SERVO 08.2008 55
