Page 45 - Build Your Own Combat Robot

Build Your Own Combat Robot
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Chapter 4 will discuss motor performance requirements, and Chapter 7 will de-
scribe various motor speed controllers.
The next step is designing the bot’s frame. This is the core structure of the bot that
holds the motors, drive shafts, bearings, gearboxes, wheels, batteries, and motor
controllers. The core structure should be solid and rigid, as the rest of the bot will be
attached to it. Remember when you’re designing the frame to leave space for the
batteries, motor controllers, and weapon actuators. Another point to keep in mind
is your robot’s center of gravity. Keep it as low as possible to improve stability.
Okay, so you’ve determined your power requirements. Next, you need to know
the current draw specifications from the robot motors. It is best to estimate this based
on worse-case situations. The last thing you want to see happen is your bot stop in
the middle of a match because it ran out of energy. Assuming that your bot is running
at stall-current conditions all the time is the absolute worse-case scenario, but this
estimate is unrealistic since stalling the motor for 5 minutes will destroy the mo-
tor. However, assuming your robot is running at 100-percent stall current draw
for 20 percent of the match time, and at 50 percent the stall current for the remain-
ing amount of time in the match, should give you a good estimate on the maximum
amount of current that you will need. Select your batteries based on the information
contained in Chapter 5. Once the batteries are selected and the dimensions of the
batteries are determined, a battery housing should be designed for the bot. The bat-
tery housing holds the batteries in place and protects them inside the bot.
Knowing what the current requirements are for your bot determines the motor
speed controller. You’ll find information about motor speed controllers in Chapter 7.
When you’re installing the motor speed controllers, you should have features in
the design to allow for cooling. Motor controllers get very hot when near-maximum
currents are running through them. You may even need multiple-speed controllers,
depending on how many motors you’re using.
FIGURE 2-2
A robot using two
Victor 883 motor
controllers and the
Innovation First
Robot Controller for
motion control.
(courtesy of
Larry Barello)