Page 99 - Build Your Own Combat Robot

LECTRICALLY powered competition robots are quite demanding on
their batteries, which must weigh as little as possible yet supply a lot of current.
such requirements push the batteries to their limits. the high current demands can
have some surprising results on battery performance, and you need to consider
this when selecting the type of battery to use.
This chapter discusses how to determine battery requirements, how these re-
quirements affect battery performance, and how to estimate battery life. At the
end of this chapter is a discussion on the various pros and cons of different battery
types that can be used in combat robots. Understanding how well the batteries
perform is crucial to your ability to build a winning competition robot.

B attery Power Requirements

The batteries’ primary purpose is to keep your robot powered during the competi-
tion. These competitions can last up to 5 minutes, so the battery must supply all the
power to the robot during that time. Selecting an appropriately sized battery that
will confidently run your robot throughout the entire match can be a significant
competitive advantage. The lightest battery will allow the robot to use the weight
savings for other things, such as weapons and armor. A properly selected battery
will have enough capacity to supply full running current continuously to your ro-
bot’s motors; and it will be able to supply the peak currents that will allow your
robot’s motors to deliver the maximum torque, when needed.

Measuring Current Draw from the Battery
You can find out from the motor specification sheets exactly what current draw to
expect when running the motor. Adding up all the currents from the various mo-
tors on your robot will tell you the maximum and typical motor running currents
to expect.
Because many of us use motors that come without data sheets, we have to mea-
sure the running currents ourselves. To do this, you need to have a good battery

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