Page 125 - Build Your Own Combat Robot

Build Your Own Combat Robot
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Grant Imahara and Deadblow (continued)
Fortunately, the Washburn family was nearby in the contestant stands. Shane
Washburn, Grant explains, was a co-worker at ILM and he had fought against Grant
with his bot Red Scorpion in previous years. Moreover, Shane’s father, Ray, was
a welder and hydraulics expert, and his brother, Jon, was an emergency medical
technician. “They heard the air line rupture and were immediately at my side. While
I was desperately trying to turn off the SCUBA tank, the Washburns and my crew
were taking the screws out of the top cover. We wheeled my robot out of the way
and the BattleBots people and Team Poor College Kids graciously allowed another
match to go before us. This bought a little time, but not much. Ray ran all the way
back to the pits and grabbed all the air fittings from my toolbox. We fixed it there
on the spot in about five minutes—I couldn’t have done it without their help.”
Despite the catastrophic failure, Grant adds that he went on to beat Kegger with
just a single onboard air tank. But there’s a lesson in the story: “Always inspect all of
your equipment for wear and damage, even if you don’t think you had any.”

P ower Transmission Basics

As stated, the purpose of the power transmission is to reduce the speed of the mo-
tor to some usable speed for the robot and to transmit the power to the wheels.
The speed of a robot is a function of the rotational speed of the wheels and the di-
ameter of the wheels. Equation 1 shows this relationship, where v is the velocity of
the robot, D is the diameter of the driven wheels, and N is the rotational speed of
the wheel. So, to determine the required rotational speed of the wheel, Equation 1
is solved for N, which is shown in Equation 2.
6.1

6.2
If your robot has 10-inch-diameter wheels and the rotational speed of the robot
is 300 RPM, the speed of the robot will be 9,425 inches per minute, or about 8.9 miles
per hour (MPH). If you want your robot to move 20 MPH, this same wheel will
have to spin at 673 RPM. This is one fast robot.
After you have an idea of the wheel speed you want, you need to determine how
much of a speed reduction in the power transmission you will need to convert the
motor speed to the wheel speed. This is done by using a combination of different
sprocket diameters, pulley diameters, or gear diameters. The speed ratios of a gear
train are just a ratio of the gear diameters.
Figure 6-1 shows a sketch of the same type of speed reduction. The leftmost
sketch shows two gears in mesh, and the sketch on the right shows a belt/chain
gear reduction. One thing to note here is that with the gear reduction, the direction
of the driven gear is opposite of that of the driving gear. With the belt/chain sys-
tem, the directions of both pulleys/sprockets are the same.