CHAPTER 17 ■ DC MOTORSMounting putty is available at local hardware stores, office supply outlets, and even some supermarkets.
Blue, white, and yellow colors are available.
Converting RPM to a Metric Unit
The metric unit for angular velocity is radian per second, or rad/s. Even though it doesn’t appear often in
advertisements, rad/s sometimes shows up in datasheets. For motors, RPM and rad/s are used to measure
the same thing, but rad/s is an internationally accepted unit in the metric system.
To convert RPM to rad/s, multiply by 0.10472 (which is an approximation of p/30).
RPM × 0.10472 = rad/s
137 RPM (Sandwich's motors) × 0.10472 = 14.34664 rad/s
To convert rad/s to RPM, multiply by 9.54929 (which is an approximation of 30/p).rad/s × 9.54929 = RPM
14.34664 rad/s (Sandwich's motors) × 9.54929 = 137 RPM
Torque Characteristic of DC Motors
Torque is the amount of twisting force that can be performed by a motor. This indicates how heavy of a load
the motor can turn. Torque is very important as it determines how weighty the robot can be, how steep of a
hill the robot can climb, and how much the robot can push or pull.
Speed and torque are not the same things. An electric screwdriver has large amounts of torque so that it
can drive a screw into or out of strong material. But the screwdriver has fairly slow speed because otherwise
the tip of the screwdriver would likely slip out of the groove at the head of the screw.
Figure 17-18. Putty for holding tachometer discs to motor shafts