Page 76 - Robots Androids and Animatrons : 12 Incredible Projects You Can Build

4.15 DC motor with gearbox head

torque of the motor is substantially increased. You could estimate
that the torque will increase by the same value the rpm decreased.
In reality, no conversion is 100 percent efficient; there always will be
efficiency losses.

Some DC motors, called gearhead motors, are built with a gearbox
attached (see Fig. 4.15).

DC motor H-bridge
55
When building a robot, one wants to control (turn on or off) the DC
motor via a simple circuit or digital signal. In addition, one would
also like to be able to reverse the motor’s direction. An H-bridge
fulfills these requirements.
It should be understood that the term “DC motor” refers to stand-
alone DC motors as well as motors connected to gearbox motors
as well as gearhead motors.

The H-bridge is made up of four transistors. [Some robotists use
metal-oxide-semiconductor field-effect transistors (MOSFETs). I
use NPN Darlington transistors.] Some H-bridge designers use a
combination of PNP and NPN transistors. In each case, the tran-
sistor acts like a simple switch (see Fig. 4.16A). When switches SW1
and SW4 are closed (Fig. 4.16B), the motor rotates in one direction.
When switches SW2 and SW3 are closed, the motor rotates in the
opposite direction.
By using the switches properly, we can reverse the current direction
to the motor, which in turn reverses the motor’s shaft rotation.
Figure 4.17 is an H-bridge circuit that uses transistors. An H-bridge
circuit is used in Chap. 5 in the sensor tester robot.

Team LRN Movement and drive systems