Specifications

Motor Control
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3.2 EXISTING MOTOR DRIVERS
Previous motor controller circuits designed within the Mechatronics Group have been
quite varied and focus on platform specific designs. The main parallel between most
robotic platforms is that they run from a 24 V battery system. This section discusses
some of the past attempts at motor control and their shortfalls with respect to this
project.
3.2.1 Outdoor Mechatron
The original motor driver design for the outdoor mechatron was custom built and
utilized both a DAQ card and microcontroller to supply control signals to the high
power circuitry. A simplified power drive circuit for the motors is illustrated in Figure
3.4. The logic control signal drives a Darlington pair which is optoisolated from the
high power circuit for protection of the microcontroller.
Figure 3.4 Simplified single switch and relay drive circuit
Relays were used to implement direction switching however it is desirable to replace
such mechanical components with semiconductors to reduce risk of failure. Another
major limitation of this design was the lack of protection circuitry. The high loads and
back emf created by the motors produced excessive strain on the components often
resulting in damage after short operating periods. Development of a new driver
interface requires switch protection and snubber circuitry to dissipate the transient
currents.