83Service Manual – SC5000
20 - Drive System
Functional Description
The drive system of the SC5000 machine consists of a single
drive wheel with an integral motor. The drive wheel connects
to the subframe with a rotational bearing and ange to
provide steering rotation.
Steering control is made through the steering column that
passes through a universal joint to translate the rotation from
the angled steering wheel to the vertical shaft and pinion
sprocket. The pinion sprocket drives a chain that wraps
around the steering sprocket. The steering sprocket has no
chain teeth, but the chain is xed to the sprocket at the ends
of the chain using standard master links.
Drive Motor
The drive motor is a 3-phase, remotely commutated,
permanent magnet AC motor; which is commonly referred to
as a brushless DC motor. Even though it is an AC motor, it is
powered from a controlled DC power source that simulates AC
power. Each of the 3 motor windings is sequentially energized
with either zero-volts, positive battery voltage, or inverted
battery voltage. This creates a rotating magnetic eld in the windings just like a normal 3-phase AC motor.
Unlike a normal AC motor that just receives blind AC power at a given frequency, the drive motor functions
as a servo-motor, in that the motor provides positional feedback back to the motor driver for the actual
rotor position. This is referred to as remotely commutated. Three encoders inside the motor report the
actual rotational position of the rotor back to the controller. This permits the driver to know which of the 3
windings needs to be energized to rotate the motor in the desired direction, and even position. This type of
motor can literally be rotated a fraction of a turn and stopped, if desired.
The motor also reports its operational temperature back to the motor driver. This is a protection feature to
prevent motor damage due to excessive heat. The drive controller can either reduce power to the motor, or if
severe enough, shut down the motor.
Drive Pedal Potentiometer
The drive pedal potentiometer (R3 pot) is a variable resistor connected to the Pin J5-13 input of the drive
controller, with pins J5-1 and J5-110 as reference voltages. As the resistance changes, the drive controller
increases or decreases drive motor speed.
The drive pedal is set up in a linear conguration, where drive speed is controlled by the drive pedal, and
the drive direction is commanded from the Main Machine Controller via the CANBus. The speed controller
interprets any voltage between 1.0V and 4.0V as a valid speed command, and any voltage outside of that
range as deadband.
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