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2.2 SPEED AND DIRECTION CONTROL
A brushed DC motor's unloaded rotation speed is determined by voltage that is applied to it while the direction of
rotation is determined by the polarity of that voltage. The magnitude and polarity of the SPARK output voltage is
controlled by sending it a standard servo-style PWM signal. The following sections describe this interface in detail.
2.2.1 SERVO-PWM CONNECTION
The SPARK accepts a standard 3-wire servo/PWM cable in the port marked PWM in raised lettering. Please refer to the
connection diagram in Figure 2-2 or the SPARK housing for polarity indicators. Align the ground/negative wire with the B
marking on the case. This wire is usually black, but may be brown in some cases. The signal wire should be closest to
the SPARK logo on the heat sink. This wire is usually white but may also be yellow or orange.
The plastic surrounding the PWM port was designed provide cable retention by exerting pressure on the housing of a
standard 3-wire cable housing. Retention effectiveness may vary depending on the cable being used.
2.2.2 CONTROLLING MOTOR SPEED AND DIRECTION
The SPARK responds to a factory default pulse range of 1000µs to 2000µs. These pulses correspond to full reverse and
full forward rotation, respectively, with 1500µs (±40 µs deadband) as the neutral position, i.e., no rotation. The spark can
be calibrated to respond to a different pulse range, see section 2.5.2 CALIBRATION. Table 2-2 describes how the pulse
range maps to the output voltage, motor speed, and motor direction.
For input pulse p
Output voltage V
(V)
OUT
Default pulse width (µs)
Maximum pulse range (µs)
REV-11-1200-UM-00
Figure 2-2 Servo-PWM Connection
Table 2-2 Input Pulse Mapping
Full Reverse
Prop. Reverse
V
= −V
−V
< V
OUT
IN
IN
OUT
p ≤ 1000
1000 < p < 1460
Copyright © 2016 REV Robotics, LLC
Motor Speed and Direction
Neutral
< 0
V
= 0
OUT
1460 ≤ p ≤ 1540
500 ≤ p ≤ 2500
Prop. Forward
Full Forward
0 < V
< +V
V
= +V
OUT
IN
OUT
1540 < p < 2000
2000 ≤ p
IN
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