17Service Manual – SC900 20 - Wheel System, Traction
Circuit Description (Driving)
When any of the three Go switches
is closed, it connects the Pot-Lo
output (0V) from the controller back
to the Throttle-Pot input. The drive
controller sees this as a full-throttle
command and initiates the drive
function. If the Reverse switch closes,
the drive will decelerate (if moving
forward) and re-accelerate in the
reverse direction.
Because the drive is receiving a full-
throttle command, the actual drive
speed is set by controlling the speed
limit input. When the Go switch
closes, the speed limit potentiometer
is properly biased with 0 and 5 volts,
and the pot wiper voltage drops from
its previous of 5 volts to somewhere
between 0 and 5 volts, depending on
where the pot is positioned.
As a result of the open-circuit to closed-circuit condition of the Go switch closing, two things happen with the
controller at once: The speed limit drops from maximum to its set position, and the throttle goes from zero to
maximum. Even though this may seem like a conict, there is enough delay in the motor ramp-up function
that the motor does not momentarily receive a full speed command (unless the speed is set for maximum).
Brake Output (Scrub Enable)
When the drive controller is commanded to move, it activates its “brake release” function by bringing the
Brake- output to battery-negative voltage. This results in both positive and negative voltages being available
to the various scrub circuits. Previously the scrub circuits were disabled, because both sides of the circuits
were at the same battery-positive voltage, and no current could ow.
This Brake- power passes through the K1 relay, and if closed, through the Brush Switch. This activates the
brush relay to drive the brush motors. It also passes to the optional detergent module to enable the solution
solenoid and detergent pump.
Refer to the “24 - Electrical System” on page 28 for a further description of the circuits affected by the
Brake output.
POT.
5K OHM
RED/GRN YEL/BLK
BLK
RED
PNK/BLU
GRA/VIO
BLU
WHT
ORN
YEL
PNK
S1
Key Switch
S7 GO RT
S2
GO MID
S3
S, REV
P1
CURTIS 1228
POT HI
3
THR POT
4
KSI
5
POT LO
13
BRAKE-
6
REV
17
B+
B-M1
M2
M1
M2
SPD POT
18
BRAKE+
14
S6
GO LEFT
R1
M
M1
MOTOR, DRIVE
-+
36 VDC
+ -
VIO
Brush
Detergent Pump
Solution Solenoid
36V
36V
0V
5V
0V
Closed
Closed
Enabled
?V
0V
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