BASIC OPERATION AND FEATURES
SX TRANSISTOR CONTROL
Page 6
October 1998
Section 2.1.1.a Standard Operation
The oscillator section of the card has two adjustable
features, creep speed and minimum field current. With the
accelerator at maximum ohms or volts, the creep speed
can be adjusted by Function 2 of the Handset or a trimpot.
The field control section allows the adjustment of the field
weakening level in order to set the top speed of the motor.
This top speed function (Minimum Field Current) is enabled
when the armature current is less than the value set by
Function 24 and the accelerator input voltage is less than 1
volt. Top Speed can be adjusted by Function 7 of the
Handset or a trimpot.
The percent on-time has a range of approximately 0 to 100
percent. The SX controllers operate at a constant
frequency and the percent on-time is controlled by the
pulse width of the voltage / current applied to the motor
circuits.
Section 2.1.1.b Proportional Operation for Dual Motor
Vehicles
A key performance advantage of this control is the ability to
achieve actual "proportioning" of motor speed. In a
non-proportioning, or single control, system when the
vehicle starts to turn, the outside drive wheel turns in a
larger circle than the inside wheel. Depending on the
geometry of the vehicle, at some degree of turn angle, the
inside wheel must slow down to prevent scrubbing of the
wheel. This is accomplished on single control system by
disconnecting the inside motor and letting the wheel "free
wheel" or "float" at whatever speed is dictated by the
outside wheel that is still under power. The main
disadvantage of this system is that no torque is available on
that motor when the inside wheel is in the "free-wheel"
mode, and performance in a turn is reduced. When the
steer wheel nears to the 90° turn angle, the inside motor is
re-connected in the opposite direction of the outside. At
this point, torque is returned to the inside wheel and the
speed is the same on both motors.
With two controls, the speed of each motor can be
regulated independently. The driver controls the speed of
the outside wheel with the accelerator input signal. The
inside wheel speed is controlled by the turn angle of the
steer wheel. A potentiometer is attached to the steer wheel
in order to communicate the steer angle to the controllers.
During vehicle manufacture, software selection identifies
each control for its application as a right or left control.
The controls are physically identical, and it is only software
that separates a right from a left control or differentiates a
control for a dual motor application from one intended for a
single motor vehicle. As the steer reaches some
pre-selected turn angle, approximately 20
o
, the speed of the
inside wheel decrease proportionally to the speed of the
outside wheel. This proportional decline will continue on a
linear path until the steer angle reaches another pre-
determine angle of, approximately 65
o
.
At this point, the inside wheel will stop, as the steer angle is
increased toward the 90° point, the inside wheel will
reverse direction and start to accelerate proportionally in
speed. As the steer angle reaches the 90° point, the inside
wheel speed will be the same as that of the outside wheel.
During this entire turn, except for several degrees when the
motor was stopped to change direction, torque was always
present on the inside wheel, providing a smoother ride
throughout the turning radius of the vehicle.
Details for adjustment of the steer angle potentiometer can
be found in Appendix A of this manual.
0
O
10
O
10
O
20
O
20
O
30
O
30
O
40
O
40
O
50
O
50
O
60
O
60
O
70
O
70
O
80
O
80
O
90
O
100%
50%
50%
100%
90
O
100%
50%
50%
100%
RIGHT
MOTOR
LEFT
MOTOR
STEERING ANGLE
LEFT
TURN
RIGHT
TURN
LEFT
MOTOR
RIGHT
MOTOR
RIGHT
CONTROL
LEFT
CONTROL
0
O
90
O
90
O
REV - SPEED - FWD
REV - SPEED - FWD
Section 2.1.1.c Creep Speed
With the accelerator at maximum ohms or volts
(approximately 3.7 to 3.5 VDC), the creep speed can be
adjusted by Function 2 of the Handset. At creep speed, the
ON time can decrease to approximately 5%, with the OFF
time at approximately 95%. At full transistor operation, this
condition will be reversed (short OFF time, long ON time).
This variation of ON and OFF time of the oscillator varies
the voltage applied to the motor, thereby varying the speed
of the motor for a given load.
Section 2.1.1.d Control Acceleration and lA Time
This feature allows for adjustment of the rate of time it
takes for the control to accelerate to 100% applied battery
voltage to the motor on hard acceleration. The lA contactor
will automatically close 0.2 seconds after the controlled
acceleration stops and the accelerator input is less than
0.5 volts or less than 200 ohms. Armature C/A is adjusted by
Function 3 from 0.1 to 22 seconds.
Section 2.1.2 Current Limit
This circuit monitors motor current by utilizing sensors in
series with the armature and field windings. The
information detected by the sensor is fed back to the card
so that current may be limited to a pre-set value. If heavy
load currents are detected, this circuit overrides the
oscillator and limits the average current to a value set by
