The steering and brake hardware
and controllers are located under the hood. Since the Polaris engine is
under the seat, there's considerable room under the hood. That's one of
the reasons we chose the Polaris Ranger. We've used up most of that room.
Overview of the hood
It's not finished, but
all the key components are in place.
Dirt shields have been
The steering motor is
a geared brush-type DC servomotor, powerful enough to turn the wheels
even with the vehicle not moving. It is connected to the steering
box below via a rubber shock coupling.
Peak motor current in
normal operation is about 8 amps at 24 volts. This was more than
the original MicroMo controllers could reliably deliver, but the
Galil DMC Econo Series controller
to the left of the motor delivers its rated current with no problems.
Galil controller and its opto-isolator board are to the left of the
motor. Previously, three MicroMo controllers were packaged and mounted
in that space, but their replacement Galil controllers have not yet
been permanently packaged. We will fit two Galil controllers and the
opto-isolator board into that tight space.
The black cylinder to
the left is a DC servomotor driving a ball screw. Located below
and behind the brake master cylinder, the high-speed actuator can
start braking within 200ms of actuation.
A pressure sensor, read
by the Galil controller, and a pressure limit switch, used to stop
the brake actuator after an emergency stop, are attached to the
brake line for the front wheels.
Emergency stop relay
Inside the box are several
automotive relays (rated for high temperature and vibration) which
perform emergency stop functions.
When the emergency stop
system is activated, the brake actuator is driven to the brakes-locked
position, the throttle actuator magnet releases the throttle to
idle, and the engine ignition is disconnected.
stop system contains a hardware watchdog device which must see a
change in its input every 200ms. That device is connected to a digital
output on one of the Galil controllers, and one of the back bed
computers must change the state of that output every 200ms, or the
emergency stop system triggers. So if any key element in the control
system stops functioning, the emergency stop system trips.
Loss of the
radio E-stop signal, or pressing one of the big red buttons on the
vehicle, also trips the emergency stop system.