Autonomous Vehicles - KPIT

Figure 3: Remote control electronics subsystems
In order to prevent any false command
attributable to data corruption, this frame has
built in checksum error detection feature. This
electronics has two separate controllers to
share the task of controlling actuators i.e. the
data packet containing wireless commands is
fed simultaneously to both controllers. These
controllers react to specific byte sequences.
Figure 3 depicts all subsystems.
A. Remote Ignition/Vehicle control: This
subsystem automates the ignition controls in
the vehicle. To crank the engine, the crank
signal needs to be held logical high (~5V) and
then should be brought to logical low (~0V).
This was achieved by using suitable
electromechanical relay with timing control
provided by the embedded controller i.e. this
served as a parallel ignition option in addition
to normal cranking operation through turning
of the key.
B. Remote Throttle: This subsystem
automates throttle operation using an
electronic drive circuit. The vehicle
implements an electric throttle whereas the
operation of throttle lever generates two
proportional analog electric signals. These
signals are input to engine ECU within the
vehicle. The remote throttle circuit
proportionally generates two similar
proportional analog signals using ADC in
response to remote throttle command of 0 to
255 steps.
C. Remote Steering System: This system
automates steering operation using a DC
motor mounted within the steering column by
cutting a section of the shaft to accommodate
this axially aligned motor. This DC motor is
controlled through an H bridge (implemented
through suitable capacity Solid State Relays).
This H Bridge thus enables direction control.
The desired steering position is achieved
through following sequence:-
(a) Based on correct steering position and
command, the corresponding H bridge arm is
enabled to turn motor right / left for 10 msec.
(b) After 10 msec run, positional feedback is
sampled using the 4-20 mA loop shaft position
sensor. Since the sensor is noisy, a number of
samples are taken to eliminate noise. Repeat
with motor running till steering shaft is within
acceptable defined positional accuracy
(embedded in the code).
Compact
RIO
+12V DC
Supply
-5V to +5V
Remote/Local
Selection
Power
drive
Control
Circuit
Absolute
Angle
Encoder
Motor
Figure 4: Remote steering system
Mechanical
connection to
existing steering
column
D. Remote Parking Brake: This subsystem
automates parking brake operation using a
motorized screw linear actuator. The
extension/retraction of this actuator pulls or
releases parking brake cables. The actuator
electric motor is electronically controlled to
achieve park/release operations. A closed
loop control system has been implemented
using limit switches to achieve remotely
commanded parking brake operation.
E. Remote Service Brake: This subsystem
automates brake operation using a motorized
screw linear actuator, a linear displacement
sensor, an additional master cylinder and
vacuum booster. The extension/retraction of
this actuator activates additional master
cylinder connected to existing brake hydraulic
lines from vehicle's master cylinder. The
actuator electric motor is electronically
controlled to achieve brake operations. A
closed loop control system has been
implemented using linear displacement
sensor to achieve remotely commanded
brake operation. The system operates the
brake in proportion to commands in form of
digital inputs 0 to 255 (no brake to full brake).
The additional vacuum booster receives
engine vacuum. Four valves are used to
switch the hydraulic circuits for remote or local
operation.
36 TechTalk@KPIT, Volume 6, Issue 4, 2013