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Note #25
Sensor/actuator list

John Nagle
Last revised May 20, 2003.

Full sensor/actuator list, to be kept current.

This is a draft. We need to fill in more of the details here.

Steering position Analog pot. (?) DC voltage, DC pwr   Steering shaft Chassis Splash
Engine speed Tachometer Counter/timer   Engine/transmission Chassis Immerse
Driveshaft speed Relative encoder Quadrature   Transmission/driveshaft Chassis Immerse
Brake pressure Pressure sensor Analog   Master cylinder Chassis Splash
Brake pressure limit Pressure switch Switch   Master cylinder E-stop Splash
Transmission position Encoder or pot. ?   Transmission Chassis Immerse
Vehicle speed Doppler radar Counter/timer   Chassis Chassis Immerse
Water temp Temperature Analog   Chassis Chassis Immerse
Kill input DC voltage DC signal   Dashboard Chassis None
Freeze input DC voltage DC signal   Dashboard Chassis None
Generator running ?       Chassis None
Generator power OK ?       Chassis None
Steering actuator DC brush Analog amp 24VDC, ???A Steering shaft Chassis Splash
Throttle actuator ?     Engine Chassis Splash
Choke actuator       Engine Chassis Splash
Brake actuator       Master cylinder Chassis Splash
Transmission actuator       Transmission Chassis Immerse
Ignition relay Relay     Dashboard Chassis None
Starter relay Relay     Dashboard Chassis None
6WD relay Relay     Dashboard Chassis None
Stop lights relay Relay     Dashboard Chassis None
Backup lights relay Relay     Dashboard Chassis None
Generator run relay Relay     Dashboard Chassis None
Generator start relay Relay     Dashboard Chassis None
E-stop output relay Relay     Dashboard Chassis None

Radar Eaton VORAD Serial port, 19.2Kb   Chassis Aux sensors Immerse
Water level 1..2 Contacts ?   Chassis Aux sensors Immerse
Sonars 1.. N ? ?   Various Aux sensors Splash
Bumper switches Contacts     Various Aux sensors Immerse
Aux E-stop relay Relay     Dashboard Aux sensors None
Horn Relay     Hood? Aux sensors None
Flashing yellow lights Relay     Various Aux sensors None
LED sign Relay Serial port   Roll cage rear Aux sensors None

Laser rangefinder SICK LMS Serial port, 500Kb   Top unit Top unit Rain
Road-follower camera   FireWire   Top unit Vision Rain
Laser rangefinder inertial sensors Inertial unit ???     Top unit Rain
Rangefinder pan/tilt head   Serial port 400W max Top unit Top unit Rain
Sensor washer (?) Relay     Top unit Top unit Immerse
(GPS and inertial systems
in sealed box with big computers,
listed separately.)

This assumes three PC/104 systems - one running the chassis, one running the auxiliary sensors, and one running the top sensor unit. Each of those is a separate subsystem, and their main (only?) interconnection is via the Ethernet. The GPS, inertial system, and vision processing take place in larger computers in the back.

Our next task is to decide on all these sensors and pick PC/104 interfaces to connect them.


  • Sensors are listed before actuators.
  • There's no fuel gauge, because we can't do anything about that.
  • Water temperature is useful both for starting (choke setting) and for slowing down if we overheat.
  • The brake pressure sensor is used for computer control of braking.
  • The brake pressure limit switch is part of the E-stop system, which drives the brake actuator until the switch opens.
  • Kill input indicates that manual E-stop has been triggered, either remotely or locally. This kills the engine and locks the brakes. A manual reset is required. The computer can still steer while stopping.
  • Freeze input indicates that freeze mode has been triggered, either remotely or locally. This stops motion under computer control.
  • Both main and aux E-stop relays must be energized to leave E-stop mode. So either the chassis computer or the aux sensor computer can stop the vehicle directly.
  • The chassis computer is the only computer powered from the vehicle battery and generator. All other computers are powered off the auxiliary generator. So the chassis computer has to control the auxiliary generator.
  • Engine speed is unsigned, but driveshaft speed is signed.