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Solid State Relays
|Controlling the Current|
While button box control was sufficent for simple exerimentations, it's not a robot until it is computer controlled.
In order to interface the computer to the relays in the electric motor control system, and latter to the solenoid valves in the hydraulic manifold, a set of solid state, optically isolated relays were used. These solid state devices allowed the very low power signal from the computer to control the Amps of current flowing through the various relays and coils in the system.High Current Control
While the solid state relays are rated to 5 amps, many of the parts used in Groundhog required higher currents. The master power switch which switched all non-computing power on and off, and the switch for the hydraulic pump motor were both implemented using large relays. This led to a cascaded control of the high current items. The computer triggered the solid state relay, the solid state relay triggered the high current relay, and the high current relay controlled the motor or main power.
Control of the hydraulics was achieved through the use of solenoid operated valves. Each valve was controlled by a pair of solid state relays. With just two three position valves, complete control of the hydraulic actuators was achieved.Fuses
In order to insure that the control of the robot didn't accidentally destroy any critical component, every line was fused. While standard practice would just place a fuse on the hot line, MSHA(Mine Saftey and Health Administration) requirements for explosion proofing require fuses on both the hot and ground lines. Therefore, the power lines to every major device outside of the explosion proof box as well as any major power line were double fused.