Mechanical Design
Excavator Arm
The scale excavator is a fixed base, 4 degree of freedom arm. Syringes are used as hydraulic pistons to move each joint, and the size and stroke of the syringes determined size of the excavator. The syringes are connected to the excavator using custom 3D printed adapters and dowel rod pivots. Potentiometers and limit switches are incorporated into each of the angles in order to provide feedback to the micro-controller.
CAD rendering of excavator arm
Finished excavator test setup
Hydraulic Drive Unit
The Hydraulic Drive Unit (HDU) is what provides the hydraulic power to the excavator arm. The original concept for the HDU used a lead screw design, but a rack and pinion drive was eventual chosen for its speed and efficiency. The HDU consists of an array of four more syringes, one for each joint. The plungers were replaced by custom 3D printed rack pistons which interface with the existing rubber seals. These racked pistons ride on bearings, and are driven by four geared DC motors.
CAD rendering of HDU
Finished HDU