1.4 - Implementation
Fabrication
We fabricated every part of our robot apart from the motor, the shafts, and the electronics. We laser cut the base of our robot, gears, arm linkages, and slider (which kept the robot stable while climbing the wall). We choose acrylic for gears because they would produce less friction and provide more strength than plywood. Everything was cut at Texas Inventionworks using 6mm clear acrylic so that the arm could withstand torques and be visually appealing. Additionally, we 3D printed shaft collars, hooks, motor mount, and some parts of the arm using standard PLA filament, in cases where more complex geometry could not be laser cut. Additionally, shaft spacers were both cut and 3D printed to provide custom spacing to ensure all components properly lined up and would not produce out of plane motion.
Assembly
The robot was constructed using a combination of laser-cut acrylic parts and 3D-printed components to ensure a lightweight yet durable structure. The most complex part of the assembly was the “crankshaft”, with the powered arms being printed in PLA and bonded to dowel pins and shoulder screws to allow for smooth rotational motion and power transmission. We determined during our prototyping that simple press fits would not provide substantial torque transmission. Any free-rotating joints were constructed with screw joints using M3 hardware and nylock nuts, to ensure a minimum in slop without adding any excessive friction. Any other fixed joint was similarly M3 hardware, torqued down to be slip-critical. The robot worked on a custom-built inclined bouldering wall that we fabricated out of plywood to mount interchangeable rock climbing holds.
A key challenge during assembly was ensuring that all three arms had the proper phase shift to ensure that the motion profile and leg spacing matched what had been designed for. This required iterative testing and small adjustments in shaft alignment and linkage timing, proving to be very difficult due to the involved nature of the crankshaft assembly.
Electronics, Circuitry, and Software Development
Our robot was designed to require simple electronics. We used a open-loop system where we had a potentiometer that controlled the speed of our robot. We used a brushed DC motor, a 12 V battery, Arduino, a motor controller, and a rotary potentiometer. The motor supplied torque that spun the gears and moved the arms of the robot. The battery power went to the motor controller which provided 12 V to the motor and 5V to power the Arduino. The Arduino then provided 5V to the potentiometer which controlled the logic of how fast the motor would spin. We had very basic software controlled logic that would take in the input value of the rotary potentiometer and relate it to an output voltage. We used software controls to clamp the output voltage range to ensure that the motor ranged from 10-12V only.