Main mechanism:
The mechanism is mostly made of Delrin links connected with 8mm steel shafts that are attached on bearings. We decided to use Delrin for this project because we would put large forces and velocities on the links. Using a weaker material such as acrylic or wood could cause the links to break easily. On the other hand, using heavier materials such as aluminum would give the mechanism more weight and, as a result, require more torque from the motor. The links were shaped on a manual vertical mill to keep the accuracy of the cuts high. Holes were made on the Delrin which were too small for the bearings to allow the bearings to be press-fitted into the links. The 8mm shafts connecting the links were cut using a lathe. The whole mechanism was set on a 2”x6”x3’ wooden plank onto which the rail and crank were attached to. From this base we also attached two 2”x4”x8” pieces of wood that were used to suspend the grounded pin upon which the throwing arm would rotate and slide around.
Spindle mechanism:
The spindle mechanism was placed at the end of the throwing arm to increase the final velocity of the ball at the release point. To create an area between two pieces of delrin, we connected the pieces of delrin by press fitting 8mm shafts into them. The spindle itself was made from small 1”x1”x.3” blocks of Delrin, 8mm shafts press fitted into them, and 1”x1” pieces of rubber hot-glued to the delrin. These shafts were attached to the delrin links with bearings to allow rotation. A small hole was drilled into the 8mm shaft that housed the spinning mechanism to allow the cable to be attached to it without slipping.
Motor assembly:
The motor we were given did not come with a bracket so we made one from a piece of aluminum we found and attached it to the motor using the screw holes at the front of the motor. The motor was then screwed down onto the wooden base. To transfer the torque of the motor to the mechanism we 3D printed small gears, one was pressure fitted onto the motor shaft and another was pressure fitted onto the shaft that was connected to the driver link. Rotating these links resulted in the rotation of the driver link and would drive the slider-crank and the motion of the throwing arm.
The motor is connected to the base with a custom made bracket. The gear from the motor is connected to the crank to drive the rest of the system.
The full mechanism, below, shows the use of Delrin bars for links as well as numerous other parts to connect everything together.
