Step 1: Mini Model

I began with building a model of the catapult using small syringes containing water. I created the larger version from this design and changed the hydraulic component to pneumatics.

Step 2: Tracing the Pieces

After testing the original model, I took it apart and simply traced the pieces on a piece of paper. Then, I scanned that drawing onto the computer and created an Autocad file which I then converted into a v-carve file to run on the CNC router.

ccmmailroom@ucmail.uc.edu_20151118_135149.pdf
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Step 3: Assembly

After the pieces were cut out of 3/4" plywood on the CNC router, I assembled the pieces as I did with the model. I used 3/4" dowel as the pegs and screws to add strength and stability.

Step 4: Pneumatics

Next, I added a base and the cylinder. The base needs to be screwed (or attached in some manner) to the ground due to the power of the pneumatics. I choose a double acting cylinder with a 3/4" bore. I also added a manual stop (in the form of a steel pipe) to the rod of the cylinder to keep it from retracting all the way.

Step 5: Plumbing

I used 1/2" hose to plumb the cylinder. In order to control the speed of the extend and retract of the cylinder, I also added a regulator. Using a 4/3, lever operated valve, I can control the extend and retract of the cylinder and also have a neutral state.

pneumatics schematics final.pdf
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Step 6: R&D

The last step is simply testing the mechanics and some slight tweaking to the design in order to get the throw distance desired. I was able to get the catapult to launch the tennis ball about 5'.

Introduction: University of Cincinnati CCM Pneumatic Projects Fall 2015