Design Blog: Ping-Pong Shooter

31 December 2024

My name is Binara, and I will be taking you through the entire design process of how I created the ping pong shooter attachment. The original task was to develop an attachment for the rover to store and shoot ping-pong balls with automatic reloading.

Step 1: Research

Every idea has to start somewhere, so the best way to get inspiration is to see what others have done. If your idea doesn’t exist, it can be helpful to break it up into smaller, existing ideas.

As with the domino layer, we will explore existing designs of ping-pong shooters:

The problem with these designs is that we’re constrained to using 2 servos, so flywheels are not an option. A system that automatically pulls back rubber bands and loads ping-pong balls could work, but it would also be complex. However, using elastic energy to shoot the balls might lead us in a good direction.

Step 2: Ideation

It’s a good idea to get some of your thoughts and theories down on paper before building them.

Step 3: Prototype

As with most of my designs, the prototype phase consists of generating a 3D design on Autodesk Inventor or Fusion 360 and then 3D printing it.

Step 4: Iterate and Evaluate (Back to the drawing board)

Design 1:

This design has ping-pong balls dropping in from above. Then a servo-powered rack and pinion push the ball into ‘wings’ designed to squeeze and pop it out. The structure is made from PLA, but the wings are made using PETG, a much more flexible material. This makes it perfect for bending and squeezing the ball.

Notes to fix for the following design:

  • The actuator does not have enough power to push the ball through the wings.
  • There is a large amount of friction in the actuator, so most of the energy from the servo is wasted.
  • When the ball is pushed against the wings, it pops straight up instead of through them.
  • The print is quite large and hard to print. Also, some structural aspects are fragile.

Design 2:

Now two servos on the back drive the same rack. The idea of this was to double the power of the ejection system. Throughout the structure, I’ve made some walls thicker, which reduced the chance of the prints breaking.

Notes to fix for the following design:

  • The actuator doesn’t have much power when pushing the ball, so the ejection system is weak.
  • The actuator doesn’t always go straight, and the teeth jam in the channel it moves along in.
  • The print is massive and has several supports that are difficult to remove.

Design 3:

The main issue in the previous design was that the rack jams when the servos pushed out a ping-pong ball. This is due to a very minor mistiming in the servos.

Next, two issues were solved in one: the roof detaching from the wings and the complexity of the prints. The roof was removed from the design and made to be screwed on instead. This allows all the design components to be printed without support, making it much more robust as it is assembled using screws.

Design 4:

After experiencing several issues with the pusher design, I went for a redesign and completely removed the rack and pinion. I made a new system with a continuous servo and a worm drive to get a lot of torque in the ejection system which lets the system shoot really far.

Final design review:

  • The actuator doesn’t have much power when it’s pushing the ball, so the ejection system is weak
  • The actuator doesn’t always go straight, and the teeth jam in the channel it moves along
  • The print is massive and has a large number of supports that are difficult to remove.

Step 5: Finalise

And finally, after many iterations, the design works. Now all that’s left is to consider a couple options to make your design perfect in the future.

  • Ease of Assembly: How easy is it to put the design together?
  • Cost: How much material does it use?
  • Aesthetic: How does it look?

Now that you have seen the full design journey, try building the final version yourself.