Automatic Ping-Pong Launcher
So it's time for probably the most difficult but also most interesting design challenge for this module. Designing the ping pong ball launcher. The objective is to design an automated ping pong ball launcher that can launch a ping pong ball over a row of coke bottles and land in a container on top of our Elegoo robot.
I wanted to make this a proper engineering challenge for myself. So I want it to be fully automated if I can. So no cocking it by hand or reloading it by hand, like a catapult or something like that. I want to try and design a fully automated reloading and firing mechanism to launch the ping pong balls.
The brief for the launcher leaves a lot of room for creative liberty in the design, so I had a lot of time playing around with designs in my head, on paper, and then committing those designs to 3D software so I can start to visualize how the system might work.
I eventually decided to go with a rotating flywheel design. Similar to those used in American football and baseball, Two motors rotate two flywheels. The ball (in this case a ping pong ball) is inserted between them and the angular momentum of the flywheels is converted into forward momentum of the ball launching it forward. I fleshed out this design and brought it to solid works to work out the mechanics of how the system might work.
This is the first design I came up with. The firing principle I was happy with. But how to move the balls into the firing mechanism was another story altogether and was proving to be the crux. In this design, I used a rotating circular plate at the bottom of the hopper. The plate has a hole in it the size of a ping pong ball. When the hopper is full, a single ball will fit through this hole and will be rotated with the plate. This hole will align with a tube below the plate, and as the ball moves over this hole it will fall through into a tube and into the firing mechanism.
I then needed the electric motors to operate the mechanism. I was lucky that i had an old lego technics set that I salvaged some motors from. These motors came with their own programmable PCB so I could calibrate the speed of each motor and when they were engaged which was fantastic once I got the software booted on an old laptop with a disk drive.
Once I finally got the software working and the motors calibrated. I was able to go about making the first prototype device using these components.
I built the hopper and circular plate from cardboard and used a combination of cardboard and tape and lego for the firing mechanism. I found that the motors at max power did not rotate fast enough to give any considerable momentum or force to the balls. I attempted to geat up the motors using a gear train, But even still. I did not have the suitable gears on hard to generate any considerable speed. So from this prototype, I decided that I needed real dc motors and I decided to rethink the hopper system.
USing tinker cad I simulated the circuit and checked that it worked like I believed it would. I went out and ordered some small dc motors that I believed would be perfect for this application. I also bought a variable resistor, a Double pole double throw switch, and a battery clip.
All of this progress was updated on my Instagram story as I went, giving a step-by-step of me designing and assembling the circuit.
I then soldered the components together using a soldering iron at home and resulted in the completed circuit. I left the motor connections unsoldered as these would need to be adjusted later.
I then turned my attention back to the Launcher's body. After some more design work i landed on a design i was happy with. Which was assembled from recycled cardboard tubes and boxes. I started with two toilet rolls, cut a hole in one and a curve in the other so that they fit together with a hole adjoining them.
I then cut a triangular piece of flat cardboard as support and taped it to both tubes, securing them together.
This upright tube would act as the new hopper and the longer tube as the barrel. In which the firing mechanism is located. I then cut square slits in the side oof the barrel. This is where the flywheels will be located.
The ball as it moves through the tube will connect with the rotating rubber wheels and be propelled forward. I then mounted the barrel to an angled base which would be the firing angel.
It was now time to add the circuitry and solder the motors in place, insert the switches and do the first firing test. I still did not have the firing selector in place, but that will be added later.
So now I had an operational firing mechanism, and it is time to add the fire selector. The design I selected was to use a cam and slider mechanism. The slider will push the balls up into the firing mechanism. Slide back, and another ball would fall in front of it to be pushed forward again.
And this was the last thing to be added to have a functional, automated ping pong launcher that can reload balls and fire by itself. The finishing touch was the sight at the front which was 100% accurate……….
And now all that was left to do was testing……. And I had to do a lot of testing to get it right. And after 15 tests, we finally got our first shot on target.
And finally, I started to pinpoint the accuracy. And slowly, all misses turned into one-hit… then two…… and finally my goal of getting three balls on target.
So we nearly have all our pieces of the puzzle! We have a launcher. We have a Robot. We have an obstacle course. Now all that's left to do is get our little guy to navigate the course. Catch the balls and return…Easier said than done right. But if anyone can do it, it's this guy. So stay tuned for the final blog when we bring it all together!!
