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  Inconceivable42 • 04/23/2022 at 17:56 • 0 comments

  GitHub Repository

  https://github.com/Inconceivable142/Beer_Pong_Robot

  How to Almost Build a Beer Pong Playing Robot

  In April of 2021 I was looking for a project to spend my ample amount of free time on. For some reason a beer pong playing robot popped into my head. At a high level I envisioned a robot that would use a camera to find cups and fire a ping pong ball at said cups. I decided a Raspberry Pi would be used as the “brain” and would handle the image processing. The Raspberry Pi would tell an Arduino how to orientate the firing mechanism. Having a 3D printer I planned to print a majority of the firing mechanism. Over the next year I would spend my time designing, testing, and redesigning various aspects of the robot in hopes of improving its accuracy. I am writing this to document all of the effort I put into to the project and in hopes of it helping someone else.

  Prototype 1

  I start the first version of my robot by trying to come with a firing mechanism for the ping pong ball. The first thing that came to mind was emulating the throwing action of a human arm with a robotic arm. But some preliminary testing with an already built robotic arm and the power from hobby servos wouldn’t provide the torque necessary to throw the ball very far. I then had the idea of propelling the ball using a fan. I decided to use a spare blower fan from a Christmas inflatable. I started the mechanical with deciding on a rotating base for the robot. I already had the base for the Thor robotic arm (http://thor.angel-lm.com/) and decided it would suite the job. I then went on to design the adapter plate for the base, mounting bracket for the launcher, and the launcher itself. In my first prototype the launcher was entirely 3D printed, comprising of a barrel and a hopper. The barrel had a servo with a rack and pinion used to stop the ball and the fan mounted at the end. The hopper also had a servo with a rack and pinion to load the ping pong balls into the barrel. The STL files for my first prototype of version 1 can be found in the following directory Prototype_1/STL_Files. Having the rough prototype of the hardware it was time to focus on the electronics. As stated before the “brains” of the robot would is a Raspberry Pi 3 Model B which controls an Arduino Nano used for interfacing with other devices. The base is controlled using a stepper motor driven by an A4988 with a 10k potentiometer to track the base’s position, the fans speed is controlled by a PWM driven MOSFET, and the servos are controlled via PWM from the Arduino. The electronics are power by a 12V ac adapter which is stepped down by a dc to dc converter for everything but the fan and stepper motor. I have created a rough schematic for the electronics in the directory Prototype_1/Schematics.

  Video Link:

  https://youtu.be/3i9wkNocgnk

  Prototype 2

  After testing out my initial prototype I found that I was having issue with accuracy. While maintaining the same position and fan speed the launched ping pong balls would be somewhat accurate but not precise. At 8ft (maximum distance of a cup on a regulation table) the balls would make it in the solo cup less than 50% of the time. After a lot of trouble shooting I hypothesized that the 3D printed barrels surface was fairly non uniform and created random drag when being launched. To solve this issue I bought an acrylic tube with less than a millimeter of clearance for the ping pong ball. I then redesigned the launcher so that the acrylic tube could be used instead of the 3D printed barrel. The STL files for the modified barrel can be found in the directory Prototype_2/STL_Files.

  After completing and testing the second prototype I found that while the precision had improved it still seemed below 50%. The data I collected for the second prototype can be found in the directory Prototype_2/Test_Data/Data1.xlsx, and as the data shows my suspicions were correct and shots are only made around 46% of...

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