PongBot
Origin Story
PongBot was initially conceived as a ball launcher that could be used to practice sports such as tennis or football. Players could practice running routes or improve their backhand
Initial Goals:
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Sensing: Target detection
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Use cameras to detect position of a player or target
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Planning: Real Time Trajectory Calculation & Maneuvering cannon
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Find the appropriate launch vector and maneuver cannon to appropriate angle
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Actuation: Launch ball with appropriate velocity to intercept target within a 1 meter radius
This project is interesting because it can help people get better at sports. It is interesting because it involves a variety of components working together: Computer vision, trajectory planning, and projectile launching. It could be used to help players get better at sports and improve their fitness. One downside is that projectile launchers can also be used to damage people or things. The information presented here should be used for good purposes only.
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Pneumatic Launcher
Dual Rotary Launcher
Design(s)
The goals have remained the same since the beginning, namely target tracking and projectile launch within 1 meter
The initial designs were actually pnuematics. Unfortunately, this designs couldn't precisely control velocity, was heavy and required expensive components. A simpler version of a pneumatic ping pong launcher was also attempted. But the core issues with pneumatics still remained. Finally, a dual rotary launcher setup was developed as this was mechanically simple and allowed for precise velocity control
The design consists of a pivoting launcher with two rotary wheels. The wheels are mounted to high speed motors that have quadrature encoders. The speed of each wheel is controlled through a closed loop controller through the Arduino. The encoder output is read by the Arduino microcontroller, which controls the PWM of L298 H-Bridge. This PWM controls the average voltage provided to the motors, and therefore the RPM. A launcher mounted camera is then calibrated with calibration images to correct for distortion and find the camera matrix. The camera feeds information back to the central computer, which runs an algorithm to detect AR Tags and returns the translation and rotation vectors. These vectors are then used to adjust the yaw through the Yaw servo and pitch through the pitch servo which. Communication between the Arduino microcontroller and central computer is done through a serial bus link. The motors are powered through external 24 Volt rails and the rest is powered through external 5 Volt rails.
Here is the system in action, going through the following steps:
1. Calibrate camera with calibration image
2. Find targets in field of view, including their distance and relative position
3. Set launch velocity with the rotary wheel loops
4. Pivot yaw and pitch to first target
5. Load ping pong ball
6. Launch ball
7. Maneuver to new target
8. Load Ball
9. Launch
Results and Conclusions
There were a number of difficulties along the way. Multiple electrical components broke, the mechanical design was tricky to sort through as well. Ultimately, the system is actually remarkably accurate, and always is able to come within one meter of the target. The system cannot achieve perfect accuracy because it is effectively open loop once the initial angular changes are sent to the yaw and pitch servos. Additionally, the ping pong balls also do not launch in a straight line as the balls compress and then pop to either the left or right of the desired trajectory. Some nice to haves would've been a more rigid mechanical assembly and precise servos to allow for better trajectory control. Depth mapping and reload mechanism would've also been nice as well
Bio
Sagar Patel
M.Eng. EECS - Robotics
B.S. EECS & Mechanical Engineering
University of California, Berkeley
Likes building stuff.
Previously founded a hardware startup, designed robot end effectors at Applied Materials Robotics, and made surgical robotic arms at Intuitive Surgical
We Take Pride in Our Numbers
3
Failed designs
<1
Meter Target Accuracy
yes
Hot Glue Accidents
4
Critical Component Breaks
100 %
Chance of Termination