Ball on Small Plate

Ball on plate in action. A simple interface is made to adjust the target position and circle radius.

Introduction

Ball on Small Plate is built with a Raspberry Zero, a camera, two servos, a STM32F103 board, and is capable of setting target coordinate, circling around the center with adjustable radius. This project is a work of team of 3, which includes shicaiwei123 and yoyolalala. Code and documents are available here. Platform details are discussed here.


Demo


Mechanical structure

First version

The 20cm*20cm plate is made of 1mm black glass fiber board. In the first version shown in the video, the plate is covered with white paper to provide more contrast between ball and plate. Below shows the original plate.

Deisigning the mechanical structure
Deisigning the mechanical structure

The plate is supported with a universal joint in the center and has 2 degrees of freedom. The angle of the plate is controled by two servos with ball joint rods connecting the servos and the plate.

Installation of plate and two servos
Installation of plate and two servos

In this first version. The camera is fixed to the base, which requires extra procedure to segment the plate from background and warp back to squre. This introduces noise to the positioning of the ball, which is the major reason for the jittering in the video.

Installation of camera and Raspberry Pi Zero
Installation of camera and Raspberry Pi Zero

Second version

By fixing the camera to the plate with carbon fiber tubes, we managed to avoid the noise. The Raspberry Pi 3b is hanged beyond the camera to reduce the load on the servos. The plate itself is also changed to yellow thus no paper is needed. This reduces friction between the ball and the plate.

Camera is connected to the plate to reduce jitter
Camera is connected to the plate to reduce jitter

A ring light is installed around the camera for better illumination.

Camera and LED installation
Camera and LED installation

Below shows the PCB board installed on the base, which is later used in project Ball on Big Plate.

PCB mother board
PCB mother board
Cheng Zhang
Cheng Zhang
Graduate Student

My research interests include 3D reconstruction, 3D detection, 3D scene understanding, etc.

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