Thursday, May 6, 2010

Team K - kakorrhaphiophobia

Main Design Concept

Basketballs are primarily meant to be shot using human hands. However, the human hand and arm is very complex to replicate using mechanical parts. As such, alternative solutions for launching objects needed to be developed. Our team chose to focus on a simple design, with two spinning wheels that would launch the basketball forward. The basketballs would be pushed from their hopper into the spinning wheels by a servo motor. The entire system would be rotated using a second servo motor. Sensing the distance to the basket was accomplished using a sonar sensor and the launch velocity of the DC spinning motors was controlled via PWM.

Figure 1.Overall view of system

System Overview

Figure 2.Aiming Subsystem

The aiming system was composed of one servo motor and caster wheels. The servomotor was chosen based on its torque and ability to accurately position the system without needing calibration every time power is lost. The servo motor is connected directly to 5V of power and is commanded using a PWM signal from the PIC microcontroller.

Figure 3.The Four Orders of Lauching Subsystem

The launching system also uses a servomotor to push the ball in to the spinning wheels. A servomotor was chosen for this task for the same reason as for the aiming system. Primarily because it did not require calibration and because of its high torque. Like the other servomotor, this one was controlled via PWM. This servo was used to push the balls from the plastic hopper into the spinning wheels.

Firgure.3 shows the four order of the loading mechanism. Figure. 3.1 indicates the initial setting of shooting. The two balls are laid in vertical way along with loading mechanism. When the system makes the first shoot, the second ball is located on push box as Figure.3.2. It makes the two balls be separated. As the pusher goes back, the second ball drops between the ball holders due to the gravity like Figure.3.3. Finally, the system makes the second shoot as Figure.3.4.

Figure 4. Devantch SRF05 Sonar Sensor Module

In addition to the servomotor, the launching system also had two BaneBots DC motors with planetary gearboxes. The speed of these motors was controlled using the motor controller board and a PWM signal. The motors were given a 12V signal which was switched on an off for different periods in order to obtain the desired speed. The wheels attached to these DC motors were also from BaneBots and were attached directly to the output shafts.

The sensing system was composed of one module: the devantech SRF05 sonar sensor. This was controlled using digital inputs and outputs from the PIC microcontroller. A high signal was sent to one pin and then immediately another pin would go low. A timer is started when the first high signal is sent. When the second pin goes from low to high, the timer is stopped. Using the time from the two signals, we can determine how far away the wall is from the sonar sensor. This was output in centimeters from the code.

How the System Works

Figure 5. System Flow Chart of the System

Figure 6. User Input Panel

The flowchart above gives a full overview of the system. Users should input the lateral distance. Then, using the sonar sensor, we can measure the distance to the hoop and can calculate the proper PWM for DC motors and the servo motor. Then, the pushing servo motor will push the ball to the wheels and shoot the ball.

Team Members and Roles
Byungjun Kim (MechE)
Jongho Lee (MechE)
Glenn Stroz (ECE)


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