Introduction:
Our inspiration for this project was the toy desktop basketball catapults that many of us had as kids, similar to Figure 1 below. We wanted to improve upon this idea where we could create a robot that is able to shoot consistently from various angles and locations; as well as automatically reload the shooter. This is an interesting problem to solve because we will have to design the system in a way where we are able to get an accurate trajectory and snap of the ball so that it will be able to make it into the basket. Due to having it shoot from more than one specified location it will consist of multiple iterations and design of linkages to be able to get all the desired shooting points.
Figure 1: Toy Basketball Shooter
Problem Statement:
For our project, we have decided to build a basketball shooting toy that would be able to shoot from different distances and angles. Some complexities that arise in trying to solve this problem is getting precise motion control over the trajectory of the ball. Since we want the shot path to look like an actual basketball to get the desired motion of the ball we will need both rotational and translational motion which can't be created through simple joints. Another challenge will be generating the quick snap of the ball at the end of the shot to get a more realistic motion. For this we will need to be able to control the force and speed input into the linkage throughout the motion of the linkages and not just the initial input. Since we want to automatically reload the mechanism we also need to consider a system that can reload the shooter without interfering with any current motion occurring. This is so that if multiple balls are waiting to be shot it doesn't reload while another ball is in motion or not yet been shot.
Proposed Mechanism:
The proposed mechanism that could solve this problem is a four-bar mechanism that has a fully rotating input linkage, that would propel the basketball from a stationary position. The output link would slowly rotate backwards and have a ball loaded in and then release forward in a much quicker motion propelling the ball forward. Ideally the input is a constant rotational velocity allowing us to quickly shoot repetitive balls as it automatically reloads. The base would be able to rotate fully in order to shoot the ball from different angles. The base will also move forward or backward relative to how far we want our mechanism to be from the hoop. In addition to the base mechanism, we propose the idea of one of the links being of variable length allowing us to control the exit trajectory of the ball.
Proposed Scope of Work:
For this project, we are aiming to make the whole mechanism around the size of the desktop toys that inspired us. Its minimum functionality will be the shooting motion mechanism, that will launch a ball consistently into the hoop. We would like to be able to control the speed of the mechanism to also allow it to shoot from multiple distances. Another functionality that we want to implement is an auto ball return and load, so that the machine could shoot indefinitely with no human interference. The analysis needed before fabrication in order to successful implement our goals include the motion path of the output link. We can conduct both position and velocity analysis to see if that ball can consistently land inside the hoop. And finally we'll need to create a timing system that can determine when a shot is initiated and when a ball can be reloaded.
Preliminary Design Ideas:
Our preliminary design idea is to use a 4 bar mechanism to launch the ball. We sketched an example shot trajectory that mimics the smooth motion of a jump shot. This preliminary design does not include a flick at the end of the motion to create a realistic finish to the shot, but we hope to include that in our final mechanism.
Figure 2: Shot Path Using 4-bar Linkage