2.1 - Project Proposal Spring 2026
Introduction:
Traditional tabletop basketball shooting games are fun, but can get repetitive quickly. Most games use a simple lever with a spring to control the ball trajectory. Once the optimal displacement is found, every flick on the lever will cause the ball to go in the hoop. This predictability reduces the challenge and excitement of the game, since players can repeatedly score without needing to adjust their timing or force. As a result, the gameplay loses its entertainment value after the optimal motion is discovered.
Figure 1: Traditional Tabletop Basketball Game
Our team will fix these issues by creating two mechanisms: one to have the backboard move along the back plane in order to introduce an element of timing, as well as changing the shooting mechanism from a spring loaded catapult to a shooter that requires the human to input the force, via a crank, making it much harder to consistently replicate similar trajectories. The shooting can also be powered by a motor for demonstration purposes. By introducing motion and human controlled force input, the game becomes more skill-based as it requires players to adapt rather than rely on a single repeated action, which also makes the game more entertaining.
Problem Statement:
Launching a ball a decent distance requires force to be applied quickly in order to generate a large impulse and give the ball a high initial velocity. This can be seen in mini basketball arcade machines, where a lever with a spring is used to achieve this motion, but because the spring supplies the force, it makes the shooting extremely consistent with enough practice. This is because the force produced by the spring depends on its displacement and follows a predictable relationship, making each shot very similar. Part of the fun in shooting basketballs is getting good at using one’s strength, which spring-loaded shooters remove because the user is not directly controlling the force that launches the ball.
In order to create a more interesting tabletop basketball experience, the shooting power for the ball must come from one’s own hands. This means that human input will be used to launch the ball, which presents a couple challenges. Determining what type of input to launch the ball will be important as it requires different mechanisms. Human input is usually slower and limited in range of motion compared to the motion needed to launch the ball, so the mechanism must convert that motion into something faster. A simple rotating link as a catapult would be ineffective at transferring the input force to the ball because the motion and acceleration produced by a single rotating joint may not be enough to generate the required launch velocity.
The launcher must also provide a large amount of velocity with a small given input due to the size restriction of being on a tabletop. The mechanism must convert a strong input to a fast output to allow for launching the ball any sort of distance to reach the hoop. This means the system must coordinate multiple motions so that the ball is accelerated quickly and released at the correct angle. A mechanism using only simple joints may not be able to create this type of motion because it would either require a large movement from the user or would not provide enough speed at the output.
Another problem comes from the fact that there is little skill in shooting at a still target when the launcher is consistent. Introducing a timing element would add another degree of skill. If the target changes position, the user would need to coordinate both the timing of the launch and the strength of their input, making the game more challenging.
Mechanism Description:
In order to convert a small push into a large velocity, a lever system is required. However, the ball launching pad motion should be a rotation away from the person, so a simple lever cannot be used. In order to launch the ball at a high speed, two four-bar mechanisms are connected such that a rotating input creates a ‘pushing’ output, as seen below.
Figure 2: Idea
From the figure above, the player or motor will rotate the crank on the right, resulting in the ball obtaining a force Fout and a velocity Vout due to the motion of the leftmost link. The ball’s output velocity can be adjusted depending on the length of the output link.
Below are some sketches of mechanisms that generate interesting motion for the backboard. First, we explored parallelogram linkage systems, which produce circular motion. For horizontal motion, we would like to implement some slider crank below the backboard if possible, though we are unsure if this is feasible. A good backup option is a servo-actuated rack and pinion for a simple mechanism.
Figure 3: Backboard mechanism sketches
Below is a very rough isometric view of our tabletop basketball game, showing the launcher mechanism.
Figure 4: Rough Sketch of Potential Design
Scope of Work:
For this project, the goal is to create a tabletop basketball machine that shoots balls with the push of a four-bar arm. We aim to have a fully functional, playable tabletop game ready to demonstrate on demo day. To reduce the complexity of the project, the backboard motion will be a simple circle, with little to no analysis.
The main part of the project focuses on the launch mechanism. Ideally, it can be constructed so that a motor can be attached or detached at will, providing two modes: demonstration and gameplay. During the demonstration, the mechanism should consistently fire shots using motor power, while during gameplay, a human will turn the crank to launch the ball.
The ball will be a ping-pong ball for its lightweight, which reduces the force required for the ball to fly far. The game should be about the size of a standard monitor or laptop, but it can be slightly larger to accommodate the mechanism, if necessary.
The most important thing to analyze is the angular velocity of the output link, as it determines the initial ball velocity and the speed at which to turn the input shaft. Size may also be an issue, and the linkages must be made as carefully and as small as possible to create enough space for everything. Finding the correct link lengths will require much trial and error as the mechanism is relatively large, so working backwards from the desired output motion may be easier than starting from the input.
The mechanism will be 3d printed, while everything else will be cut from acrylic or wood. All mechanisms will be controlled via an Arduino and motors. The launcher and backboard may need encoders to get their position if fancier setups are desired, such as having the game always make a perfect shot.
Preliminary Designs:
In our preliminary design, we have 3 diagrams: the left four-bar, the right four-bar, and the full mechanism. The right four-bar is where the input force will be applied at O2, either from human input or from a motor. This then creates a pushing motion in the left four-bar system, which holds the ping-pong ball and then launches it. Overall, the full mechanism shows both four-bar mechanisms working in unison and the calculations that support our idea.