04.1 - Project Proposal
The development of automated and robotic systems are necessary for societal progress, with applications ranging from terrestrial manufacturing and skills training to the autonomous deployment and operation of scientific payloads on extraterrestrial surfaces. A common engineering challenge across these domains is the design of mechanisms capable of executing physical tasks with high degrees of precision, accuracy, and repeatability. In mission-critical applications, such as the robotic manipulation of geological samples or the deployment of satellite components, the predictability of a mechanism's dynamic behavior is mission critical.
To validate the analytical models that govern the performance of these dynamics systems, engineers frequently rely on the development and testing of laboratory-scale apparatus. These physical testbeds provide an essential platform for investigating the fundamental principles of kinematics, dynamics, and energy transfer. They allow for the empirical verification of theoretical predictions and the characterization of non-ideal behaviors, such as friction, material deformation, and the influence of aerodynamic forces, which are difficult to model with high fidelity. The development of robust mechanisms for projectile motion serves as a foundational exercise in the disciplined engineering practices required for these larger, more complex systems.
The primary motivation for this project is to design and create a mechanism that produces an adjustable and predictable trajectory for launching a small ball. Simple launch mechanisms, while functional, are often subject to significant sources of variability that result in a wide dispersion of projectile impact points. This variability stems from inconsistencies in the energy imparted to the projectile and from uncontrolled aerodynamic effects. The successful execution of this project requires a systematic approach to design that goes beyond basic concepts and into a more rigorous application of mechanism theory.
The core objective is to design a mechanism capable of imparting a consistent and predictable amount of energy to a low-mass projectile. This system will be a testbed for studying fundamental principles of mechanical engineering. The successful completion of this project will demonstrate competency in the following areas:
Energy Transformation: The analysis and design of a mechanism to control the conversion of electrical energy into kinetic energy.
Mechanism Design: The combination of a complex linkage capable of generating a prescribed, non-linear motion profile from a simple input.
Dynamic Analysis: The analysis of projectile kinematics and the characterization of deviations from an ideal ballistic trajectory due to aerodynamic perturbations.
Problem Statement
The objective of this project is to design and develop a robotic pitching machine that serves as a training tool for children learning to play baseball. The focus of this system is on helping young players improve their batting form, timing, and coordination rather than achieving high-speed pitches (e.g., 80+ mph). The machine should provide a consistent and automated practice experience while allowing for simple operation and adjustability.
To achieve this goal, several key technical challenges must be addressed:
Ball Launching Mechanism: The system must be capable of launching multiple wiffle balls consecutively at a controlled and adjustable velocity and frequency. The process should be nearly automatic, meaning the machine should reload and launch each ball with minimal human intervention.
Force Transmission: A reliable and repeatable method of transferring energy from the power source to the ball is required. The mechanism must generate enough force to project the ball at the desired speed while maintaining consistency across repeated launches.
Ball Path: The machine must ensure a consistent and predictable trajectory for each pitch.
This project cannot be effectively achieved using a simple mechanism due to the level of control, coordination, and repeatability required. Conventional pitching machines typically use complex mechanical lever arms, spring assemblies, or multi-gear flywheel systems. These designs are also intended for high-speed pitching, which is not the intent of this project.
In summary, developing a pitching machine for children requires a more refined and coordinated mechanism that prioritizes consistency and predictability over speed, ensuring a reliable and effective training experience.
Mechanism
The mechanism chosen to solve this problem is a combination of a 4-bar and a crank-slider with the ability to modify the angle of the sliding portion of the mechanism. This feature, combined with the complex motion of the end effector, will allow the user to adjust the launch angle, and therefore, the height of the pitch. The complex motion of the end effector imparts a ‘flick’ to the ball that is intended to replicate the rotation imparted to a human pitched ball, resulting in a consistent behavior from the ball. To dial in the output of the mechanism, a PID control system will be implemented at the software level to ensure a consistent output that does not overshoot.
The team expects that the two control parameters inherent to this mechanism will allow for a significant degree of tunability in the system. However, there are certain limitations that this project is likely to tackle in any significant manner. For example, implementation of a variable spin component to the thrown balls is beyond the scope of this project, and would likely require a more general-purpose robotic assembly to achieve.
Statement of Scope
The team will design a mechanism that has configurable launch velocities and angles for a standard whiffle ball (approx. 9 inches in diameter). This launcher will be controlled with two separate electromechanical actuators: a motor and a servo. The servo will be used to create a system with variable kinematics, while the motor will be used as the primary power source providing energy to the whiffle ball.
The team intends this mechanism to be user-friendly to adjust throw height and speed, as the target audience for the design is children between the ages of 7 and 11 or parents of those children. Typical examples of mechanical user-interface components that the team is considering include: knobbed potentiometers, haptic multiselect knobs, or a rotary indexing plate. The target for the range of launch angles is between 20 degrees and 60 degrees from horizontal; the target for the launch velocity is between 2 m/s and 8 m/s.
Preliminary Design
The team has a preliminary CAD design and angular/translational velocity profile constructed. They intend to add a treatment of rigid body contact between the whiffle ball and the mechanism in their next steps to help determine the range of achievable launch angles and velocities. From there, the team will iterate on the link lengths and relative positions to determine a combination of parameters that will allow the mechanism to fill the previously-defined velocity and angle targets.
Figure 1 - Preliminary Mechanism CAD
Figure 2 - Preliminary Velocity Profile Analysis
Figure 3 - Source Sketch for Velocity Profile Analysis