13.1 - Project Proposal Spring 2026
Introduction
Skateboarding is a pretty complex activity as it requires a good combination of both coordination and balance to go on a rolling platform, riders have to propel the board by pushing against the ground while remaining stable on the moving deck, so in this project we aim to tackle the idea of making a mechanism that can automatically propel a skateboard by making a complex position and velocity profile of a leg that pushes against the ground, as this mechanism has to operate while attached to a moving base and apply force repeatedly in a coordinated motion profile it presents a very interesting kinematic and mechanism analysis.
Description of the Problem
The goal of this project is to design a mechanism that produces a cyclic pushing motion against the ground while mounted to a skateboard. The mechanism must generate a specific end-effector trajectory that propels the board forward.
The end effector must move downward and backward relative to the skateboard to generate propulsion, then lift off the ground and move forward to reset, repeating this motion continuously while maintaining stability on the board.
This requires a nonlinear kinematic trajectory consisting of a pushing phase and a recovery phase. Simple revolute or prismatic joints produce only circular or linear motion and cannot generate the required asymmetric ground-contact path, so a multi-link mechanism is needed.
Key challenges include maintaining a stable attachment to the skateboard frame, generating enough backward ground force to propel the board, and ensuring the foot clears the ground during the return phase so it does not create friction that slows the board. The mechanism must also coordinate link lengths and joint motion to produce the desired push cycle, making the problem well suited for linkage synthesis and kinematic analysis. Additionally, force constraints must be considered so the motor can move the crank and links effectively while the links remain strong enough to push the skateboard but light enough for the motor to drive.
Description of a proposed mechanism that could solve this problem
Our main idea for this is to have a single leg linkage that was inspired by the Jansen walking mechanism, which uses a set of interconnected links so that natural, pushing foot motion is produced.
This proposed mechanism consists of a grounded frame which would be attached to the skateboard deck, a rotary input link which is driven by a motor, a multi-link leg assembly and an end effector foot.
This mechanism replicates the human knee motion as when the crank rotates, the linkage keeps the foot relatively flat during the push phase and then lifts it during the return phase, making it well suited for this application.
Another idea would be to use a four-bar linkage with an extended coupler link, as this would be a simpler mechanism that could generate a similar pushing trajectory.
Proposed scope of work for final project
Our planned project steps include:
Conceptual Design: Select the mechanism type and sketch possible linkage configurations and mounting locations.
Kinematic Analysis: Perform position and velocity analysis of the mechanism, simulate the foot trajectory, and optimize link lengths to achieve an effective pushing motion.
Mechanical Design: Design the linkage system and mounting frame, select materials, and determine joint types.
Fabrication and Assembly: Build the linkage components and mount the mechanism securely to a skateboard platform.
Testing and Evaluation: Observe the resulting motion, measure the effectiveness of propulsion, and compare the actual foot path to the predicted trajectory.
Due to time constraints, the project will primarily aim to demonstrate a single functioning leg mechanism capable of producing a pushing motion. If additional time allows, the system could be expanded to include improved propulsion efficiency or additional legs. If we have enough time we could also include automation, stopping and starting leg movements with an arduino and controller.
Preliminary design ideas
Our preliminary design is focused on evaluating the movement path of a Jansen Style linkage, including the link lengths and angles for desired motion (position and velocity analysis). Additionally, the basic structure outline requires a vertical frame mounted directly to the skateboard deck, which would serve as a ground link. In order to reduce the wobble of the moving platform, the leg assembly will be placed as close to the board as possible with substantial structural supports. We are also considering designing a specialized end-effector pad to ensure sufficient friction when pushing against the ground. To ensure proper functionality, our initial design phase includes verifying the mobility of the multi-link Jansen assembly to be exactly 1 degree of freedom using Gruebler's equation, and ensuring the input crank satisfies the Grashof condition for continuous rotation.