13.3 Project Prototype and Iteration Documentation

Our prototyping process consisted of developing our Jansen linkage mechanism intended to push a skateboard forward. We started with simple physical prototypes and gradually increased complexity as we tested motion, geometry, and structural reliability.

Our first prototype was fully 3D printed and focused primarily on understanding the geometry and physical construction of the Jansen linkage. This first design was built much smaller than required, which made it difficult to evaluate realistic motion and force transfer. The reduced size also caused challenges in maintaining precise link spacing, and several joints interfered with neighboring links during motion. Because of the small scale, we determined the links would not move as smoothly as expected. A photo of this iteration shows the compact structure and our early attempts at establishing the linkage geometry and validating the basic motion of the mechanism.

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3D printed links from first design. For reference on size, the holes themselves where only 3 mm

In the second iteration, we scaled the mechanism to a larger size in order to better visualize the walking motion and test its ability to push an external object. For this version, the links were laser cut from 6 mm acrylic, which allowed us to create more accurate link lengths and hole placements compared to our earlier 3D-printed prototype. This prototype, which was demonstrated during our prototype demo, successfully showed walking motion but was ultimately slightly too large for practical mounting on a skateboard. The increased size created additional torque demands on the input crank and made the structure more difficult to stabilize during operation. Despite these challenges, this iteration allowed us to evaluate motion more effectively and confirmed that the overall walking behavior of the Jansen linkage was achievable.

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Second Prototype with acrylic links

During these early builds, we encountered several geometry-related challenges, particularly in achieving smooth motion without collisions. Many of the links initially collided or interfered with one another due to incorrect length relationships or improper joint placement. We addressed this by repeatedly adjusting link spacing and with 3D printed spacers, link placement on joint and testing motion manually. These repeated adjustments were critical in improving motion smoothness and ensuring that each link followed its intended path without contacting neighboring components.

Our early designs used nails as rotational joints; however, these joints tended to spin loosely and gradually loosen during motion, reducing accuracy and stability, and allowing motion in unintended plane. Additionally, we attempted to stabilize the ground links using 3D-printed handles, but these proved ineffective for maintaining consistent alignment. These limitations highlighted the need for more precise and durable joint and mounting solutions in future iterations.

Another focus of our iterative process was evaluating materials and manufacturing methods. Initial links were made from easily accessible materials to allow fast modifications, but several links experienced bending or breaking under load. Based on these observations, we plan to transition to wider laser-cut links in the final design. Laser cutting will allow us to increase the width of the links while slightly reducing their length, improving overall strength and durability while maintaining proper geometry.

For the final design, several improvements have been identified based on lessons learned during prototyping:

• A gear will be added to the input crank to provide more controlled and consistent motion.

• The width of the links will be increased while slightly reducing length to prevent breakage and improve structural strength.

• Precision holes will be laser cut to match bearing dimensions, and metal rods will replace nail joints to prevent loosening and ensure smoother rotation.

• The previously used 3D-printed ground supports will be replaced with rigid links mounted directly to the skateboard structure.

• The A and L link lengths will be combined into a single link using their calculated hypotenuse length to simplify geometry and reduce potential interference.

• A smaller skateboard will be used to reduce the force and torque requirements needed to move the system.

• A dedicated mounting structure will be designed to securely attach the mechanism to the skateboard.

For our current prototype, the primary goal was simply to demonstrate the motion of the Jansen linkage leg, specifically the pushing leg that will ultimately generate forward motion for the skateboard. While this version was not fully integrated with the skateboard structure, it successfully demonstrated the feasibility of the walking motion and provided valuable insights that will guide the development of the final design.

Bill Of Materials: