9.3- Design Process
Brainstorming/Initial Idea Inspired by self-folding robotics research from MIT and Harvard, the fundamental challenge of this project was developing a minimalist robot that can transition between a flat 2D state into a functional 3D machine. From the outset, the design focused on utilizing a single motor and a 4-bar mechanism to achieve continuous forward motion using as simple a construction as possible. The team determined that a symmetrical slider-crank mechanism would be the most effective solution. This mechanism converts linear slider motion into vertical buckling , successfully forcing the flat chassis to transition into a rigid 3D structure—a process defined as Phase A (Extension).
Design Iterations
The linkage system and its joints required significant iteration to balance friction, structural integrity, and simplicity of motion:
Iteration 1: We initially considered a string & pulley system, but this was abandoned due to a lack of rigid pushing force.
Iteration 2: Our first rigid prototype utilized fully 3D-printed pins. This resulted in high joint friction and "slop," and the linkages cracked under torque.
Iteration 3: To resolve this, we iterated to a hybrid design featuring a laser-cut wood track with precise 8mm metal shafts and M3 screws, which drastically reduced friction.
Iteration 4: We shifted to a simultaneous dual-leg system to gain stability horizontally.
During prototyping, we encountered additional issues, such as incorrect angle stoppages and bearing friction where the link faces met. Furthermore, the configurations and angles of the rubber feet led to asymmetrical friction not occurring, which caused a back-and-forth motion instead of forward locomotion. Resolving these required extensive calibration and flex testing.
Here is an in-progress videos while we were turning the oscillations and the foot placement.
To overcome the physical failures observed in Iteration 2, we implemented a reinforced linkage design by increasing the inner bearing radius and wall thickness at the joint hubs to prevent cracking during metal shaft press-fitting and high-torque operation.
Some additional design considerations throughout the prototyping phase were some changes to the designs for the motor mounts for the arm design, changes to link 4 in linkage length for the final design, as well as changes to the overall plate design to support a dual-leg system which would become iteration 4.
Prototype Our designed physical prototype was built to prove the kinematic viability of Phase A (Extension). The system dimensions were finalized to guarantee a 1-DOF kinematic transition: L1 (Ground) at 100 mm, L2 (Lower) at 70 mm, L3 (Upper) at 50 mm, and L4 (Slider/Ground) at 20 mm. Gruebler's Equation confirmed that our primary system is M=1 (1 Degree of Freedom).
Final Design After validating the kinematics, the final design shifted toward motorizing the system and enabling Phase B (Retraction), which utilizes friction to drive a walking gait. The final design successfully employs an Asymmetric Friction Model. During the "Push Phase," high friction anchors the foot, propelling the body forward. During the "Pull Phase," reduced friction allows the foot to slide back and reset. To secure the power source for this continuous motion, we implemented an optimized base integration by improving the cradle geometry to securely anchor the 12V DC motor directly to the wooden base, minimizing vibration and power loss.