5-bar Linkage Quadruped Robot

2/2026 - Present

Demonstration

Gait Logic: Swing, Stance, and Cycloid Motion

Each leg alternates between two phases:

Swing Phase: Leg lifts off the ground and moves forward.
Stance Phase: Leg stays on the ground, moving backward to push the body forward.

The foot trajectory follows a cycloid curve — the natural path of a point on a rolling wheel. This creates a smooth, bell-shaped lift that starts and ends at ground level, reducing mechanical shock and jerking.

To convert foot position into servo angles, I use inverse kinematics (IK) — calculating the required joint angles in real-time rather than using pre-recorded lookup tables. This keeps the motion fluid and adaptable.

Project Repository

All code, 3D models, and wiring details are on GitHub:

https://github.com/jaydentheinventor/5-Bar-Linkage-Quadruped-Robot

using GeoGebra for simulation

Leg Design

Using flexible Thermoplastic Polyurethane (TPU) for my robot's feet is an excellent choice to absorb vibrations and provide traction. However, 3D printing this material proved to be quite challenging; it requires elevated print temperatures and is highly hygroscopic (meaning it rapidly absorbs moisture from the air).

Beyond keeping the filament dry, I found that fine-tuning my slicer settings was critical to overcoming gaps and separated wall lines on the lower layers. To tackle these issues, I implemented the following adjustments:

1. Lower Coasting Volume

My Fix: I reduced my Coasting Volume (cutting it roughly in half to around 0.02 mm³ – 0.05 mm³) and lowered the Coasting Speed.
Why it works: Rigid filaments build up intense nozzle pressure, requiring a high coasting value to prevent blobs at the end of a line. In contrast, flexible TPU loses its pressure almost instantly when the extruder stops pushing. Lowering my coasting volume ensured the extruder kept pushing filament closer to the actual end of the wall path, eliminating gaps while still preventing a blob at the seam.

2. Increase Initial Layer Line Width

My Fix: I set my Initial Layer Line Width to 120% – 130% in my slicer.
Why it works: This forces the printer to output wider, thicker lines on the very first layers, physically squishing the plastic together to bridge any gaps between the perimeters.

3. Increase Initial Layer Flow (Extrusion Multiplier)

My Fix: I raised my Initial Layer Flow or First Layer Extrusion Multiplier to 105% – 110%.
Why it works: TPU acts like a flexible noodle and compresses inside the extruder gears, leading to an initial lag in material delivery. Increasing my first-layer flow compensated for this compression and prevented early under-extrusion.