Potential Course(s) Implemented:

• First-year Engineering course
• Sophomore-year Engineering course
• Highschool STEM related courses

• Applying knowledge of mechanical forces and torque
• Practice approaching design challenges parametrically
• Optimize a product design given constraints
• Design a soft robotic system to accomplish a task
• Evaluating competitors and stategizing design

Pneumatic actuators convert fluid energy (typically compressed air) into mechanical motion [2]. In soft robotics, this energy is introduced into flexible chambers, causing controlled deformation rather than rigid movement.

One of the most widely used pneumatic soft actuators is the McKibben artificial muscle, originally patented by Richard Gaylord (1958)  [3]. When internal pressure increases, the braided sleeve constrains radial expansion and converts it into linear contraction.

As pressure increases:

• The actuator diameter increases

• The braid angle changes

• The overall length decreases

This produces controllable linear contraction similar to biological muscle behavior.

At a simplified level, the generated force is proportional to internal pressure and effective cross-sectional area:

Force ≈ Pressure × Area

While real behavior depends on braid geometry and material compliance, this relationship provides the foundational understanding for actuator force output.

As internal pressure increases from atmospheric to elevated pressure levels, the actuator contracts in stages. The relative pressure change determines contraction magnitude and force output.

This behavior is governed by:

• Internal pressure

• Braid angle

• Actuator length

• Material stiffness

Understanding these variables allows students to predict contraction force and displacement under controlled pressure inputs.

The McKibben muscle in this project is used to actuate a leg mechanism. The contraction force generates torque about a pivot point, producing motion at the foot.

When actuated:

• Muscle contraction produces a backward and downward force at the foot

• Ground reaction forces increase grip

• The system generates forward propulsion

When pressure is released:

• The return element restores the leg position

• Ground reaction shifts

• The leg resets for the next cycle

This alternating interaction produces locomotion.

To analyze the leg, we apply the basic torque equation:

T = F · d

Where:

• T = torque about the pivot

• F = applied force

• d = perpendicular distance from pivot to force line of action

It is important to note that d is measured from the pivot to the line of action of the force, not simply the point where the force is applied.

When the foot is stationary and the system is analyzed statically, multiple forces contribute to the torque about the pivot.

The combined torque relationship can be written as:

T = Ff df + Fb db + Fm dm

Where:

• Ff = foot reaction force

• Fb = return band force

• Fm = muscle force

• df, db, dm = respective moment arms

This equation accounts for all forces acting on the leg system and allows students to model equilibrium conditions and predict system behavior.

Through this analysis, students develop understanding of:

• Pressure-to-force conversion

• Torque and moment arms

• Multi-force equilibrium

• Mechanical advantage in linkage systems

• Converting linear contraction into locomotion

This theory connects soft robotics to core mechanical engineering principles including statics, mechanics of materials, and fluid pressure systems.

• Introduce McKibben muscle behavior

• Build and test artificial muscle

• Review project goals and competition criteria

• Develop preliminary robot concept

• Design mechanism for forward motion

• Consider directional control and reversibility

• Test under load conditions

• Develop mechanism to collect “food” tokens

• Optimize for reach and efficiency

• Validate performance through testing

• Improve reliability and structural stability

• Optimize collection + locomotion integration

• Iterate design based on test results

• Teams compete in timed challenge

• Points awarded based on collection height and quantity

• Bonus points for efficiency and performance

Competition Duration: 10–20 minutes
Higher elevation tokens = higher point value