Final Design Solution

Overview of Design

Scissor Mechanism within Unicorn Shell

The design of the turtle consists of a walking mechanism with a scissor linkage housed in a rigid turtle shell actuated by a McKibben Pneumatic Artificial Muscle which is controlled by a pneumatic circuit that is powered by a 12V air pump.

Walking Mechanism

The walking mechanism is consisted of three main components: A scissor linkage to generate locomotive motion, a base plate, and our unique "unicorn" turtle shell designed to accomidate the includion of the McKibben.

Scissor Mechanism

The McKibben muscle generates a very limited, one DOF range of motion that is dependent on its initial length. Our scissor linkage design overcomes these shortcomings of the McKibben by converting the limited McKibben contraction to a wide sweeping arm movement. Our design maximized the limited motion, converting 1cm of McKibben contraction to 3cm of arm movement, and the tips have an anisotropic surface casted from silicone.

Scissor State 1

In state 1, the McKibben is pulling on the bottom joint and the scissor pulls the arms forward

Scissor State 2

In state 2, the pressure in the McKibben is released, allowing the spring to contract and the arms sweep backwards, pushing the turtle forwards.

Base Plate

The base plate for the scissor mechanism constrains its motion in the axial direction, and is secured to the heated inserts inside the shell via M6 screws. It serves at a connection point for the shell and scissor, ensuring the components are fixed to provide movement to the entire turtle, and includes cutouts for the irreversible bearing wheel and the screws in the scissor.

"Unicorn" Shell

The shell is the housing for the walking mechanism, and is designed to direct the force produced by the McKibben to the spring via a pulley mechanism. Its shape utilizes the full available space inside the stuffed turtle, and its extrusion protruding into the head is what makes the design possible with a Pneumatic actuator. Cutouts were designed for the one direction bearing that maintains forward motion, and sinks were added in for heated inserts to secure the base plate. The shell is 3D printed out of PLA allowing for rapid iterations of the walking mechanism design, with a lid designed to protect the mechanism from loose stuffing inside the turtle.

Top Shell

Bottom Shell

Valve

The valve consists of a tube with holes to allow air to flow through at certain points, and a piston inside that blocks one pair of holes at a time to create two output states, and the position of the piston along the tube is manually controlled by the user. The valve is machined out of acrylic stock, and a viscous lubricant is applied inside to maintain the air seal between the piston and the tube.

Pneumatic Circuit

The pneumatic circuit works with the valve to control the air flow to the McKibben. Powered by a 12V DC air pump, the circuit consists the valve positioned between the pump and the McKibben, allowing the user to manually control the actuation and deflation of the McKibben, and thus oscillatory motion of the walking mechanism.

Two Air Circuit Configurations

Equivalent Circuit Diagram

In the above diagrams, the pump serves as a voltage source, the valve serves as a switch and the actuator acts as a capaciter.

Remote Control Kit

A remote control was designed to house the control system, and stow the wires of the pump. Cutouts were designed to allow for the interchangeability of different valves, and allows for future designs to be incorporated in.

Educational Curriculum

Our robot is designed to develop engineering and logical intution for children ages 8-12 through the five following learning objectives

Understand the movement that is happening within the turtle
Understand the parallels between the pneumatic circuit and electrical circuits
Understand the logic of the valve component is correlated to the logic in computer programming
Build their own scissor mechanism by observing the provided parts.
Understand how the anisotrpic surface creates friction.

The turtle comes with a workbook with diagrams to help kids understand the concepts and assemble it together, and information to help parents guide their kids in learning the engineering concepts.

Market Research

We conducted surveys with parents and educational professionals to understand the market need for an educational toy similar to this.

Valve and Scissor Kit

The circuit kit was curated, consisting of a scissor mechanism on a sled, with a McKibben positioned in line with the spring allowing for the visual understanding of the mechanism inside the turtle

This video shows how the turtle moves and the toolkits that come along with it.

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