I. Introduction

We are creating a robotic crab. This will include an outer casing that will mechanically open as the legs are extended out. The legs will function as a Jansen Linkage, where there are two legs on either side, with gears and a DC motor driving the steps of the legs. Examples of this mechanism can be seen in Figure 1 and Figure 2. This robotic crab was designed with real-life crabs in mind. A crabs shell is meant to protect it from its environment, which leads to the creation of the outer casing design of our robot. The legs were also inspired by crabs as they allow the crabs to crawl in various terrains while having extraordinary stability.


Figure 1.	Figure 2.

The goals of this robot mechanism are as follow:

The bottom doors can correctly open
The robotic legs and base can support the weight of the whole robot
Can stably walk a defined length
Is fairly easy to build

There are several design considerations. The first is to make the linkages attached to the door open the door fully and correctly. To do that, we will have to make sure that our calculations are correct. Another important design consideration is to make sure that the legs fit inside the outer shell without any interference from the other components inside. We will also have to consider how to design the robot steps in a way that two of the legs on either side will always be in contact with the ground for stability.

We will know that the robot mechanism is a success if all the goals and considerations are met. The motion that we expect to see in the robotic legs (Jansen Linkage) motion is shown in the kinematic diagram shown in Figure 1. The motion that we should see in the shell is shown in the kinematic diagram shown in Figure 3. We will be using mostly wood from TIW to laser cut the shell and most of the Jansen Linkage. We will also use bolts and hot glue to hold everything together as well as 3D printed joints. We will be using pneumatic hinges used in kitchen cabinets for the bottom doors of the shell. We will use a stepper motor and lead screw to push the platform connected to the legs and bottom doors out.

Figure 3.