Picture of Simulation of Robotic Arm Gripper
Every year, I participate in a challenge called the FIRST Robotics Competition. I and my team must come up with a robot design that must meet certain specifications in order to compete successfully. Most years, my team has built prototypes to see whether a design has merit. Here, I show an alternate method, using a physics simulation application, Autodesk ForceEffect Motion (available on your favorite iOS device), to test designs in a similar manner.
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Step 1: Concept

Picture of Concept
As an example, suppose I was to build a mini robot arm to pick up a chicken egg. We would like to pick up the egg easily, so we will require there to be an inch of clearance on each side when the gripper is open. Such an arm might look something like this. Some considerations must be taken into account in order to pick up the egg successfully.

First of all, the arm must be able to pick up the egg without dropping it. Secondly, the egg must not break when it is picked up. As a result, there should be a range of forces we can use on the egg.

The design of the arm will consist of two four-bar linkages for the two sides of the gripper, with a piston supplying the force. The head of the gripper will be coated in rubber.

Step 2: Simulation - Check range of motion

Picture of Simulation - Check range of motion
Now, we have a potential design that we would like to see if it meets our criteria. Here is the design sketched using Autodesk ForceEffect Motion.

To see whether it will pass our one-inch clearance requirement, we can trace the tips of the gripper to see its arc of motion.  

Looking at the graph information, we can see that the peak displacement for each side of the gripper is 1.018”, so this design does indeed pass our clearance requirement.