15.1 Initial Proposal
Introduction
We will be creating a robotic crab that can scuttle side to side and reverse direction. The linkages in the crabs legs will be designed such that there is a period of ground contact and a reset period. To remain stable this motion requires some legs to maintain ground contact and others to be in their rest period. The crab presents a number of design problems that need to be addressed to get a realistic and natural motion this includes: the dwell time for the linkage for ground contact, the stride length, minimizing the number of actuators, optimizing the number of legs, creating a complex and synchronous motion, and designing a position profile that meets our desired output.
Problem Statement
Crab walking requires precise coordination as the motion of each limb must be synchronized with delays to one another to ensure continuous motion. Challenges also include finding balance during movement, as the supports (limbs) will either be in contact or not be in contact throughout the movement. For these reasons, we cannot use simple joints for the motion.
Mechanism
The basic mechanism will consist of 3 legs on each side synchronized so that there are always 3 contact points with the ground, this imitates the walking mechanism of a king crab and guarantees stability. The mechanism will be timed with a crank on either side of the system moving three Klann linkages each. Then in order to change direction a mechanical reversing system will be implemented to reverse the direction of travel after a fixed number of revolutions/steps. This allows for the complete removal of electronic controls from the system instead, using just a motor and mechanically controlling everything else.
Proposed Scope
We will first work to analyze the position P on the end of one link (i.e. the “foot” of the crab) to determine distance from the main body and linkage lengths/angles, then work on time delays between multiple links on one side of the crab to ensure constant motion in both lateral directions. We intend to have a fully functional, self-running mechanism in the end.
Other Proposed Leg Mechanisms
Oscillating Motion