MK0M Initial Prototype

A project log for ARX Hand Project X1M

An advance modular 3D printed mechanical prosthetic

SupercellSupercell 05/21/2020 at 17:240 Comments

Initial prototype for a fully mechanical design. This prototype mainly looks into the viability and properties that a whippletree mechanism has on the actuation. 

The whippletree system that's designed into the palm consists of a rotating block with a channel for each pair of fingers, index-middle and ring-pinky.  Each channel allows for slipping between the pairs of fingers to provide independence between fingers when either is obstructed when closing. When either pair is fully obstructed, the rotating block allows for further independence between finger pairs.

The use of a whippletree allows for fingers to be independent of one another which give a more variable and conforming grip around an abject. For example in the case of holding a ball in the palm, the index and pinky will be able to surround the ball more tightly than if the fingers were dependant on one another. 

The whippletree design does however bring one downside in that it doesn't handle loads very well at extremities at pinky or index. An example where the hand may have issues is when it may be holding a bat outwards which places most of its weight closer towards the index. This issue might be due to how the whippletree can behave like a lever with reduced mechanical advantage when one side of the load is fixed. It might be possible to help reduce the effect by distributing the main actuation cord further out on the whippletree block.

Overall, the design showed promise as the whippletree was able to allow for a better conforming grip but at the cost of reduced strength against unevenly distributed loads across all 4 fingers. With the reduced strength, a pulley system for increased mechanical advantage is a must.