When thinking up of ways to control and manipulate the hand I ideally wanted to keep it as simple as possible while also having the motion as human and dynamic as a real hand. Examples of this more mechanical focused motion can be seen in robots such as this one;
With that in mind I decided to not try and individually control the “knuckle” joints on each finger but allow one motor and an intelligent design capitalise on the dynamics of a material and its application. I liked the idea of a fishing rod and how when a force is applied to the end of the line it flexes and bends in proportion to that force. I wanted to try and apply this somehow in in my mechanical design.
While developing my own ideas I did some research to see if there were any existing solutions similar to my idea that had achieved my desired outcome and to my delight I found an ingenious design on instructables.com here .
I gathered as much of the materials I could and attempted my first prototype. Here is my attempt.
Step one: I picked up some flexible waven from an electrical wholesaler. I ideally wanted a smaller diameter but they didn’t have any in stock at the time and as this is for just prototype building I didn’t mind.
20mm diameter flexible waven
Step 2: using a scissors and a ruler I cut out desired lengths of the waven to roughly match the length of my own.
20mm diameter flexible waven
Step 3: using an electricians knife I cut notches into the fingers, each notch is akin to a knuckle.
Step 3: I measured out the required length of thread required leaving enough at the end for attachment and control later. knotting the top end and then threading it up through the middle of the waven. once it was at the top I looped it over and affixed it with some electrical tape to the outside ridges and to the inside wall to ensure it wouldn’t come loose
Measure required length and knot the top end
thread it up through the tubing
loop over the top and affix it to the outside of the tubing
Step 4: I repeated steps 2 and 3 for each finger and the thumb. It was then I realised that I hadn’t left the bottom of the fingers long enough to attach them to each other nor had a surface upon which to mount them so I had to improvise. Using another length of the waven I cut notches into and threaded all 5 lengths of twin through to a common point. and used electrical tape to affix them into place.
Step 5: I added a palm again using some of the waven and joined with more electrical tape. this was to make it easier to hold and also to see how I might have to construct the final hand.
Step 6: I mounted it on my soldering Iron station using its crocodile clips and added a “wrist” to aid in demonstration.
Mounted front view
DT009 Final year project
Here is a video briefly demonstrating full hand and individual finger control
This method of getting the fingers to bend is perfect for what I want to achieve. The range as seen in the video is limited due to my bad layout and construction of the hand as before mounting each to the palm section I tested each and their flexion went from straight vertically to a full arc (the tip was able to touch the base of the finger).
This experimental construction was very beneficial in getting a feel for the strength of the material and its functional abilities.
I am currently working on a second prototype to troubleshoot some of the issues in this version.