# Strength discussion about the human mimicking robot hand design

Hello Sketchup Folks. I am continuing my discussion about a design for a human mimicking robot hand. It doesn’t seem reasonable to create a robot hand that can mimic the human, but it does not have the strength parameters of a human hand. I am trying to create a robot hand design that has both dexterity and strength. I just finished a YouTube about the thumb, showing how it moves. Here’s that url: https://youtu.be/clQBrGGMY7o
I am planning the next YouTube to show how the the design has enough strength to support a 200lb robot, thus this would be 50lbs holding capability for each finger (thumb not included, I don’t think the thumb gives tension force support when the hand is on tension). I will see if I can add a Sketchup drawing file here.
Finger Force Vectors v29.skp (7.0 MB)
Hmmm… well that seemed to work. I find it fascinating that a ligament under the finger can act to allow the finger to support weight, that seems counter intuitive to me. The issue that conflicts me is whether the “curling up” feature requires the the attachment phalange (the most distal phalange) has to be of sufficient strength that it will flex 90 degrees and no more to withstand the pulling force of the ligament (113.7lbs), see the force discussion in the Sketchup file I uploaded). I found a bending force calculator: Bending Stress Calculator
and it says that most distal phalange will need to be a full rectangular cross section in order to withstand that pulling force, but as I study the drawing file, I am not sure if there is a bending force on the phalange or not. Weird. Anyway, the YouTube (I hope) on the strength discussion I can create it soon. I think I will divide it into two YouTubes, one about the finger curling up around a rod, and the other showing that the Cardanic joints are strong enough (if one uses the 2205 Alloy stainless steel to create them). Anyway, enjoy! Dr. Gray