Week 1: Project Proposal

Hands

My initial idea is to build a posable hand. They'll probably need to be motorized to fulfill the electronics requirement. I would like to allow for as much range of motion as possible, but I'm limited by the complexity of the mechanism I can create.

Mechanism

The two main choices for how the finger segments are connected are hinges and ball socket joints. Ball socket joints would allow for complete freedom of motion, and if the hand is restricted to just being posable, that would be a perfectly reasonable solution. I'd probably just use screws to tension the joints just like metal armatures for stop motion are built.



Ball socket joints actually offer much more motion than I need. Hinges allow for most of the motion I desire with just limited differences from actual hands. Hinges are much simpler to actuate using either a motor at the joint or by pulling tendons. I'll probably end up using tendons with springs and servos to actuate hinge joints. There is an existing project which does a similar idea, but only uses servos to contract the fingers with nothing keeping them extended. I'd probably use some springs to provide tension opposing the servos. I might choose to use the servos to extend instead of contract so the hand can have some gripping strength by loosening the tendons. There are also some projects focusing on the control side which will need some thought on my part.
http://archive.fabacademy.org/archives/2016/fablabcarnegiesciencecenter/students/170/mechanical_design.html
http://archive.fabacademy.org/archives/2016/fablabcarnegiesciencecenter/students/170/machine_design.html
http://fab.cba.mit.edu/classes/863.14/people/alan_kwan/Final%20Project.html
http://fab.cba.mit.edu/classes/863.11/people/daniel.rosenberg/p6.html
http://fab.cba.mit.edu/classes/865.15/classes/measurement/articulated-hands.pdf

I designed some finger segments using OnShape. Their version of parametric design is using configurations to provide lengths and other values. Those numbers can be adjusted later to tweak the model without having to start from scratch or dig into the model. Making changes is fairly robust for 2D sketches, but it starts to get a bit questionable for 3D shapes. Often, sketches based on faces are anchored to weird points. Sometimes if the lengths change too much, the entire model can break. This would be obvious in cases of impossible parameters, but it sometimes happens for no apparent reason.



.stl file

Stretch Goals

If the actual mechanism for the hand is working, it might be possible to route wires through the fingers for power and data. Adding additional mechanical features might also be possible. Finger Ideas:

Alternative Ideas