Robohand

The following is an overview of how I went about about creating Hollies unique Robohand.

The first step involved Hollies father creating a series of alginate molds of both her left and right hands. Instructables gives a large number of tutorials on this process, with a number of them being focused on hands.

He then used these alginate molds to make plaster models of Hollies hands.

Design Plaster cast

I then took these plaster models and used a technique called Photogammetry to turn these models into Computer models. The particular tools I used were 123d catch and Autodesk recap 360. These are both free Autodesk products that let you turn a number of photos into a 3D model.

Design Photogammetry fullNow the hand looks a little different from the white plaster cast.

I used a grey paint to bring out the contrast in the hand.

I also added coloured dots to the hand which gives myself and the software reference points to find in 3D space.

The final addition I made used a giant coloured QR code, which the model rests on. The QR code serves the purpose of helping the software know the surface is flat, as well as giving reference points to pick. The colour is also there to help me identify which precise square I’m using as an alignment mark. Trying to identify a black square out of many black squares is needlessly difficult.

The resulting model looks something like this:

Design 3D scan model

Not very useful, so I used another free bit of software called Blender, to edit out the parts of the mesh I don’t need.

Blender gave me some useable models, but photogammetry isn’t perfect and so I used a somewhat less free piece of software called Zbrush to tidy things up further, as well as to re-position the fingers.

Design Blender Scan cleaned up right Design Blender Scan lower res

Quickly back to Blender to create a printable model,to scale things correctly and to mirror Hollies full hand. Then I printed out the first models on my Lulzbot printer. This gave me a direct comparison to the plaster cast hand to check.

IMG_1605a

I will describe how I combined the two models to  create the fitting hand in Part 2