Let's Make Robots!

TJ snow angels and pulley kebab


Today I decided on the arrangement of my Theo Jansen legs on the side of my future robot. I place one prototype on a piece of cardboard and traced the outlines with the legs in all possible positions. Like a robotic snow angel. This way I know what the "footprint" of the entire mechanism against the side of my robot will look like. And if one leg will hit a neighbour when flailing about.


Turns out that the belts I bought are just a little longer than the shortest possible distance. Center to center they will be spaced 28 cm apart. The board you see will be the flank of my creature and measures 80 cm. The rear and front legs will overshoot this board by just a tiny few cm.

Because I do not wish to run six shafts all the way starboard to port side, I came up with a "double hull" idea. Each flank will consist of two sheets of plywood, seperated by a piece of pine of the exact size required to house two pulleys. Here is a prototype of my pulley kebab.


From left to right you see: a bearing (buried in the plywood), brass washer, two aluminium timing pulleys, a brass washer, a bearing and a collet.

The legs will sit left in the picture, hugging the outer hull. In between the sheets of ply sit the pulleys and belts. Protruding on the inside is just short stub of the shaft. I think. Not decided yet.

Still to figure out: a way to make a crank that will sit firmly on a 4 mm steel shaft. And I have no idea how much torque it will endure. Somehow plywood feels inadequate.

[edit 24 april: trying out my new Theo Jansen banner]

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Aluminium is softer than brass. If your tools are limited to a jigsaw, a drill press and some hand tools then I would stick with aluminium.

Note: When we say aluminium it is actually an aluminium alloy you are buying. Pure aluminium is too soft for most uses. Different aluminium alloys have varying degrees of hardness. You may want to google the subject. I think your local store will just sell a general purpose grade of aluminium but it wouldn't hurt to ask after some research.

They do mention the exact composition of their alloys. For flat bar, I can choose between two or three alloys. But I will probably pick the most common kind that has the right dimensions.

Yeah, you'll want to stick with 6061. The other relatively common alloy, 7075, is harder, and works well in cases where you need a hard surface but can't anodize. Here's a really good guide to the various aluminum alloys (they also tell you all about the various alloys for most other common metals too, it's a great site).


Second time I read this.

And I want to comment.

But I need words.