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Thursday, September 3, 2009

¡Aye! Robot....

Working on the robot some more and trying to figure out a way to add the Turn Axis to the leg assemblies using parts that I have on hand... this is turning (no pun intended) out to be a bit difficult. I have four legs and I only have three bearings in my junk pile that have extended inner races and a flange to keep them in place. The second prototype leg that I built had a 'yoke' for the Rotate Axis that I made by bending some sheet metal. That worked fine for both prototypes in fact and can be seen pretty well HERE. Its the part that is acting as the base with the legs hanging over the table in the pictures.

I think some of the stability and jitter problems were enhanced by having this piece made in such a flimsy way and I'm sure that trying to make a robot walk using a piece like that won't work. In fact I am having some doubts if this think can ever walk! So to be sure that i was going to have something rigid enough to allow the legs to pivot and not bend and give I decided to use extruded aluminum box beam for this part. Besides I happen to have some extruded aluminum box beam laying around so i cut it in one inch lengths on the band saw.

The box outside dimensions are 3" X 1.5" X 0.125thk wall. Pretty hefty stuff for what I am doing but that is what I have laying around and the wall thickness is enough to drill and tap into. But just having it is one thing and figuring out how to mount a bearing (or make one) so that it can rotate is another. I'm still left with three bearings of the right size and four legs. Maybe I'll get lucky and find something that I can make some bearings out of or another approach. Still in thinking about the walk cycle and how much rotation I'll need is making me wonder if a four legged robot is going to be stable enough. Three points define a plane and keeping the center of gravity in the triangle means it won't fall over. But how will a four legged devise walk? I suppose that I will find out when it falls over the 40th time or so.

I cut one of the sliced box beam pieces and drilled and tapped. The leg assembly on the left sits in this and rotates down. The prototype sheet metal one is in the upper right of the picture and some shoulder screws and a bearing that would be perfect if I had more.

Meanwhile I'll keep building parts and putting stuff together. If I don't find anything laying around that I can turn into four bearings I'll break down and go buy some hobby bushings or bearings... Having three perfect bearings when I really need four is frustrating!

At some point soon I'll do a layout in CAD or on paper to work out how this thing will walk. I'm getting close to having a good idea of how much it will weigh and more importantly how high up the center of gravity will be.

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