4 May 2009 Roko   » (Apprentice)

First Assembly of all Four Legs

Leg Parts straight from waterjet sized

Parts from water jet cutting

I received the remaining water-jet cut parts from Big Blue Saw a couple of weeks ago, and have slowly been working on taking them from rough water-jet cut pieces, to parts that will actually fit into the robot. The water-jet cuts are fairly rough when looking for precision parts, which is why a lot of work goes into the rough parts in order to get things to piece together nicely. To be honest, though.. I wish I had a CNC mill/router that I could have used to precisely cut the parts myself.

Waterjet edges sized

Water Jet Edge Finish

This isn’t to say that water-jet cutting is bad, but it is what it is. You have to account for the fact that water-jet cut parts aren’t 100% perfect to minute tolerances. Some of the issues I have with these parts are that the water-jet seems to have cut at a bit of an angle, which causes tolerance issues requiring some filing work to make sure everything fits together nicely. That said, I’m still happy overall with the water-jet cutting, and would recommend it to anyone trying to make more complicated shapes or numerous parts. I wouldn’t have been able to make all of the more complicated/curvy cuts by hand as precisely and quick as the water-jet service does. Plus, the edge finish has a pretty cool rough effect (Although I will be smoothing it out for this particular robot)

Four Legs in progress

Four Legs!

After a lot of work machining the parts, I finally put togethor the frame of the robot with all four legs for the first time (minus the robot’s feet, which I haven’t gotten to yet). There’s still a lot of tweaking and some machining I have to do on these parts before they’re finished, and then there are a lot of small parts that I still have to make. It’s been around 5 months since I started this project, and things are really starting to come togethor, but I’m thinking it’ll still be another few months at least before the robot even moves, let alone moves in a fashion resembling autonomous walking. At least it’s finally starting to look like an actual quadrupedal walking robot.

Stepping the shaft from 4mm to 3mm sized

Stepping the Axles

I also turned the axles on the lathe recently. Eight of the axles are simply straight 3mm shafts, however the four hip/base axles are 4mm in the center, and 3mm on either end with a center groove to hold an e-ring which is used to keep the flat-flex cable in place, and out of the gears. I still need to put the axles on the mill in order to flatten them out to keep set screws in place, and to drive the potentiometers I am using for axle position sensing. I’ll post more on those in the future when I get to that stage of the build

One of the other things I still need to complete are the motor controllers, and the actual robot’s brain (likely a Gumstix Overo, but I would have to make my own carrier baord). I have tweaked and fixed small bugs in the design of h-bridge prototype I built in the fall, however I want to move the same circuit into a shape that will fit into the actual upper-leg side piece. Luckily that gives me more space to work with than the current itteration of the board (which will be used for controlling the inner four motors), so it should be a relatively easy task once I find the time.

Syndicated 2009-02-08 22:07:44 from Roko.ca

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