Hexabot: Build a heavy duty six-legged robot!

Step 4 Machine the motor linkages

After cutting and drilling the metal, you'll want to machine the linkages that connect to the motor and transfer power to the legs. The multiple holes allow for changing the step size of the robot (though you can't do that on mine, I'll explain why in a later step).

Start by cutting the 12" aluminum block into two ~5" pieces, then drill and mill the holes and slots. The slot is where the motor is attached to the linkage, and the sizing of it is dependent upon the shaft of the motors that you have.

After machining the block, drill two holes perpendicular to the slot, and tap them for set screws (see second image). My motors have two flats on the shaft, so adding set screws allows for extremely rigid attachment of the linkages.

If you don't have the skills or equipment to make these linkages, you could take your part drawing to a machine shop for manufacture. This is a very simple part to machine, so it shouldn't cost you much. I designed my linkage with a flat-bottomed slot (so I could secure it with a preexisting bolt on the motor shaft, as well as take advantage of the flats on the shaft), so that's why it needed machining in the first place. However, this linkage could be designed without a slot but rather a large through hole, so all the work could theoretically be done on a drill press.

The drawing I used for machining can be downloaded below. This drawing is missing the dimension of the depth of the slot, which should be marked as 3/4".

Comments

[m5industriesinc]

where did you guys buy the mill and how much?

[gesso]

4 flute endmill in aluminum... You make me cry a little sir (4 flutes can get filled with chips, 2 flute is preferred for alum). and beeswax works much better than tap magic for alum as well. just my 2 cents. Otherwise very awesome :D

[rpantaleo]

Huh, they never taught us that in the machine shop training course I took two years ago (4 flute vs. 2 flute). I definitely had some flute-clogging problems when I was milling those slots. Thanks for the tip!

[trebuchet03]

Kinda expensive - but extremely useful in matters like this :) Awesome project, however :) Did you do any kinematics on the linkages to determine step length, speed, etc? Just curious :)

[rpantaleo]

I wish I could say that I did - but I didn't. Everything was based on intuition.

[DELETED_lsloan]

(removed by author or community request)

[rpantaleo]

Actually, all the legs are the same length. The bolt that attaches each middle leg travels around a circular path (the size of this circular path is determined by where the bolt is attached to the drive arm/linkage, which is driven by the motor). So, each leg is not only moving forward and backward, but also up and down, and the up and down movement actually lifts the robot slightly when a step is made. By contrast, the front and back legs are fixed to only rotate about their axle/bolt, so they only move forwards/backwards. The principal reason the robot can move is because of the up and down motion of the middle legs.

[DELETED_lsloan]

(removed by author or community request)

[rpantaleo]

It can turn either way that you described, but moving the sides in opposite directions works best.

[DELETED_lsloan]

(removed by author or community request)

[mrdspecs]

You've got my vote for the Craftsman contest as well!