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<\/a><\/p>\nThe main pivot shaft for the fork assembly. Made from a 3\/4″ diameter round of aluminum that was 800-grit-sandpapered to just under .750″ to fit through the bushings with some wiggle room, then milled appropriately.<\/p>\n
I chose to go with a live shaft over my usual preference for dead shafts since I wanted both fork arms to take the stress of lifting an opponent. Whether or not this decision will haunt me later – like the bot sagging in the middle just enough to jam the live shaft in bushings – I will have to see.<\/p>\n
Taking .015″ off the 0.515″ thick raw waterjet-cut pieces to make them (essentially) .5″ thick. I could live with a thousandth or two like most half inch plate stock, but not what amounts to 1\/16″ of extra width over the entire fork assembly.<\/p>\n Before starting, I gave the mill head a quick tramming<\/em> (squaring), since I had used it to cut angles. Having a mill head “out of tram” or not square with the table will cause all your parts to become out of square. Successive, offset passes will have a sawtooth-like texture and won’t be smooth.<\/p>\n I did a rather hasty job, since I didn’t really care that much , so there is still a very, very light unevenness in the surface as the picture shows.<\/p>\n Planing down the fork arms was a little more interesting. These things are about 16 inches long and rather difficult to grab with a vise. I could machine one long section at a time, but there was an Awkward Middle Zone\u00e2\u201e\u00a2 where the two straight lengths met which would always hang off the edge of the vise. And thus there was chatter.<\/p>\n The second one was better, since I figured out a better way to stuff it in the vise, but a small Awkward Middle Zone\u00e2\u201e\u00a2 still remained.<\/p>\n Yes, proper procedure is to mount it straight to the table with clamps, but that’s too much effort. It’s really shiny, however!<\/p>\n Putting the Giant Set Screw hole into the top of the fork arms. I’m not going to show you how I actually did it, of course, and instead show a pre-process picture involving an edge finder.<\/p>\n So being satisfied with the arm work for the night, I turned my attention to assembling the drivetrain in its final configuration. It does seem like I will need a low-side tensioner, since with some running-in the belts began to stretch and started skipping on the motor pulley.<\/p>\n This is bad, so I’ve orderd some more little random rollers and bushings from McMaster to mount on the front. Testing showed that this “low-side” tensioner adds just enough tension to stop the belt from skipping.<\/p>\n Test-assembling the fr0k base structure. This was the first episode of “How the hell am I going to put this together?” – I won’t be able to reach the countersunk screws on the inside front without some sort of right angle ratchet or ball-ended wrench.<\/p>\n Mounting the assembled fr0k base to the frame. Hey, the interior is now totally enclosed!<\/p>\n Final assembly of the fr0k arms. It’s shiny – absurdly shiny, with both machining marks and the polished aluminum surface.<\/p>\n And so, Friday night’s Pretend-O-Bot is a second clampbot salute<\/a>, only slightly less rigged. It’s looking almost finished…<\/p>\n What’s the extra hole on the end of the main shaft for? A potentiometer, of course, to keep track of the arm position. I’m not running any more open-loop appendages on the bots if I can help it. Eventually, I will settle one of several hundred trillion potentiometers<\/a> that MITERS has around, and design a bracket for it to mount on.<\/p>\n Alright, back to it. Each arm motor has a single output bearing, so I broke out the boring head to make a pocket for it.<\/p>\n I love the boring head. Here’s a clean “Loctite Finish” on the bearing. A Loctite Finish is a very close-toleranced seat or hole which lets the object to be mounted slide in with only a light push. A drop of green Loctite will then retain the object forever.<\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n