Ãœberclocker Update 10: How the Hell am I going to put this together Edition

Monday, July 21st, 2008 @ 0:02 | Bots, Project Build Reports, Überclocker

There’s a very good reason why most real engineering groups and companies have multiple designers and some times even dedicated review committees – so one dude doesn’t make half of whatever is being engineered at 4am and absentmindedly forget to account for how it will attach to the other half.

I’m starting to run into little episodes of “Wait, how am I supposed to assemble this?” when putting finished parts together. Barely-accessible screws , questionable attachment methods, and mismatched hardware and holes to name a few…

Good CAD programs (like CATIA) actually have tool clearance detection and machining simulation (helping also to avoid “Wait, how the hell am I supposed to make this?” syndrome). Having messed with CATIA some, I will only say that its user interface designer needs to be brutally beaten with a monocrystalline turbine blade.

Recapping the weekend of work…

The 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.

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.

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.

Before starting, I gave the mill head a quick tramming (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.

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.

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 Zoneâ„¢ where the two straight lengths met which would always hang off the edge of the vise. And thus there was chatter.

The second one was better, since I figured out a better way to stuff it in the vise, but a small Awkward Middle Zoneâ„¢ still remained.

Yes, proper procedure is to mount it straight to the table with clamps, but that’s too much effort. It’s really shiny, however!

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.

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.

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.

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.

Mounting the assembled fr0k base to the frame. Hey, the interior is now totally enclosed!

Final assembly of the fr0k arms. It’s shiny – absurdly shiny, with both machining marks and the polished aluminum surface.

And so, Friday night’s Pretend-O-Bot is a second clampbot salute, only slightly less rigged. It’s looking almost finished…

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 that MITERS has around, and design a bracket for it to mount on.

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.

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.

In another episode of “How the Hell am I going to put this together?”, I realized that several holes on Ãœberclocker were spec’d for different screws than I had purchased, like the rotating hinge for the clamp arms. I needed a half inch long shoulder screw with a 1/4″-20 end thread for this one… but alas, none were to be found in the pile of random screws and bushings.

I have a feeling that Ãœberclocker is going to be a very difficult bot to service once assembled. Here’s hoping it NEVER breaks.

And the last piece for Sunday night is the beginnings of the clamp actuator. The waterjet-cut raw pieces were drilled, milled, and threaded to final spec. Go figure, I’m missing the proper spacer to actually mount it.

No Pretend-O-Bot for Sunday night, since… well, it looks the same. This week is the LAST THREE WEEKS(!) before I leave for Atlanta, and I only have three more full weekends to make this thing work. Where did all the time go? Why does class start in 6 weeks?

Bot on!!?

 

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