I have taken over 100 pictures of the build. I take an excessive amount of buildpics.

This is actually not a bad thing. I have grown to like documenting my work as much as I can manage. You know, so in case I lose my memory for some reason, I can find out how to do it again.

Yes. Anyways…

More drills! I got some more 18 volt drills off mysterious, sketchy Yahoo Stores. Oddly enough, now that I’m actually looking for a 18v drill with the standard 36:1 gearbox, I can’t get one. Yes, these are the 900RPM type. Handy if I want to have a spare gearset for the drivetrain (which I do).

So, for the curious, the Great Neck “brand” of imported 18 volt drills also have 24:1, 900 RPM gearboxes. I’ve seen these at multiple retailers, like this.

Down to business. I couldn’t find any 4-40 cap screws, so I had to assemble the clamp actuator temporarily with little computer standoffs. Here it is mounted to its pivot by a shoulder screw and spacer (one of my new favorite building methods). The actuator is free to swing on the pivot point.

In yet another episode of “How the hell am I going to put this together?” I discover that screws do indeed have heads. This one contacts the sprocket, and will need to be counterbored a bit into the clamp arm in order to pass the chain later on.

Onto the actuator again. Here’s the beginning stages of the leadscrew assembly.

The 3/8-12 Acme screw has one end slightly turned down and bored to fit the 4mm shaft of the B62 motor. A 6-32 set screw drilled down from the screw surface holds onto the shaft flat and transmits torque (You can see it barely sticking up by the bushing).

This turned down section also runs in a short 5/16″ bushing. So, between the B62’s output bearings, the close 4mm shaft fit, and the outer bushing, the screw itself is pretty stiff.

The other end of the screw is also slightly turned down for… Well, I don’t know. It must have been for something.

With the leadscrew firmly stuck on the motor, it was time to work on the other end of things. The clamp hinge-pivot-clevis-trunnion-whatever is a multipart assembly consisting of the leadscrew nut, a nut holder (LOL U SED NUT), and the aluminum cutout of the pivot block. The nut holder is made of a 1″ round of steel.

Yes, I chucked an endmill and was using it to drill holes. How else can I get smooth, clean, flat-bottomed holes in a single shot?

So things got a little too hot during the turning process (by which I mean I was jumping back every few seconds because another smokingly hot oil-covered steel curly sliver would land on my arm). Using mad engineering skills, I make a convenient chip guard.

The lathe stepped up the game by firing chips under the guard. I bit it and just put on some welding gloves.

To keep the assembly together, I turn to my perennial nemesis, the retaining ring. I hate retaining rings with a passion – that’s why I use them, of course. To ease my suffering, I actually went and bought a set of retaining ring pliers with interchangeable heads.

Conveniently, a giant hacksaw blade measures in at the exact right width to cut a slot for this retaining ring. And so the Amputee’s Cutoff Tool was used to slot the nut holder (with the spindle running, duh).

A quick trip to the mill to add a hole and a slot and I have a nut holder (so I don’t have to hold my own nuts, of course). The hole is an on-the-fly part design change, since I figured a press fit was nice but not very serviceable.

Add one leadscrew nut. A set screw keeps the nut in place. Since this nut should only ever see a compressive load (lifting robots with the clamp arm is a bad idea), I don’t count on this being too much trouble. However, it’s equally less trouble to drill the set screw hole into the nut itself, so that might happen some time too.

The 100th Ãœberclocker build pic is of the nut assembly. Add to the nut holder assembly the pivot block and two Belleville discsprings, and it makes compliant clamp arm. When the arm clamps down onto an opponent, the motor will continue to drive the nut assembly (since it floats in the pivot block, held in by the retaining ring), compressing the springs and adding a bit of “preload” to the clamp arm. This means the entire system doesn’t have to be wound up in order to clamp firmly.

It adds a bit of compliance to the system, but is not designed to save the assembly if the opponent decides to force its way out of Ãœberclocker’s grip. The next failure point down the line is the end of the clamp arm itself.

Unfortunately, I couldn’t actually test this part, since I redesigned the nut holder on the fly. Originally, a bronze bushing separated the pivot block from the sliding nut assembly, and the neck of the nut holder was 1/2″ – which is what I ordered springs for.

However, in a fit of laziness and after discovering I didn’t order these bushings, I just decided to make the neck a bit wider and run it directly in the aluminum. It’s moving all of 0.1″ maximum – does it really need bushings? There are things in this world that don’t need bearings since they won’t last long enough, move fast enough, or need enough precision to warrant any (Ãœberclocker’s clamp arm is all 3).

Of course I forget the springs no longer fit – time to get different springs.

Shoved onto the leadscrew assembly, the (almost) complete clamp actuator. I don’t have the little metric screws to mount the B62, nor 4-40 socket head cap screws to attach the actuator body.

However, it’s fun to just putz the thing up and down the leadscrew. I didn’t get the “precision” Acme nut and screws, but it’s still very smooth, and can push with an absurd amount of force – theoretically over 200 pounds (translating to about 30 at the end of the clamp). Dunking it in some EP grease should make it even better.

While I was waiting on some people to finish welding in the machine area, I finished out the drivetrain on both sides by mounting the motors and adding belt tensioners. To dismantle the drivetrain easily, I only have to release the large tensioning roller, freeing up enough teeth to slide the wheels off.

There’s enough tension in the belts to not slip on the motor pulley under constant (hold-wheel-down-on-table) load, but only a drive test will reveal the true performance.

It’s ALMOST THERE!

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!!?