The robots are slightly less skullfucked.

Only marginally, though. What physical work have I performed in the past week or so to bring them back to competition spec? Relatively little. Shipping lead times and oh god i need to finish these scale CityCar wheel modules has mostly kept me away from the robots.  However, during this “productive downtime”, I’ve made steps into testing part fabrication and designing system upgrades such that they will amount to less work than building one whole robot from scratch.

Now, depending on which side of my projects you know the best, that’s either an imperial asston of work to be blitzed all in one week, or just an hour on the waterjet and 11 on Facebook.

Überclocker Remix

In the last Überclocker episode, I presented this crude representation of the new drive gearmotor layout:

The trickiest operation involved in manufacturing this design is the process of turning a deep internal part, the 2nd stage carrier / 3rd stage sun gear, into an output shaft mount. This would be relatively simple if I had more advanced tools such as a broach (or the patience to hunt them down), but in MITERS, the set screw, “elastic compensation”, and Loctite reign supreme. In this case, I decided to go for the press fit.

The 3rd stage sun gear in a DeWalt gearbox can support a center bore of about 12 millimeters. The pinion itself can be shaved down to a 14mm shaft relatively easily, so that’s the route I took.

Before that, though, I decided to finish the easy operation of turning down the clutch flange on the first stage ring gear, so the overall diameter is under 1.75 inches. Here is where I discovered the quality of metal sintering on DeWalt gearboxes as compared to the cheap import drills.

Harbor Freight (and co.) drill gears make steel powder when machined. These gearbox parts made curls. The amount of pressure needed to get steel particles to fuse together into a ductile solid is pretty incredible.

While I was jiggling the machine levers, I started to think about how to fixture the 2nd stage carrier such that I could perform concentric operations on both sides. The problem is that I needed to turn down both the outside diameter of the gear and the inside diameter. While I could have made a chuck spacer such that the 3-jawed chuck could grab the thin flange portion of the carrier effectively, I wasn’t as confident in how concentric the 3-jaw chuck ran. It is, after all, a shady eBay chuck.

The solution was remembering a trick I was shown once called pressure turning. Essentially, pressure turning amounts to pinning the workpiece against the spindle so hard that friction alone is enough to transmit the cutting forces. To do this, you need a live center with real lubricated rolling bearings. Luckily, we had one. I mounted the carrier in a loose-fitting collet that just acted as a buffer space for the planet gear pins. The collet was not tightened or closed. Then, I rolled in the live center and cranked down on the tailstock quill. Hard.

This is where you get to find out whether or not the lathe headstock has good thrust bearings. The Old Mercedes started making an ugly crunching noise, which was luckily silenced by a few liberal squirts of spindle oil into the semi-exposed thrust bearing race.

One side benefit of this turning method is that the piece always stays with the live center, so it mitigates workholding wobble that might otherwise be present.

A few passes later, all the gear teeth are gone. It is not shown in this picture, but I added a new retaining ring groove in the same setup.

I turned down the former pinion to 14 millimeters dead on – enough to snugly fit a needle roller bearing onto. As 14mm is a hair under 9/16″, I flipped the piece around and locked it in a 9/16″ collet. Now the center bore was accessible (no blockage by the tailstock), and I bored it to a hair under 12mm diameter.

Here’s the hollowed and turned shaft, with needle bearing, retaining ring, and some shims. I got a bag of 0.1mm shims from McFaster-Carr to take up any axial error resulting from inconsistent retaining ring groove cutting.

It’s been a long time since I’ve made such a mechanical and machining oriented post. I must say it’s very refreshing to just mince metal again. Here’s the insert stub shaft undergoing the one operation it actually needs, which is flat-milling. I bought some 12mm precision-ground O1 steel rod, which seems to go for 5 eggs and half of a slice of cheese per 6 feet on McMaster. Because I could finally be confident in the shaft diameter, I could just end-tap it and then put the flats of cheap waterjet gear retainment (+9000) on it.

After the flat cutting, the stub shaft was Beast-Fitted (an advanced cousin of the press fit involving beastly strength) into the hollow former pinion.

And suddenly, I turned a planetary gear carrier into an output shaft.

That’s all the work Überclocker for now. I was mostly concerned with how the pressure turning process would actually work, and how tightly the single needle bearing output could be made by someone with my level of machine patience. Overall, I’m confident the single bearing output can work – there wasn’t a good ball bearing or doubled ball bearing selection for the shaft sizes that could be made from the output gear.

Left to do on these “FrankenWalts” is making the aluminum gearbox case and shoving everything inside. After that, Clocker should be running again.

Cold Arbor

Arbor is currently well-strewn about my robot table at MITERS. Much of the work on it in the past week has been inspecting the parts and designing the upgrades. Last time, I was investigating how to make the “structural loop” of the saw arm wider for more stability:

The dark red and blue are the positions which I hope to extend the anchor and hinge points to, such that they use the entirety of the robot frame for support. I’ve made alot of progress towards that, as well as  redesigning the claw actuators to fit their new home in the robot’s anterior. Here’s the rundown:

In short: The saw actuator is now hinged at the rear, and the claw actuator is slung underneath the original saw actuator hinge point and drives the claws themselves through a slightly ass-backward inverted crank linkage. See if you can visualize how the claws move:

It took a while of stuffing and alot of happy hardcore to get that design through. The claw’s grabbing capacity (grabacity? grabass-ity?) remains the same – from frames about 6″ tall to those about 1.5″ tall. I have to recut the claws themselves to conform to the new angular displacement range, but that’s easy.

An overview of the new situation. The claws are now driven together by a single rigid crossbar instead of two roughly independent-but-sort-of-coupled-still-you-know-just-friends ball links. This should constrain the whole leadscrew nut assembly from just rotating itself to a point where seizing friction causes difficult letting go.

I originally spec’d a 1/2″ diameter carbon fiber tube to replace the 7″ or so of steel Acme leadscrew that wasn’t being used for its Acme-ness, but decided that saving 6 ounces was not enough to justify buying 3 feet of CF tubing at a price of around $50 – just to use a few inches.

An overhead view better shows the claw linkage crossbar as well as the FrankenWalts dropped into position. For Clocker’s gearboxes, I only have to make face-mount holes, but for Arbor, I need to make side-mount holes.

Now here’s the exciting part – the replacement for Deathrunner. I’ve elected to change out to the Mini-EV-alike motor with one caveat: that it be “pre-geared” to drive the worm gearbox. The motor rotates at 18-24,000 RPM no load, unlike Deathrunner, which barely hits 4 or 5 thousand on a good day. Driving the wormbox at 5-digit revs is just going to turn most of the power into heat.

As luck would have it, I have most of the wreckage of a Banebots 48:1 P80 gearbox. The 4:1 stages of this gearbox have identical sun and planet gear tooth counts, so I have gears left over to bore out as a motor pinion (since I can’t find the original motor pinion).  I intend to use 1 stage as a 4:1 pre-ducer. In the above image, the MEV-alike and the preducer gearbox have been modeled in more detail.

In total, the gear reduction from the motor to the saw will be 120:1. That’s  higher than most lifter gearboxes. With the self-managing torque characteristics of the DC motor, I really hope Cold Arbor will rip some serious shit at D*C.

With all of the replacement parts designed out (oh, minus that front frame assembly, which will be addressed), I’ve ordered parts and intend to get all this fabbed soon.

It’s August! That means the end of the summer build season, MIT’s Freshman Orientation, and most importantly, Dragon*Con, are all coming up soon.

In other words,

AAAAAAAAAAAAHHHHHHHHHHHHHHHH

D*C’s Robot Battles has been my annual robot party since 2002 when I first began spectating (and 2003 when I began competing). I’ve tried to go every year possible – 2007 was the big exception because my very own freshman orientation trapped me on campus then. I’ve always enjoyed the atmosphere of the event moreso than most other competitions just because it’s so not serious business. It’s a primarily sumo and show-off event because of the limited audience protection, at least for the 12 and 30lb class events – even more tame than the NERC Sportsman class I entered Überclocker and Cold Arbor in for Motorama. The event is seriously almost as old as I am, and it’s always been like that.

So now… speaking of Clocker and Arbor, how are they doing?

Yeah… about them robots

That doesn’t look too good. The bots have all been sitting, piled on top of my cart of miscellany, since February. They’re relatively undamaged as far as active combat robots go, but Moto took its toll on the drivetrains. I went through 4 and a half gearboxes at Moto, running through all of my spare 24:1 drill gears. After Arbor was eliminated from the competition, I harvested its gearbox parts to keep Überclocker running…but not for too much longer.

Long story short, Arbor has 1 semi-working drive side and Clocker has zero.

cold arbor

Here’s Arbor after retrieval from the cart skydeck. Past the drivetrain (or lack thereof), it’s also been the subject of parts harvesting. I think I’ve stolen the two Dimension controllers (which were briefly used to run Segfault), the Spektrum receiver, and the 5 volt BEC out of the electronics bay – those are all scattered about MITERS and so need to be retrieved or replaced.

One of the issues I intend to address is the front frame assembly. First off, it’s physically bent about a degree and a half. Not much, but several of the braze joints in the bend region have failed and some of the sheet metal has become twisted. This was probably just a result of battle, but either way it’s unsatisfactory.

Much of this front assembly was designed using 5AM Joltgineering™, therefore structurally unsound. I want to do a better job making it stiffer, so the plates may be recut and rebrazed.

Gearbox issues aside, I’m otherwise satisfied with the drivetrain. The oversquare wheelbase and central mass location means that Arbor actually handles very well. The drive is fast, but the super-soft McMasterBots wheels were grippy enough to avoid uncontrollable sliding. I’m also satisfied with how the Delrin hubs have endured in the front half of the drive.

Comparatively, ‘clocker handles like a total brick since all of its mass is in the rear 33% of the robot.

But I’m extremly dissatisfied with how the whole swinging saw assembly is mounted. If you call, several months ago in the last Arbor update before the Motorama update I never wrote, I said:

However, this was the first time that I discovered that Arbor would never work as I anticipated in its currrent configuration.

I was referring to this. In what must be yet another symptom of 5AM Joltgineering™, I somehow made the entire 14 pound swinging saw pivot off the front sheet metal assembly. As in, everything. All moment loads, all bending, and all shocks were transmitted through the beefy 3/8″ aluminum saw pivot mount…. right into the 1/8″ aluminum plate in the front. The above picture shows the “load triangle” pretty well.  One point of the triangle is located at the left side by the actuator trunion screw, and the other two are effectively shared by the two cap screws from the right side (front) and the screws on the top and bottom, which… happen to be missing, and probably were all through Moto.

From a Course II standpoint, this assembly is one giant piece of unwanted flex. It became very clear during Moto (and during testing) that the entire saw was prone to pulling itself into the material (or opponent) and becoming stuck hard simply because the whole frame twisted several degrees due to the torque of the worm gear drive.

My plan for redressing this problem is to make the saw’s structural loop much larger. Effectively this means swapping actuator positions – placing the saw actuator at the back end of the robot and the claw actuator where the current saw actuator is.

The light red, green, and blue lines indicate where the current structural loop of the saw lies, and the dark shades show where it should lie after modifications. The bigger the loop, the more the structure can resist torque about the orthogonal axis (in this case, the direction of saw rotation). But because I’m keeping the green line a constant length, I should have the same “swing” of the saw available.

As long as I’m wailing on the saw assembly, I might as well talk about Deathrunner. It’s been shiny, menacing, powerful, and reliable, but Deathrunner is going to be replaced with something else for D*C.

But why? Well, Deathrunner weighs 4 and a half pounds, was wound somewhat hackishly (the number of turns and wire fill percentage is a total waste of the stator), and hangs awkwardly off the saw arm. Even worse, it’s sensorless. Now, I could very well add sensors, but then I run into the problem again of not having a sensored controller powerful enough to feed it – no amount of DEC modules will drive this thing. I noticed that the sensorless controller had problems keeping up with sudden changes in the motor speed, such as those caused by the saw biting something.

Overall, the weight could be better used by a short Magmotor (!) or something similar. It’s much easier for me to control a DC motor, and I don’t have to worry about its transient response.

For now, the candidate motor is a big DC brush motor about the size of the classic Mini-EV. It otherwise seem to share all the MEV’s charactistics, such as being fast and obnoxious. Since it IS a fast motor, I might put one stage of “pre-gearing” on it by harvesting parts from one of several junked industrial planetary drives I have in the cruft pile.

überclocker remix

Poor Überclocker.

Being 1 event older than Arbor, it’s more beat up. A few things are bent, screws are missing, and there are little saw nicks all over the place from Freakin’ Enforcer, but fortuntely the major structural components are still sound.

Again, the number 1 issue is the drivetrain. More precisely, it’s the lack of one. A combination of “DeWalt motor into Harbor Freight drill gearbox” and battle impacts destroyed both gearboxes. At the event, I pulled parts from Arbor to keep them running, but ultimately Clocker lost out of the tournament by virtue of not being mobile enough to attack anything.

Besides the gearbox, the external portions of the drive have been flawless.

Well, most of it. This right side has apparently been gimpy since fight #2 at Moto because the internal binding screw backed out, so the standoff went all over the place. In the grand scheme of things, an easy fix.

I have about this much space if I want to switch to a stock solution like the Magnum 775 motors (which actually seem to be a bit too long). If I want to keep the current drill gears arrangement, I’d have to return to 550 motors because I’m out of 15-tooth pinions for 24:1 drill gearboxen. That would be a pretty stiff power and thermal mass sacrifice that I don’t feel like making.

Or I could keep fucking around with drill parts. A while ago, I posted some information about the 3 speed DeWalt (read: legit) drill gearboxes to Delphi Robotland, including a gear ratio count and pictures of all the stages.

With some crafty adaptation of the 2nd stage gear carrier’s sun gear, I could use the first two stages as a 17:1 planetary gearbox that has bigger and meatier and more gears than the comparable import-class drill. I started thinking about it, and hopped into Inventor to model some of the major components.

Here’s a preliminary layout showing some of the changes to be made to the parts. The sun gear will be turned down to a 14mm stub shaft, which will ride in a 14x20x12mm needle roller bearing. Its center is bored out to 12mm.

The first stage ring gear with the weird wavy flange remains as the first stage ring, but I intend to machine off the weird wavy flange to save on diameter. The second stage ring gear (the one with the dog clutch teeth that are unmodeled above) will remain the same.

All the ring gears will be heat-shrink-fitted into a custom aluminum casing…

…which looks the same as the current Clockerbox, and is made from the same 2″ square aluminum.The difference is that now the motor mounting plate is actually a plate instead of, say, the entire back half of the gearbox. It makes things a bit easier to manufacture.

The output gear will be the same one on the robot now, and will ride on a short chunk of 12mm drill rod shoved into the bore of the former sun gear, and with a Double-D profile machined into one end to simulate the old Clockerbox output shaft.

Dropped in place…

This new assembly is about 0.1″ longer than the current motors, which is an acceptable change.

I might switch Clocker over to the same kind of McMasterBots wheels that Arbor currently uses. It doesn’t hurt to have more traction on the D*C stage, especially since going from 24:1 to 17:1 is going to boost the robot’s top speed even more.

Here’s where I get to find out if my robot driving skills have faded any from the 2003 Test Bot 2.0 days.

While I have the gearboxes designed, I’m debating whether or not it’s worth just going with the 775 gearboxes because they are a stock solution – that is, I don’t have to build them. It’s mostly a matter of cost versus time spent – I could buy the 4 gearboxes (assuming Arbor also needs a pair) for $400 or so, or build two FrankenWalts for virtually free, and if necessary, two more for about $100.

It comes down to do I think I can get them done in under approximately 32 hours because my time is apparently worth about that much this summer.