Archive for August, 2010

 

Dragon*Con 2010: Clockerboxen / FrankenWalts

Aug 18, 2010 in Bots, Cold Arbor, Project Build Reports, Überclocker Remix

They’re done!

Well, one of the new drive motors for Überclocker is, anyway. The bot edges closer to being reassembled and rewired. I’m going to devote this week to getting Clocker running, and bringing Arbor as close to it as possible. The next week, which is essentially the last one, will go to finishing Arbor as well as packing the robots up for shipping to Atlanta. That’s right – I can’t bring 2 full robots and all their support equipment with me on the plane. It’s not a TSA issue, and never has been – I’ve been flying with robots since the 2006 RFL Nationals. Instead, it’s a matter of Airtran billing me up to the sky for very excess baggage. Clocker by itself last year ate up to the second category of oversize and the first category of overweight baggage, which cost me a pretty $95 or so. Add to that a second robot and I might be forced to shove them on air cargo. Instead, I can build two small shipping crates and load them up to 50 or 60 pounds, then send it all UPS ground.

What this means is that I have to physically send away the robots several days early, lest they not make it in time for D*C. We’ll see how this goes.

In the mean time, a lathe chuck.

…holding one of the gearbox end plates. No matter how many times I complain about it, I always end up coming back to the square chuck. It’s simply the quickest way to turn out revolute-symmetric parts on noncircular substrates. This is the motor mounting end.

And this is the gear holding end. The needle bearing assembly from yesterpost presses into the bottom-most bore.

The ring gears press in like so.

The original second stage shifter ring gear gets pressed all the way to the bottom of the cavity, at the second shoulder from the top. The trimmed first stage ring sits at the first shoulder level. All of these are \m/etalfits, which is a variant of the Beast Fit, which is an extension of the 20-ton-hydraulic-press-fit.

In the above picture, I have also installed the needle bearing. I took more care on this bore because compressed bearings reduce to the degenerate case of a solid chunk of metal.

I dropped the DeWalt gears in to confirm axial spacings and diameters. Result: splendid.

The first stage gears actually sit about 1/8″ below the surface of the gearcase. This is by nature of the DeWalt motors, and is something I just compensated for with a 1/8″ tall boss on the motor mounting side (visible in the first picture).

Repeat ad nauseam and add in a bit of mill time, and here are the gearcases with drilled holes. Because these parts were again square and rotationally symmetric by 90 degrees, I was able to pull off the Pop-Lock-Flip-It-and-Reverse-It to great effect. Who needs to move machine axes when you can just move the part around?

Now with more tapped holes!

Something disturbing that I noticed on Überclocker during its Motorama showing was that the DeWalt motors were starting to come apart at their crimped seams. These motors were designed with ease of manufacturing in mind, and feature rolled-crimped-and-folded sheet metal everything. The face plates in a motor are normally retained by bolts or are one-piece constructions, integrated with the can itself. But these are crimped together – or rather, were, since the mounts I used only held them by the faceplate.

Solution: tack weld! I dropped a small bead in 4 locations midway between the crimps. This ought to hold them…

The big moment!

Because I replaced (forcibly, and irreversibly) the pinion on Clocker’s 14.4v DeWalt motors with a HF drill pinion, I actually had to break out my two stock 18v motors to use on these gearboxes.  The combination of lower gearing but higher voltage motor will actually cause Clocker’s top speed to remain roughly the same.

To my relief, everything fits. There’s about a millimeter of axial slop in the gearset if I loosen the retaining ring and just let all the internals slide. I find this slop to be totally acceptable, since even if I engineered it to be spot on, after the first match it will be off by a millimeter anyway.

Finally, the new drives mounted in the robot.

The increase in length by about 1/8″ means that the endcap of the DeWalt motor is now tangentially contacting the supports in the back.

What’s left to do on Überclocker? Surprisingly little. I need to make one more hollow gear carrier for the other side, but that’s it. All of the other work on the drivetrain is just putting it back together. However, I might make some hubs for the McMasterBots wheels that are compatible with the existing hub structure.

I ripped all the wiring out of Clocker such that I can’t effectively put it back together the same way, so the robot will be rewired from scratch. It’s better this way, because I felt like I could have routed quite a few connections better than the first time around.

Arbor is currently hanging in limbo as I wait for parts to get cut, but depending on how many drill gears I can salvage, I might not actually make a replacement DeWalt drivetrain for it. Arbor never had a gearbox stripping issue at Motorama – in fact, I harvested a working gearbox from it to fix Clocker up.

TO DRAGON*CON!

Überclocker and Cold Arbor: Dragon*Con 2010 Update 2

Aug 15, 2010 in Bots, Cold Arbor, Project Build Reports, Überclocker Remix

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.

Hub Motors on Everything, part III: Dual Interleaved RazErmotor

Aug 09, 2010 in Project Build Reports, RazEr rEVolution

In the last RazEr episode, I whipped up the mechanical design for the monster truck wheel that will be the new scooter motor.The giant ass-magnets came in last week, as did the aluminum pipe that I purchased for the can, and the new bearings from my favorite shady eBay bearing house. So now, I’m going to build it.

Additionally, with the advent of the DEC modules and the chance to start completely from scratch (as opposed to rebuilding the old RazEr motor over and over), there is one experiment that I have been meaning to try on a motor like this. But first, some pictures.

The can of the motor will be made from a 4″ OD, 1/2″ wall aluminum tube. Here, I’m turning and boring the can to bounding dimensions on the Old Mercedes. Boring this thing out was an entertaining process, since the longest boring cutter I had only cut to 2.25″ depth, and the motor tube interior had to be a minimum of 2.8″ deep. As such, I had to hang the bit way out for extra depth and angle it counterclockwise slightly so the tube wouldn’t hit the shank. This resulted in a plenum of squeeeeeeeeeeeeeeeeeeeeeeeeeal that probably lost everyone in MITERS at the time a few years of audial health.

Luckily, the finishing pass on the bore cleaned out all the chatter, and the resulting can is the single shiniest thing I have ever made at MITERS. I adore fresh carbide inserts.

The tube handled threading very well, which was surprising, but is probably a result of the large diameter.  The thread itself is a 3.5″-24 thread, which isn’t any sort of standard as far as I can tell.

For the magnet can, I decided to save the trouble of machining a long steel part on our machine, and instead tripped over to the heävy \m/etäl machine in the automotive shop. Yes, the same one I was trimming down little plastic propellers with. While I’m generally not a fan of the larger lathe because of its impersonal feel and lack of cross slide locks, there are some times when there is no substitute for several tons of cast iron – namely, when you’re deep-boring in steel like I was with the motor cans. There was absolutely no chatter, skipping, or unsteadiness whatsoever.

I finished the inner diameter slightly larger than designed to loosen the very optimistic air gap of 0.3 millimeters.

Complementary shinies. The magnet can will be pressed into the aluminum outer shell after the magnets are installed.

Speaking of the magnets, here they are. 2″ long, 1/8″ thick, and 1/2″ wide. I purchased enough for two motors just in case I ever want to make RazErWD.

After finishing the major machining, I began harvesting the stators out of the copier motors. These are motors from a Xerox Phaser 4400 laser printer (Okay, so it’s technically not a copier motor, but copiers have this stuff too) that I snatched off Ebay in a sleep-induced motor binge.

These motors come apart reasonably easily – the can comes off after the front retaining ring is removed, then the stators just unscrews from its mounting post. So convenient compared to the pressed-and-Loc’dtite motors that I’ve had to deal with for RazEr in the past.

Cleaning the carcasses was easy, if not a bit repetitive. Here, I’ve lined them up inside the can to check for basic clearances.

And now the magnet gluing process begins. Again, I printed out the Handy Dandy Gobrushless Magnet Placement Guide. The seven magnets in there now are all the same pole orientation – they’re far enough away such that they do not affect each other, so epoxying them all down was easy.

MITERS received a shipment of legit extra-long set fiberglass lamination epoxy, so it meant that I didn’t have to deal with my adhesives setting on me as I was trying to maneuver the magnets in place. RazErmotors of the past have just used cheap hardware store hour-epoxy, or even worse, 5 minute epoxy.

After leaving these placeholder magnets to bake for a day, I returned to fill in the opposite pole. I found some +14 Balsa Wood Strips of Convenience that tucked tight into the gaps between the magnets. This was absolutely phenomenal, since that meant I didn’t have to play the (here physically impossible) game of inter-magnet balancing.

I found some glass epoxy filler hiding in the chemical supply shelf, so I mixed some of it up for placing the last magnets. I also filled all the gaps and edges with the stuff, so hopefully this can is much more structural than ones I’ve made in the past.

dual interleaved razermotor

The whole reason why I titled this post. I’m actually going to make two essentially independent motors inside this one motor. Why? Because I have enough volume inside the monster truck tire to put two motors, duh.

Well, that and the fact that the motor architecture is amenable to such modifications. The end result should let me push 4 times the amount of power I could otherwise flow through the windings, with the added bonus of double redundancy.

The average 12-tooth 14-pole LRK motor is generally wound in a “skip-tooth” configuration. Below is a diagram of a typical LRK winding (from the Crazy German R/C Aircraft Guy of all CGRAGs) and what a  motor wound like this actually looks like (from the BWD scooter, again).

I have historically wound my motors in the “distributed LRK” style, which spreads the single winding out to two adjacent teeth, with coils facing opposite directions. This is diagrammed out on the same site. The first observation that can be made is that the two (or four, if you count the other side of the motor) windings have different chiralities. This is something that has bitten me in the ass before.

The LRK winding in conventional Crazy International R/C Airplane Guy notation is A-b-C-a-B-c where the dashes indicate unwound teeth. The dLRK winding is AabBCcaABbcC. If you look carefully, there’s two full conventional LRK motors hidden in the winding, facing opposite directions.

  • AabBCcaABbcC
  • AabBCcaABbcC

Therefore, the second observation is that two interleaved motors can be wound on the same stator. Optimally, they would share the same Hall sensor commutation points, which are identical to that of a straight dLRK motor.

The consequences of this dual motor setup should be four times the maximum power of said standard dLRK motor. This is because each winding will be half the length, produce half the back-EMF, yet have half the phase resistance. Twice the current can flow, but the torque constant will be halved, and there are also twice as many windings now. However, because the back-EMF is also halved, the motor will tend to spin twice as fast.

Roughly speaking.

To effect these ends into the new RazEr motor, I have prepared the “RazEr Double DEC’er” board, a variant of the skate controller boards that I specially bred (designed) to fit into the available space in the scooter, which is more square.

Notice how the Hall sensor inputs are common to both DECs, as is the throttle and other signal pins.

I actually designed these boards a while back (before DIR became a legitimate idea of its own, and when I was just seeking to make a 2WD scooter), but with the above modifications made so the DECs are chained to eachother, I sent the boards to be fabbed.

…Yeah, I was a cheapskate again and went with the unmasked, unscreened board option. Hey, at least they conduct in the places they should.

Steps left on RazEr rEVolution:

  • Finish making the motor! I need to machine the center axle & stator mount, then fit the stator. The endcaps also need to be machined.
  • Cut the frame pieces once I get my aluminom slabs in.
  • Wind the motor with the dual interleaved LRK winding (which will most likely fuck with my mind at least once).
  • Assemble the RDD board and see if my crazy idea actually works
  • SCOOTER PARTY

RazErBlades: Finally, some real testing

Aug 05, 2010 in Project Build Reports, RazErBlades, Stuff

I handed the RazErBlades off to someone who can actually skate, and as a result, they actually look pretty epic. Thanks Josh.

Now to build four more and find some more misfit friends so we can storm Anime Boston or something as the entire cast of our most favorite series featuring misfits with automobile skates.

Dragon*Con 2010: My Robots Are All Totally Skullfucked Edition

Aug 04, 2010 in Bots, Cold Arbor, Project Build Reports, Überclocker Remix

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.