Archive for August, 2013

 

12 O’Clocker: The Completion, and Überclocker Upgrades for This Year; Dragon*Con panel information

Aug 26, 2013 in Bots, Twelve O'Clocker, Überclocker ADVANCE

What a week! 12 o’clocker was completed early on, then I began to focus more intensely on upgrading and repairing Überclocker for this year’s competition. 12 o’clocker is currently working and undergoing test driving. It handles enough like Überclocker, but I hope to be able to second-nature the peculiarities of its operation. Plus, it’s fast. Just how fast? Find out now.

Continuing the manufacturing of the “solid state reactive outriggers”, I needed to drill some 1/4-20 clearance holes through the Rockwell C44 hardness spring steel. The week before, I purchased two solid carbide drills off eBay for a cool $7 each – if you have the patience, eBay is a wonderful industrial and machinery supply house – to do this one task. These are straight-flute bits designed specifically for drilling shallow holes into very hard metal. The straight flute maximizes stiffness, but of course does not allow for very deep holes.

Carbide wins over steel any day, and this process was totally straightfoward. The curls that came off this thing could cut you open in an instant – to prevent this from happening in MITERS, I hammered them all apart and trashed them before anyone could discover them on the mill.

Here is an assembled leg. The aluminum end blocks are also drilled clearance, and a bolt holds each end block together. I elected to take this route over threading the aluminum because the bolt could impart much higher fastening forces without stripping the thread.

The legs mounted. I unfortunately didn’t have any lower profile nuts, so the big locknuts on the end kind of function as 2nd-order fish-hooks. Strange how a normal 1/4-20 nut – just about the most common possible nut – couldn’t be located this time of day. I bought an entire bag of 1/4-20 Keps and grade 8 plain nuts from McMaster in retaliation.

With the bot now mechanically done, I turned immediately to electrical work. Remember the original CAD picture and how it had the cells in the middle and the RageBridges above the motors? I found that arrangement wasn’t optimal. Instead, some arranging of parts in real life found a better arrangement which kept the battery mass in the rear. This arrangement did however force me to mount the Ragebridges vertically. That, and the batteries shouldn’t be lying directly on top of the drive motors because that would be unfavorable to the motors in high impact applications… like combat. I needed to come up with a vertical rack for the controllers, and some kind of shelf for the batteries.

I went back to the 3D model to generate these required components. This is the result, after a few minutes of staring. The black vertical guides hold a hardboard (HDF, pegboard) plate upon which the RageBridges are bolted. Two auxiliary motor supports keep the battery from jouncing on the motors directly; these were originally slated to be made from Delrin, but I only had enough of the material left to do this right exactly once….and didn’t. So they ended up being made of HDF anyway.

The little squiggle at the bottom is a flexure joint to keep these plates tightly stuffed onto the motor. Unfortunately, they were made pretty much useless in HDF.

I decided to make the battery first, since it could take a first balance-charge overnight while the Ragebridge mounting end guides were 3D printed on my Up? machine. The first step is to select a group of “relatively” matching cells out of the cell medley. I generally reserve the highest voltage, most closely matched ones for EV use. This is because robot packs may be frequently swapped out and charged externally (with the implication that you’re usually using an R/C style balance charger), but an EV pack needs to be buried inside the vehicle and out-of-balance or weak cells can degenerate from lack of charge monitoring very quickly. It actually took a little while to gather enough middle-of-the-road cells. The majority of the A123 Collection hovers at 3.29 volts these days, and I was looking for cells in the 3.20 to 3.25 range. The camp is pretty well split 90%-5%-5% between good ones, shady ones, and ones that are totally dead (defined as an OCV of under 2 volts).

The end-to-end architecture of the pack meant I had to fold over the interconnecting battery braid once I was done with a joint, and I had to do these one “string” of 3 cells at a time. Usually, in a professional setting, packs like these are made by end-to-end soldering using a “hammer head” iron tip, or with spot welded tabs which are then similarly folded over.

A side effect of folded tabs is that they are well exposed on one side to attach the cell taps for balancing to.

Many of my robot and rideable things have featured custom A123 packs. If you’re interested the basics of assembling a custom pack, here’s a short writeup getting the basics of the process by a former duckling student of mine. With some… uhh, more detail and rigor, this is essentially what I train people regularly to do these days – after all, if we’re going to have a pile of donated batteries, it is better to train people to safely and correctly use them than to try and hide everything. In my opinion. If you’re a safety bureaucrat, you may disagree.

Balance taps added. These days, I usually don’t bugger with soldering and crimping my own JST terminals, but buy balance harnesses off eBay en-masse and cut them up. These are professionally crimped and molded, and usually only cost a few dollars.

While the battery pack balanced, I uploaded the print job to the Up printer and by the next morning it had produced the RageBridge rack in question. The HDF parts were laser cut.

RageBridges pulled “from stock” and mounted to the rack. I’ll totally have some of these at Robot Battles.

In the process of wiring it all up. Notice that I’ve bussed the wiring together on the RageBridges – this is one shortcoming of the current style design which I openly acknowledge. Recall that these things were designed originally to replace two Victor 883s in Überclocker. It had 2 sets of power wires already, so it stayed like that in the “production” versions.

The battery is just coated with 2 layers of heavy polyolefin heat shrink, and then unceremoniously stuffed in place. There’s just not enough room to pack all the wires in – a bit of stuffing has to be done. Unfortunately at this point I decided to scrap the glowing 12:00 idea because I didn’t have any space left in this thing to add an EL inverter.

The last few bits of distribution wiring added. Notice the small yellow and brown wire on the right side. This is a direct battery tap for whenever I decide that I have the capability of adding gaudy lighting.  The master power switch for this bot is just “disconnect the battery” – as such, the battery wires are just run outside the bot. When on, the wires are stuffed into the protective confines of the front right frame rails. The RageBridges are set to 25 amps (drive) and 20 amps (weapon motors), which is a pretty egregious waste of their capacity. I’m strongly contemplating a RageBridge “mini” version that retains the Hysterical Current Limiting scheme but can be more finely tuned for amperage at the low end – say 25 amps continuous and 50 for short terms.

With the wires complete, it was time to function-test and pack everything up! I had to play “change the motor wires” a few times to get 12 o’clocker’s control directions to match up with Überclocker

Here’s the ‘press shot’, so to speak, of the completed bot. The weight is 12.05 pounds.

Yes, it’s over, but I’ll remove one of the standoffs from the clamp arm if it’s really that bad. Or just wear the wheels down a little. Worst cast, I’ll replace the steel drive sprockets with aluminum ones.

Remember that part where I said it’s fast? It’s like, unnecessarily fast. Here’s how fast it is:

The calculated ideal top speed with these new motors is somewhere north of 20mph (30 ft/s). In the narrow hallway I wasn’t confident enough of its straightlining ability to push the throttle to full. In the narrow arena confines, it will never be able to hit this top speed, but the acceleration (also shown in the video) is blazingly fast. I think 12 o’clocker is going to warrant a slightly different strategy against opponents than Überclocker just due to it speed. The extra speed overhead will give me some room to maneuver around and behind people instead of strategically avoiding head-on engagement like with Überclocker.

I found out in sparring matches with Turboencabulator that I needed some more current on the lifter and drive, so the adjust-o-knobs were turned up to 30 amps (drive) and 25 amps (lift). Those extra few amps made for substantial improvements in the lift.

Here’s the D’aaaaaaaaaaawwwwwwwwwwwww size comparison shot with 30lber Überclocker. 12 O’clocker is currently ready for action. Speaking of which…

Überclocker

The big change I wanted to make to Überclocker this year is making a more robust clamp actuator. As recapped before, the issue with the Cold Arbor harvested actuator is that it was slowly destroying itself from being made of untensionable chain drives, and the lead screw was damaged pretty badly at Motorama. The shallow pitch leadscrew also made it prone to “bolting” itself, tightening to the point where it couldn’t loosen again. The reason I purchased the IGxx gearmotors was to see if they can act as a commercial replacement for my custom hacked drill gearboxes. That post concluded that yes, they could, but not in a way I would like, so I made the hybrid all-metal gearbox from two of the ones I purchased.

The gearbox was later wrapped into an actuator design:

The architecture of this is very similar to my other custom actuators. The gearset is from Vex (I’m obliged to say every time I mention Vex: When the hell did they get so legit?). In the center of the top gear is shoved a machined down McMaster fast-travel ACME leadscrew nut. The two bronze bushings supporting it are flanged to also handle the thrust loading, and not shown in the model is the gigantic loogie of grease that this whole thing will be basked in.

The lifter model refined a little and inserted into the robot model. This actuator orientation better uses the leadscrew length (instead of having like half of it as filler length just to reach the clamp arm. One thing that I don’t like about it now is that it does not actually shield the motor that much better. With a standard-can speed-400 (RS-385) type motor, it’s okay. But, I only had “long can” motors (RS-395 type) that won’t grenade at the 26v electrical system, and those stick out a little further. The standoff is there as some degree of protection and as a lower travel limit for the leadscrew.

It’s totally fine against blunt-sided bots, but a good high speed wedge drive can probably reach the motor and bend it. I almost want to re-engineer this whole system from scratch instead of just patching parts onto existing structures.

This is what the reach looks like. If I *am* facing a blunt sided opponent, then this actuator is also a nice “hard stop” for the back of the fork. It doesn’t really stick out that far.

It was time to start cutting metal. Here’s the ACME nut about to lose about 50% of its volume! The threads had to be machined off and the part turned to press-fit diameter, then cut off at 1/2″ long. I was wasting 2/3rds of it by mass, but until McMaster makes raw Acme nut stock…

The nut turned down and the gear bored out. They are to be combined using copious amounts of green Loctite and an arbor press.

Pictured behind it is one of my “troll drawings” – in which I put about 10 parts on one page with just enough dimensions to remind myself of what I’m doing. Some times it even fails at that.

The lower gear is attached to the motor by… well, not much. I machined a hex adapter from some steel hexagonal stock. It’s set screwed to the motor, and the gear simply sits on the hex. That’s it – that’s FIRST Robotics engineering for you. It just has to last the season.

What everything looks like when put together. On the bottom (motor side), the hex adapter is supported by another one of those R1212 bearings.

The new leadscrew cut to length and with attachment flat machined.

And finally, everything mounted in the bot. See how far that motor sticks out?

When the clamp is down (in a position ready to close on something), it isn’t a problem since the motor is well shielded by the aluminum body of the actuator. I guess one thing that I have to watch out for now is someone taking a high speed run at me when the clamp is all the way up.

I extended the umbilical cord from the bot to account for the new actuator placement, backing up the wire the entire way with heat shrink.

Fully installed, wired up, and with a healthy dose of lithium grease. I ran some tests where I practice “clampbot yoga” using Null Hypothesis as a chew toy:

This new actuator is great so far. With the actuator motor’s Ragebridge half set to 15 amps, I can literally run it from endstop to endstop, full speed, and still release in either direction. The RB’s fast current limit algorithm helps here, as does the high lead angle of the screw so it can never “bolt” itself together. The clamp speed has also increased to about twice what it was before. Clocker should miss less grabs now because of this upgrade.

I sparred Clocker briefly with Null Hypothesis (feat. Jamison as the pilot of Null) just to shake everything up from Motorama and to try and catch problems early:

Guess this wasn’t really that representative of a match – the floor is super slick polished concrete, first of all, instead of hard outdoor carpet. However, I did confirm my vulnerability to someone getting stuck between the springy legs and the fork. Careful maneuvering will be needed to make sure this does not happen.

I put the bot away for a few days to work on 12 o’clocker, but with that affair now complete, it was time for some pre-competition preventative maintenance.

I tore down both drive halves of the bot completely to check for issues. Are the DeWalts still in one piece? Is anything really, really worn down?

I mean, besides those wheels. They’re pretty destroyed, and only got more destroyed after Motorama from demos and sparring. I did make spare wheel stock before Motorama, so I decided to give Clocker 4 new wheels and keep the half-worn front tires as spares for now. (Due to the way the fork can load against the ground, Clocker goes through back wheels much faster than fronts.)

All I needed to do to swap wheels was to use one of the spacer rings holding the sprocket away from the wheel as a template to drill clearance holes into the new ones.

Überclocker is now cleaned and buttoned back up.

At this point, both of the bots are totally ready to fight tomorrow if need be. However, the story doesn’t quite end there. In these past few days, I also went and upgraded certain parts of my 3200lb 2WD wedgebot to prepare it for the 1000-mile (one way…) trip to Atlanta and ideally back. That’s a story for later on.

Dragon Con 2013 Panel Info

I’m coming back as a speaker this year on two panels for the Makers & Robotics track at Dragon Con. See the full schedule here!

The first one, CAD and Maker Resources, is an extension of my talk last year on where to buy things for your mechanical whirlygigs and doobobs. Except this time, I’m focusing more on how to make nice things. By this, I mean exploring using free and free-ish CAD programs to better design out your projects before laying into a piece of aluminum with a plastic safety scissor, and taking advantage of modern rapid prototyping and digital fabrication resources. Basically, How to Build your Everything Really Really Fast for Kids who Can’t Build Good.

It’s been my observation that many folks, especially those already well-versed in the EE and software side of things, are dying to get into mechanical projects, so it will focus on such possible routes to start immediately instead of mocking things up with plywood and hot glue. Having been on all 3 sides of the proverbial coin (the knurled edge is a side, I swear),I’ll explain why hardware, and especially mechanical, projects are more involved in general and how they differ from the typical fancy PCB.

The second is in conjunction with my partner in hoodrat shit, Adam, and will concentrate on Electric Vehicles. The panel last year was a primarily discussion and Q&A driven session where we used peoples’ questions about EVs to dive off, and that will remain the same this year. Hopefully some hardware will be in attendance too.

I’ll at least try to have a set of slides made for both of these; no guarantees, of course, that they are actually representative of the panel. If the media resources are available, I will record the sessions and upload them after the fact.

12 O’Clocker Epic Post

Aug 19, 2013 in Bots, Twelve O'Clocker

Damn. This past week -and-a-little has seen 12 O’Clocker basically go from a plate of aluminum to an essentially complete bot minus wiring. I’m making good time for Dragon*Con 2013 after all, it seems. In a slight departure from my usual day-by-day- updates, I’m going to make one single epic post capturing the construction up until yesterday or so. I tended to stay later than usual in the shop in the past days, and writing up daily posts would have pushed my already marginally stable bedtime out to a level which would have made interacting with anyone else… difficult.

As I mentioned previously, by the time I made the introductory post, I had already frozen the design and put most of the parts down on aluminum. The first stages of assembly were doing finishing machining on these parts, as well as machining that which I could not figure out how to waterjet. These days, my ‘style’ is reducing everything to a waterjettable or McMasterable condition and trying to minimize manual machining operations. After mechanical assembly was complete, I spent time figuring out where exactly the electrical components – batteries and RageBridges – will be mounted internally, and this is the stage of the bot right now. Here’s forty pictures (from #24 to #64!) for your amusement. I recommend packing drinking water and high-carb food supplies.

This is the final series of parts made for this bot – previous parts, seen in the upper regions of the picture, were rolled in with a waterjet-cutting session for the SUTD summer go-kart class (which I still owe a full writeup on, before I completely forget it!). In most respects, 12 O’Clocker is a pretty simple bot, and there were (relatively) few parts to be cut.

One thing which mystifies most people who see me waterjet is that I manually path everything. I started this habit some time in 2010 when I was getting tired of losing entire plates to the shoddy Autorouter built into OMAX Layout. When I manual-path, I instruct the machine to make one part at a time (holes and all), then move onto the next whole part, and I try to route in a fashion which does not cross over anything it cut before. Because the path includes only whole parts, the plate can accidentally shift (such as in the all-too-common nozzle collision with a pre-cut piece) and I may only lose that one part. The autorouter likes to do all the holes and internal features first for some reason, so if anything messes up, you usually lose the entire sheet. It took only one $200 write-off to permanently scare me into manual pathing. Additionally, I use the Tab function like a maniac, on anything that looks like it can stick up and bump the machine, and on all plastic parts.

This way, I can route an two-hour-plus long job, then practically go to sleep and then come back to find everything all good. Okay, so I don’t really go to sleep, since the machine still needs abrasive feeding.

So here’s everything! The obligatory picture of the pile of parts includes all the aforementioned waterjet-cut puzzle pieces, a few different motors, and Delrin balls.

I machined the black Garolite, my choice of robot covering, on low-pressure to avoid substantial delamination. I further suspended the Garolite on a piece of waterjet brick, which offers a much higher support density. Without these two addenda to the process, I’ve always had massive delamination from Garolite. In this plate, the delam is limited to areas around the holes and initial pierces.

I design the holes in these parts to be already on-size for finish tapping without having to redrill (usually). The first step in assembling a puzzlebot is to tap with threads that which needs to be threaded. Because all of the holes are necessarily thru-holes, it’s easy to chuck up a gun tap (spiral point tap) into a drill and then just go at it. I mixed up a little cup of machining coolant (high-lubricity oil-water suspension – a.k.a the juice that flows in every CNC porno) that I dunked the tap in after every part.

In the background is one of my collections of random cordless tool motors. I think there’s like 50 drills (most of which are parted totally down) and like 10 cordless saws in there.

Next up was machining down the main lift shaft bushings. My approach to live weapon axles is to make them huge, and usually this implies buying metal tube stock to use as shafting. Now, the difference between metal you buy as shaft and metal you buy as tube is that the former is implied to be precision-finished to a size under the nominal (i.e. a 3/4″ shaft might be .748″) so it for sure will fit through your bearings and other driven parts. Tubing has no such guarantee, and in fact is usually oversize. The cheap 3/4″ 6061 surplus tubing I purchased was a cool 5 thousandths oversize.

To compensate, I bore out the bronze bushings on a lathe beforehand – the dimension needed, plus a thousandth or so for the bearing squish fit into the housing. These days, Tinylathe is my tool of choice if only because it’s like 5 feet away.

There was one problem I ran into right away. I didn’t have the right bearing to support the lift motor shaft. I ordered it, but it most definitely didn’t come on time, and I was sort of itching to put this together instead of waiting for the parts. That, and I couldn’t find the 13-tooth sprocket I originally specified. Since 12 O’Clocker isn’t going into space or (ideally) poking around inside an organ, I decided to make a design change on the fly to adapt to the parts I had on hand.

The bearing was going to be a 6803 type, 17mm bore bearing to basically envelope the hub of the sprocket. The 13 tooth sprocket’s hub was just the right diameter to shave down a little and throw into a 17mm bearing.

I had on hand 12 tooth sprockets left over from the EV class, and a 6802 type bearing (15mm bore). I decided to machine an adapter to turn the 26mm 6803 housing into a 24mm 6802 housing, and machine down the smaller sprocket hub to 15mm. This increases the reduction of the lift arm just a hair, which is  differentially speaking to my benefit, since it would both slow down the lift another few % as well as reduce the required current to lift an opponent.

….but in the end, I just shoved a machined Delrin donut in it and called it a day. Didn’t even machine the sprocket.

This is a very slow-moving part already, and drill gearboxen already have bearings! The whole purpose of this bearing is just to reduce the bending load (versus shear load) on the shaft. It doesn’t need to be sophisticated, and can just be Delrin, the venerable bearing-grade plastic I had a few rods of. After spending all of 3 minutes on this, I moved on with my life.

Assembling the puzzlebot now.  The part precedence I designed in means I fasten together the center towers, then the U-braces on the ends, then finally shove the sides on. If you’re thinking of designing a puzzlebot, and don’t read anything else in this whole post, read this: all of these parts were cut on an artificially close nozzle offset so all external dimensions are about .005″ smaller, and all internal dimensions .005″ larger. This is a cheat code to account for the waterjet’s taper between entry and exit sides, something inevitable unless you are really rich-ass and have a taper-free or 5-axis cutting head.

If you don’t have the ability to run a custom offset, then you must design all the slots larger and tabs smaller in CAD. Or, you’re going to be miserable filing and grinding everything.

These parts required very light belt sanding to take off the burrs and tabs, and only in a few cases a hit to the thickness of the tabs.

I’m sort of round-robin machining parts here – in one round, me versus everything. I put the puzzlebot aside and tested the fit of the Angerboxes. Beforehand, I threw these gearcase models on a Dimension 1200ES machine to be made from ABS plastic.

It turns out that the drill gearbox CAD model I had used a smaller diameter ring gear by about 0.5mm than the ones I picked out from the Tomb of Tool Parts. These drills are usually similar enough to swap parts into each other, but different enough that any design involving them is going to jump your precision-havin’ ass in an alleyway. I had to machine down the ring gears a little to fit them.

After a radial pass, I sliced off just enough to contain one stage. These ring gears are made via sintering, so it turns to powder when machined. This is actually the sign of a shitty sintering job, but hey, $20 cordless drills.

6801 type (12mm) bearings support the 12mm drill spindles.

No, I’m not using those plastic gears – they were just the first things I grabbed from the Tomb of Tool Parts to test thickness fit.

After verifying that everything fit as designed, I put these gearboxes down and went to…

…the lifter gearbox. This is a totally stock 18v-native, 36:1 drill gearbox that I replaced the first stage gears with spare steel ones. The 12 tooth sprocket seen in previous pictures was bored out and threaded for its 3/8″-24 spindle. The long standoff piece at the end spaces out the reverse-thread M5 flat-head screw which typically locks a drill chuck in place.

Another blob of 3D printer poop with a drill gearbox shaped cutout will hold this motor in place. I basically made this mount to let me emulate the motor mount style used on Überclocker, which uses DeWut motors with side mounting holes. The generic drills don’t, so the sandwiching mount does.

Overly-long 1/4″-20 cap screws fixture the motor to its mounting cradle. In soft plastics (or at least, anything where $fastener_hardness >> $material_hardness), you generally want 3+ fastener diameters to take advantage of the material strength.

As a random aside, the recommendation for situations of comparable material strength (say aluminum threads with steel bolts) is one screw diameter, and materials of nearly equal strength just 4-5 threads. This is why steel nuts are usually made really skinny – count the threads on the inside of a typical machine nut some time.

The first pretend-o-bot! At this point, I was getting pretty damn excited to see this thing finished.

After the pretend-o-bot assembly, I moved on to the last item of the day, which was to put together the top clamp arm. This was a quick standoff assembly job.

I attached the end-effector, the rubber bumper, with a convenient chunk of 1/8″-wall aluminum square tube I snagged before getting to that part of the design.

The next window of progress was spent making some of the repetitive side parts. Seen here is my “sheet of every part drawing since they’re so damned simple anyway”. The majority of these are standoffs of various kinds.

The inter-fork spacers are designed to be made using some 3/8″ OD, .050 wall 6061 tubing. This was way better than the other option, which was to drill out all of those from a solid rod.

Pictured above are all the fork standoffs and two of the Angerbox output shafts in progress.

Axle pins attached. This is my first intentional foray into single-support wheels in a long time. Single-support wheels tend to last … not very long in combat, so I made everything here overkill. First, half-inch diameter axles on anything that weighs 12 pounds.

The 1/4″-20 bolts are unnecessarily long, to give the aluminum a stronger core, and the threads are actually embedded under a half inch of clearance hole as to preload most of the structure where the most stresses from impact will be seen.

It’s often these little unseen details which can make or break a design, and I’m really hoping for make this time.

Time to assemble the fork! Like Überclocker’s fork everything I build now? , this is just a pile of plates and standoffs…

…that looks like this. If there’s one lesson I have to summarize 2.00Gokart and the SUTD summer EV class with, it’s tighten your damn bolts. Untightened and unloaded structures are just flappy metal noodles.

Moving on now to the drive hubs, these are simple Delrin one-piece jobs. Since Tinylathe is too cute to contain a 1.25″ Delrin rod all the way through, I had to cut off chunks and sacrifice about 1/2″ of length off each to grab them.

The final machining step for these hubs is to purposefully chatter an endmill through them. Why? It’s once again the difference between buying shaft and buying metal rods. The aluminum rods I had standing by are just plain-finished loose-tolerance rods! They’re actually much larger than their nominal 0.5″ (more like 0.505-ish), because you’re supposed to machine them to something smaller with more precision.

Well, I didn’t have a .505 drill bit, nor an over-size reamer. Nor a boring bar long enough. The shortcut is to take a super-rigid cutter and purposefully guarantee it no center, so it just has to deal with it. I basically revved the spindle to full speed and manually shoved the thing through the center bore.

It made a terrifying screeching racket, but the end result was a bore crudely enlarged to about .510″ (varies greatly…)

Fits great though. Here’s 12 O’Clocker looking like someone stole its rims. In reality, I haven’t bored and machined the wheels yet.

The wheel assemblies were, again, designed to smash together quickly and template itself for finish machining. It has four parts – the wheel, a 1/8″ thick ring spacer, the sprocket, and the Delrin hub.

Here is one wheel as a test fit, and the clamp arm assembled on for looks. At this point, I called it a day for assembly because I discovered I ran out of 2″ long #4 screws. I needed long bolts to go through the wheel and spacer and into the threaded holes in the sprocket, acting as lug nuts.

I moved onto making the rest of the irritating small parts. Here are five blanks for the eggy-rolley-cam tensioners machined out.

Because they differed only in length, I lined them up one next to the other on the MITERS Bridgeport and drilled the off-center holes in one shot.

While downstairs, I revisited an old friend, the MITERS South Bend 10L, upon which many of my freshman and sophomore shenanigans were first performed. For how hard it gets wailed on by students, most of whom aren’t experience machinists, it’s never had any problems. 1950s style brute force tends to come out on top. I used the machine’s much larger swing to chamfer the tips of the main lift sprocket.

The MITERS lathe to me represents roughly the most useful machine size for the general hobbyist. It’s a nominal 10″ swing machine, with a 42″ bed, and a big through-bore. Tinylathe is too damned small, and the other machines in this building are enormous – 16″ and 19″ swing. I think the 10″ class has just enough feedback to enable really precise work on small parts, but can still contain sizeable workpieces like wheels and round plates. Plus, my favorite lathe (I have one, just like I have a favorite weird 1980s Japanese cargo van) is the Monarch 10EE, nominally a 10″ machine. Round dial, please.

Here’s a collection of little side parts. The shaft collars are for transmission of lift torque to the main lift fork, and you might notice on of them took me a few… tries. I tried taking eyeball and by-feel shortcuts on the Bridgeport right away again, but remembered about as fast why I only do that for machines I use every day and know exactly the recent alignment history of: because not everyone trams the head and squares the vise. Whoops.

Well, time to bust out the edge finders.

Fast forward to Day…. three? four? Whatever like 2 days ago was. I had dug out my box of 1.5″ long #4-40 screws, but they’re still too short!

Or are they? I decided to get this damned thing together, buy 2″ bolts later, and just counter-bore the shorter screws into the wheel for now, so they could still reach the other side.

So here we go. All 4 wheels counterbored up and installed!

Next comes the lift axle itself. The shaft collars are loosely scrwed into to the forks, the lift shaft slid through, then the screws tightened. The white residue on the shaft is a healthy dose of Teflon anti-seize paste. The reason is that this time, it’s aluminum shaft collars and an aluminum sprocket rubbing on an aluminum shaft. Without this intermediate layer, I would soon have a very curiously shaped solid aluminum modern art sculpture as all of the above galled into eachother and became one. The antiseize lets the clutching action of the clamp shaft collar still occur.

I maneuvered the lift chain tensioner into place and secured it for the time being. It will be adjusted out slowly as the bot wears in the lift chain.

Chains typically stretch a few tenths of a % shortly after installation as soon as they are loaded, since the burrs and high spots from manufacturing get worn down quickly. In my case, with so many custom sprockets, the net amount is a little more because I also have components besides the chains to wear in.

Here is a more detailed view of the eggy-rolley-cam tensioners. The ball bearings will directly push the chain (no intermediate sprocket teeth here).

The bearings themselves are type R1212 bearings, which is part of a series that is basically the 68xx of the English unit world. I’ve spent a long time searching for thin-section inch bearings that don’t cost $9000 each, and for the 1/2″ case, at least I have found the R1212. Apparently the other sizes (3/4″, etc…) are nonstandard and its code depends on the manufacturer. In contrast, searching ‘R1212 bearing’ gives me a world of generics.

With the tensioners ready for installation, I went hardcore after finishing the Angerboxes. The motors I ended up using are some unknown 12V (ish?) 550-class motors I found in a bin. The reason is because I’ve actually ran out of matching shitty 18v drill motors! I have a mishmash of gearboxes with motors, but I couldn’t find two matching 18v motors, especially not with the 36:1 standard 9 tooth pinions. Oddly enough, I have more 24:1 drills than 36:1, and this gearbox depended on the (far more common) latter pinion. I harvested some pinions from the Tomb of Tool Parts and pressed them on these motors.

Now that I’m running 12v motors, I’m actually going to drop back from the planned 8S (25.6v) system to a more sane 6S (19.2v) system. 30-lb Clocker does run a 8S-equivalent system, but with “real” motors which are 18v native anyway. A 12v to 24v overvolt in this case would have given me an unacceptably high top speed and would probably bake the motors in short order.

Three harvested, mismatching metal gears ride on the output pins, and the whole thing is closed from the back from harvested mismatching wear washers. I’m like the Iron Chef of making stuff from shitty drill parts. I did say that all of these drills tend to be the same enough…

Here’s one Angerbox closed up with another one awaiting. The shafts have milled flats (not quite visible) to aid in using set screws properly.

The first installation of all drive parts on one side is complete! This spent a few minutes just running from a power supply to seat all the bearings and run in the chain. A portion of the back wall is now covered in a very weird vertical black splatter mark, like a highly precise mechanical crime scene. The same process was repeated for the other side.

Lift chain in place! Now I could manually wang (that’s a strict technical term) the fork up and down and backdrive the motor.

One issue is that switching to a 12 tooth from a 13 tooth sprocket meant my original tensioner design doesn’t tension very much any more. I’m almost at the limit of travel and the chain will most likely slack beyond that limit. The narrow confines of these 3 rolling elements should not cause deraining problems, though. Worst case, I’ll put a spacing ring around the outside of the tensioner so it can push further.

Clamp actuator now installed, and run back and forth a few times with a dose of lithium grease. This motor will definitely be unhappy on even 18 volts, but I’m hoping the current mode of the RageBridge can delay the onset of magic smoke arbitrary far into the future.

After all this was done, I turned the bot over to install the bottom plate.

I decided to get a start on the very last item on the list of manufacture for the mechanical side: The springy legs. I segmented the 3/32″ thick spring steel bar into two 8″ lengths with an abrasive cutoff wheel and selective belt sanding. These will have two holes each put into them with a solid carbide drill bit, then have the accessories attached.

Here, have some robot googly-eyes.

These are actually the front rollers for the legs above. The axles these things ride on are 1/4″ diameter hardened steel shoulder screws, counterbored all the way into the Delrin ball, and extending halfway through the aluminum. This is to make sure that bending impacts are borne as much as possible by the aluminum and not the weaker threaded area of the screw.

This is the mostly mechanically done pretend-o-bot , with the only thing missing at this point being the legs. I cut out a “window” using 1/16″ LDPE sheet to cover the 12:00 and give it some contrast. I hope to have this whole thing back-lit by a big EL panel.

That’s it for now. I’m going to now compile the previous day-ish, and whatever happens today and tomorrow, hopefully into one more post to complete the construction of the bot. That, and reveal the upgrades to 30lb-Überclocker for this year!

It’s Robot Season! Time for a tiny Überclocker. The Announcement of 12 O’Clocker

Aug 10, 2013 in Project Build Reports, Twelve O'Clocker

Wow, how’s it almost the middle of August already? You know what this means?

That’s right. Basically, for the past few years, every late July and all of August has been spent rage-prepping robots for my annual robot party that I’ve gone to compete at since…

2003.

Holy shart, this one better be good then! And what better way to make it good (…besides having functional robots for once, I mean…) than returning to the 12lb class from whence I came?

It’s been a long, long time since I had a functional 12lb class bot. My parting shot at the class was in early 2008 with Test Bot 4.5 at Motorama 2008. At the time, the NERC Sportsman 30s were just barely becoming a thing, and after that event, I decided to participate in the class instead. The 12lb class at the time was just becoming infected with the “Brushless Penis virus”, in which builders rely increasingly on spinning larger and larger chunks of tool steel with larger and larger brushless motors, leaving the class designs polarized towards either those or heavily armored boxes without other redeeming features. Matches basically came down to who got in The Hit first and often ended with both bots being disabled or otherwise gimpy and hobbling.

It’s like being a dubstep groupie – always about The Drop, but with robots, so half the match you’re just waiting for The Drop and talking for days afterward about how brutal The Drop was while picking splinters of A2 tool steel from your forehead.

That game got boring for me fast. So, I spent my next 3 distracted years building dysfunctional versions of Überclocker, until last year when I finally seemed to manage something remotely interesting.

With Überclocker Advance seemingly performing up to snuff at Motorama 2013, and only needing very minor repairs and upgrades for this year (to be detailed soon), it was time to think of new robots. If I were actually good about sketching out my designs, what would follow is a small thesis worth of fantastic fun machines, none of which would actually qualify for conceptrobots.blogspot.com.

But what I really want is a tiny Überclocker. Ever since version 1 back in 2008, I’d wanted to scale it back for the 12lb class. This hasn’t ever happened yet since I’ve had enough fun getting the actual Überclocker to work properly. I’ve also thought of doing up a beetleweight or antweight version. Past that, the thing which has kept me from developing the idea further is that I was reluctant to build a bot for one event: Robot Battles is the only event I am aware of that has a “sportsmans 12lb” type competition – even though its own competition is much different and came way, way before the modern era of robot fights. Events like NERC Motorama would force me to run this elaborate contraption with the brushless pen0rs.

I’m not sure when I decided to actually pull the trigger on this design. Originally, I was hoping to make a grand comeback with Test Bot 5. I’ve completely designed Test Bot like 17 times over since 2008, but the basic flavor has been the same – a 4-bar lifter with a solid and fast drivetrain. Sadly, this is as far as I got on the last ‘redesign’:

Not even sure what I was getting at any more. Oh well. Those saw motors aren’t even available now.

I figured that all of my fresh-built bots will have some kind of weird teething issue if I start this close to the event, and that would be quite an embarassment to the Test Bot name. I’ll bring that back when it’s ready. Maybe having a 12lb Clocker would encourage the development of the 12 Sportsmans up here quicker – there’s been plenty of talk about it, of course, but we just haven’t quite hit critical mass yet.

Like Überclocker Advance, I jumped into Inventor and made up a quick sketch just to get the dimensions down and see what might fit where. This is where this entry will degrade entirely into CAD pictures!

This skeleton drawing was made about 2 weeks ago when go-kart season was in full swing. Part of what I wanted out of this bot was a bit of ridiculousness. After all, it’s a small Überclocker, and any good chibi version of an existing thing must emphasize its best features. This bot was going to be all fork – or at least the fork will prominently feature in the design. The body will also be shrunk into something with a higher aspect ratio for a bit of the goofy look.

I had in stock several 2.5″ “McMasterBots” wheels – the 40A type – for what I can only imagine was the next Test Bot, so I elected to start the design with this element, even though I think it would have also done great with 3″ and 4″ wheels. Some times, you just need to “ground” the design somewhere or you’ll never start. So this bot will be tall, with tiny wheels (but still plenty of ground clearance), and a giant fork.

One question I had which I tried to solve early on was what to use for drive motors. In the 12lb class, if you’re a pusher type, drivetrain-tensive bot, a set of 500-class motors is about the norm. When “hobby tool” sized cordless tools were easily available in the early and mid 2000s, four of them with their RS-380 motors made a typical first bot for many folks – and Test Bot’s third incarnation which last competed in 2005, and should still be around here somewhere, still uses them. I really wanted this 12lb Clocker to have a forceful drivetrain, since it would likely need to travel around carrying an opponent.

Speedwise, my choice of wheel size precluded using even the 24:1 single speed cordless drills – it would have been dirt slow. I was spoiled by Überclocker Advance’s near-20mph top speed and excellent handling with the 40A wheels, and I wanted something similar for this bot. I briefly considered a set of Vexboxen, but at my required ratios for direct drive (wheel-on-gearbox) it would have been too long with a motor, and would have made the bot like 16″ wide – almost as wide as 30lb Clocker.

Space-wise, an external chain reduction similar to the near 1:1 indirect drive of 30lb Clocker was the most feasible, since it meant I could keep to a single speed gearbox. To minimize size, I decided to make my own gearboxes:

The hell is that? It’s what I’m calling the Angerbox. Like Vexbox and Ragebridge, and other similarly pissed-off sounding robot parts. What it really is is a 3D printable case that holds half of a drill gearbox. Similar to what I did on Test Bot back in the day, cutting a drill gearbox in half and (preferably) using the all-metal output stage nets you a 6:1 reduction. What you see there on Test Bot’s motors is a 2:1 spur stage feeding into the 6:1 planetary output stage, creating a 12:1 gearbox that gave Test Bot a nice 15mph top speed.

I plan to implement that roughly 2:1 reduction using the chain drive this time. 6:1 direct on my 2.5″ wheels would give a top speed of like 25mph, which is a little over the top, but would burn out the motors quickly.

Here’s the Angerbox placed in the frame for first sizing passes. I also drew in various sprocket pitch circles to see what ratios made sense. In the end, I settled on an external 14:24 drive, yielding, with the 6:1 planetary and anticipating overvolting the 18v motors (since I have an asston of working motors with destroyed gearboxes from Null Hypothesis) to 8S (25v), to get me a top speed of 18mph.

Why a 14 tooth on the motor? It was the smallest sprocket that had a hub big enough to enlarge to 12mm bore (drill shaft size) and have enough meat left to hold a big set screw thread. Most times, “the math” doesn’t take these physical considerations into effect – this is one of the big lessons I try to get across in my Silly Go-Kart Camp, that you can math until the end of the world but your project still must exist physically, which implies other constraints.

A 12:24 would have been a clean 2:1, but the sprocket would have been so small that attaching it to the drill shaft would have been damn near impossible without machining the drill shaft down to size (weakening it greatly of course…)

I imported the old drill parts from Test Bot’s CAD files (after cross checking with my bag of drill parts to make sure I actually had the correct types), so here’s what the mostly finished angerbox CAD looks like. The stock drill shaft will be cut down to fit in the bot. The case will be a quick 3D printed jobbie (Hey, the drill cases are originally made of shitty plastic anyway, okay?)

Using my 2D drawing as a visual reference, I started designing up the actual parts. Unlike all the Überclockers ever, this design will feature “overhung”, or single supported wheels. I tend not to favor them, but both weight and goofy looks might force me to use them this time. To make up for the single support, the axle pins are huge for a 12lber: 0.5″ aluminum to be made with my left over 7075 stock. A little bit of overkill, but the fatter the axle the less bending they experience for the same load.

At this point, I’m just trying various different layouts of parts to see what makes the most sense. The batteries, just a single string of A123 26650s, dominate the decision. I decided to make the frame tall enough such that they can stand fully upright, or else the square footage of the bot was going to increase drastically.

Hmm, I *could* make the bot longer and ditch the sloped rear to gain a bit more interior volume. This was, again, one of about 5 or 6 ways I arranged the parts before moving forward.

Another config again, still with a flat back. This was the frontrunner for a while…

Until I realized that with a flat back, 12lb Clocker was hopeless if flipped over, which it fuckin’ will be, most definitely.  That made me switch back to the sloped sides, and it also made the bot’s profile more symmetrical. This design would allow the rear wheels to touch the ground just a little to putter me around for a quick escape. I’ve moved on to the more important parts now – the fr0k. Other elements such as the drive chain tensioner (imported straight from 30lb Clocker, mostly for placement and looks) and the clamp actuator have also been rough-placed.

This clamp actuator has quite a history. I made it all the way back before Dragon*Con 2008 for the the original Überclocker when my previous design failed in testing right before departure. Between this and the imported 6:1 gearbox idea from Test Bot, this bot is bringing back some serious history! The original 20:1 (or something) small gearmotor on it was stripped, so I replaced it with a 9:1 HP Pololu motor. This thing was the first custom linear actuator I built, which made me go crazy afterwards with the Cold Arbor actuators.

I’m going to stick a stock 36:1 HF type gearbox on fork duty since I have many of them and they can be easily converted to all-metal gearing because of the identical 6:1 stages. That and because I need all the reduction I can get for this dumb fork. A 60 tooth sprocket is the output stage, driven by a 13-tooth sprocket on the drill shaft.

Why 13 teeth?! This size sprocket is small enough, and the spacing of the drill motor serendipitous enough, that I’m just tapping it for the 3/8-24 thread on the drill shaft and threading it the fuck on there. A 12 tooth’s hub is too small and a 14 tooth doesn’t get me as much reduction.

With the almost-5:1 reduction from the 36:1 box, I’m still looking at 150 rpm on the arm shaft. This is something like 10 ft/s of linear lift speed. Fast enough to be used as a really bad hammer!

The motor will be mounted by some 3DP’d clamps that conform to the shape of the gearbox. I designed this part to be serviced just like 30lb clocker – four screws and the whole motor can drop out the bottom. No more removing 75% of the bot to fix one thing like last year, ever.

Getting close to the final appearance here. I’ve added a first-pass geometric model of the clamp arm. I literally picked reasonably random numbers for the rise and slope of the portion where it attaches to the fork. Brought it in, see how it looks, and change if needed.

This is, of course, another lesson I try to teach in Silly Go-Kart Camp – at some point, you gotta start putting your design down and stop trying to solve for every dimension analytically before you open Solidworks. Once you have a starting base, then you can adjust and optimize dimensions and placements based on constraints and whatnot. That’s why I just started throwing rectangles at trapezoids at the beginning.

Too many times I’ve witnessed people sitting while staring blankly at sketches on a piece of paper and an empty CAD screen, not knowing what to start designing first. The answer: all of it. Right now. Or I will fail you.

I went through quite a few iterations of the clamp motor placement, too, before realizing the best position is basically where I had it first. In this position, the motor is well out of the way of the action and the leadscrew length can be kept short, which in this bot is critical for weight.

Notice the Clampy Shaft Collars of Unintended Power Transmission. I’d use the stock 3/4″ flange collars on McMaster, my favorite for go-kart steering linkages, but they somehow got EVEN MORE expensive. And they’re steel.

Can’t do that on this bot. I just bought some aluminum clamp collars and will just drill my own damned holes in them, because when you average it all out I make like $9 an hour anyway and I know drilling 6 holes is going to take less than 3 hours.

Getting a little more detailed up front now. I’ve added the leadscrew attachment joint and the lower fork standoffs. The leadscrew will be anchored directly to the fork this time – it will be a little harder to disassemble if I JUST need to get to the anchor, but the screw itself will be easily disengaged with one epic set screw. This is for simplicity and also weight savings.

Clocker’s “reactive outriggers”, or its spring loaded leggy things, are kind of its trademark. They’re also responsible for the various tricks it can do to opponents, like driving while clamping them or twirling them in circles.

On 12lb Clocker, a discrete ‘shock absorber on swingarm’ setup would be unnecessarily heavy for how rigid it needed to be. So I had a bright idea of making a flexure leg using a stick of spring steel as a leaf spring.  It only took like an hour, 2 FEA simulations, 3 Wikipedia pages, and a few MATWEB searches to do what amounted to a simple bending-beam problem, but using what’s available in the McMasterBots catalog, I found that either a 3/32″ or 1/8″ thick 1075 steel strip that’s 1/2″ wide will work. The 1/8″ was a ‘worst case’ estimate of a 12 lb opponent hung all the way out on the end of the fork and the legs deflecting no more than 1/2″ at the tip.

So what do I use? Well, I just bought 1 strip of both and will make both of them. I really want to see how this bot drives on one or the other before deciding.

Attachment-wise, aluminum machined anchors hold the spring to the body of the bot, and it passes under a standoff extension of the front axle pins, starting the bend at that point. Kinda-sorta – the “roller” constraint means it will actually start bending before then, but the distance from the standoff to the anchor is short enough that I don’t think it will contribute significantly.  At the tip, another machined anchor will be bolted to the steel and have a little ball roller riding on a shoulder screw coming off it.

To machine the Rockwell C44 spring steel, I snagged a cheap F size carbide stub drill off eBay since finding this around campus will be less than likely (nor do I want to ruin someone’s $50+ carbide drill by being too enthusiastic with it!)

Quick overview shot now that the major geometries are in place. Out of a practicality concern, the fork isn’t as stag-beetle-esque as I had originally hoped for.

At this point, I imported 30lb Clocker for a size comparison. Clocker is a huge 30lber – by footprint, it’s larger than some classic 60lb Lightweight Battlebots. This is due in part to the need to contain most of an opponent, and a long wheelbase/wide track make for greater stability once contained. So Clocker has never been very dense.

12lb Clocker is a little better in that department, but it’s still pretty big for a 12lber. It’s a full 14″ wide and 9″ long if you only consider wheels, and this isn’t too bad, but this increases to 17.5″ from back of wheels to front of fork.

With major parts complete, I checked the simulated weight: 11.4 pounds including the top and bottom armor, which are not visible in this picture.

Oh boy. This is without wiring, without modeled chains, and without most big hardware. It’s time to start “gothic cathedraling“, as I call it. Since these plates are going to be waterjet machined, I only have “cut through” or “not cut at all”, so things will look pretty spider-webby when done. First to go is the big sprocket.

Before starting on the “cathedraling” proper, I designed in all the corner gussets and final top/bottom armor attachment points. The torsion box up front and the gusseted C at the rear are very similar to how 30lb Clocker is set up.

The “cathedraling” this time is mostly X trusses, nothing too special. For kicks, I decided to add a simulated chain, and boy am I glad I did.

I totally forgot that, even though there is a pinch roller tensioner in the posterior run of the chain, the anterior (front) just goes straight down. And intersects my frame rails.

A bit of modification to that area later and I was all set again, only gaining back like 6 grams.

Cathedraling complete, and now with top and bottom covers mounted, including the huge obnoxious 12:00 cutout up top.

Why 12:00? Because it’s 12 o’clocker!

I really want to get a big EL panel kit and put it behind the cutout and have it blink 12:00 like an old VCR or broken alarm clock.

The weight as shown is 10.6 pounds. I’m now within the realm of possibility for making weight after factoring in the rest of the hardware.

The last detail I needed to address was the chain drive. The tensioner I imported straight from 30lb Clocker would work just fine, except the wheel placement would have caused the bottom run of the chain to hang like 1/4″ below the frame bottom! That’s just asking to get snagged on something and broken, leaving me stranded (again).

Not allowing that to happen. I rerouted the chain over two smaller roller tensioners such that for the most part the undercarriage is clear of chain runs. If weight allows, I’ll put a 1/8″ polycarbonate or other lightweight shield over this area to prevent accidental mishaps.

Here’s a better size comparison between 12 o’clocker, Überclocker Advance, and the 2008 version of Test Bot. So I guess 12 o’clocker isn’t really that big – TB was a full 12 x 12″, plus a few more inches of wedge and lifter arm.

Since the kart class caused my updates to run behind schedule a bit, I’ll put out a spoiler: The parts for 12 o’clocker have already been machined, and I can hopefully assemble most of the bot this weekend! Also on deck is a report on 30lb Clocker’s new clamp actuator, and more info on the D*C Robotics Track panels I intend to do this year.

 

DERPDrive: The Assembly; Plus, Some Other Neat Parts: IG32 Gearmotors and Scooter Pulleys

Aug 06, 2013 in Beyond Unboxing, derpdrive

It’s been a little while! My entire previous week was spent preparing and organizing the big summer MIT-SUTD go-kart race which went down on Sunday. Yes, that’s a thing. The summer class is not totally over yet, so that report will come shortly.

In the mean time, I want to pay attention to something which has been a little neglected over the past month as I devoted more resources and time to making sure the class ran on schedule and people were able to finish up. That something is DERPDrive, which, given that I found one of my structural frame tubes being used as a go-kart wheel chock the other day, was pretty damn forgotten. Luckily, it’s now assembled and already through one attempt at a test fit for which I could not conjure enough macho to accomplish. It’s general knowledge that I look just as home in a Miku costume as anything else, and sheer manpower is not one of my notable traits. The test fit will be repeated once I can get a team-lift going.

Here’s what all took place.

After watching the paint dry, DERPDrive was unceremoniously shuffled to one corner of the shop as the students’ build season really started kicking in. Over the course of a week or two, all kinds of mayhem landed in my parts box – from safety goggles to tools to other people’s drivetrain parts. One thing that I keep trying to instill in high-intensity overachieving engineering students is how to pick up your own droppings as you work, and how throwing all your tools from the day into the nearest bin doesn’t constitute cleaning up in the least. This occurs with varying degrees of success.

Since the primary mechanical parts of this thing had already been machined and ready weeks ago, all I needed to do was assembly. This went quickly:

In this configuration it has already been mistaken for a motorcycle jack or some kind of pressing tool.

The next steps in assembly included mounting the astronomically huge bearing blocks. Into these 1.25″ bore blocks will be mounted a solid (unless I feel like saving about 2 pounds out of over 100) 1.25″ steel keyed shaft. The holes next to it are for a 3/4″ steel auxiliary shaft, and holddown method for all of them is 1/2″ fine-thread bolts and grade-mismatched-because-that’s-all-i-could-find hex nuts. These things are surprisingly cheap on the surplus market.

They’re also built for serious slop. I assume the target market is people who assemble entire production machines in a cave, with a box of scraps, because every part of them is adjustable.

The mounts are slots, so they can slide back and forth. And the bearings are captured in spherical housings, so you can have shafts that are just eyeball-aligned. So that’s how Tony Stark did it.

The next degree of freedom to adjust is centering the 11″ go-kart wheel and hub in the center of the swingarms. I mounted the wheel on the hub and eyeball-aligned it, then clamped the hub in place. When the wheel is mounted, I can’t reach the keyway clamping screw , so this adjustment needs to be done beforehand. Normally, these hubs are used on the very end of an axle, not in the middle.

The Big Axle assembled. Notice the overlay on top of the frame jacks – this is 1/16″ 80A neoprene rubber glued to the steel. A thin compliant layer ought to increase the amount of friction generated by the jacking force. That’s the intention anyway – I don’t think I will have “detaching issues” when the wheel is down with a few hundred pounds on it.

Now this thing is getting scary. The 52 pound D&D sepex motor is now mounted, and I’m really, really having trouble wrestling this thing around on the bench. It is just now dawning on me that this might be a little more hardcöre than necessary.

But just think of how awesome of a go-kart it will make had already made! This motor has had an interesting MIT tenure for sure.

The midshaft is now mounted. The little sprocket for the final stage is behind the larger one in the front. Between the two stages, the total gear ratio is 8.66:1, which should yield a top speed of about 15 miles per hour (for a certain high field current of the motor – field weakening, a feature available in the Alltrax controller I’ll be using, will produce an artificially high top speed if acticated).

While the motor is capable of much more power to push the vehicle faster, recall that I’m gearing for a high enough thrust force to get the van out of my parking garage, not to do really awkward silent cruises in front of local night clubs while implying that I have something which hangs down really low.

This whole rig now weighs north of 110 pounds, and getting it down from the bench was probably one of the most precarious situations I’ve found myself in.

It’s time for a test fit…

The crime scene. The plan was to back DERPDrive, facing the right direction, under the two frame rails it will squeeze between, and then hold it in position while I tighten the jack screws.

Alright, I definitely didn’t think this through very hard. Minus the jacks, that’s roughly what the assembly’s going to look like once installed. I accidentally found out that my spring preloading setup works really well when I trapped the swingarm against a jack and was still trying to lower the whole thing.

After a multitude of jacks and bottle pistons and failed attempts at bench pressing the thing up to where it needs to go, I decided to give up before dropping the entire van on myself. This is gonna be a 3-hoodrat effort at the least, and I might need to fiddle my way back onto the lift. I got it almost there – but the whole “hold this thing with one arm while trying to reach the jack screws” thing was just not happening at all. This will certainly be troublesome in the future when I have to deal with 1000lbs of batteries and 200 pounds of Siemens motors. Now we know why I build little things most of the time…

What’s nice, though, is finally getting off the bench. Can you tell which half of this bench I parked one of my project heaps on for a month?

More DERPDrive will come after I secure a test fit!

slightly past unboxing: IG32 gearmotor, timing pulleys

I’m not sure I could call this section beyond unboxing, since there wasn’t much to unbox, so let’s roll with slightly past unboxing then?

It’s August, and there is exactly 1 thing I do in August and that is robots. I need to get my fleet gear for Dragon*Con, which is basically in three weeks including travel time. Yep, I’m in that situation again.

Here’s the situation. Überclocker desperately needs a new top clamp arm actuator since the previous one was so damaged at Motorama (see the bottom of the event recap). The leadscrew got pretty chewed up since it was the first thing to hit an opponent that really sunk deep into the fork, so it would bind at the top of travel. And it had more than enough bottom travel, letting the top clamp actually poke out under the fork, which was just unnecessary. Plus, the oddball chain drive I designed is only getting worse tension-wise, and it really has to go.

I wanted to rebuild the clamp actuator using a stock gearbox (so I can have multiple on standby) and not using those damned chains. It should be much lighter than the current half-a-drill setup I got going on, and not nearly as powerful, because there’s no reason to need a full 550 motor on grabby duty.

I already have a fast-travel (1/2″ per turn!) precision leadscrew and nut, so I’d just need to find a motor with higher ratio to get a manageable clamping speed. Going from 0.1″ to 0.5″ per turn would mean a motor that spins 1/5 as fast, or is 5x more geared down. This puts me in the neighborhood of a 30:1 gearbox with a 25,000 rpm motor (18v drill motor overvolted to 7S lipos, or 25.9 volts).

I took recommendations for reasonably nice gearbox, and one of the candidates (recommended by Jamisong) was the IG series from Super Droid Robots. I’ve seen these before, and had been eyeing them for a while, but never had a reason to buy one since I’d been well-pampered by chopping power tool motors. They seemed like a nice compact solution that I could merge with a 400-class motor for less weight.

So I ordered three for kicks, adhering to my 2n+1 Rule of Procurement for Stuff I Can Afford.  One for using, one for backup, and one for fucking around with!

Here they are! Cute little setups, really. The RS-380 class motor it comes with is quite possibly the mildest wound motor I’ve ever ran. The gearbox itself is constructed from a few die cast aluminum parts, and the ring gear is steel with an aluminum over-sleeve-wrap-thing.

…but that’s all I have to say that’s productive and nice.

What is with you people and plastic gears?

The first stage is bullshit plastic! Ostensibly it’s for ‘noise reduction’, but all I see is cost cutting. I will gladly pay like $5 more for some metal in there.

Well there goes any potential of overdriving the motor significantly, or replacing it.

The difference in gear strength is incredible. So you go from 2.5mm thick plastic gears to 5mm thick steel. That’s way, way more of a torque increase than the plastic can handle. If those 2.5mm gears were steel, too? Certainly, then the progression of torque makes sense. But this is just cost cutting, one that happens in enough gearboxes today to piss me off.

So for $20, I’m not going to argue at all with what you get – I’m sure these things work for exactly what they were designed for. But damn, I’m not going to put up with this for actual robot use. Glad I got three – because my intention for the bot is to combined two of the gearboxes into one that has all-steel gears. The untouched one can be for emergency backup or something where I know I’ll have to go extra sissy on the throttle.

Next up on the list is something interesting I found on TNCscooters while I was putting together a weekly student group order list.

It’s a big timing pulley! Specifically, it’s a 5mm HTD pulley, 80 teeth, that has a center thread which mates with most threaded scooter hubs. These seem to come in three sizes.

Even though the material looks like very crudely cast aluminum, this is still good to see existing because typically, you can’t find HTD drive pulleys in very large sizes from industrial suppliers. At least not in a form which could mate to a purchased wheel in this sector of industry.

Here’s an example of the kind of rim you can thread these pulleys onto. The thing on the left is a typical 8×2 tire rim (example 1, example 2). For non-regenerative vehicles (which do not perform motor braking), you’d probably want a strip of teflon tape or other anti-seize tape on the threads, lest over time these two things become one piece of metal. For regen vehicles, there’s not much choice but to use some light threadlocking adhesive to prevent the pulley from unthreading upon motor braking.

If you aren’t inclined to use the cheesy cast aluminum thread, then those four little hole pilots in the center near the raised hub is the exact same spacing as the four lug nuts on said rims! So, you could do it standoff style by drilling through the pilot holes and bolting it directly to the rim.

This is a typical arrangement of the two parts. On the left side thread, you’d mount a band brake rim or brake disc adapter or similar.  This ought to help those who want a synchronous belt drive like melonscooter but have found that commercial HTD pulleys are a pain to interface to without machine tools.

So concludes another episode of Slightly Past Unboxing! Coming up next are a full report of this summer’s go-kart shenanigans, and a catch-up of what I’ve already been doing with the robots in preparation for Dragon*Con.