Archive for August, 2016

 

Roll Cake Rises; Überclocker 4 Begins

Aug 26, 2016 in Bots, Roll Cake, Überclocker 4

On this episode of “Charles is still CADing everything distressingly close to Dragon Con“, we continue with the development of Roll Cake to the point of completion, as well as begin with I CAN’T BELIEVE IT’S NOT OVERHAUL! Überclocker 4! I depart for DC 2016 in a few days, so there will hopefully be some updates on the physical construction of these bots on the road and in Atlanta.

So I spent quite a few days on and off puzzling over how to place components in Roll Cake. As I said last time, putting square things into a triangular robot often requires a lot of compromises and “dimensional exhuberance”.

This was one of the choice placements, using a 850mAh 3-cell lithium battery, the same kind used in Colsonbot. I also had a few 1000mAh ones used in Stance Stance Revolution, but they proved to be too long in every configuration here.

One of the other “mid experimentation” screenshots. I tried locating the battery on the same side as the drum motor. This involved pushing the drum motor to the interior of the bot, an option I was not favoring since it means the drive pulley was going to be pulling on the motor can farthest away from its bearings. This would end in certain tragedy.

Plus, it’s not like this side of the bot somehow had MORE length to put a battery in!

I decided on the configuration seen here after more component juggling. This places the battery in the flatter configuration (meaning it sticks out of the side more), necessitating making the whole bot wider by about 1/4″ to accept it. However, this meant the servo could be on the same side as the battery, which was highly advantageous.

Here, I’ve also generated the motor pulleys. The wheels were a design I already had; it is a little hard to tell, but the pulley sections have a V profile instead of the square bottom usually seen in small round-belt drive pulleys. I’ve found that this tends to give better grip for small pulley diameters, working a little like a V-belt. It also tends to be more tolerant of misalignments, since there is no square side for the belt to suddenly grab and be pulled off, and is also auto-centering.

The tires are a takeaway from Colsonbot and SSR, and are actually 1″ diameter rubber grommets (for sheet metal panel holes where, for instance, wiring or tubing pass through). They’re made of soft rubber and can be easily stretched over a hub. In this application, I’ve stretched them to being 1.25″ diameter.

Due to the tightness of the space around the battery, I did something I rarely do – simulate the chain or belt path. The 3/32″ roundbelt drive unfortunately has to make a Cleveland Left past the battery, in an area with minimal clearance. I specified and ordere some tiny little type MR63 bearings for this job – 3mm ID, 6mm OD.

 

Here’s the belt path simulated . It will need some grooves designed in into the frame to clear. I didn’t want to make the wheel pulleys any smaller due to the limitations of the round belt – too small a pulley and they don’t grip nearly as well.

 

The belt kink also allows the motor drive pulleys to achieve nearly 180 degrees of wrap. So at least I know that part isn’t going to be slipping! It also directs the belt up and away from the drum motor.  I changed the drum motor to a slightly larger 2836 type motor which has a larger 4mm shaft. This desketchifies the pulley mounting significantly. The motor has been moved back to the interior of the drive pods, with the region around it beefed up in thickness and ribbed for its pleasure and rigidity.

All of the control electronics have now been moved to a pocket on the right side of the bot.

With the sides of the bot figured out as much as I care to, it was time to move to the clutch triggering mechanism. You know your unibody design has gone horrifyingly wrong when you have to start slicing the view to work on stuff.

The channel cut into the body here holds a sliding bolt-like structure which will be toggled by the servo.

Like so. This is shown in the retracted position, where the linkage holds the planetary gearbox’s output ring stationary and therefore the dog clutch ring spins freely.

And in the “This kills the servo.” position, where the sliding bolt impedes the motion of the dog clutch gear, forcing the output ring to begin spinning. This throws the cam linkage.

Based on the advisory speed of the clutch gears, which is 237.5 RPM (950 rpm/V * 11V battery / 2:1 gear ratio, then divided by another 22:1 in the gearbox) and the width of the valley between dog clutch teeth, the servo will have roughly 70 milliseconds to move the sliding bolt. These servos are rated at 0.11s per 60 degrees, and the bolt travel only needs about 15 degrees, so I HOPE there’s a healthy margin here.

The directionality of spin matter s alot. The frame is only bracing the sliding bolt in the configuration shown where the dog clutch gear is spinning clockwise. This means Roll Cake actually does have an “upside down” since the drum can only spin in one direction to use the flipping linkage. Hopefully, in a bigger version of the bot, this shortcoming will be addressed.

During this design work, I was thinking ahead a little as to how to 3D print the final product. The unibody turned out far too complicated to print in one piece, so I elected to split it into 3 pieces – left, right, and center.

One problem though. The bearing mounting supports for the drum, which are also the pivot points for the hinged flippers, make the left and right sides not completely flat if I sliced the part on the inner faces of the left and right sides.

I decided to make those rings a separate print each, allowing me to print the two halves concave-side up using no support structures, which results in a cleaner print.

Therefore, I added makeshift bolt holes on the inside of the drive sides, which eventually will have screws threaded through into the bearing mounting rings.

Each side had features added which allow me to fasten the side covers. Because the bot wasn’t symmetric, the attachment to the center U frame was different on the left and right.

One last detail was how to pass wires through. Besides the through-hole at the very back of the bot, which is supposed to fit a threaded rod (a last ditch everything-is-fucked way to keep the bot together), I put in two more semi-through-holes linking the left and right via the central frame. One will pass the battery cable, and another will be servo power and drive motor wiring.

I moved onto the final little details of the bot. Drums aren’t that effective without little feeder wedges to direct opponents into them, so I made small extensions that will mount metal — likely spring steel – wedgelets.

The side covers contain a few more injection-mold like elements to line up with the left and right sides. These will be made of heavily fiber-laden Onyx material as a desperate bid to fend off other weapons. Unfortunately the bot was already a bit overweight at this point, so no real armor here!

With the addition of the wedgelets and filleting every interior corner, the design is complete. To service either side of the bot, the five countersunk screws are unscrewed (the shoulder screw for each wheel axle is not bolted in, having clearance holes for the heads, so I can run the bot without sides easily and also not have to juggle wheels each service.

The hypothetical open position of the flipper.

And here is a “transparent frog” photo showing the incredible mess going on inside this bot. Like I keep saying, I’ll be damned if it does anything meaningful besides self-destruct.

And now I cut up the frame for 3D printing! Five parts total – two sides, the center U-frame (which will be heavily fiber-braced), and the two bearing support rings.

As a preview for what Roll Cake looks like IRL, here’s a pretend-o-bot from this past weekend. There will be build reports!

I CAN’T BELIEVE IT’S NOT OVERHAUL!

This post is now about wheels.

Hah, you thought you were getting a Überclocker design update. Well, in a way, it’s highly relevant, since I’m designing and casting custom wheels for this build from urethane resin and 3D printed molds.

One of the shortcomings of Overhaul this year at BattleBots Season 2 was the horrifyingly bad traction in the arena, compounded with my choice of wheel being poor for an overpowered drivetrain. I discussed a lot of this in the beta match recap. Basically, after the tournament, I was determined to investigate making my own wheels after seeing a few builders (including Beta) do the same. For me, the goal was less to get a specific wheel size or custom geometry than to find an alternative to the thermoplastic rubber Colson wheels, since nobody to my knowledge makes a real vulcanized-rubber 5 inch tire.

After doing some Internet Research, I decided the easiest way to start was to go with a polyurethane compound. There are many choices in that space designed to fit different applications.

Most of it, though, is optimized for some kind of mold making and so was hard to find relevant information for . That’s in fact one problem for me coming in as an outsider to the industry – I don’t know the industry words and niches where different terms mean different things. I tried finding natural rubbers and synthetic rubber base ingredients, as well as vulcanizing compounds (‘cure packages’) for natural rubber. But the only companies I was able to get ahold of were in the moldmaking & casting industry, and they’re so specialized that they didn’t know anything outside of the use of their product for moldmaking.  Anyone with connection to the world of flubby substances is welcome to make recommendations – I really want to create a wheel with the same durability as a vulcanized rubber tire, like a car or go-kart tire, just with a softer compound. Now, slicing bits of tread off real tires and bonding/screwing into a custom hub is a possibility, but I really want to look at the next level up in elegance first.

As luck would have it, I was at the Detroit Maker Faire that weekend with the usual Power Racing Series crew. I had come only to help marshal the race and act as a tech/safety inspector – Chibi-Mikuvan sat out this race since I had not repaired the damage from last year’s New York Maker Faire. 10/10 would get sunburned again. I managed to get ahold of some Smooth-On company reps at a booth, so I got to hassle them with questions about the gooey substances they manufacture, including such cold-open gems like “So, what rubber would you use for a Battlebot wheel?” Based on the response, I’m apparently better at picking up middle-aged company sales reps than the ladies.

After 10 minutes of explaining what the hell it is I’m actually doing… since they’re mostly here again for the moldmaking and resin casting of tiny figurines and the like, two compounds came up very quickly – ReoFlex, a urethane rubber, and Simpact, a “rubberized plastic” as they put it. Both are, as far as I can tell, urethane-based. ReoFlex comes in softer Shore hardness ratings (20-50A) and Simpact in higher ones (60-80A). For reference, a skateboard wheel is usally 70 to 80A, a car tire around 60-70, and Colsons that are used in robots are usually their 65A Performa line. They were both recommended for higher tear strength relative to other similar products, which is important for wheel integrity.

So I went to Reynolds Advanced Materials locally and got a few hits of the stuff.

Lovely. Now what? Do I just pour one into the other and run for it?!

I next designed a core to hold onto the rubber tire. I knew nothing about this, and couldn’t find any good resources about “How to design cores for urethane rubber wheels”, so I freelanced based on what makes sense in my head. Those features were:

  • Lack of hard square edges – gradual transition angles between rubber and plastic
  • High surface area for good bonding
  • No overhangs that can trap air bubbles
  • Through-hole features to enhance gripping the rubber in case bonding fails

That’s what I came up with. Just a basic tapered V shape that has a bunch of through-holes around the permieter. I referenced the outer dimension of a 3″ Colson wheel, so if everything fails miserably, I can bail out to Colson wheels.

I desigend it so it could be 3D printed without support structures, so I can pass it directly from print bed to mold. Speaking of mold,

I then designed up a two piece mold that the wheel core sits in. The tread around the outside was added as an additional element to help traction in a box environment. The argument of tread vs. slicks has been a perennial subject in robotland, and now with my experience in the BattleBox, I think it’s pretty critical to increasing your effective traction. While a smaller bot like Clocker won’t really need it, I wanted to experiment with the molding aspect more, so treads it is!

The reason I think a light tread pattern is beneficial is because while you’re not trying to displace water or mud like in a road car tire, or grab onto rocks and dirt off-road, there is still plenty of fine powder-scale debris in the average arena. This debris is made of little metal bits, worn tire rubber, and SET SCREWS some times loose hardware. A tread that helps evacuate this debris would help put more rubber on the floor.

Tread design is one of those things I could spend a lot more time reading about than I had patience for at the moment, so I went for a simple helical groove pattern. The idea of the helical groove is to keep the contact patch relatively consistent (think meshing with the ground like helical gears) while trying to spread box debris sideways.

The mold was designed as one piece and then split into two pieces. Registration pin holes (not shown here) will keep the two mold halves aligned when together. A hexagonal bushing fits in the wheel and also keeps it centered in the mold.

By the way, I FINALLY, after literally 10 years, learned and used what Autodesk Inventor has for “part configurations”. In Solidworks, configurations are variations on a part stored in the same part file, so you can make different length standoffs, or different sized wheels, that each have the same feature history – no Save Copy As bullshit. In Inventor, this has been JUST barely out of my workflow path to be annoying enough and JUST stupidly named enough (SERIOUSLY? iPART???) that I have, almost on principle, never learned it. As a result, when I need to do a project that will make use of Configurations, I actually use Solidworks. And when I do my own stuff where my CAD file structure can be a Nightmare beta, I just Save Copy As or liberally spam Derived Components.

But that’s no more, because I watched a 5 minute Youtube video showing the basics of iParts, iAssemblies, and iMates, and just freelanced the rest based on expectations and mapping from Solidworks.  So there! Now I’m fully Solidworks-free :p

And that’s how I made a 2″ wheel and mold just by editing some numbers in a table!

The molds were printed using the Mark Two machine in basic nylon, almost hollow. These didn’t need to be structural, after all, just quick to make.

Mold halves with finish-sanding on the flat face (there was a small amount of warping) and installed registration pins.

The retainment method is by a single hose clamp.

This is what the wheel looks like seated into the mold. A 1/4″-20 bolt keeps the wheel core tight against the bottom of the mold to prevent overspill.

I mixed up a dose of Reoflex 50 and put it in a borrowed vacuum chamber to pull out air bubbles. The mixing process introduces air, which makes your material basically a shittily-blown foam once cured and robs it of structural integrity (and surface smoothess & dimentional accuracy for people making cast objects from the material).

Next came the gentle resin pour. Simply fill to the top of the rim!

This is what the wheels look like. Pretty bland B R O W N color, but this can be pigmented if I so desire (Miku Blue wheel time??)

They feel pretty durable, but only testing will tell. This involves actually having a bot together to use them. So on the next episode: How to Scale your 250lb BattleBot and not Hate Yourself, a Self-Help Book by Charles.

Roll Cake, the Revenge of the Wubba-Wubba Drive

Aug 12, 2016 in Bots, Roll Cake

It’s time.

Time for what, Charles?!

It’s…

ROBOT FIGHTING TIME!

I bet nobody saw that one coming! It’s always robot fighting time here at Big Chuck’s Robot Warehouse & Auto Body Center! I’m your host, Big Chuck. And today, we’re going to talk about OBAMA’S ANTI-WEDGE AGENDA flywheel flippers.

Actually, let’s talk about all stored mechanical energy flipper weapons. I’m talking about flywheels and springs, but not including pneumatics. Those former two approaches have been rare penguins in the world of robot fighting, and I think there have been only a half-dozen or so successful ones, meaning it worked consistently or at all.  They both need methods to carefully input mechanical work, decouple the source, and then carefully couple the storage medium (be it flywheel or spring) to the output.

One of my metrics for how difficult a design is to pull off is how many approaches there are to the problem. I always love to pick on the “small vertical drumlet” design as an example. If you take a look at the registration field of a big open event like Motorama… or hell, even BattleBots Season 2, you see a lot of the same design topologies show up repeatedly. In the open-arena environment, those designs are the apex predators, and over time, the design space gravitates towards them. Almost all small vertical drumbots look alike and have the same idea about weapon design and drive, because it’s what’s proven to work, and if you want to win, you want to build what works.

On the other hand, just about every flywheel flipper which has existed has used a different approach to “access” the energy stored in the flywheel. You have the direct flywheel-coupled low speed punter and the automatic-tripping dog clutch of Dale, the “Jam a Colson in it” of Magneato and Zach’s previous bot Jack Reacher, and the face-cam spinning ring of Warrior (which probably has the all-time flywheel flipper high score).


The inside of Warrior (Clan…Dragon… SKF) showing the cam ring and notched linkage which rides in it, released by a servo.
Original photograph by BoomBots, rediscovered later by Kevin Hjelden

That, in my opinion, is how you know a design is still a challenge. Not to dismiss the effort that goes into building a small vertical drumlet, since reliability in a design is always difficult to attain. The way I see it is that the less a design is “settled” on a single approach means the less people have attempted it.  When it comes to spring and flywheel flippers, the engagement of the flywheel is always the sticking point. It inevitable requires tricky machining or unwieldy linkages and couplings, or clutches. Get any of these wrong and you just make a kinetic energy grenade in the arena, which is fun to watch for everybody except you.

Now, I have a fair bit of history with trying to design flywheel flippers and spring flippers. It’s in fact one of the designs I’ve tried to work on the most. For example, we now take a trip back to 2006. I had to rummage through not one, but two old hard drives to find this photo directory!

 

This was the first time I put together a “two ended” bot design. That means it has an active KE weapon that’s also used to actuate a flipper in the back. I had an interest in a design like this for a long time due to the existence of Warrior, but wanted to see it in a vertical spinner; at the time, Nuclear Kitten was still quite successful (I was, you see, the prototypical Small Vertical Drumlet kid, and this gives me infinite hipster cred, right?). After Dale build the 2nd OmegaForce, I thought that the triangular shape was well-suited to a design where the flipping linkage was a scissor type design, which just hinged on the bot, riding the ground, until commanded to open up.

It was always this opening up which was the hard part, and in fact this is as far as that design ever got. I can find no additional photos or Inventor files relevant to it.

Fast forward about 5 and a half years, and here we have the bot for which the original wubba-wubba drive post was made. This is the first time this design is being made public, because it never got far enough for me to want to write a design post. I designed a few variations of the “KE kicker” weapon, which was an internal flywheel (the large aluminum shell stayed still and the “Hard drive head” looking thing spun around it) geared around 40:1 to the kicker.

The actuation mechanism was a one-sided Differential Analyzer style torque amplifier (reasonable video here). God that’s a lot of link text in that sentence. Essentially, the post-geared flywheel spun a winding drum, around which a steel cable was wound loosely a few turns. The steel cable connected to the scissor linkage on one side and a small winch motor on the other. When the winch motor pulls on the cable, it tightens around the drum and transmits the force instantaneously to the linkage. As long as the winch motor wanted to spin faster than the drum (i.e. apply a force on the cable), the linkage would move. If the winch motor stopped, the force is released to the degree that the flipper linkage tries to pull against it back downwards. If the winch motor is powered the opposite direction, the linkage closes again since the drum cannot grip the now loosened steel cable.

It was something I read about in a textbook, then tried winding a string around a spinning motor shaft and pulling weights with it across a workbench. I was confident this idea would work. The ‘winch’ was just a fast DC motor running a sector gear that had hard stops, such that in one rotation of the drum, the motor is forced to stop and reverse, and that linear distance covered by the drum rotation was enough to fold the linkage out.

The design above did not progress further because it was too heavy. My desire to keep the mechanism coaxial made it too heavy. Furthemore, I recognized that the motion only worked in one direction. There was no powering closed, only gravity and any springs I put in the flipper mechanism to help it back down.

That didn’t stop me from making an updated less-heavy version of the kicker, which involved an external flywheel:

 

Now, this flywheel was super interesting, as I had forgotten I ever designed it. What you see is a P80 gearbox with a brushless motor built onto it.

 

Yup, you can tell this was thought up in my Era of Designing Silly Hub Motors. P80-flywheel-motor!

In the end, this design also never progressed beyond the point shown. And I honestly am not sure why – I may have lost interest and moved onto rebuilding Überclocker, or I still thought it was too messy to work well.

By the way, another artifact from late 2006 in my “D:\old\Backup of C\old\pics\old\….” directory was this:

That’s a Test Bot version 5 concept with a spring flipper. Looking back at this mechanism from where I stand now, it’s clear to me that I at least learned 1 or 2 things at MIT, which I think was the idea of going in the first place. The mechanism, while sound in theory, has a lot of nuanced problems that would have made it not work.

The idea of the mechanism was that there was a block with a ratchet/hook (think roller coaster climb ratchet) which could be moved along the bot via leadscrew. The ratchet preferantially springs towards the center of the bot and can grab a movable block which compresses the spring as they travel along the leadscrew. At the end of travel (back of the bot), a small ramp structure forces the ratchet away – this structure is not modeled here) and pop goes the spring. Then it has to travel all the way back to the start and hook the ratchet over the block again to reload. Works in principle, and I can see it working IRL with some critical geometry changes.

This, too, was as far as that design got – those who knew me in that era would know that I went to a standard 4-bar lifter for Test Bot in 2007.

So, as you can see, I’ve had a lot of false starts when it comes to these things. For the longest time, in fact I’d say since I produced these first designs in the mid-2000s, I’d never attempted to build them, writing it off to “Well, Dale and Whyachi have already done it more elegantly than I can, so why bother”, and distracted myself with grabby-bots and vehicles of questionable utility to society.

Well that’s kind of a shitty attitude, isn’t it? And one that I keep trying to beat out of others, such as my former students, whenever I had the chance. So why the fuck don’t I just take my own advice?!

People who read the MarkForged blog might have already seen a preview of this design. I wrote that article as a part of their marketing push for the new Onyx material (which is currently the only 3D printing material I care about), when this design was in an earlier stage. It was also heavily summarized for a general technical audience. Now, it’s time to dive into the full gory details of development!

Wubba-Wubba Drive’s Revenge

I first began reading about compound planetary systems (Hereafter: wubba-wubba drives) for a MIT Media Lab project during my freshman year in 2007, when we were trying to package a high-ratio steering servo inside the wheel of the CityCar project. I mentally filed the WWD away as a useful mechanism, but the filing cabinet was in a mental block scheduled for demolition due to blight suffered from Charles’ Angsty Emo Middle School Years, and as such the record was lost.

So I forgot about it until the BO-Px motors in 2.007 showed up, and it renewed my interest in exploring it. That’s how the “Wubba-wubba-bot”, which was never named, came to be.  It was a compact way to get the reduction I needed without multiple stages of planetary gears.

After the BattleBots season was over, I was looking for another “family” of robots to build, so to speak. The past couple of years have seen me rebuild and revise Überclocker, my clampy-grabby bot bloodline. With Clocker finally retired (FOR REALSIES) after its tournament win last Franklin Institute, and with the summer robot season in effect, I was thinking about what other less-loved design to pursue for the next little while. A lot of conversation with Landon (of The Dentist) about flywheel flippers… because, I love you guys, promise, but let’s make the Dentist even more out-there for #season3…. made me remember the Wubba-Wubba Bot and how I left that design hanging in space.

What if I started with a small concept and grew it eventually larger and larger? One of my problems was starting with a 30lber, I think. It made for too much of a material and effort investment into something which would probably not have worked. And with my recent habit of 3D printing stupid beetleweights, it was abundantly clear to me that a 3lb concept would be the way to start. After all, I had recently scrapped both SSR and Colsonbot ( RIP ), so had spare running gear for a small robot.

I still lacked a way to actuate the linkage that was satisfactory, however. One of my reservations about the cable-driven system was that it only powered on the opening swing, and could not apply force the other way. Furthermore, if the flipper were forced open externally or could not close (something caught under it, mechanism damaged and jammed, etc.) there is a risk of the cable bunching up and becoming tangled. A possible failure mode is the bot getting stuck with the scissor link open upside-down (or facing straight up) without the ability to close the linkage again.

All hypotheticals, but a design like Warrior poweres both on the upswing and downswing. When I was designing the Wubba-wubba Bot, I briefly entertained an alternative engagement mechanism which was brought back up while talking about designs with Landon.

The best way to describe this method is probably to watch this video of my ‘toy gearbox’ that I made for the design:

Here’s the first rendition of that toy gearbox, showing the split ring gears and compound planets – planet gears of slightly differing tooth count, but conjoined.

The way this new triggering mechanism is intended to work is that stopping one of the ring gears forces the other ring gear to spin at a speed determined by the compound planetary gear ratio. Stop the other, and the former rotates in the opposite direction at the same ratio. Basically, you pick a “ground” (zero velocity) and the other output is forced to spin with positive or negative polarity.

Say for example one ring gear is connected via a cam linkage to the flipper (the ‘cam gear’), and the other is ordinarily free to spin, but can be stopped a large brake or dog clutch (clutch gear). The stopped clutch gear becomes the ground, and the cam gear is forced to rotate the linkage. Let go, and the linkage stops the cam gear from rotating continuously, so the clutch gear goes back to freely spinning.

This method was one that I discovered by accident in 2012 spinning the WWD model, but I was intent on exploring the Torque Amplifier cable-driven method. When the original Wubba-Wubba Bot design was shelved, so was this idea.

The advantages of this method of engagement include a large cylindrical engagement surface which can be arbirarily large (e.g. to act as a brake band rotor, or give more surface area to a big magnetic clutch, etc.) and an all-mechanical power transmission once engaged, without being reliant on friction surfaces. Furthermore, it permits designing the cam system to give a sinusoidal acceleration. This means no crashing an energy source suddenly into a mechanism and forcing it to match velocities, but the movement of a cam attached to this gear can start at a point of maximum leverage.

I think I got more excited than the Dentist team over this design, so naturally I had to go make a ‘toy model’ to play with, which is shown above and in the video. The gear with the cam lobe, obviously, is the ‘cam gear’ and the other one the ‘clutch gear’.

And so begins the tale of Roll Cake, which was a robot name suggestion given to me a while back (for no particular design) by Rebecca, also of the Dentist team.

How do you start designing a 3lb-class drum spinner? With a drum!

I cooked up a fairly basic 3 pound drum. The body is made of a spare aluminum billet, and one endcap is removable and has a pulley built into the endcap. The teeth are made of 1/2″-13 socket cap screws. In this weight class, this is a somewhat common approach for drums.

Notice that the shaft is keyed. I played a little while mentally with the topology of the drum feeding into the gearbox, and decided that a live shaft was far less troublesome to deal with than a dead shaft. Reason being, I’d have to make a gear that mounts and spins on the drum anyway, and it would need to be large enough to support its own bearings.

 

I began generating the ‘toy gearbox’ that was seen above at this point. The planet teeth and pinion were chosen very carefully: They’re BaneBots P80 3:1 and 4:1 planet! The plan was to machine them down and shove them into each other to create a ‘single stage wide’ compound gear. The larger ring gear, at this point, was intended to be made from a piece of P80 ring gear, with the compound ring waterjet-cut.

That changed to the compound gear being 3D printed using Onyx material in order to save space and integrate the actuation cam. The “clutch gear” now has the aforementioned dog clutch teeth “cut” into it. In a bot this size, I elected to use the good ol’ stick in the bicycle wheel spokes method of stopping the clutch gear. There will be a solenoid or servo that carefully pokes something solid into the gear’s outer ridges.

If this arrangement is confusing, here’s what’s going on inside. The drum is the flywheel, the live shaft (not pictured) drives the pinion gear (sun gear), which drives the larger half of the compound planets.

After some drum adjustments, I went onto lay out the shape of the bot. The triangular shape is established here. I was fairly set on the shape and the double-sided flipping linkage, as it was a part of the original vision. The dimensions were, for now, best-guess as to what I’d need, and my job in CAD is just to make sure changing them later is not too painful.

Made solid and with a wedge cutout. This is when it started looking either like a slice of cheese, or a cake slice, and when the name “Roll Cake” was adopted. The shorthand project code I assigned to this bot for CAD files and stuff – such as “cb” for Clampbot (Uberclocker), and “gc” for Overhaul 2 (Giga-clocker!) is “wfo_”…. what WFO stood for I will leave a mystery.

A little more shape definition and with imaginary component placements. My tactic with unibody beetleweights is to start with a shape and “machine away” what I don’t need. I design things a lot more like what I’d do for an injection molded product, minus things like draft angles, but doing so means it won’t be that hard to MASS PRODUCE COLSONBOTS FOR EVERYONE! YAY!

The next most critical thing to do was define the arm linkage. I drew a circle that was my ideal “cam throw” and generated a V-shape linkage to fit the rest of the bot. The dimensions were all “dartboard legitimate” at first, then tuned to get the desired swing.

This was modified as dimensions required, but the linkage could open to around 45 included degrees total. There’s no point in having too much throw, as the opponent is liable to just come off, but too little means having to transfer kinetic energy in a shorter window, leading to higher part stresses. This is a general sense of things – absolutely no dynamic simulation was done whatesoever.

The sketch linkage was replaced by Real Life Flappy Things built from them. These hinge from an extension of the live axle bearing housings, and will be made from .075″ aluminum sheet. Reasonably rigid, not that heavy.

The “big cut” opened up the interior of the bot for linkage placement. I next modeled the linkages themselves. The cam connector link has one “big end” that wraps around a 6808 type (40mm bore) bring bearing, which is what sits on the cam itself. The other linkages are basic dogbones. These guys will be 3D printed from carbon fiber-backed Onyx, a material we have lovingly named Reinforced MarkForged Carbon-Carbon (RMCC), for maximum rigidity against buckling.

Notice now that the body halves are now hollowed. From here, I’ll be adding internal bosses, ribs, and cavities for the components.

I next generated the anchors to the upper and lower flaps. This actually resulted in some geometry shifting as far back as shifting the drum, so I could cut out two identical flaps in 2D (from a flat plate), fold them the opposite way from each other, and end up with the hole spacings I needed. Otherwise, the upper and lower flaps would be different parts completely.

I started running into a problem while testing the swing of the linkage on either side. There is NO position at the front half of the bot which doesn’t interfere with the linkage swing!

This meant there was basically nothing holding this bot together side to side. The live axle can’t be counted on for structural rigidity, though shaft collars at either end would help keep things together.

So the solution was to delete the crap out of that whole area, and go back to the “big cut” in the center to fatten up the back of the bot. Above is the linkage  shown in full deployment. When folded, it sits in the circular cutout at the back laterial frame member.

One solution to the “can’t hold the bot together” problem is shown here – fatten up the back frame rail and extend it into a U shape that hugs the sides of the bot. This basically sealed the decision to 3D print the frame as 3 or more pieces – left, middle, and right, and join them together. The center can be made of high-rigidity RMCC while the sides can be more conventional nylon and kevlar, which is lighter and a little more compliant.

So there we have the looks of the bot and the general placement of things inside. Coming up next? A weeks-long adventure actually trying to fit things inside. It turns out a triangle is a crappy shape to put square and round things into. Also upcoming soon, the rebuild of Uberclocker version 4.0!