Now that there is an #BrandNewSentence.
Ladies and gentlehams, this is a Golden Dumpster.
It’s several things. First, it’s the prize if you win the Norwalk Havoc event held roughly monthly at the 50Day Makerspace in Norwalk, CT.
Second, it’s a repainted Dumpsty desktop dumpster. No, this is not a joke; someone’s real life job in a shop and assembly room somewhere is manufacturing tiny dumpsters for consumption by edgy postmodernists everywhere.
Third, it’s about to be digitized and turned into a robot for Dragon Con.
Yes, this is truly the state of combat robotics today. This is what we’ve become, when all of the Ampflow brushes have melted away and all of the poorly-restrained Li-poly batteries have vaporized, the essential oil of the Harbor Freight drill gearbox. Welcome to #PostmodernRobotics.
In a way, it kind of is in the vein of those two. They’re all supposed to take the super cereal sport and turn some element of it upside down for entertainment. As you know, I tend to complain about how overly tryhard the sport has become especially with folks getting into the sport only building spinners (or worse…. only operating the same spinner for the better part of a decade) and focusing on win counts at rigid tournaments. Not that I have a strong moral basis to stand on here, since I obviously had my own era of “tryharding”. But regardless, in the position I am, I might as well keep at injecting whimsy wherever I can!
This dumpster is actually Jamison’s – not mine. I only took Roll Cake to one Norwalk Havoc event for kicks (where it did disturbingly well in a rumble, more than I expected by far!). It was bequeathed to me while Sawblaze was in temporary storage at Big Chuck’s Auto Body – you can kind of see it peek out in the background of a few photos.
Basically, we both wanted to see an assbot made for Dragon Con. With the time horizon for rebuilding Überclocker/30-haul vanishing, I decided to punt on the project instead of rush it (see, I’ve learned SOMETHING about project and scope management) and focus on putting on a show for the convention.
Obviously it was going to be almost completely ineffective as an entry – that was kind of the point. It’s too small to put any really worthwhile drive power in, at least not without actual engineering effort, and the dumpster itself actually weighs close to 8 pounds – it’s not a plastic shell, it’s actually stamped and welded steel sheet (speaking of engineering effort for questionable ends…).
My “goals” (???) for this build condensed as I was buttoning up Vantruck lighting. It was going to have powered flipping lids actuated by servos, and an internal vape system to emit a lot of thick smoke. I was just going to drive it around the convention as a neutral political statement – you can project any insecurity you want upon it! It doesn’t mean anything and nothing matters! True #Postmodernism!
I made it a curiosity goal to see if I could get it to “self right” with a linkage that allowed the lid to extend far enough. Granted, it can only ever self-right from one face only, so how much would it really matter? Does anything actually matter?
After a couple of iterations, I found a good enough solution where a 120 degree servo travel was enough to get about 200 degrees of output travel. The linkage consisting of the servo crank arm, the lid, and the coupler link in between basically was almost toggling at both ends (very folded one way or another), but was much more squared up when the lid was vertical, or when it would have the apply the most force to “get up”.
I was going to need a hefty servo – probably a 1/4-scale size – to do this motion anyway, so I was browsing for candidates as this process was happening. The short turnaround time before I was leaving kind of mandated a Jeff Bezos Special, and I ended up just going with one of these generic “60 kg” servos. No, they don’t weigh 60 kilograms, but allegedly put out up to 60 kgf-cm of torque. Do they actually? Who knows?!
They come in 180 and 270 degree travel varieties for different applications, with the latter being more rare, so I constrained the design to use the 180 degree type only just in case I had to find a spare. Always be prepared to quickly service your miniature flaming dumpster?
I was going to keep the drivetrain simple, using some 25mm diameter Pololu gearmotors I’ve had since forever. The “25mm diameter gearmotor with a centered shaft” seems to be a very commoditized motor form factor, and many generics exist and are popular with beetleweight (3lb) builders. Pololu sells a “HP” line which uses a hotter-wound motor that pulls more power, whereas the common ones on eBay and Amazon are very tame.
The drive layout was going to be 4 individual modules, with 4WD. Instead of just slinging a robot frame under the dumpster (sorry, I can’t take myself seriously typing that), which would pretty much guarantee it tipping over all the time, I wanted to hide the drivetrain within the bottom by making flange-mounted modules that attach to cutouts.
The drive bits itself are just four machined aluminum hex hubs for 1.625″ Banebots wheels I had on hand – dating all the way back to #CandyPaintAndGoldTeeth (which is a bot that REALLY could use a reboot!), and the motors are clamped in place with a U-shaped block.
I made sure to add an external support bearing for the wheels, since these motors do not have all that much output shaft support; one of the ways they get broken easily in battle is just by applying too much force to a directly-coupled wheel. They really should get external support, even in beetleweights (some get away with it using very soft and foamy wheels like Lite Flites), and definitely in anything heavier.
Here’s what it’ll look like from the bottom. The wheels are basically pushed out as far as they can go into the corners for …. stability. Yeah, stability!
I made the rest of the linkages based off the skeleton sketch model. By this point, I actually got the “60kg” servo in house, so I measured up its stock arm and designed a linkage to be sunken into it (for maximum torque transfer if this thing really can push 60 kgf-cm, I didn’t want to just rely on 2 or 3 screws)
And here we have the more-or-less final design, minus a few electronics detailed which were mostly freelanced as the build progressed. Let fabrication commence!
Making the cutouts in the bottom of the …. dumpster … was actually more strenuous than I thought. This thing is straight up made of 18 gauge steel all around. Thicker than most Mikuvan body panels, as terrifying as that sounds. I used a Dremel with an abrasive wheel to make the cuts, then used a 3D printed prototype of the motor module as a drilling template.
These components are 3D printed in Markforged Onyx, a part of this balanced breakfast. The wheel outer bearings are thin-section Inch bearings I got a long time ago for Roll Cake – they’re type R1212, 1/2″ bore 3/4″ OD and 5/32″ thick. I rather like them for doing little inch-centric quick projects, such as this one!
Four of the motor modules assembled together. This is a very formidable beetleweight drivetrain, all things considered.
I went just maybe a little nuts on engineering a flaming dumpster by making the servo linkages all use ball bearing pivots. Seriously?! Yes – when you build a complex bot like Roll Cake, you end up with a million little bearings you bought but don’t end up using, and can peruse through later.
These bearings are type SMF83 – 3mm bore, 6mm OD, and flanged. They’ll ride on 3mm shoulder screws (also left over from Roll Cake iterations). Ball bearing pivots reduce the friction of linkage joints by a good order of magnitude or more, and reduce slop since they don’t need to have inherently loose fits – for a linkage as edgily-designed on the verge of toggling as the lid, I figured it would be a nice touch.
There are a couple of little 3D printing tricks that I’d like to point out. They’re not too visible in these photos, so it’s easier to show a CAD screenshot:
Basically every part on this bot is printed at an angle with the part not oriented “flat” like what’s common. I started doing this years ago, probably by accident while trying to print an awkward part, and realized it confers a lot of advantages.
First, you can distribute a load on a 3D printed parts in all 3 planes by tilting the part – at least going from one plane of loading to two.
In a part that has multiple orthoginal axes of pin joints or screw holes, instead of extremely compromising on the strength of one axis by forcing it to be loaded “between Z layers” where deposition modeling is the weakest, you effectively slice the part to include them in a skewed fashion.
That way, for example, my pin joints and bolt holes are all grabbing material on the 45 degree plane, each capturing many layers of material – clever part design with this in mind can even result in fasteners that capture the entire width and length of parts. This approach also makes 3D printing embedded trusses and other lightweighting shapes more effective for the same reason: the geometry permits material stress transfer into more planes and axes at once.
Second, by tilting some features, you can avoid support lattices in hard to reach places or which would cause poor finishes in a precision-requiring area. A lot of the parts were printed without support, only a “brim” on the lower 3-5 layers to promote adhesion.
The downside is your printer has to be in good tune to do this, since it involves printing almost exclusively in 45-ish degree overhangs and support lattices generated may be much smaller. I trust the Markforged machines to do it – a tunable RepRap-family printer might need some intensive training beforehand.
The electrical deck was freehanded from a sheet of 1/8″ Garolite, and the battery cradles and clamp designed up and thrown on print also. I designed around a set of 4S, 1.8Ah packs I already had, but made sure the cradle was big enough to support the next size up like a 2.2Ah or even 3.0Ah for longer run time. Remember, I was out to drive this thing around for the better part of a day, so it’s carrying about 4x the amount I would ever expect a beetleweight drivetrain to use in one match already.
While this was all happening, I was also waiting on paint to dry. Because of course I will make it Miku-colored!
I ran into some serious issues with painting it, though – the Golden Dumpster is in fact made from painting gold over a regular green dumpster, which is green paint over the bare steel. So I was adding shitty spraypaint on shitty spraypaint on more shitty spraypaint. Some of it started crinking up and detaching in chunks, which was unfortunate. I decided to just forget about appearances – a weathered dumpster with chipping paint and dents just sells the story!
Anyways, here’s the motor pods and electroncis deck dropped in and screwed shut.
The electrical system was actually a little bit of a conundrum. The big servo preferred 2S lithium voltages (7-9v or so), the drive motors were 12V rated so it’s best to run them at that or higher (hence the 4S battery chosen – 14.8V nominal). Most vapes run at only 1S (3.7V) or in that neighborhood. The receiver could take up to 12V in, but the Pololu R/C relay should stay around 5V for best reliability.
I ended up digging out an old adjustable BEC (R/C power supply) from the pile of robot electronics, which could be tuned to 7.2V, an old 6-cell nickel battery voltage. This would feed the vape power (and a mini air pump that is needed to actually push the vapor out with force) and the receiver. I tested the Pololu relay and inspected its diagram to see if there was anything that bad about running it on 7.2V instead of 5 – nothing ostensibly besides possibly overpowering the relay coil itself. Overall, 7.2V was a reasonable compromise for everything on board.
The BEC unit and Pololu R/C relay get globbed onto the electrical deck, next to the most overkill possible controller for this application… a spare RageBridge. Talk about being under-employed!
The smoke effects actually got super interesting. What you see here is two CosCloud units provided to me by their creator Alina. They actually figured all of this conundrum out for me (and you too! and many others!). I was otherwise going to a literal vape shop to buy literal vaping gear to make my own.
I’ll be running two of these “smoke generators” in series to line up with 7.2V pretty well, and the air pump in parallel with that group. This whole assemblage drew around 3 amps at Full Vape, which was quite tolerable with the 10A-rated BEC.
The final packaging and zip-tying now commences.
And here’s what it looks like from the outside! The final weight – 11 pounds 8.8 ounces. Hey, there’s room for a… weapon?
The dwarf dumpster fire, in its natural habitat.
And what it looks like in action at the convention. The secret is to turn on the Vape Turbopumps for a few seconds, then open the lid and watch it all waft out. This thing was an absolute riot everywhere it went, and it fulfilled the “neutral projection target” social experiment perfectly. I heard quite the range of things referred to while pointing fingers at it, from the usual remarks about Congress and the presidency, to the Marvel Cinematic Universe, Disney, Game of Thrones, Star Wars continuations, game companies…. there are apparently many ongoing uncontained dumpster fires in society as we know it.
Some of them even move around and come to you.
You can see #YourWaifuIsTrash in action in this Dragon Con music video (skip to 8:15 if the time link doesn’t work!)
And finally, we make it to the Big Day at Robot Battles!
I’m a dope for not getting to it sooner – somebody had to point out to me that the dumpster was missing an UWU face (yes, it’s a face, not a sound…. today you learned?!), and so one was hastily appended with markers.
This thing managed to actually pull off a win. I did it by basically bull-baiting the opponent at the edge of the stage and letting nature take its course.
Of course, it couldn’t push anything, could barely get over the “arena” borders which are left beat-up on purpose, and had issues with turning in place under its own weight and the traction of the outdoor style carpet of the stage. So that was all! I also entered it in both rumbles at the end, but it got bowled over rather quickly in both rounds. Nevertheless, I consider #YourWaifuIsTrash a win, because what is a win in #PostmodernRobotics? It’s whatever you want it to be!
This thing came back from Dragon Con working just fine, so it will live on as a stupid prop for all of eternity. I’ll probably repaint (read: just spray over it AGAIN in more shitty spraypaint!) it soon and begin adding choice tasteful decals.
Do you want your own? The CAD files in STEP, IGES, and Parasolid are available on the References page!