Archive for March, 2018

 

The Overhaul 2018 Design & Build Series, Part 1: Because of The Implications

Mar 23, 2018 in BattleBots 2018, Bots, Overhaul 2

Here we go! This post is all about design and redesign. What I’ve decided to do is instead of making a master post of all of Overhaul’s problems and issues I wanted to address, I’ll just stream it as I go. This stems from sitting down to write such a post and then realizing that okay, I actually have a problem with damn near everything. I was 2000 words in and hadn’t even gotten out of the discussion of shortcomings.

One of the most important things you can learn as an engineer is proper project scoping, whether your own or on a team with others, and how to spot and pre-empt scope creep. Well if that’s the case, I just watched my oscilloscope grow legs and bail out of a window, which is a shame, since it cost a lot of money.

Yeah, there’s 1001 things I want to change about Overhaul, but I obviously don’t have the time-money product factor to make it all happen. So I whittled the list down to some of the topics I covered previously, as well as new ones that came about from observing Motorama.

There were both easy to execute changes such as simple part replacements, and also more involved design…… overhauls….. which needed my attention more from the start.

The easy stuff included

  • Higher gearing for less top speed and more control over its own inertia, experimeted on with Clocker.
  • Getting rid of the “rocker” drive configuration by using a smaller center wheel – I want all 6 wheels on the ground at all times if I can manage it, especially with the added torque of a higher gear ratio.

More difficult and needing frame mods and new subassemblies, we have

  • Moving to all Brushless Rages for controllers! This basically meant throwing out the whole electrical deck, which I felt was too over-engineered for Season 2 anyway with its full polycarbonate enclosure.
  • Changing the lift gearboxes to the BaneBots BB220 line, which I had used in a few consulting projects between 2016 and now and which was better suited for high-torque loads. Luckily, this is easy since they are the same physical size.
  • Designing up a bracing system for the frame rails where they are current unsupported between the center and front wheels
  • As seen previously on the first design post, moving to the new actuator design which is more compact and should be much more durable.

And finally, what needed comprehensive redesign:

  • A new clamp body (the Overhaul anteater-dolphin-horsecatbearpig-raptor head) to accommodate the new actuator design
  • Changing the arm and lift hub such that the arms are universal, not mirrored weldments. This wasn’t a problem during Season 2 so much as I wanted to maximize the swappability of parts – if I had to replace a left arm twice, I’d be out of those but not Rights. If the arms were simple flat weldments, they could stand in for each other.
  • Changing the armored wedge design to be more effective – and since Motorama, optimizing for a wedge-fight mode versus a spinner-mode
  • For the latter spinner fight mode, going to a full front-spanning plow arrangement.

Since I was already starting off on the actuator, I decided to move onto the next most logical place first, which is the things that actuator mounts to. When you’re doing almost completely freeform design, you have to anchor it some place. When I taught the EV design class, I called it “grounding” the design – basically, you have to start somewhere, so just pick one and come back to it later as the design evolves.

I had a few concepts sketched for the new lift hub. It basically had to be compatible with the existing arm and gear bolt pattern and be the correct width, so actually designing it was a matter of picking a fastening method which made sense and trying to get it lighter. By “making sense” I meant moving away from the engine head studs holding the previous setup together, one which I no longer favored.

Basically, the longer the threaded stud, the more you have to torque it down for overall rigidity in the things being fastened. I also couldn’t locate an easy source of replacement studs in a higher strength grade than approximately Gr. 5 in the 2 different lengths needed, whereas I could easily find very high strength bolts. Recall that the arms had to be flat now as a design goal, so the whole lift hub is wider anyway, so the bolts may be rather short (well, 3″ and 4″ versus 6-7″ of stud length)

So I made the decision to abandon modifying or adding spacers to the existing lift hub – more spacers, more places for preload loss – and make a whole new hub.

This is the object that resulted. It keeps the profile and spacings of the current hub, but becomes a steel tube weldment with threaded 3/8″ thick endcaps. The length of the barrels on each former arm is just added to the length of the hub, keeping the whole liftgear the same width.

Since I would most likely be the one welding all this up, I could add stupid shortcuts that real welders would probably shun me for.  That’s the reason for those weird little tabs on the bottom, so I can fixture the holes relative to each other easily!

After shadowing Overhaul 2′s principal welder Skunkadelia , and having done more welding in general for work related projects, I’m now more confident enough having picked up my welding skills again to design around it more. I used to despise welding, and still kind of do, but hey, somehow this robot is 50% welded steel shapes so I might as well learn to maintain it.

I kept mulling over the arm design as I decided to whip up a temporary Überclocker-esque wedge shape. Notice the lack of side-wubbie engagement at this point? I was thinking I could get away without them, but Motorama showed me quickly they were probably necessary – as many wubbies on deck as possible.

I included the sidebar in this screenshot to show the process of generating the surfaces and planes needed to define the completely-lacking-in-perpendicular-features wedges.

Adding the backstop plate in a similar fashion to what I was planning for Clocker. After raw sketch lines, I generate surfaces using the sketch profiles.

I then use a Thicken operation on each surface in turn to make them into solid “plates”. At this point, there’s no joinery, because I was just interested in pounding out the shape.

In continuing the “nearly a visual mockup” theme, I then moved onto the fork arms themselves. I decided to dispense with the “tube skeleton and welded plates” method for not really being beneficial over just being made of plate weldments. The tube cuts were always less precise than the waterjet- and laser-cut plates anyway, and part of the reason Overhaul 2 was missing the inter-fork bracing standoffs Clocker had was because none of the holes ended up lining up.

I also committed to having all of the new steel parts made of commonly-found 1/4″, 3/8″, and 1/2″ steel plate. High strength steels like AR400 are far harder to find in thicknesses thinner than that. I had a lead on 3/16″ material fine, but sourcing the 4mm plate last season for the fork and clamp sides was an adventure. Very few steel companies list it as a product, because who needs a 1/8″ thick dumptruck body or mining shovel? It also gave me the option of making things from normie steel (mild/hot and cold roll low carbon) to just use geometry over sheer material strength as a design rule.

 

 

The forkss are now fully made from interleaved plates. Here I’m playing “connect the dots” with tube bosses and gusset plates. I made this plate adaptive so I could still change the  sizes slightly and not have to manually regenerate it.

Here is where I decided to make the forks from plain mild steel. I had the opportunity and supply chain to use AR steel for them as well, but decided against it. Essentially, if the forks were very rigid, they had the potential to easily wreck everything upstream (the lift shaft and hub, the towers, etc.) if somethng hit them directly. With a few geometry changes, I could get the forks to be rigid enough to take the potential downward force from the clamp.

Again, with the basic shape of things established, I went onto the next piece.

I started thinking about “Limited Liability wedges” for Overhaul about the same time as when I cooked up the idea for Clocker. Overhaul’s front is a slightly different shape than Clocker. The chamfer that forms the sloping face is smaller and so the frame rails of the bot extend further forward.

This means there was only so much liability I could limit if I kept the tall rubber wubbies, since by design, they kept the old style wedges flush with the forks. While I probably could have hard-mounted them to keep everything low-profile, I wanted to keep that level of shock isolation and break-away behavior provided by the wubbies in case an attack on  a vertical weapon goes wrong.

I therefore switched the design to a shorter wubbie style , which through the angle of the sloped front, set the ‘intersection line’ of the slope with the ground back a good 3 inches or so. This finally let me have enough fork prominence to make it worthwhile.

Above is the quickly thought up revision 1 of the design, which was basically “make slope piece, add pokey thing”. The idea was fine, but obviously that pokey wasn’t going to last long as a piece single-supported from a plate.

I extended the slope and front vertical pieces off the edge and extended the “pokey thing” as a gusset piece. Now this looks better topologically.

With basically all the elements of the bot that I wanted to redesign in place, I mirrored things and imported the Season 2 clamp to get a first visual.

ADD SAW TEETH AND SPIKES AND HOOKS TO MAKE IT EDGIER

This let me have a sense of which components needed to be bumped and shifted. Overall, the forks are 1″ longer than they were in Season 2. I wanted more prominence in general in order to attack with them first. These wedges are there only to help stablize the bot in most lift instances.

My goal for the clamp profile was to shift it forward more and also make it a little lower profile. Overhaul’s Season 2 clamp design was almost exclusively to house the huge actuator, and it actually looked a little ungainly to me. Plus, the taller the clamp, the more likely it is to get stuck sideways (which the ears are actually placed to prevent).

I simply exported a copy of the clamp profile and ripped most of the features out of it, including the awkward bump of motor-saving.  The hole positions shifted around a lot with the geometry changes, of course, so they had to come and go as I needed them.

After a few tries, I found a near perfect alignment of holes that actually let me mount the actuator in a position I long wrote off – with the motor pointed forwards. This configuration was modified slightly to adjust the motor spacing. It allowed the use of a very short leadscrew to achieve the range of motion desired, so I was much less concerned now about leadscrew rigidity.

Now with 100% more ear. I re-imported and adjusted the ear model, keeping it as a folded single piece. The plan was still to make the clamp sides from 4mm AR steel. I also added an alignment tab for welding. This was the extent of the work I did before Motorama.

One of the first things I did after Motorama was go back and edit the heavy anti-spinner wedges. Clocker doesn’t have the two front wubbies, nor the two sides, and I became even more convinced that Overhaul’s triple-plane constraint was a good design choice. Future Überclocker will have a more design-true layout rather than being a cartoony model.

I made a multi-faceted edge that was just a flat plate where the side wubbies are mounted. Recall that Overhaul’s season 2 wedge pods had fully angled sides, and I had an interior gusset piece which mounted to the side wubbies. I decided to flatten this area out in order to give even less things to grab onto – the prominent gusseted back edge was pretty much an invitation to getting the whole thing ripped off forwards if I miss an approach. Reinforcement of the area would be taken care of by a cross piece (green outline near the front wubbies) and a flat lower gusset.

This was the result. I rather like it – it adds to the new edgier aesthetic of the bot and is much lower profile and less bulky looking than the Season 2 wedges. The 2nd-angle transition to the pointed backstop plates is also much sharper, hopefully adding a stronge upward vector to someone’s deflected shot.

At this point I started becoming weight-paranoid, and so I just rage-added every remaining major part of the bot I could think of. What’s not shown is a pattern of several dozen (if not over a hundred) socket cap screws that make up the frame hardware.

There was also beginning to be a large weight difference on the order of 7-8 pounds between the heavy anti-KE configuration and the lighter wedge-match and vertical weapons configuration. I was just going to let this play out, since I could always add some kind of ballast if needed or make a smarmy lawn-care attachment to fight Hypershock with, but I wanted to leave a healthy margin for the improtant parts.

Notice something about the pointy wedges? I swapped their sides on the bot design! This obviously also works in real life, and is partly the reason I chose the design I did. I could even go in lopsided if I mounted two left or two right ones. An “arms close” configuration like this is that I would imagine doing for a fight against another lifter/flipper, whereas forks apart are what I would take on vertical weapons with since I can try to make close flanking passes and try to get under one of their corners.

Finally, we get to the crux of my Motorama ruminations.

I pulled the CAD back up one day afterwards and went alright, that’s it… this is happening and I will make weight for it no matter what

Basically I took the existing heavy wedge design just completed and bridged the two halves with a single U-shaped front plate. Reinforcing features have not yet been added underneath, but they will be.

This added about 8lb to the front – a little less worse than I thought, really, and that was without selective weight reduction cutouts. I like this already.

As I said from my Motorama conclusion posts, having a full-span front wedge probably could have turned my tournament around. On Overhaul, it is also wubbie-supported in all 3 coordinate planes in both compression and tension as opposed to just a flat plane of wubbies. It would take a lot of me fucking up in order to lose this thing in battle. The team started nicknaming it the “dethplow”, so Dethplow it is.

The plow also allows me to address another Motorama quibble, which was having to back up and attempt to bring the fork down. I made another configuration which I termed “T-rex arms” since they are half the length of the full length forks.

They fit fully behind the plow when stowed, but if I have someone trapped, I no longer have to back up, but can clamp and lift as normal.

rawr i am oversaur-cathorsedolphin-shark…..bearpig

The clamped-opponent orientation does change a little since the tooth now has significant overbite, but whatever – spinner matches are a matter of survival, not looking good.

I tabbed everything together and added five longitudinal gussets and one transverse rail to brace up the front and underside. The total weight of the dethplow is around 30 pounds!

Next up on how to CAD an Overhaul: Moving through the other systems making the revisions I wanted to do.

Motorama 2018: How Not to Scale Model Test Your BattleBots, The Remix

Mar 18, 2018 in Bots, Events, Overhaul 2, Überclocker 4

I had originally intended to go to Motorama 2018 solely for #vantruckjustice and to serve as an event volunteer and purveyor of Ragebridges and Brushless Rages. But with the announcement of Season 3, it became clear to me that I really should take the opportunity to get some practice driving in with 30-haul a.k.a. Überclocker v4.

Not only was my list of “things I didn’t like about Overhaul” extensively long, but based on my experiences after Franklin Institute and Moto 2017, I had several mental strategies against KE weapons I wanted to try out. Better do it on the small scale where it’s less expensive, right!?

So onto modifying Clocker!

One of my recurring themes in the past few event reports where I ran Überclocker has been the idea of reducing my wedge cross section against vertical drum and disc style spinners. I’ve had a theory for a long time now that broad armored wedges/plows are actually a liability against those kinds of weapons, despite being more effective against horizontals. There’s nothing better to confirm my theory besides Blacksmith vs Minotaur – in which Blacksmith actually does quite well against Minotaur until the latter manages to land a square hit upon the front of Blacksmith.

Essentially, a vertical weapon will tend to bend up your defenses by hitting it at a single point along its bottom edge, effectively making the length of the plow/wedge useless especially if the vertical weaponed bot has a feeder leg of some sort.

One countering strategy is going fully vertical with your defenses, like a crossing vertical bar of steel or something, making sure you hit the weapon before any feeders are able to touch you. Whoops! used this reasonable effectively against totally-not-Minotaur for quite a few hits.

That doesn’t quite work for me, though, because Clocker/Overhaul both have lifting forks.

 

Another strategy is minimizing your cross section ot exposure to those weapons by being extra pointy, giving them less of a chance to hit something important. This is also a strategy that I began moving towards with other ‘wedge fights’ – a broad surface is, again, vulnerable to any imperfections in not only itself but also the floor. I wanted to explore this strategy with what I call the “Wedges of Limited Liability” seen above – basically turning the armor pods into little shanky forks. I designed them to follow the profile of the existing wedges, out of the same 4mm-ish AR500 material.

These are a few ounces lighter apiece than the regular ones, which is going to mean a couple of pounds at the Overhaul scale. So it was interesting to begin thinking of the configurations I could get – freeing up a few pounds on Overhaul could let me add other attachments or additional armor (e.g. if I had to face Beta again, I’d spend the extra pounds on top armor).

While I was at it, I also redesigned the normal heavy wedges in the style of Overhaul. I had thought about ways to retain the double-angle feature but significantly reduce the number of pieces needed to construct it. Overhaul’s wedges were rather complex and made of 9 individual pieces each. I came up with an idea of making the second angled facet into a ‘backstop’ of sorts, attaching directly to the outside surfaces through extended tabs that also acted as gussets.

In essence, the above is what Overhaul’s new wedges will look like, but with some geometry placement changes. Clocker’s front is a lot more tapered than Overhaul’s, meaning the ‘backstop’ begins too far back to be really useful here to protect the gear from another Glasgow Kissing. I was more interested in the construction and their potential behavior towards deflecting  hits in general, rather than specifically trying to address last year’s weakness.

One change that has been on the docket since Franklin late last year was changing Clocker’s gearing. Using the lowest RPM/v rated NTM 42mm motors was still too much – I rarely exceeded 50% stick travel while driving, and the constant burnout mode the motors ran in during each match made fine control actually rather difficult. To give the bot more control over its own inertia, I was going to go to 11:1 P60s (from 4:1) but with a bump in motor Kv from 650 to 750. While this reduces Clocker’s nominal top speed drastically to only 10mph from like 20, it was going to mean more speed in a useful range. A lot of my strategy relies on being able to carefully control my approach and orientation to opponents, after all.

The same changes will be carrying through to Overhaul, but less drastically – I’m changing only the external motor sprockets, from 15 tooth to 12 tooth, moving the system reduction from 8:1 to more like 10:1, which is what Sadbot has been running in testing and whose maneuverability characteristics I like more. It will reduce Overhaul’s nominal top speed from 19mph to 15mph.

By the way, the NTM Propdrive 42mm series have a Mabuchi RS-700 size bolt pattern and a 5mm shaft, which mates with the Banebots P60 700-series motor blocks, not the 500 size.

Since I finally blew up the clamp collar joint at Franklin, I drilled the sheared bolts out and replaced them with a pin drive. The holes in the gear were bored out, and the “pins” in the shaft collar are actually shoulder screws with their heads milled off! I literally tightened shoulder screws into these holes and then clamped against the screws on the mill and blazed the heads off.

The shorter 4238 size motors, in combination with the 2-stage gearboxes, actually end up at the same length as before! This package is fairly potent and is a brushless 30lb drivetran of choice currently. The same two beta-version Brushless Rages still run the bot, dating now all the way back to Dragon Con 2017 and carrying the bot to victory at Franklin, then several demos at MassDestructions.

Fast forward a few days and an uneventful (!) vantrucking trip later, and here we are at the event:

So I didn’t get a chance to actually weld up the new heavy wedges – they’re shown sitting in a pile next to the bot, ready to become accessories. Since the only welder on site was a 115 v MIG welder powered by a 50 foot extension cord, my plan was basically to add some little barriers to the existing wedges in the form of strips cut from the new design.

Clocker’s first match was actually a “wedge fight” against the twin over-powered wedgebots of Boom Boom. This match was conceptually easy, but a little frustrating because Clocker kept digging into the wood floor. It was in fact too pokey and I could barely maneuver forwards. So it really wasn’t that good of a test of the Wedges of Limited Liability at all.

My next match was against Botceps, a pretty classic vertical eggbeater style spinner. Built pretty much like a BattleBotsIQ/NRL archetype, it had a very potent 50mm TPPower inrunner on the weapon. This was one of those “if I make a driving mistake, I’m kind of done” matches, so I had to be on my toes. I don’t have a video link of my match here at the moment, but should I discover one, I’ll add it in.

As you can see, I did end up making at least 1 driving error – at the beginning, a few seconds in where I missed a charge and Clocker went halfway across the arena. Luckily, the weapon motor fizzled out barely a minute in, but I did lose the tip off one of the forks and the left pointy-wedge.

The punt that send Clocker up and over also squished one of the outer rail mounting screws clean out of its hole.

At one point, I managed to execute my anti-vertical spinner strategy well, plunging the pointy-wedge straight under the weapon of Botceps – which managed to machine the entire row of rake teeth off it! The match ended with a serendipitous flip which put Botceps on its face (“doing the thing” in robotland) and without weapon torque, it was stuck in that position.

My next match was against Crippling Depression, a pretty innocuous-looking bot (by design) that actually puts a massive amount of power into the undercutter disc – two NTM 50-series motors, which is more motor than Glasgow Kiss. By the way, its builder Robert Cowan has a very detailed video series on a lot of engineering subjects, including full video reports of the build of CD. Basically if I were more keen about doing video versus text, I’d be like that! So go Like and Subscribe™

Clocker didn’t make it out of this match all that well, and I ended up tapping out.

The disc of CD hits very hard, and very low – lower than most of my side rails, so it polished off a lot of the bottom screw heads. It was also positioned just at the right height for Clocker to barely ride up on it, meaning I would actually lose a head to head pushing match. With brushless drive and weapons, we’re now squarely in the era of 30lbers with absolutely no compromises – CD and Clocker have identical drive motors and identical gearing!

The super low level of impact meant a lot of extra stress was put on the wedges here, and it never actually got to ride up to the point of hitting my welded barrier strips. In fact, the first few hits managed to bend down the corners of the left side wedge enough that I had some trouble driving afterwards due to it being hung up on the arena floor on occasion. It also caused the rubber shock mounts to shear off early, leaving me with fewer defensive options as the match wore on, until both the wedges came off and my only real strategy was to try and stay on him. You can see some of the resultant impacts causing a little bit of “Cobalting” on the right side (upper of image), but the middle tie plate kept this very limited and I didn’t even notice while servicing.

Eventually, the disc ended up shearing out a few sprocket teeth and jamming the drive on one side, so I just wiggled my way around until I decided I got the idea and should probably keep it repairable for the loser’s bracket.

This was about the moment I realized that disc weapons (and by extension, shell spinners and other lower-prominence weapons) were going to be a much different story than the archetypal big bar spinner in terms of how to fend them off and deflect their energy, and I decided Overhaul needed a full-span front plow style defense no matter what. Watching Jamison fight CD later on with megatRon confirmed this belief even more. I’m pretty sure if Clocker had a full span wedge, even a connector plate between the two halves, it would have gone differently.

I was losing wubbies at an alarming rate and did not have any more spares, so I had to source them from other builders. Clocker was short spare parts in general – I never got to waterjet additional frame parts or cast new wheels either, since the decision to go compete was made in very short order. This event was actually a great study in how far the design would go on attrition alone.

That was all for Saturday – on Sunday, my first match was against BEAM, a tiny Tombstone. A rookie bot that was still BRUSH-POWERED and with an EV Warrior motor at that! Basically running a classic car in battle, but it had done tremendously well up to this point.

Poor guy was probably being gunned after by every BattleBots competitor there, who saw him as “tombstone practice”. Honestly, so did I, because it could portend the results of #season3.

For this match, I was only able to get 4 wubbies per wedge, and changed out to another used wheel which didn’t have huge chunks gouged out of it. I also cut off the bent tips of the forks so they were a bit shorter, but now much less structural than they already weren’t to begin with. It is what it is, given the lack of preparation.

So how did Overhaul do against Tombstone?

That’s, uhh, not very typical, I’d like to make that point clear. Well, it seems like the front fell off again – much more epicly this time!

With as much handicap as the bot was facing, I sort of ‘drove for broke’ in this match and was determined to see how pure attrition would play out. I think I was actually quite happy with how I was able to deflect Beam repeatedly, even getting it to do The Tombstone Dance a few times.

I felt like I had Beam reasonably until roughly the 2 minute mark when one motor was knocked off internally causing it to lose drive one side. I then just kept pivoting to try and meet it with the wedges.  Also, I again kept the arms up to try and keep them out of the way of the bar, but ultimately they still ended up in Full Dab; these arms for Clocker were built quickly to Sportsmans’ class specs, so any sideways ping is going to bend them.

Near the end, though, one of my welded barriers came off due to lack of penetration from the event welder. At the last possible second, we got in a good head to head charge, and….

Clocker’s frame rails are made from 7075 aluminum, which is really a mistake. I already had the plate when it was being designed, so went for Easy first. 7075 is more brittle than 6061, and will crack instead of bending. You can see that clearly in the arm tower that took the brunt of the last hit. This is why Overhaul’s entire frame including the arm towers are 6061, and only the liftgear and clamp & actuator aluminum housing parts are 7075.

From watching videos in slow motion, Beam was able to climb up the de-barriered wedge much like Glasgow Kiss and firmly planted the bar into the side of the head, which of course shoved everything out the other side. The lift gear was also made of 7075, and I lost a chunk of it near the end – check out how clean the shatter line is. It’s barely bent at all along the rim and still sits quite flat on a table.

The ears were also obviously very suboptimal – they were re-printed, but weren’t bridged or braced and so had the same kind of failure when the bot landed upside-down with an opponent – they simply bent the aluminum clamp sides and rotated, making Clocker adorable and droopy for most of the match.

With the base still working fine after the drive motor was reattached, I entered the Sportsman’s rumble to run around like a dumbass. The P60 motor plates only have two screws, not four, so it was asking a lot to hang the entire drive motor off them. This is actually why Overhaul’s motor assemblies have bracing plates behind the motor endcap. Dumbassery was achieved until Pitter Patter sniped the power link with its sawblade.

So that’s Motorama 2018 for Überclocker. Going 2/2 against three heavy KE weapons with almost no spare parts was certainly more than I expected, which was more along the lines of instant vaporization. I think I confirmed about every fear I had for Overhaul, whose upgrades were almost done at this point otherwise, but now needed revisiting.

but what about the Implication?

I spent the joyride back from Motorama consolidating everything I learned while running Clocker and as well as watching other matches including the final few fights with megatRon, Beam, Cripping Depression, and others. As a fair percentage of the builders at Motorama were also building for #season3, we did some bonding at the event and over pizza dinner Saturday night to consider strategies for the “full size” bots.

In terms of the knowledge gained from testing, it’s a fairly established rule of thumb in the community (if you ask) that “designs don’t scale”. The sentiment is you can’t expect to scale up or down a design 1-for-1 in terms of material sizing and dimensions of weapons and motors and expect the same kind of behavior. It’s a consequence of a whole lot of square-cube laws: motor power scales by volume, kinetic energy stored in a spinning weapon by square of velocity but also implicitly square of weapon dimensions due to moment of inertia changes, material strength both by dimension cubed and linearly by yield strength, etc. It’s why historically speaking, a scaled up or down version of a successful design might perform horribly.

Essentially, the idea is that at the small-bot scale, the energy transferred and dissipated in a hit tends to be much less than the energy needed to permanently deform a material of a given strength and size. This is how 3D printed 1lb and 3lb bots fly around arenas and bounce off walls on a whim and keep going. It’s related to the concept of why you can drop an ant off a building and have it survive the fall, but not an elephant. As robot dimensions increase, the kinetic energies stored in weapons – whether spinners, or transferred in a powerful flipper connect, or in the form of a hammer tip – begin overtaking the ability of the material to elastically deform and dissipate energy, so you end up with a lot more things bent out of shape rather than two heavyweights suddenly reappearing at the other side of the arena.

I mentally call this idea the “robot Reynolds Number” when comparing designs of different sizes: to get the same physical behavior, a bigger robot has to be simultaneously more powerful yet built more rigidly. Consider it characterized conceptually as the ratio of average kinetic energy transferred per hit in a weight class to the material yield stress * volume used in your robot ( KE [J] / σᵧ [Pa] * volume [m³ ). The best example I can think of is probably how Big Ripto and Triggo (30lbers) can both bounce around arenas like beetleweights – but both robots are made of hardened steel when it comes to the bodies in contact, whereas plastics or even aluminum is likely to just deform in the same application; as well, they both cram about 4 to 5 kW of weapon motor power behind them, which is actually more than an order of magnitude from the typical beetleweight (3lbs).

What this means for me is that I have to be careful with interpreting the results of my matches. For instance, it’s highly unlikely that Overhaul will get sent flying end over end from a single spinner hit such as that from Botceps, but rather depending on what gets hit, I’d lose one of the wedges or have a pretty big chunk bitten out of the frame. The best-in-class KE weapons in BattleBots right now run right around 15-20 kW and around 50-100kJ. Going back to Blacksmith vs. Minotaur, you’d expect with strength-invariant scaling that Blacksmith would easily hit the box lights, but rather what happens is the frame/wedge deform and fasteners begin failing.  Also, in my match against Cobalt, my one good deflect was the end result not of being ultra-rigid, but backing the hit with the arena floor by virtue of the rubber-suspended wedges, which is obviously something I want to keep.

While the exact physics won’t carry over through scaling, concepts will. For example, I am fairly confident that

  • Weapons of low prominence, such as discs/drums/shells, are best kept away from you and interacted with lightly since they are less likely to grab entire portions of your bot at once, rather chipping away at it. This is best illustrated by how megatRon was able to keep Crippling Depression at bay with a single low front armor piece, whereas CD had more inroads to damaging Clocker’s separate armor pieces.
  • Weapons of high prominence, like the archetypical spinning bar or single-tooth style weapons, should be more readily deflected if possible, since they have more potential reach (i.e. far more “bite per tooth”) and less predictable reactions. You want them to go away from you as much as possible. I rather enjoyed a lot of the driving against Beam and making it do “the Tombstone dance”, and even the small welded barrier strip made a lot of difference until it failed.

Ultimately, I had to rethink Overhaul’s armor approach and how it interacts with the lifting forks.

  • I came away 1000% convinced it needs a Full frontalplow-like surface up front. It’ll be heavier – I will make weight for it somehow. One downside of separate wedges is only one set of rubber mounts takes all the load of an impact, and while my Cobalt flip was perfect, 99% of hits I take won’t be that perfect. A spanning plow will allow the mounts on both sides to take the load. Besides that, it will obviously decrease the amount of open corners Overhaul (and Clocker!) has. In fact, the plan was for the original Overhaul 1 to have such a thing, but we ran out of weight.
  • I had to retain the ability to lift independently of being able to deflect hits. Did you see me pin CD and Beam against the wall several times, but having to back off to try and get the forks underneath them – which in both cases had bent up beyond the point of usefulness? That’s how they escaped and the match continued. I need the ability to corral spinners against a wall but keep the arms tucked behind the plow, maybe exiting via a small cutout. Overhaul has a set of short arms which remain behind the wedge profile – imagine a cross piece in front of them connecting the two wedges.
  • Beyond just dealing with horizontal KE weapons, Overhaul needs a “Wedge of Limited Liability” of its own, which still supports the bot during a lift but otherwise takes the form of a skinny fork or tine so vertical weapons and things like flipper spatulas have less edges to find. I didn’t get to exercise the WLLs of Clocker this time against a vertical drumlet weapon like Other Disko, Mega Overload, etc. but I did like piking it under Botceps. Depending on the length of the tines, it could be effective on its own by being jammed under vertical spinners, for instance.
  • I need to learn to drive “dirtier”. What this means is foregoing my desire for continous showy and aggressive action – something I am used to in the 30lb Sportsman’s class – and instead maximizing my usage of pin times and arena-outs. Jamison is a more strategic and methodical driver me in this regard – he drives to win, whereas I tend to drive to shitpost. Compare his style when fighting CD (and other heavy weapons) versus mine. In the BB arena, survival is going to be key since we are more in the realm of throwing elephants off skyscrapers than insects. The NERC arena doesn’t really have facilities for arena-outs, but the BattleBots arena does, and I think it will be a key portion of my strategy. Bounce bots up and away, keep them corralled, and try to manipulate them behind the low walls and screw embankments.

Once I got back to the shop, it was time to refactor Overhaul’s design a little. Stay tuned for those updates!