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

Friday, March 23rd, 2018 @ 2:29 | 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.

 

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    One Response to “The Overhaul 2018 Design & Build Series, Part 1: Because of The Implications”

    1. bob Says:

      i’m very moist