Wow! Can you believe it’s ONLY been only a month since the last Overhaul 2 D&B series post?? I felt like it was last year. Time flies when you’re trying to finish a robot.

So the truth of the matter is, if you might have guessed, the competition and season filming is already done. Everything was packed up and shipped on April 5th. Prior to that, the build season got hurried, so I prioritized having a robot over blogging – I know, such shame. Now that I’ve recovered, I can finally return to writing the design and build up. The plan from here is to finish up the design and move onto the build process, because now I have a whole new set of content to pre-game – the event itself! Those posts will be released as the show airs, because spoilers.

Anyways, the very last portions of the design for me to reach before “first-plass competion” was the top armor plate. After that, I could go and revisit parts of the design which nagged me or just didn’t seem right.

The nice thing about having a design that’s almost done is that the last few parts are easy to generate. That’s usually what causes me to CAD more efficiently after I start putting some parts down – there’s less of a need to “design” than to “wrap this thing around that thing”. Conversely, it’s the first few parts that really define the function and shape of the assembly, so you can’t really just skip that.

This top plate is just a “follow the outline” exercise, similar to the bottom plate. The anticipated material is 4mm titanium. I allotted that for weight, but might also make one from 7075 aluminum to save another (roughly) pound and a half in case it’s needed.

I decided to open up an air vent in the “giga bracket” on each side right above the SK3 motors, and save some weight by not having the armor extend out over them. From the previous post, one of the things I wanted to have was a cooling fan which pulled air through important parts of the bot – namely the drive motors and motor controllers. A mockup of the fan is shown near the upper right, where there’s a spare cavity in the bot. It’s a 92mm high-speed server rack cooling fan, and it fits almost perfectly between the frame rails.

To facilitate cooling, I also added a ventilation grille feature at the very back of the bot. This admits air through the battery pack area (which is shorter than the electronics deck), which allows it to flow through the motor controllers. The batteries need minimal cooling, if any at all, so their placement in the air path is incidental.

Save for some minor dimensional changes, this was the end of the top plate. You’d notice that the master switches are just kind of hanging out in the open… That will be a problem to solve later. For now, I declared #yolo and moved on to the obviously most important part of OH2 if you listen to everyone else: the ears.

Fun trivia about Overhaul 1 which most people still don’t know: The famous ears of the bot were a 11th-hour, Hail-Mary addition to aid exclusively in self-righting. The bot was pront to becoming stuck upside-down in a tilted position, and the ears forced the bot to always fall straight backwards if overturned.  This was due to the clamp arm being very tall compared to the bot’s footprint. The same issue is present in OH2, so the ears make a return!

To generate the ears, I first used the model to calculate where the center of gravity of the assembly was when the bot was upside down, and basically rotated the assembly in the view window until I found a satisfactory “line of tipping”. We did this on OH1 with the physical bot, but it was also simple to do in CAD. The idea of ear positioning is to make it such that there is no stable position in the tilted upside-down position because the ears force the center of gravity to act past that “line of tipping”, levering the bot over onto its back.

For instance, in that position, the ‘line of tipping’ is defined by the ear contact point and the back left corner of the frame. The center of gravity acts behind that line, meaning in this condition, the bot will always fall on its back. This hard to “see” in one screenshot, especially in a perspective-eliminating isometric rendering.

The caveat is that this line of tipping is only valid for a certain range of clamp arm positions. I tried to find a compromise with the arm in an arbitrary halfway-up position, like if I was trying to grab Bronco at a bad angle and got wanged (that’s a technical term) over. If the arm were fully raised, there was no position which satisfied the criterion, so like in OH1, I always need to make sure that I begin powering the clamp arm downwards as soon as I think the bot’s about to go over.

Using the “best guess” without an ear already in place, I generated the shape using the side of the clamp arm as a reference plane. Like OH1, the ear will be a bent plate weldment attached to the side of the clamp arm. Once I had the general shape, I went back and forth in the assembly to tune the dimensions little by little. The determinant was a combination of “stickout” vs. aesthetics – too big and pointy, and it started looking ridiculous. Structural stability was a far lesser concern, since it’s still a large L-section of AR400 steel involved no matter what, but obviously the larger the ears, the more they wrench on the side of the clamp arm.

Trimming a bit of material for weight purposes primarily. The way this will be loaded in the majority is “up and down” from landing, so I was less concerned about the front to back taper being intact.

This is more or less what the final ear design will look like. Now, working on this caused me to remember something that I made a few weeks prior – the big gnawing tooth up front. Remember it from this post? It was made to “have something there” and now I need to think about it again. I was facing down having to get the thing manufactured, or somehow make it myself, and it was starting to be worrysome.

Version 1 of the tooth was a one-piece affair made from a big chunk of tool steel. Version 2 takes the “important part” and makes it machinable from a much more commonly found flat tool steel stock. The total thickness is 1.5″. To make up for the thickness difference between the clamp arm plates, the triangular upper profile of the tooth will just be made into some 0.75″ thick spacers, to be cut out of aluminum.

And with that, every element on the bot is “first-pass complete” in some form. Notice that the arms are still the slightly older curved design which I explained in the Pointy Things post.

I changed the color of the pontoons to more reflect the original concept. Short of a few changes made later on during “production”, this is what the final bot looks like.

the manufacturing process begins

There’s a big change in how OH2 will be made that is a departure from anything I’ve done before, including the OH1 build.

What’s going to happen is I’m outsourcing all of the “big machining” – the frame rails, the actuator parts, etc. – to outside machine shops. Not only that, but the large steel parts are going to be laser-cut through a commercial steel vendor. I’m basically only taking care of minor manual operations or “just need 1” kind of parts.

This is a monumental change from everything else I’ve built, where the majority of parts have been made by me, in-house. I’m taking this step for a few reasons:

• I decided that it was worthwhile to trade money for time due to the splitup of team JACD from Season 1 – I could no longer count on equally-skilled friends who can take a CAD file and go make it, then come back and keep working together. My team this season would be more “minion” than anything else, so I had to make sure the complex-skilled tasks were taken care of.
• If I chose to do all the machining myself, I would have to be literally machining from now until the season, on machines which I could not guarantee that I had consistent access to. Factored in with leaving MIT proper, and I couldn’t guarantee that I would be able to machine anything short of using manual machine tools.
• Equals Zero Designs still needed my attention and I’d rather be spending as much time as I can making sure RageBridge 2s didn’t have too many teething problems or manufacturing issues popping up in the field.

What this means is that the relative cost of the build was going to go up immensely, even with my contacts at Chinese production shops. I estimated each frame as being around $5,000 of machine work, and obviously needed more than one frame for spare parts. That’s always a trap with building bots – you never really build one robot, but more like two or even three, because what’s the cost of losing a match because you did not have any spare parts to restore functionality with?

Overhaul 1 was built for an all-up cost of around $9,000. With the machining estimates for both the aluminum frame and steel armor plating, I was looking at a minimum cost of $16-18,000 if not more. Oh boy, glad those RageBridges are selling…

I put togther a package of detailed drawings and accompanying models, like the one seen below for one of the frame rails:

 

Techinical drafting instructors and machine shop foremen, start cringing.

I play very fast and loose with my drawings – basically if it gets the point of the part across, it’s fine by me. One of the upsides of working with a “bot vendor” like Team Whyachi is they “get it” – combat robot parts tend to worry much less about precision and rigorousness of dimensions, because after 1 hit, it won’t matter any more.  But it’s hard to communicate that to a local machine shop.

The package of drawings was shopped around very briefly to a few places I’ve had work done with before. It was furthermore segmented into a few parts – the big aluminum frame, and some smaller but still critical pieces like wheel hubs which I wanted dozens of in order to ensure the supply of spare wheels. That way, if a shop had time for the frame, they could take that, but if one didn’t but could still run smaller parts, they could have the smaller hardware.

The bigger your production run, generally the more attention you get from a shop. Small, quick turnaround one-offs are about the worst possible pieces you can have hired out. Companies exist which specialize in that realm, but I can’t afford them :P

While awaiting word on quotes and lead times, I began to put together parts to be made locally. For example, the electronics box (revision 1) layout for waterjet cutting is below.

The plan as of late January & mid-February was to perform the support work in-house and using MIT equipment I still had access to, assemble all the electronics, motors, and batteries, and integrate them the same week that I should hypothetically receive my parts in mid-March.

As a preview of things to come, the first parts to return were the drive wheel hubs, made by a local (Boston-area) CNC shop I had done some business with a while back…

Aren’t they gorgeous? In the next episode, we’ll see how they go together…

In the mean time, if you haven’t already, make sure to Like & Subscribe!™ the Equals Zero Robotics facetube.

No, I haven’t gotten into the electronic music industry, but a lot of electronic was definitely consumed during this stage of the CAD! The build season is in its last week or so, which means I’ll be prioritizing shipping a working robot with build reports and more photos to follow the April 5th ship date.

With the mechanical design basically complete for the first pass – everything at least having a shape I can think about later if need be – it was fine to give the electronics a home. The typical electrical system for a bot like this is relatively simple, and components come in bite-sized modules that just need to be mounted to something in a vaguely robust manner. Rarely do you see fully custom PCBs or integrated controllers, unless the builders are electronics engineers by practice or hobby (an example is Dale’s bots).

OH2 is sort of a mix of the two cases; while I’m not using my own RageBridges due to the simple fact that they have 2 wires instead of 3 do not run brushless motors, the controllers I am running are extensively hacked and modified to serve in ground traction application (More on that soon, I promise!) But they’re still in their original cases, so my job is kind of easy – THROW THEM IN THERE WITH SOME VELCRO AND DOUBLE SIDED TAPE AND BE DONE WITH IT!

Nah, I think I ought to do just a little better. Since the functionality of the system is a known quantity from my testing with Sadbot, I was out to optimize the survivability and serviceability. Particularly, the goals of the electronics containment structure (hereafter nicknamed the e-deck) were:

• Full self-containment – basically, a robot control system in a box, with receiver, power supplies, and cooling as the cherry on top. It wasn’t just going to be a box of motor drivers.
• Rapid swappability – I planned to build two or more, and if something happens during a match (but I come out on top), swap the spare unit in and deal with the damaged one later.
• Pursuant to the first two requirements, be internally modular or easy to service so I can remove the broken component relatively easily.

Historically, when I’ve made an electronics enclosure at all in a project, it’s been a constructed (usually t-nut) box made of polycarbonate or some other plastic. So let’s start with what I know. First, here’s the layout and the space I have to work with.

At the time of this design version, the Hobbyking Graphene batteries  had just arrived on the market, and I was eager to try them out. OH2 is not a bot which needs to pull hundreds or even thousands of amps in an instant like a kinetic energy weapon would do, and the new large-capacity Graphene packs (12AH and up) were highly attractive. I designed around the 12Ah 6S packs to begin with. They’re represented with external rough dimensions provided by the HK product page here, in gray. To their left is the final configuration of the DLUX 250A motor controllers after playing with exact spacing.

I decided to start with the “known known” and package the batteries up first. They were going to occupy the only large contiguous space in the back of the bot, which was originally designed to fit four of the Hobbyking Nano-Tech 8Ah packs that OH1 used. These are actually slightly shorter than two of those back-to-back, so I had a little more room to play with.  I made a “minimum dimensional enclosure that’s a clean fraction above the size of the packs”. The enclosure will be made of  1/4″ polycarbonate, likely waterjet-cut, with plenty of my special-sauce t-nut joints holding everything together. This part I’ve done dozens of times, so I left the geometry simple for the time being in order to move onto the rest of the system.

By this time, I had begun receiving lots of parts in the mail, and I began realizing something very distressing – that two Whyachi MS-02 switches were going to be too large to fit. The newest BattleBots rules now require you to have independently-switched weapon and drivetrain power systems. While I had submitted an application showing two Whyachi switches, actually trying to size them in the design showed me that this was mostly ‘last minute homework question’ and practical. Essentially, yes I could fit two MS2 switches, but I would prefer not to.

So naturally, in keeping with the trend for this bot – I designed me own. Gee, can you make touching two wires together scientifically any more complex? Yes, I can.

Here’s what’s going on inside that block of nondescript 3D modeling clay. Hint: It’s not much. It’s literally a gigantic Fingertech switch. I designed it such that the square area of the face of the switch (where you crank the contact) is half the size of a Whyachi MS-2, so I could fit two side by side in the space of one MS2. It goes “back” further, but I had that dimension more available.

I didn’t want to get fancy with the contact method, so Fingerth-style “tightening two conductive things onto each other” was the way to go. The terminals are 1/4″ thick copper, and the contact is a 1/2″-13 brass socket head screw. Brass isn’t as conductive as copper, but sheer area makes up for it here – the cross sectional equivalent is a 6 gauge copper wire.

That is revision 1 you see up there. Come build time, I’ll show some updates to this design that make it more refined and less terrifying to use, with the possibility of it being a future Equals Zero product. For now, once again, the shape is set and I can stop thinking about it for a little while.

I’m playing the layout game a little more here, having added a RageBridge 2 to the equation. Instead of “rack mounting” like I am going to do with the DLUX controllers, I decided to lay it flat. The reason behind this was that Rage2 is rather short (heightwise, from the heat sink plate) compared to everything else, and I needed the same area to also be occupied by the switches. If the Rage were also vertical, I’d have needed to push everything sideways, right up to the width between the motors. Leaving some breathing space in a big bot is good for serviceability, the fact that I didn’t want to optimize the design into a corner right away notwithstanding.

I began generating an ESC box in the same manner as the battery box. Check out those big bus rails – that’s how power distribution will be handled. While thinking of ways of avoiding a gigantic tree-root of wires splitting off into smaller wires, I was reminded of the existence of bus bar products after digging through my wiring parts bin and finding some car audio power distribution blocks.

However, most industrial bus bars look like this, which requires putting ring terminals on the controllers. While not the end of the world, I usually prefer the direct wire contact style of the audio distribution blocks. There’s also busbars which look like this, more commonly called ground bars, in the audio power distribution block style. I started shopping around for them, before the realization that they are simply blocks of metal with set screw holes tapped into them hit me.

Well, fine then. Not like I wasn’t going full hipster on everything else electrical already, right? After doing a bit of research on bus bar manufacture, I decided to get some alloy 6101 aluminum from McMaster-Carr and just drill and tap some holes into them. 6101 is the most conductive aluminum alloy in common use for electrical appliances. Aluminum has less conductivity than copper, but you make up for it using more. The equivalent cross section of the bars I modeled is 6 gauge copper wire at the minimum.

The bus bars are offset horizontally from each other by about 1/2″. With another set of holes oriented vertically, it means I can stick a hex wrench through a hole in the top one and land it in the set screw socket of the bottom one. To prevent accidental crowbarring of the circuit (nevermind the fact that the whole bot’s going to be turned off, battery disconnected, and most likely this whole electronics deck removed from the frame when I work on it), the screw access holes will be given little nylon bushings to insulate a passing tool.

The final bus bar design is made from the 6061 bar stock, are 1/2″ x 5/8″ in profile, and about 8″ long each.

Moving on from generating the crude rectangular-box housing to stitching the edges together in my usual style.

Shown also are Anderson 75 amp Powerpoles. It’s a well known fact in the robot world that the 75A Powerpoles are actually capable of substantially more than 75A in bursts. Since I’m not a giant spinning weapon, I needed something which was more substantial than an XT or Deans connector, but to size an actual industrial connector to my load “like 200 or so amps” would make OH2 just one big connector. I brought in two pairs of them to check on the available height for mounting.

In a way, I’m counting on running extremely high voltages to avoid using high current to push power (the alternative being a low voltage system like 18-24v and like all the amps ever).

 

It began being easier to look at in dark wireframe mode – basically Shaded with no shade. Wireframe was too messy, and the transparency of modeling in polycarbonate with default looks meant it was still hard to see the edges. Above, I’ve added the slots for the #4-40 t-nuts.

I toyed with the idea of a backplane connector style of battery attachment, where the Powerpoles are mounted to the polycarbonate enclosures, and the whole assembly kind of snaps together and gets bolted in place. I even modeled a 180-degree rotatable Anderson Powerpole mount to do this, seen above.

However, the more I thought about it, the more I wanted electrical connections to be as compliant as possible, not hard-mounted. So, the bot-side electronics enclosure will get this Powerpole mount, but the battery itself will just have a loose connector pigtail.

After establishing how big the enclosures were, it was time to flow a bracket around them to hold them in place. This had potential to be the largest part ever printed on a Markforged machine yet, so I was highly tempted.

The premise of this universal bracket was to contain the enclosures using massive areal contact of something mildly compliant (nylon), and also to presenting vertical bolting features to further restrain horizontal planar movement as well as vertical movement.

It also acts an air guide shroud for the drive motors. At this point, I’d been thinking of ways to do forced-air cooling of the whole system, and the holes & vents in the electrical deck were created with that in mind. I was planning on having a central fan somewhere – likely in the empty space to the right of the lift motors and having it pull air through the bot.

Here is the completed Everything Bracket, with its own mounting features.

I’m now at a point where the whole design is basically “first-pass complete”, meaning I know where everything goes and what it should do, even though it might not be well thought out or optimized. I find that this point is a very helpful one to reach, because the changes you’ll make to the design tend to be evolutionary instead of revolutionary (scrap it and start over). Not to say I haven’t done the latter, but…

In the next episode, I’ll introduce some of the very last CAD kibbles before the real fun starts – the build reports!