Previously, on How to Build an Overhaul…

dramatic over the shoulder camera angle here

charles stares intently at a lathe on autofeed

 –
CHARLES
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“this insert seems a little dull and i want some mountain dew”

Machining the parts for the lift clutch was well under way by early March, and parts were coming in almost daily. Our goal was still to have “the robot minus the frame” done by the 3rd week of March, when the CNC machined frame was to arrive. For instance, here are infinite wheels:

After confirming that one hub works, it was time to make all of them. Now, these Colson wheels are made of polypropylene with overmolded rubber. The plastic is so soft that it would rather mush around than be cut, unless it had no other choice. Broaching the wheels made all kinds of neat Colson art, like so…

The next step to assemble all the drive wheels was to chamfer the tips of the waterjet-cut sprockets. Chamfering the tips makes the sprocket more tolerant to side-to-side chain slop since the teeth become narrower, and so the chain has more wiggle room before it tries to catch between teeth and fall off. And I can think of no better application where your chain is likely to have a sudden amount of side to side slop!

There were 30-something sprockets to machine, and I needed a solution to make life simple.

Enter MarkForged…

I designed a jig that the sprockets bolted into – they had the correct center bore and two keyways to drive the sprockets, and were made using several layers of Kevlar reinforcement for strength (This wasn’t a critical application that had to be Kevlar – it was honestly what I just had loaded in the machine at the time. Any of their fibers would have been as rigid, or more rigid). On the inside of this print was a hex socket that fit a 1/2″-20 nut. A 1/2″-20 bolt runs through the body, giving it even more rigidity, as well as retaining the sprocket. It was then easy to chuck the jig into a lathe, holding the sprocket away from the chuck, and quickly chamfer both sides with a cutter. Then simply swap the sprocket out and continue!

The other piece shown is a portion of the electrical deck. It holds the robot-side main battery connector onto the electrical box, and was included with this print because why not. I wanted to try out the dimensions in real life to see if any adjustments had to be made.

After broaching the 5″ and 3″ colsons, I began to become concerned about how easy the wheels were to broach.  While the 5″ Colsons had plenty of material at the hub, the smaller 3″ ones had a significant portion of the hub’s radial thickness removed when I broached them. This was concerning, because the reduced material ring beyond the keyway, coupled with the sharp keyway edges, and the fact that the front wheels would be under the most stress when lifting an opponent, meant that the wheel was likely to crack apart.

Not cool. So one of the first “dynamic redesigns” of this build is now needed – the front wheels. I decided to design a MarkForged printable hub, to which a polyurethane tire is bonded.

The 3″ Colson wheel also only covers about half the hub width, as smaller sizes don’t come in the 2″ wide size. The new front wheel would be equally wide as the rest.

The outer ridges are to increase the surface area available for the eventual glue bond.

Here are some “cheat code” features to optimize the part for a MarkForged machine. Right now (as of 6/2016), their slicing software doesn’t yet allow you to prioritize “internal” features, such as holes or bores. All fiber lay is from the outermost perimeter inwards. The reasons for this are many (including feature recognition challenges), but bottom line is, I can’t tell the slicer to fiber up the keyed bore itself.

So in a manner similar to the “hairline split holes” method of 3d printing parts with more perimeters, I added a few Slots of Persuasion to forcefully route the fiber layers into the places where I need it – the keyway area. The fibers will handle the majority of the power transmission stress, so I was less worried about the plastic necking down here.

I also could have made the wheel a “C” shape, with the ends of the C so close together as to be almost touching – and in real life, the plastic would bond together anyhow – but I wanted to avoid having a single linear weak spot in an otherwise complete structural loop. So, little guidance slits won out here.

I then added a few Holes of Persuasion to force some fiber layers towards the outside layer, and some towards the inside of the hub surface.

Here is a finished wheel! See the keyway being surrounded by fiber, as are the inner and outer surfaces for the most part. I could have put Kevlar into all the layers, but decided to be a bit more economical. Each wheel contains just barely under half a spool of Kevlar. The rest of the volume is simply densely filled.

I’ll be the first to admit that I am not a master of composites and adhesives. I used whatever glue McMaster called “urethane glue”, part number 7493A21. My criterion for selecting this adhesive was “Says Urethane on it, does not require an expensive-ass dispensing gun or carefully pushing out with a stick, and comes in the little cute bubble packet”. This is roughly the same process used to select a bearing grease for Mikuvan’s front wheel bearings (“Well, it has a picture of a car on it”) and those haven’t blown up on me…. yet.

Help me.

The tire material is a soft urethane tube, McMaster part number 87235K74. I cut rings off the long tube I purchased, 2″ wide to accommodate the hubs. It gets stretched over the hub after the hub is throughly coated in the urethane OH GOD IT DOESN’T COME OFF AND IT’S STUCK TO EVERYTHING adhesive. I wiggle the tire on and use the dribbles to fill gaps and create edge fillets. Then I leave the wheels alone for a day or two.

The evening I put these together shall forever be remembered as Urethanocalypse 2016.

Here’s a pile of infinite finished wheels! Well, semi-infinite. We decided that a 100% set of spares was sufficient to start. In the event of post-match damage, swap the wheel for a known good one right away, then deal with the repairs after

Next up, infinite spider couplings. Notice how there’s a lot of “infinite” on this bot? Again, a manifestation of the design goal that is making all of the spare parts in one shot, with the parts themselves designed to be easily replicable. Other builders prefer building 1.0 robots first, then working on spare parts.

All of the spider couplings are broached for 1/8″ keyways to slide directly on the lift motors.

And finally, we get to….

Infinite SK3 motors.

This is where I introduce Equals Zero Robotics’ 2nd sponsor for the 2016 BattleBots season…

…

HOBBYKING!

…

Yes, that HobbyKing, a familiar sight on this website for many years!  I was in talks with them as early as Sadbot running on the dlux 250 hacks. Originally, it was just for more dlux 250 units, but I decided to go deeper. The robot community has a love-hate-love-again relationship with HobbyKing’s legendary Chinesium offerings, and many smaller bots have used HK parts to great effect. But can they play bigger?

Either way, some great exposure potential for HK, so they agreed to send goodies my way. One of these shipments was a nontrivial percentage of the world’s supply of SK3-6374-192 motors.

Another shipment was more running gear for the bot:

 

Critical subssystems and support equipment, all sponsored by HobbyKing.

Overhaul 2 will be running the 9XR Pro radio system with the long-range 433mhz R/C gear, to get me off the 2.4Ghz band. I wanted out of 2.4Ghz entirely – everything from other robots, to WiFi, to production running wireless lighting and microphones and the like, lives in 2.4Ghz. Last year, a few people had control difficulties (including yours truly) in the box, and I was not out to repeat that.

Next up are battery chargers and charger power supplies, as well as some BEC units to run the logic power (receivers, gaudy lighting, etc.) since the ESCs do not provide 5v power. Speaking of ESCs…

What’s missing is a boatload of DLUX 250 controllers.

Let’s rewind a few weeks here. What happened was that I compiled a bill of materials to send to Hobbyking, which included 12 dlux 250 controllers. Everything on the list was packed up and shipped to me, except the DLUX 250s, because…

I’ve gotten confirmation from the manager that this product has been completely discontinued and the factories are no longer making them.

Oh, snap.

After some highly intense back-and-forth over e-mail about possible replacements, I decided to spring for swapping the 250A model for the 160A model.

This was a very stressful decision. R/C amps are usually 0.2 to 0.5 of a real amp* and I was getting concerned about the real ampacity of these controllers. While I had familiarity with them from the BurnoutChibi project, the lack of large-package FETs (in favor of a sprinkling of small surface-mount FETs) and smaller thermal mass was the clincher. I also didn’t have a handle on their reliability – the only DLUX 250A units I’ve ever killed were due to my own stupidity, such as hard shorting outputs or leaving the bus capacitors off.

It was therefore imperative I get units in hand as soon as possible, as even the stock quantity of DLUX 160s was getting low (less than 15 remaining around the world in stock, as I recall). I really need to hand it to Hobbyking here for trying to round up stock in such short order.

*this statement is not backed by any form of science but is pretty accurate

The DLUX 160A controllers came a few days after the rest of the shipment. I immediate got cracking on tearing them open to see what I had to change for in the SimonK firmware. Luckily, the answer was not much. I had to redefine a few resistor values, and also set a correct deadtime (these switched slightly faster due to the smaller FET packages), but otherwise, they were the same pinout and layout. Go figure, but just to make sure.

I then uparmored them like I would the DLUX 250A, but these only had space for one big ol’ capacitor, which is better than nothing!

A set of three DLUX 160A controllers fully modded up. I was going to whip these things in Sadbot to ensure they don’t explode.

I removed the 250A controllers from Sadbot – now a valuable and rare commodity – and tied these guys in, then proceeded to drive around like a maniac, just like I did with the 250A, and lift & self right and do other things with the pokey stick.

Here’s a test video showing a little bit of it. The open floor tests were to try and stress the controller with many reversing and turning instances, and the sliding was induced by keeping the wheels spinning (drawing wheelspin current) as much as possible.

(RIP Frozen fans and normal people)

The controllers passed this test solidly, I’d say. I was beginning to smell SK3 windings before the controllers became too hot to touch, so that’s a good thing.

However, while powering up Sadbot for another test a few days later…

A minor smoke event occurred.

One issue with R/C controllers, especially large ones, is that they scale beyond their hardware designs that were originally put together for small ones. Without proper gate drive, and with the possibility of mixed parts in the power stage, if one FET blows up, it tends to start taking the rest with it. And some times, this happens almost spuriously. This is how a controller works for someone and not for the next person. Add to that the quality control generally associated with hobby parts, and….

Okay, let’s be clear: THERE IS NO SUCH THING AS A MINOR DLUX SMOKE EVENT. The whole thing is seemingly made of thermite, or the mix of materials acts as a rapid propellant, because it was over in 5 seconds, a foot of flame, and a huge plume of smoke. I was in fact fearful of a lithium fire with the batteries next to it, and was getting ready to shove the whole thing off the loading dock. The polycarbonate battery box from Overhaul 1 protected the batteries, luckily.

This was all that remained…. As you can see, the entire PCB is actually burnt in half.

By this time, I didn’t want to try to investigate yet another controller. And unless I were willing to pop out Brushless Rage™ in three weeks and get it right the first time, this is what I was going to have to deal with, and part of what I committed myself to doing – using big R/C parts in big robots – from the very start.

So it was time to put the controllers down and keep moving. I asked Hobbyking for a large stockpile of the 160A units to be laundered my way ASAP. I decided to formulate an electrical system continuity solution which used the DLUX 250As remaining (5) as much as possible, and substituting in the 160s if absolutely needed, but ensuring that I had a full bot set of DLUX 160A controllers right away.

While I was doing these tests, the others had finished machining the motor mounting blocks for the SK3s, and keying the shafts.

Ah, finally, all my ducks in a row!

The difference between a “left” motor and “right” motor is simply which direction the wire leads come out, to keep the wiring in the bot convenient.

 

The next step was to assemble all the gearboxes. Four left, four right, and four lift motors were to be assembled. Again, a 100% overhead (hehehe, overhead for Overhaul) such that we could pitch in a spare set right away and mull over the broken ones in the pits later.

Notice the delicious strawberry jelly on the left. Mmm, extreme-pressure additives.

Here’s a fully assembled drive motor, with retaining bracket!

Repeat like 20 billion times

Okay, so I lied about getting away from controllers, again!

Overhaul 2 still has that 1 brushed motor onboard, the A23-150 micro-Ampflow motor to run the clamping arm. To use this motor, I needed a high voltage (12S capable) DC motor controller.

Now, I had designed a 8S-capable motor controller of some type a little while ago, and in fact, one of the original RageBridge 2 plans was to have it be 12S-capable. But I decided to scale back for expense and usability reasons – most everyone runs these at 6S (around 24v) or in extreme, unsupported-by-manufacturer (AHEM, WILL BALES) cases, 10S (36-42v).

To change Rage over to the higher voltage specification was actually an intensive job, basically rebuilding the board. The main capacitors were changed to 50V types, the MOSFETs to 60v parts, and a lot of other little things moved along with them – such as changing the gate resistors to accommodate the new drive needs, and the logic regulator to a HV-rated part.

In the end, I whipped together two HVRage™ units for the clamp motor, and tested them (see the small blue wires used as scoping points) to ensure nothing was going to get TOO fiery.

And this is the conclusion of Overhaul 2: Actual Electric Boogaloo (sorry Orion). Next up? A Series of Tubes:

Side note: Overhaul 2 swag is now up on the BattleBots store, if you haven’t seen yet. All artwork by Cynthia! Proceeds of sales do go to the builders, so you’d be sponsoring supportng Overhaul for #season3!

 

This is it! Now that my incredible van hangover has cleared, it’s time to get back to build reports. With 2 weeks left to go until the SEASON PREMIER OF BATTLEBOTS ON JUNE 23RD 8/7c ON ABC!!!! my hope is to clear the build itself and discuss the runup to the event as the season starts. As OH2’s matches are aired, I hope to immediately turn around and prepare analyses of them within a day or two. OH2 is not part of the premier itself, but look for it in the next few episodes that cover the preliminary rounds and beyond!

So, after seven episodes of working through the design – eight if you count my love affair with brushless drive – it’s time to start persuading metal into shape. At this point, it was late January, and I’d just gotten a load of RageBridge2 units in, so we were busy in “fulfill the delayed crowdfunding campaign” mode. It was between RageBridge logistics juggling that I was placing the first orders for materials and parts. As I mentioned in the last design post, a majority of the machined parts for this bot were going to get sent out to external shops which I’d done business with before.

I spent a portion of December and January shopping the design out to a few places, both domestic and in China, to gauge interest more than anything. Here I am, showing up with basically two dozen unique parts, for which I need quantity… 2…. or thereabouts. My contacts are largely production-oriented shops, since I needed, say, 250 DeWut casings or 500 RageBridge 2 heat sinks. They have otherwise much larger jobs that occupy machines for a week at a time. So it wasn’t surprising when only a few replied saying they had the capacity for it at all, much less the ability to turn around quickly.

Robot build seasons are always a blur, and a huge and complex robot even more so. In high school doing FIRST Robotics, it was easy to lose track of where on Earth the past 6 weeks went, and I was definitely in a similar situation with this build! I’m basically going off the photographs’ dates now to reconstruct the series of events which led to Overhaul 2. We begin in mid-February into early March as parts began arriving.  Yes, began. Basically everyone was cutting it this close for a variety of reasons, some of which I’ll likely talk about only after the season finishes airing.

So here we go! First, the main cast of characters involved.

• Me, the principal designer and I suppose electrical system lead, since OH2 has the most hipster snob electrical system imaginable. I also machined stuff occasionally, I guess.
• Cynthia, who assisted with fabrication and also creating the team aesthetic and presentation, as she is a graphics designer and illustrator.
• Paige, chief waterjet babysitter and machinist/fabricator.
• Matt, Paige’s boyfriend and Biology & Premed student, so we trained him on whatever needed doing at the time.

Oh, also, as the build progresses, I’ll be sprinkle CAD shots back in as things need validation or redesigning on-the-fly as disasters occur. I assure you there was a lot of that…

The stinger photo at the end of build report part 7 was of wheel hubs. This was the only “mass produced” part for OH2, since I knew I was going to need spare wheels no matter what. I sent this out to a nearby CNC shop, ARMSET who turned this around in about a week and a half.

During the intervening time period, I tried to work as ahead as I could on minor fabrication of the associated parts, such as sprockets and wheels. Additionally, I wanted to get a start on one of the weirdest parts of the bot – the welded plate armored pontoons up front.

What’s the same thickness as 5mm steel? 5mm plywood, and I think one of these substances is a little easier to put together over and over! I bought some birch model plywood from a local wood distributor, and then proceeded to barge back into my own former shop to use the laser cutter.

My rationale when putting this thing together: Wherever I can shove the hot glue gun, I can shove the MIG torch. This assembly process went as smoothly as I had hoped, and I ended up building 3 of these to test the assembly order, i.e. “Where do I spray the steel boogers first?”

Here’s a completed armor module in plywood!

 

I gave this pontoon a healthy coat of the closest color to Miku Blue I could locate in a Home Depot spraypaint aisle. For the record, this color is Rust-Oleum’s “Gloss Seaside”. The camera white balance isn’t happy here; it’s a lot more aqua in real life.

One of the design choices that we were making early on during the design submission period was the robot and team color palette. Overhaul during Season 1 was naked-ass steel and… red, I guess. There wasn’t much thought put into anything except making it do robot things, so we just went with a red and a gray, similar to MIT’s palette, where gray was just made of #stonecoldsteelaustenite.

This season, I was out to transition the robot to something blue. Specifically, during the early design stages that were detailed in Part 2, when the new application was being prepared, I was all set to make a Miku-themed robot. I shit you not, this is a never before seen concept image which I put together (because of course I did):

Yeah.

Now that I’ve scared everyone away, I can say that this concept was not used because there would have been basically no way to use a copyrighted character as a team mascot or have the character prevalent throughout the robot and team.

So the #mikubot concept was scrapped, but the color lives on.

Here is a round of sprockets (that’s a technical term for a group of sprockets!) that fit on the hubs. They’re waterjet-cut from 3/16″ 7075 aluminum plate. Basically, the idea at this point was to assemble wheels as soon as the hubs got in, and then keep assembling drive and lift motors and electronics until the frame got in

The other small parts on the left are retainer brackets for the SK3 motor rear ends.

Other interesting things also began arriving. For instance, these two piece of oil pipeline oil-filled nylon bearing stock. The large rotating arm parts will use machined nylon bushings for radial support. They’re moving at a low speed, so I opted to use plain bearings. Bronze would have been nice, but heavy. I figured at this bulk level of usage, the nylon would do just fine.

One of the first electrical system experiments I wanted to verify was the custom master power switches (a few pictures down). Recall that I designed these because fitting two Whyachi MS2s in the bot was becoming a daunting prospect when accessibility was factored in i.e I wanted to retain the side approach arming.

Shown above are some copper contacts that were cut from 1/4″ silver-plated copper bar, supplied by McMaster. It seems like this silver plating is largely decorative, because it was coming off if I was rubbing it too hard – probably for anti-corrosion purposes only. Oh well.

The internals of version 1, as simple as you can get. The body is a nylon with fiberglass print, made using a Markforged Mark Two.

I’d like to take this space to welcome Markforged as the first sponsor of the team this year. You’ve seen a lot of action on this website and on Jamison’s site with Markforged parts, and they know there’s no better application to have their parts mercilessly beat on to show the technology! Markforged is providing Mark Two prints and printing services on their print farm.

 

While this edition seems to work just fine (it conducts! Yay!) I wanted to refine it more and also fix the fact that the hex key could, under some angles of insertion, be the first thing to close the circuit. Obviously you don’t want this to be the case. I also wanted to add a biasing spring to lessen the likelihood that if the closing torque was insufficient, that the screw would just back off and leave everything disconnected (or worse, constantly arcing). Here is the version 2 updated basically after I finished printing Version 1. The black nylon bushing proides a long entrance guide for the hex key so it can’t touch the switched contact under normal use.

After a McMaster order, the version 2 is completed. With a dab of conductive contact grease on the spring, the action was smooth and repeatable. I was satisfied with the design at this point, so I printed more with very minor dimensional changes for fitup.

Around this time, my order of wheel bearings arrived. They’re 5/8″ bore needle roller bearings that are pressed into the hubs. Shown also is a single 5″ Colson wheel which I test-broached with 1/4″ keyways.

This work was done just in time prior to the arrival of the first big batch of parts that needed significant modification and work, which is the drive and lift gearboxes…

Oh god that’s a lot of Banebots.I ordered 10 4:1 gearboxes and 4 16:1 two-stage gearboxes, plus a basket of spare carriers, shafts, and gears.

My personal guess was that if the gearboxes were going to fail, the 4:1 drives would fail first due to rapid reversing and direct shock from the drivetrain, like running into things. The lift gearboxes would be reasonably isolated from torque impulses by the 12:1 external gearing and the clutch. I ordered enough gearboxes for drive such that I could build 10 drive motors and, in accordance to the serviceability inherent in the drivetrain design, just swap out motors and deal with piecemeal repair later.

That’s one of the things which trips up newbies some times is how expensive everything gets once you factor in the ability to repair rapidly. While the initial cost outlay might be high, what is the cost to you of losing a match when you could have been able to put the machine back together if you had parts?

Two things needed to happen to the Banebots gearboxes to turn them into drive and lift motors. The motor mounting blocks had to be machined down to 1/2″ thick, and then the hole patterns drilled. Paige and Cynthia took up this job using some of the equipment in the IDC and CNC mills in the same building.

I continued the “weird science” part of the build by working on the two-speed shiftable “P90X” gearboxes. For this, I waterjet-cut out of O-1 tool steel a replacement planetary carrier:

That’s it on the right. This carrier has (reduced size) teeth and fits perfectly into the ring gear on the left. It has hole patterns for both 4:1 and 3:1 gear stages. The idea is that the sliding ring gear either is anchored to the gearbox housing, or is meshed with this carrier and spinning with it, bypassing one stage.

Here’s a comparison of the carrier plates after I transferred the pins over. The next operation for this setup is to chamfer the edges of the carrier teeth and create a mating chamfer to the ring gear, such that they can collide and mate smoothly.

The other side of the ring gear needs to be firmly affixed to the front output block of the P80, since the ring gear is no longer held in compression between the two blocks. To do this, I basically turned the four dowel pin holes on the ring gear into holes for four shoulder screws. Notice that I’ve already cut off the ring gear here, too.

The four pins that were in the output block were removed, then their holes drilled out directly and counterbored on the other side for the shoulder screw heads.

We interrupt this build report for….

EPIC LIFT GEAR! From now on, every time I say EPIC LIFT GEAR! it will be in bolded capital letters with its own exclamation mark. Consider it a single lexeme. Anyways, the EPIC LIFT GEARS! arrived from…. Amazon. These are giant spur gears from Boston Gear, who lists its basic catalog on Amazon Prime. I’m super happy about this and encourage all industrial suppliers to do it.

Part 1 of the EPIC LIFT GEAR! is the 42 tooth, 12 pitch intermediate gear, which will be turned into the lift clutch. The other EPIC LIFT GEAR! above it is the 6 pitch output pinion. It will be face width reduced – I don’t need the ridiculous 2.25″ face width – and then broached.

I used the MITERS Clausing lathe to bore out and dish the interior of the 42 tooth gear, and also cut off its hub. This is it – the intermediate EPIC LIFT GEAR! will just have a bushing in the center such that it can spin on the clutch shaft.

Next up was the clutch shaft itself. In the latest McMaster order, I put in for a length of 1144 steel, commonly used for high-stress round things. This needed to be turned from a 1.5″ round into a 1.25″ shaft with two 0.75″ ends and a 1.25″-12 thread on one end.

I decided to practice threading again on some aluminum first, since it had been a while since I last made giant custom threads, and I was also unfamiliar with the new MITERlathe’s threading controls.

I then mounted the shaft in a mill to do the secondary keying operation. This keyway is for the 6 pitch EPIC LIFT GEAR!, since the 42 tooth intermediate gear will be sandwiched using clutch plates. However, I decided to make the keyway full-length such that I could make the clutch plates themselves keyed, to assist in torque transmission.

A little bit of Scotch-Brite and wire brushing to deburr the threads, and the clutch shaft is completed.

Here’s what the clutching setup looks like for now. I had yet to receive the order with clutch lining material and giant conical washers, and the pressure plates still need to be cut.

While this mechanical work was going on, I was working ahead a little on the electronic side of things. Little I know the build was about to take a tragic turn…

dun Dun DUUUUUUUNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN

 

By the way, Overhaul 2 swag is now up on the BattleBots store. Builders get a cut of the sales of all swag, so here is your chance to indirectly sponsor Equals Zero Robotics!