The Barber Surgeon (OK, Google, play 'Barbra Streisand' by Duck Sauce)

The Barber Surgeon

As one thread ends, another begins. Writing up the build history of Crossblow was actually really helpful in designing the new iteration, as it helped remind me of all the decisions I’d made over the years. So, with zero prizes for guessing what I’m CADing right now, here’s the full progression of The Barber Surgeon.

Origins

The design really came from two places. Firstly, as mentioned on the Crossblow thread, was Robot Arena 2. I used to play a fair bit of this, and it’s where my medieval team theming originates. A Barber Surgeon, for those who don’t know, would be the individual in the village with all the sharp knives. His job would be as primarily medical, but would also work cutting hair, and even inflicting some gruesome punishments on behalf of the law. Therefore, it seemed a good name to give a Sawblaze-inspired bot. This was back in 2018, when the saw was having a real renaissance. For anyone wondering where the rust graphic came in, that was also RA2 - it’s one of the default chassis textures, which I then added to with my own custom texture work. Rusty surfaces and bloodied saws seemed like a suitably menacing aesthetic.


An early and later iteration of The Barber Surgeon in RA2.

It even fought, in Good Robottal’s Superheavyweight Tournament.

Up until this point, it was a fairly standard 2WD/4WD Dustpan Sawbot. But in 2021, I was on a call with Jevan Woodrow, helping him workshop ideas for his first Beetleweight. At the time, he was particularly keen on mechanum and omni drive, but I had my doubts about the pushing power of these wheels. I wanted to incorporate a weapon type that only needed to be delivered, rather than needing to push, and one of the designs that came out of that discussion was this, slightly rough, MS Paint drawing.


The initial concept sketch for The Barber Surgeon

While Jevan rejected the idea, I couldn’t stop thinking about it. It hit that perfect intersection of uniqueness and potential effectiveness that inspires me. I discussed in the Crossblow thread about how Bugglebots somewhat conditioned me to want to do original things, and there seemed like a niche here. Shatter! had not long debuted, and a fresh-faced new builder called Thomas Yau had started competitng with a Mechanum lifter called Deja Vu (Whatever happened to him?). No one else had yet attempted omni wheels on the beetle scene, and Crossblow was in a great place, so I began to CAD. The plan was to build a highly mobile drive platform, that could strafe to constantly keep it’s weapon facing the opponent.

The Build


Oh, TinkerCAD…

It’s a pretty 1-to-1 translation of the initial concept into a 3D space. I made some fairly simple design decisions, lifting the 3:1 HTD5 belt system and propdrive 2836 directly from Jamie McHarg’s Sawry, Not Sawry. The drive would be the already-reliable 22mm BBB motors, running on those old K2 VEX29s. The wheels were off-the-shelf 48mm Omni Wheels, of a type widely made to be Lego compatible. These particular versions, however, were designed to fit a brass hex hub. The arm would be powered by an old Crossblow 3S servo, running on 1:1 nylon gears. It would end up using a servo extender to allow the arm to move through it’s full arc.

At the time, I wasn’t able to easily access any machining, despite using it for Crossblow III, so made the decision to go for another hand-built machine, using 10mm and 5mm black RG1000. The first step was to get a rolling chassis. I was pretty sure that OpenTX could do the required mixing through the transmitter itself, but I had to make sure!


The assembly begins.

It took a little dialling in, but I was able to adjust the individual output of each motor to get a consistent sideways movements. The rule of thumb, for a left strafe, in a 3-wheeled, kiwi-drive layout, is that the front two wheels should be running clockwise, at about half the speed of the rear wheel, running counter-clockwise. For the brushless motors in Barber Surg3on (discussed later), the current levels are 20%, 20% and 38%, so it does take a little fine tuning.

https://fb.watch/xbG9reC9JD/
The first drive test - apparently Facebook videos don’t seem to embed here

It ran! And it ran smoothly. I now had a functional drive platform to build upon. I took the rolling chassis to Lego Wars filming that May, and prepared to start on the rest of the bot. BBB had an event coming up, explicitly for new builds, which gave me plenty of time (until August) to complete the project.


Team M&B in May 2022, with Crossblow III meeting David Harrison’s Crontsblö.

Completion to Competing

In reality, the build ended up being a little more rushed than expected, as I made the late call to bring Barber Surgeon for a first test as a whiteboards competitor at Rapture Gaming festival. It went together pretty much as described above. I selected an 80mm saw blade with some pre cut mounting slots that I could widen to M3s - I hadn’t had much luck drilling through other steel blades. A pair of fixed titanium paddles were screwed to the front, the idea being that a saw bot would benefit from having a fixed platform to push into when cutting, rather than lifting itself up. The plan was to hastily finish it in time for some initial testing and stick time, then to fine tune it and make adjustments before Subterranean Showdown.


The night before Rapture, still awaiting final weapon assembly, and some 3D printed gears from Tom and Gus.

The day of Rapture arrived, and the field size had shrunk, due to some last minute disruption and dropouts. The reserve pool basically shrunk to nothing, and I was asked if I could please enter Barber Surgeon into the main competition. I agreed, somewhat warily, but I wanted to help out the EOs to put on a good event. If you’ve read the Crossblow build log, you’ll know that Rapture 2022 was not a good day for me in the slightest. Crossblow blew it’s wiring loom out after it’s first fight, and the additional pressure of running a second bot lead me to stepping away from the event completely.

Barber, however, did get two fights before that point. It’s debut match was appropriately against the UK’s other strafer, Thomas Yau and Deja Two, and we were both very excited for how the match would turn out. Barber got very easily high centred on the static forks going into the fight, but some light persuasion from Dave Weston’s pliers bent them enough that the robot could drive smoothly. It was a fairly tame fight, where we both struggled with clearance, and Deja Two ended up losing power, but it was nevertheless what I was wanting from the day - data to improve the machine, specifically with the ground clearance. It’s very important for all three wheels to be in contact with the floor at all times in order to move as expected!


Brothers in Strafe.

The second fight was against Gaelic Gladiator, a green eggbeater, built by Shane Lale, and the importance of all three wheels became even more evident, as he clipped one of them early on, bending a motor shaft and leaving me limping. I was determined to get in some weapon usage in this fight, and while I couldn’t manage a full pin and cut, the saw landed some glancing blows, before some JSTs (ew) in the circuit couldn’t handle the current draw and gave out. I ran without forks in this fight, to combat the clearance issues, instead replacing it with some bent HDPE arms, but without the leverage to push against, the saw just skipped off of my opponent.


Baby’s first (attempted) cuts.

The repairs to Barber Surgeon were not too severe, but the tight turnaround, and level of work to do on Crossblow meant I withdrew from the event for my own mental health. To add to the dumpster fire of a weekend, I discovered that, since Barber had been bumped up to a full competitor, I’d lost my guaranteed spot in Subterranean Showdown. This was an understandable, but bitter pill to swallow, as if I’d just left the bot home, I’d have had more time to finish it, and have been more focused on Crossblow. The path not taken, eh?

Going Underground

Thankfully, some dropouts meant that I was still able to attend, so I removed most of the JSTs, and added some floppy forks from Crossblow, and primed myself for Bristol. Unfortunately, my scales were a little off, so the picture below is not how it actually fought, but it’s still my favourite of this robot.


Forks, HDPE arms, and dutch angles. This was literally taken in the coach station on the way to the event!


After weigh in, sans scoop. Locking bar restrictions also (rightly) got a lot stricter, so a large clamp was borrowed to secure the arm

The event can be pretty quickly summarised. The first round was a three-way melee against Comoran and ‘Loophole’ - since the event gave priority to ‘new’ robots, Sam and Gus built half scale versions of their dominant verts, Bby Shrekt and Bad FutherMucka, and entered as a cluster. A destructive opponent is rarely how you want to begin an event, and with Comoran very quickly disposed of, I was left to fend them off myself. Thankfully, the new forks made strafing around the arena a breeze, and I was even able to pin Mini BFM for long enough to cut a gash in its lid. My attitude to most events, especially with new robots is that if they do what they’re designed to, win or lose, I’m happy. This was that fight for Barber Surgeon. Shortly after, the damage from the twin verts wracked up, as they snapped my weapon motor shaft and split my saw, taking the win.


Evidence. It worked!

It became clear, though, that I had far too high a TPI (tooth per inch) value on my saw blade. Sam helpfully recommended an 80 TPI blade as I began work on the extensive damage. At Rob Webb’s suggestion, I swapped the motor shaft for an M4 bolt, but the weapon never ran right again. A disloyal wheel quickly ended the second fight against GrabberWobba, and the final match became a glorified weapons test for the then-unknown Icebreaker. Barber limped into a final rumble with the events’ other overhead weapons, then retired. The servo horn had begun skipping, so even the arm was pretty mediocre.

I learned a lot from the original Barber Surgeon. Mainly about over-spec-ing my connectors and components, and about how nice maching really is when compared to a hand build! I was pretty happy to leave the project there and move on. A new, saw blade would be fun, somewhere down the line, but that was it. Sion, though, ever the robotics devil on my shoulder, had other thoughts. ‘What if you make it a hammer saw?’, he said. And so, after an continuing bad run of things with the Crossblow IV/King Crossblow saga, I made a return to Barber Surgeon in late summer 2023, ready for something new.


Barber Surgeon II’s entry into my little book of robot designs.

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Harder, Better, Faster, Stronger

Barber 2 was basically a whole new robot. It began as an attempt to learn Fusion360 on a project that didn’t really have any stakes, fully intending to apply those skills to King Crossblow. I definitely learn better with a practical application for my learning, though as a result, it was a very messy fusion file that had to be rebuilt several times as I learned the software!

I designed arounds parts I had to hand. As with Crossblow IV, I had a ton of excess 22mm BBB motors around, and although the reduction on their gearboxes isn’t as big, (16:1, rather than 19:1 iirc) I had some 1806 conversions already prepped. Sion had also donated some parts - a pair of SK3 motors and some 6mm drisc disks - traded for a big pancake motor I had, bound for Leviathan. The forks were 3mm Hardox, built for Crossblow IV.


In hindsight, it was huge… ‘You’ve built a boat’

Given it was never really intended to be my next build, and my green-ness with Fusion, it wasn’t exactly my finest work. But as the CAD began to come together, I felt the irresistible pull to build. I signed up for War in the Wirral, a little over a month away, and pulled the trigger on ordering and manufacturing parts. There wouldn’t be time for a metal order, so I was locked into using the 3mm Crossblow forks, Sion’s Drisk Discs, and a lighter, asymmetric design that I’d added to the same metal order on a whim. Although I knew that it would likely not self right, I put one of the 1806 gearmotors on the arm, to give it some speed.


Phwoar!

Details in Design
I’ll post a few pictures of the build. The chassis was made with heavily pocked black RG1000 and HDPE, in 8 and 4mm. I also wanted to try out TPU, this new-ish flexible wonder material, so trialled it as side armour, or ‘bumpers’ as I’ve always called them. I printed some gears from PLA, as well as some new wheel cores.

One of the main flaws with the off-the-shelf wheels was the heavy brass hex hubs that they were designed to fit. They’re long, too, dramatically increasing the footprint of the build. The robot was already pretty big, as the odd angles of the motors made it difficult to position the arm motor and front left drive motor around one another, so any opportunities to reduce that was a must. Lastly, the injection moulded wheels were costly, rarely in stock, and fragile. The complexity of omni wheels makes them very susceptible to spinners! However, the rubber rollers and plastic axles usually survived the hits, so printing my own cores, designed to fit smaller, lighter, pololu hubs was a no-brainer.


Red PLA was already on hand.

The gears were 3:1, single helical, with only a d-shaft press fit planned for the initial assembly, with plenty of spares made up!


The beautiful 3D jigsaw of CNC.

The 1100Kv SK3s meant a 1:1 reduction would put out around 180mph. I initially mounted an aluminium O Ring pulley for the first stage, hoping the slip would help on weapon hits. A 3M HTD Belt ran to the second stage, with everything running on various needle and ball bearings.

‘How do you drive that thing?’

One of the (many) drawbacks to Barber Surgeon, in concept, is that it needs five motors to run! Each wheel needs individual control, as well as the arm, and the disc! In order to simplify the wiring loom, from early on, I’d picked out a 4 in 1 ESC designed for drones - a Skystars KM55A, running AM32. This had capacity to control all three drive motors, and the hammer arm, while a Skystars Talon 40A, left over from Barber Surgeon 1, ran the weapon. This significantly simplified the wiring loom, once each channel was flashed to be reversible.

On the transmitter side of things, I realised I never covered that in my last post. The right stick is set up as usual - Forwards, Backwards, Left and Right. Strafing was controlled by the left/right on the left stick. For Barber Surgeon 1, the saw was done on the potentiometers at the top of the transmitter, while the arm was mapped to the throttle. This was awkward, and the saw was operated on a set-and-forget policy. For Barber Surgeon 2, I wanted to bring it all onto the sticks, learning Logical Switches from Alex and Scott. This meant that when the throttle stick - and the spinner - reached 75% power, the arm motor would pulse for half a second forward, then in reverse at 25% power on the return stroke.

Practicalities in Practice

Had everything gone to plan, had all my parts arrived on time, and had my design worked as intended on the first go, Barber Surgeon would have competed at War in the Wirral. It’s never so simple though, is it? A morning in Jamie’s workshop got the build close to completion, but my last minute crunch time was wiped out by an over three hour train delay. It was overweight and flawed in a few ways, not least the belt system, as the O-RIngs slipped a little too much. A machining error had turned the pocked lids and baseplate into a full depth cut, but even that blessing in disguise couldn’t defeat my dodgy maths, as it was still overweight! Wirral turned into a fun day out, time with friends, advice and design input, and a chance to drive Boom Zoom in a whiteboard. It was a monumental effort in the timeframe, and I was left with a design to tweak and finesse in the months before Battle in the Burgh.


Near completion, just before Wirral. If that train had been on time, who knows? Next time I wouldn’t need to leave it so late.