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.