The Ballard of the Beverage

I thought it was finally time to write my first forum post, here goes!

Carbonated Beverage V1 (a.k.a. Wheely Swiss Cheese)

Design and Build

I built the original Carbonated Beverage for BBB Beetle Champs 2022. The inspiration came from watching Tom Stanton’s videos making an RC plane powered by compressed air stored in pop bottles. I’d been faffing around ineffectually with designs for a spring flipper and decided that pop-bottle based pneumatics would be way more fun.

It quickly became clear that there was no way an antweight could accomodate all of the necessary gubbins so it was time to build my first beetle!

The design for V1 was focussed around a single objective: pack as much yeet into the flipper as possible. This meant two things:

  • Having a lot of force behind the flipper.
  • Having a big arc on the flipper to apply that force over the largest possible distance.

First, force:

The beetleweight rules limit pneumatics using non-rated components (like pop bottles) to 50psi, meaning I’d need an area of at least 300mm^2 meet my lofty flipping objectives (this would give me 100N). I couldn’t find an off-the-shelf gas cylinder anywhere near this size for the kind of money I was willing to pay, so I decided to fabricate my own.

I ordered some plastic syringes and some pneumatic fittings and made this:


…not the world’s best photo; I’ll see if I can edit in a better one later.

Getting it to work was surprisingly straightforward. The hardest part was finding an effective lubricant. After trying PTFE, graphite powder, WD40, water and the oil I use for my bike chain, all without success, I gave up and set the problem aside. A few days later I was washing up when inspiration struck. A couple of drops of fairy liquid did the job perfectly!

The internal area of my cylinder was just over 600mm^2, giving it a theoretical force of 200N (~20kg) at full pressure! I’d originally made a single-acting cylinder, hoping to use elastic bands to close the flipper, but I couldn’t get this to work reliably, so I pivoted to a double-acting cylinder design that both opens and closes the flipper.

With the gas cylinder sorted, it was time to think about compressed air storage, and I would need A LOT. The downside of that large cylinder area and going for double-acting is that each flip would cost about 160ml of air. I spent forever trying to find some way of fitting a bottle inside the chassis without making the whole thing too big to ever make weight. Then another moment of inspiration. Bottles are light. So light that I could have more than one, and put them on the outside of the robot, using redundancy instead of armour.

A trip to the local bike shop furnished me with as many dead inner-tubes as I could carry. From these I salvaged the valves, which I fitted to the bases of some pop bottles liberated from the recycling and voila, I had my air storage.

The final pneumatic component was a 3/2 solenoid valve to control the gas cylinder. Surprisingly this only cost £10 on Amazon, bringing the total cost of my super-buget pneumatics system to maybe £40, including failed experiments.

Electonics wise, I used a pair of BBB 22mm motors with some terrible (but cheap) brushed speed controllers. The solenoid valve was controlled through another brushed ESC, which I just used as a switch. The ‘brain’ was an ESP8266 (Wemos D1 Mini) which talked over WiFi to another ESP8266 inside a hacked PS2 controller. This works really nicely but boy was it a faff to set up. Fortunately I’d already done the hard work for an antweight project, so I just had to tweak the code slightly.

Finally, the chassis. Since I was optimising for yeet I wanted the maximum possible flipper arc to try to transfer the force from the gas cylinder over the biggest possible distance. This meant designing a very long wedge.

Being aware that this was getting large, I tried to make the bot as narrow as possible to keep the weight down. The result was this monstrosity.

Several hours of CAD later, I ordered some 10mm HDPE and booked a CNC induction at Exeter Fablab.

After much overthinking, and several pages of questionable trigonometry, I decided to go with a straightforward pivot-linkage between the cylinder and the flipper.


Time for a test-flip!

And there I was, I had a robot that could drive, flip and, to my delight and relief, self-right. Just a few tweaks and I would be ready to roll…

The night before the competition was spent testing and weighing. This revealed two problems:

  1. The pneumatics leaked.
  2. It turned out that my rough-and-ready weight calculations had been made when I was still planning on a using single-acting cylinder, and the 3/2 valve for the double acting one weighed over 100g more. This added to the fact that I’d been a bit optimistic about how much certain other components would weigh and I was way over the 1.5kg limit.

The pneumatic leaks were just a matter of covering everything in PTFE tape and ramming the pneumatic tubes into the push-to-fit valves like I was trying to shove them through solid steel. With those sorted, I took the biggest drill bit I could find and got to work adding >80 go-faster holes in the chassis. By 8pm my drill was smelling pretty toasty, but I was done.
…and then it occured to me to weigh the bottels after pressurising them. I turns out that 4 litres of air at 50psi weighs 20g. At this point I’d run out of space in the 10mm chassis for any more holes, but the 5mm flipper was still intact. Another 20 holes and I was done.

I was finally ready. I packed a bike pump and a sack full of spare bottles and headed for Bristol.

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Beetle Champs 2022:

I started the event with the fastest bugfix of my life after discovering that the wheels didn’t stop when the controller was unplugged :face_with_peeking_eye:. Good thing I brought the programming cable!

With that sorted it was time for my first ever beetle fight.
Waiting on stage for my turn in the arena I was extremely nervous. What if the bot didn’t start? What if the electronics immediately died and all my hard work was for nothing?
I finally got to the arena, and was able to breathe a sigh of relief when the 'bot responded to the controller and I drove to my corner. But I couldn’t relax for long. Facing off against me were Bakugo, a compact little drum spinner and Zephyrous, a giant face-spinner with the power to defy gravity. My fingers tightened on the controller as the countdown began…

What followed was quite possibly the most exciting 30 seconds of my life to date. I went straight for Bakugo but didn’t quite manage to get underneath for a solid flip. After that, there was no more time to think, just react. Not that human reaction speeds are really up to the task of fighting in an arena containing Zephyrous. I suspect the best way to fight it is to stay still and hope it self-OOTAs before it lands on you.
I got several near-flips on both opponents, but was never quite in the right place. Bakugo landed a solid hit on one of my exposed wheels, splitting the retaining cap and bending the motor shaft, but I was still going. I continued to duel Bakugo, but staryed a little too close to Zephyrous and bang! One of the bottles exploded. As the vapour cloud from the decompression dissipated, I prepared to rejoin the fray, but somehow found myself directly between both spinners, and a massive hit, seeming to come from both opponents simultaneously, sent me soaring across the arena and crashing down into the OOTA zone.

As a first fight, this was awesome! A full-body immersion in the barely controlled chaos of robot combat. I returned to the pits to re-straighten my motor shaft and, with the generous donation of a spare twist hub from team Rust in Pieces, I was ready for redemption.

My redemption fight was against the beautiful Axe-olotl, which turned out not to be an axe-bot but a vertical spinner. The fight got off to a tense start, with my botched box-rush allowing Axe-olotl to spin up and take a swing at my exposed side-armour. With some help from the flipper I squeeked away, and turned around to try to get in a flip, but couldn’t quite get underneath. Axe-olotl went for another attack on the side, but ended up with its forks stuck under the arena side. I freed it with the flipper, but unfortunately Axe-olotl had stopped (I later learned that the fuse had blown). With permission from Axe-olotl’s driver I gave it one more flip to satisfy the baying crowd, and with that the fight was over.

In the round of 32 I was drawn against Resistance, a veteran 4WD push-bot with great control and a very slick aesthetic. This was probably my best fight of the event. Resistance got in a couple of early pins, before I managed to manouvre the fipper underneath and flick it upside down, which seemed to compromise its control a little. Sadly at this point damage from previous fights, and my poor choice of speed controllers were taking their toll on my drive, and I partially lost power to one of the wheels. This caused me to jam the front under the arena wall, but a few kicks from the flipper helped me wriggle free. Resistance siezed the initiative, dragging us both towards the pit, and after a complicated moment the nose of Carbonated Beverage was hanging over the edge, staring down into oblivion with the wheels spinning helplessly. Another kick from the flipper and I was free, but my damaged drive prevented me from making good on the escape. Another nudge from Resistance saw me trapped in the pit-side corner, a position from which I was just too long to escape. Heedless I fought on, escaping the pit’s clutches again with yet another flipper kick, but resistance would not let me escape, and one final nudge saw me inescapably high-sided right on the precipice. The fight ended one second before I was counted out, and the judges rightly awarded the victory to Resistance. Great fun all round.

Wrap Up

So that concludes Carbonated Beverage’s first event. The bot had been a crowd-pleaser for its whacky design, and I was given the Best Newcomer award, which made me very happy :grin:. I left with 1000 ideas for improvements to make.

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Carbonated Beverage V2

Upgrades:

Beetle Champs had been a blast, but had also revealed some flaws in the design. That long thin body made it very slow to turn and only presented a small ‘danger zone’ meaning I had to catch opponents exactly right to flip them. The exposed wheels were also a liability. I therefore went back to CAD and redesigned the chassis.

The new 'bot was wider and shorter. Shorter does mean less energy in the flipper, which I partially compensated for by making the 'bot taller to increase the angle between the gas cylinder and the flipper to increase the force. I also added some TPU wheel guards, and a manual dump valve to make it easier for arena marshals to depressurise the bottles after fights.

This time around I designed in the gofaster holes before CNC cutting. Having been so close to the weight limit with version 1, I also went down from 10mm to 8mm HDPE. This actually brought me in almost 150g underweight. May have overdone it!

I also overhauled the electronics, replacing my terrible drive ESCs with a Tarakan from the BBB shop, which has served admirably ever since. I also swapped out the ESC I was using to control the solenoid valve for a power transistor, which was smaller, cheaper and lighter. Hooray!

Finally, I printed some mounts for the bottles to keep them off the ground. With the mounts in place, Carbonated Beverage becomes a very wide robot.

Subterranian Showdown 2023

CB’s next event was Subterranian Showdown. This was a blast. Probably the most fun I’ve had at a robot event. The “new bots only” entry requirement meant there were loads of unique and interesting designs on show, including the inaugural appearance of the delightfully whacky Reptile Dysfunction and the internal combustion engine powered No More Mr ICE Guy, which makes the most terrifying noise of any 'bot I’ve ever encountered.

All fights here: https://www.youtube.com/watch?v=4iaw830viA8&t=860s

Fight 1 was against Wet Lettuce and Angry Angry Anteater. I came out of the gate strong, getting straight under AAA and knocking it onto its back. I didn’t want that to be the end of the anteater’s very first fight, so I gave it another flip to put it back on its wheels; but sadly it landed on some debrits and was high-sided and counted out. Meanwhile Wet Lettuce were having some drive issues. Happily they managed to fix these later in the competition, but in the meantime they were easy prey for CB’s flipper.

Next up was a tense battle with the Foo-d Fighters cluster. There were 4 of them and it felt like every time I managed to flick one away another two would appear to take its place. The fight went the full two minutes. By the end of it I’d damaged 2 of the 4, but the elastic bands I’d foolishly added to my wheels in a last minute effort to improve traction had got tangled around one of the drive motors, causing me to loose power and control. In the end, the judges awarded the win to the food fighters, but I can’t be upset about a fight like that. It was too much fun!

My next opponent was a collection of 'bots under the banner of “Lynn I’ve put a spike through my foot!”, bringing back memories of scout camp misadventures. Half of my opposition spontaeously threw a wheel across the arena, leaving them open to a flip which luckly knocked out the link. That left me 100 seconds of desparately trying not to self-pit whilst fending off a tiny littly horizontal spinner that just would not get on the flipper. In the end I settled for butt-pinning it against the arena wall, running down the clock and damaging its wheels. At the end of the fight the judges awarded me the win.

And that was just enough to get me into the top 8, where I faced the horizontal spinner Live Laugh Love. A botched box-rush gave him ample time to spin up and hit me, over and over again. A chance hit on one of my angled rails almost sent LLL into the pit, but it came back with a vengence, and seconds later I was high-sided with my nose in the air. A final hit exploded my remaining bottle, disabling the flipper and with it my only hope of wriggling free.

Post-fight inspection revealed that the almost-pitting hit had ripped right through my rail.

And there was a 7mm gouge in the 8mm armour protecting my battery :grimacing:


So I guess I spec.d the thickness perfectly :sweat_smile:

My wheels were no longer particularly wheel shaped.

And the head of one of the screws holding my Tarakan in place had been ripped off, and then re-inserted upside down a few mm away.

Also, my shoelace-based battery holding system TM had been cruelly severed.

In spite of all these injuries however, all of the electronic and pneumatic components were intact, so I’m counting this as a win for the chassis design.

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Carbonated Beverage 2.1

More Upgrades:

Gyroscopic Steering:

My main takeaway from Subterranian Showdown what that the handling (and my driving) needed work. In particular, my box-rush would benefit significantly from an ability to drive in a straight line.

After some research, I soldered in an MPU6050 accelerometer/gyroscope and coded up a control-loop to keep the actual rate of turning consistent with the position of the contoller stick.

I was all ready to write a full PID controller, but in the end a super-simple proportional feedback loop was sufficient. I didn’t even have to calibrate it, my first guess was perfect!
…right until I painted latex rubber onto the wheels. Lesson learned: calibrate after making changes to the drive setup.

This is a clip of the steering before calibration. It’s clearly overcorrecting, causing the shaking, but look at those gorgeous straight lines!

To test the new setup, I swapped the left wheel for a larger one from CB1 and the 'bot still drove in a strainght line! Result! :smiley:

Extra Armour:

Since I had some spare weight, I bolted some middle-of-aldi 2mm steel brackets to all of the bits that Live Laugh Love had mullered. Specifically the rails and the battery housing.

Odds and Ends:

I also reprinted the bottle-holders slightly longer so that the bottles wouldn’t catch on the top of the OOTA zone wall.

Finally, I replaced my shoelace-based battery mount with a more traditional screws-and-plastic setup.

Last Minute Faffing:

I was proud to be ready for my next event days ahead of time. All that remained was to remove the battery for transport.

Due to some questionable design decisions, this required removing the whole side plate, which in turn required removing the wheel hub to access some screws. Lo and behold, I stripped out the hub’s grub screw, leaving it permanently attached to the motor shaft, and therefore permanently obsctructing the screws I had to remove to get at the battery.

And so it was that I found myself once again attacking my own hardware at 8pm the night before an event.

Half an hour with a hacksaw achieved nothing obviously useful, so I changed tac and cut the wires on the motor, allowing me to slide the whole assembly out without having to remove the hub. I then soldered in a connector so that I’d be able to repeat the process for battery changes at the event.

Almost 8 hours of sleep later, hopped on a train to Bristol

Beetle Brawl 2024

With these upgrades in place I took CB to Beetle Brawl, where I fought many terrifying spinners, a saw bot (Kairos) and a hermit crab made of steel (Wedge Against the Machine).

All fights here: https://www.youtube.com/watch?v=ncrPL-5Ki5Q&t=1233s

TL;DR: I enjoyed the event, but lost all my fights. I couldn’t get under Wedge Against the Machine and the flipper was knocked out early on in all my other fights, making it hard to do the thing.
On the bright side, my new steel brackets did sterling service. One taking a hit from Baby Dead Bod and the other from Saw Loser (probably). Baby Dead Bod wasn’t anywhere near full power and still managed to bend the steel an the HDPE, so the damage would probably have been much worse without the plate.

Outside the arena, I had a great time chatting with other roboteers, swapping tips and ideas and spectating the fights.

LHG Pub Beetles 2024

I spent an evening straightening out panels and brought the same bot with very minimal changes to LHG pub beetles.
This being a chill event, with a minimal time investment on my part meant I could just relax and enjoy the fights. And what fights they were! I got to duel two other awesome flippers: AoB, which uses an ingenious compresser-based pneumatics system, and Flick!, a really punchy spring flipper which absolutely wiped the floor with me (after I foolishly went in with a setup I hadn’t tested for self-rightability).

I also got a great flip on Die-Fi Hotspot, a big scary gyro-walker with a massive hub-motor based spinner, which was scary even in HDPE form.

All fights here: https://www.youtube.com/watch?v=dvsMsMTiAVc&t=476s

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What’s Next?

The last two events revealed several problems with CB’s current design:

  1. The ground-game is poor, which is a real problem for a flipper.
  2. The flipper is very vulnerable to getting hit by spinners, and it breaks when it does.
  3. The current design doesn’t self-right as reliably as the original.
  4. The 'bot seems to lose power towards the end of longer fights.

Another obvious flaw is that the bottles are pretty vulnerable, but I consider this more of a feature than a bug. Besides, they have proven able to survive glancing blows from spinners, as they’re a difficult shape to get a good bite on, and being light tend to bounce away. This is why I sometimes leave them trailing on the pneumatic tubing in spinner fights.

I’m not sure what’s causing problem 4, as the battery should have easily enough capacity to run two motors for the duration of a fight, and I’m not seeing big voltage drops between the start and end of fights. My suspicion is that there’s some underspec’d wiring in there that’s heating up and adding resistance. Failing that, upgrading to 4s and/or swapping out the brushed motors for brushless + gearbox equivalents should sort this out.

1, 2 and 3 probably call for another chassis redesign. I’d love to be able to make the 'bot a bit smaller to save some weight for forks, and a boxier front section could protect the flipper and potentially improve the angle between the flipper and gas cylinder for more kick.
The problem with all this is the solenoid valve. It’s reliable and has a good throughput, but it’s big, heavy (220g!!) and has a terrible form factor, with pneumatic tubes coming out of both sides, making it hard to find anywhere that it fits nicely. Any redesign is predicated on finding something better.

I haven’t been able to find a smaller 3/2 valve, but I do have a 2/2 valve capable of running a single-acting gas cylinder, so one option would be to go single-acting. Instead of having the cylinder push the flipper open, I’d turn the flipper into a leaf-spring, which is pulled closed by the gas-cylinder when pressurised, and released by venting pressure.

I wonder if anyone’s ever done a pneumatic spring flipper before :thinking:

Exciting an idea as this is, my attention is currently diverted to a new 'bot. Something just as whacky, but hopefully a little more competitive…
Design log coming soon to a BBB forum near you :wink:

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