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Thread: Babróg - Beetleweight Lifter Build Diary

  1. #1
    This (admittedly late build diary) is for Babróg, my third beetleweight design, and is modeled directly after my featherweight robot Barróg Doom. Similar to the Léim’s, the name once again is somewhat of a bilingual pun, where it sounds like a baby version of the larger robot Barróg (it works even better in Irish, where the world for baby is “babóg”). Despite how similar both bots look in general shape and weaponry, the end build turned out to be on the polar opposite of Barróg Doom’s design philosophy; while Doom used mostly air to protect its key parts, Babróg is a densely packed brick of a bot by comparison, mostly due to the sheer difficulty in fitting everything in that I wanted to the bot while keeping within weight (both bots have the same 10mm HDPE outer armour!).

    The finished robot, in its standard configuration.

    The horizontal config, with no forks and a static grabber arm for better stability.

    The drive is the same as Léim Thart: two cheap 22mm gearboxes paired with an 1806 2300kv brushless motor and KingKong 12A ESC’s, but this time with a drive inspired by Saw Loser, with custom moulded 3D printed wheels, held onto the drive shaft with a square nut/grub screw combo, and using HTD3 belts to drive the front wheels. The lifter is driven by a Robostar 53kg/cm servo, with a 7:11 ratio (14T to 22T) using HTD5 (HTD3 belts kept slipping). The bot also uses a UBEC Duo which provides 5V to the receiver, and 12V to the servo in place of the direct 4S Turnigy Graphene 0.5Ah battery which powers the drive. The grab and lift mech is similar to the FW Mantis, using a cam with a slotted hole for the travel of the grabbing arms and lifter forks. The bot has two main configs, a vertical setup with three 3mm Hardox forks, and a horizontal setup reusing the cursed 2mm grade 5 titanium wedge from Léim Thart and a static thicker plastic lifter. There are a few more unique quirks with the bot, but for now I’m going to link the build log on my team’s Facebook page:

    For now, enjoy a few select photos from the build, with more on the FB post, which should be public to all:

    One of the earliest versions of the CAD. This build would allow me to use moulding for the forks and wheels for the first time.

    The internals, one of the tightest wiring jobs I've had to do yet!

    A look at everything inside, mainly the lifter setup, as well as the drive and ESC's.

    The link mount, probably one of my favourite bits of wiring on the robot in general.

    The fork mounts, similar to the Barróg's, they can be adjusted height wise to be flush with the ground no matter what.

  2. #2
    BBB Beetle Champs 2021:

    I arrived at my first beetleweight in two years feeling rusty but unusually confident. Everything I had wanted to get sorted in the build was finished on time, the machine made weight with far fewer compromised than last time, the weapon had the power to lift a full beetleweight with little trouble, and the drive seemed to be responsive, grippy, and free from the issues Léim Thart had. My main concern with the build was the weapon servo: Robostar servos have been sketchy from the experience of other builders I’ve talked to, and there was only a very small window that the servo could move within, otherwise it would continuously rotate (weirdly, this only happened going in one direction). The bot was able to self-right within the sweet spot travel of the servo, but only just, and any tweek of the mechanism could leave me vulnerable. Nonetheless, I passed the tech checks and was ready to fight.

    Babróg at the pit table, ready to fight for the first time!

    Fight 1 VS. Spotty Botty, Inferno:

    My first melee promised to be interesting. Spotty Botty was a grabber control bot that looked quite nicely built, and seemed like it would be able to push me around easily. Of the two opponents though, Inferno immediately stood out as the more dangerous: the bot look typical of the 2WD egg beaters that had become so dangerous in the US BW scene, and the driver Will Thomas was a robot combat veteran with a record of both fantastic builds and driving ability.

    Fight starts at 2:52

    Sure enough, within seconds of the fight beginning, I was already hit and turned upside down, and Inferno wasted no time in taking shots at my vulnerable lifter assembly while I attempted to self-right. Those initial hits bent my front armour, making the robot “bouncy” to drive, and Inferno kept landing hits on my side and, critically, the underbelly of my robot, wheels included. I was definitely suffering from my lack of recent robot combat experience, as I struggled to keep Babróg straight and continued with what by now should have seemed as ill-advised strategy of going face first into Inferno’s weapon. Eventually I lost one side of drive, and after a few more painful exchanges I lost the second side of drive, rendering me immobile.

    Broken bits following the beatdown from Inferno.

    I was pretty shaken after the fight if I’m honest. I had really underestimated the power and speed of my opponents, and overestimated the strength of both my wheels and my ability to self-right. Inferno had been no joke, taking chunks out of my lifter, side panels, and even bending my 3mm Hardox forks like they were aluminium! The square nuts had partly done their job of stopping the D shaft from rounding itself out, except now the shaft simply dug into the plastic on the opposite side of the shaft, which ultimately led to the same outcome. It was probably always going to end up like this despite my testing, though Inferno’s direct hits on the wheels almost certainly accelerated this process. What’s worse, I stupidly chose not to make any spare wheels for the event, so it looked like I wouldn’t even be able to make my second redemption fight. I have to give credit to my opponents though: Spotty Botty made a valiant run in its later fights, and the one solace I’ll take from losing to Inferno was that Inferno would go on to win the event entirely!

    The wheels following the fight, note the grey moon-shape at the top of the hub, that's where the shaft opened up the plastic.

    Fight 2 VS. Oubley

    Any hopes I had of having an easier match for my redemption battle were shattered when I was paired up with Oubley, another 2WD egg beater built by Sam Graham and technically the reigning champion as winner of the BBB Summer Showdown event recovering from a shock loss in its first fight after getting its forks stuck under the arena wall (fun fact: each of my five last BW fights have starred a winner of a major event, Daedalus, X-301, K2, Inferno, and now Oubley). My only option for drive was to superglue the now buggered wheels onto the shaft, pop on my spare lifter forks, try to get my driving style back in order, and absolutely send it into Oubley and hope for the quick knockout, even if I knew that no matter what, I was likely on borrowed time.

    Fight starts at 38:58

    You can see in the fight that getting to recompose myself and calm down was having an instant effect. I was able to stay out of Oubley’s weapon, orbit the drum, and get around to the sides and control him. Then, almost miraculously, I was able to pin him to the wall, get the grabber in, and hold him suspended off the ground, something I was never able to do even with the original Barróg Doom! I tried to get him out of the arena, but unfortunately I didn’t quite have the height, and as soon as I had him out of my grasp, one of the sides of drive had once again given way. After some futile spinning, I ended up flipped over again, without the travel to self-right. As a last ditch attempt, I manually messed with the trims on my transmitter, sending the servo into its weird glitched out continuous rotation mode, and it gave me just enough travel to self-right one last time! It didn’t make much of a difference though, as by now the other side of drive had failed, and I was immobile, ending my second BW event in a row with no wins.

    The robot after both fights. Visually mangled, but surprisingly OK underneath!


    After the first fight I was feeling pretty miserable with the robot, but my second fight had left me feeling pretty optimistic for the future of the design. The wheels had failed once again, but there was an improvement, and there were any number of steps that could be done to improve their reliability (better material choice, more metal in the mounting etc). What’s more, aside from the wheels, everything else on the machine worked spectacularly well: the drive was fast and grippy, with no motor/gearbox failures, the armour stood up to plenty of abuse from two of the most powerful weapons at the event, the forks could get under opponents without getting caught on the arena, and the lifter had the power and surprisingly the durability to do what it needed to do. The latter was the biggest surprise; I had heard horror stories about the Robostars from other builders, but even continuously rotating against the solid wall that was the top plate, the servo wasn’t phased. It seems like the plastic construction of the bulkheads allowed for some flexing in the design as well, and the servo flexing the chassis and skipping on the pulley acted effectively as a clutch for the weapon. Babróg was 90% of the way from being the bot I envisioned, I just had to put a little extra effort in.

    A small preview of some of the upgrades to come!

    Major props to the crew in Bristol for all the hard work by the way! The event was incredibly entertaining to watch when I wasn’t losing, and it was fantastic to see the city and everyone in the BBB once again for the first time since the pandemic. Everyone who helped me in the pits was invaluable, and I’d like to give a particular shout out to Rob for his help while sharing our pit table, and Rhys and Fed for allowing me to drive their experimental crusher bot for a whiteboard event plus the gladiator. I intend to compete at the upcoming BBB Beetle Brawl in February 2022, and hopefully this one will go a little better!

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  4. #4

  5. #5
    The weapon was slow, certainly slower than what Doom can do, though this was more a limitation of what options were available for me at this weight class. The next most common lifter setup at BW level would have been a 37mm motor, but those are much bigger, longer and heavier, and with space already at a premium it was no dice. The servo was a risky choice, and certainly not a fast one, but it could lift an opponent without killing itself which was the main goal, and being able to hold an opponent suspended in place is its own advantage.

    The fragility was mostly due to 3D printed components, everything short of the grabber arms was PLA+. I didn't really expect the lifter forks to take much abuse since they were recessed into the bot, but I've had to reconsider that approach after the damage I took at BBB. I'm hoping to bring a lot more HDPE back into the mechanism going forward for the event later this month.

    The final issue with self-righting was more due to the fact that the weapon was powered by a servo, not a motor. This meant that I had to finish a self-right within a limited range of motion, and while I had been able to tinker around with the geometry of the grabbers and the gearing just enough to get it to self-right semi-consistently, it wasn't as reliable during the fight. I have plans to bring much more motion into the mechanism so that this should be a non-issue going forward, which should give me a self-righting time of a little over a second; not ideal, but certainly an improvement.

  6. #6
    So with a week to go before the 2022 BBB Beetle Brawl, I’ve decided to get myself together enough and actually post about some of the upgrades I’m making to the bot before the event. I was mostly happy with how Babróg performed, but there was definitely room for improvement. Fortunately, Christmas saw me acquire probably the most useful tool I’ve gotten since my 3D printer: a 3018 Sainsmart desktop CNC machine. The working area is small, and it won’t do anything to most metals, but for working with plastic it would allow me to do things I’d never thought possible before, both for weight saving and general construction. With this in mind, my goals were to beef up the more vulnerable parts of the robot, and to find weight wherever possible to make those upgrades.

    The CNC machine, with my "pragmatic" solution for cleaning swarf without an enclosure.

    The majority of the weight saving was achieved by pocketing parts of the side armour, up high in the parts where the robot wouldn’t be hit normally, while also being an easy first job to get myself accustomed to the CAM workflow. From there I cut out new lifter cams and forks to replace the previously 3D printed parts, the latter using a new design entirely to be possible with a 2.5D operation. Finally, given how the old side bumpers had shattered after a single hit, I decided to try to make them from solid 20mm HDPE. The operation took a while to pull off and the finish is a little fuzzy, but the final product works, and should be far more durable.

    On top is the new side armour, while the old hand-cut one is on the bottom. Both new sides save around 30g.

    An assembly of all of the outer armour, including the side, top, and front pieces, along with the side bumpers.

    The old 3D printed components next to their milled HDPE replacements.

    Electronically, I began looking for ways to extend the range of my lifter servo. After not having any success with a servo extender, I decided to open the servo up again to get an idea of how I could manipulate it. Fortunately, I noticed that the potentiometer was only linked onto the gearbox (to get feedback on which position the servo was in) pretty loosely. This meant that I could simply position it into a position where it assumed the servo was at zero on the sticks, use some glue and tape to prevent it moving further, and leave it loose in the servo assembly, no longer connected to the main servo transmission. This way, it would be able to rotate infinitely in either way, and stay still when the stick was in a neutral position, essentially behaving like a normal motor, bypassing the internal servo ESC’s weirdness in how far the servo could travel (this also saved me from having to mess around with manually soldering resistors, something I’m very grateful for after my experiences with the original Léim).

    The potentiometer. Interestingly enough, my 4mm motor d-shaft fits the potentiometer perfectly, which was handy when I was trying to get it centered to 0.

    Finally and most importantly, I wanted to strengthen the wheels up to prevent the failures of November. My experiments with printing in tougher materials such as nylon would be costly and time consuming to implement, so instead I simply decided to look at ways I could improve the existing PLA design. As the problem last time was a result of the shaft digging into the plastic on the opposite side of the square nut, the simplest solution was to put another static square nut on the opposite side of the shaft. This one wouldn’t have a grub screw, but would mainly provide much more surface area and greater resistance in the most obvious direction the shaft would want to move towards. Prototyping was done on simple pulley assemblies before I felt confident enough to scale the design up further.

    This is from the second batch of moulding I ended up doing, before this I had made four rear wheels for stress testing. This batch includes six rear wheels, two front wheels, and four lifter forks.

    I finally gave the wheels a proper “torture test” last week, doing everything I could think of in my power to break them (pushing loads heavy enough to stall them, rapidly going back and forth, attempting to drift them, doing J-turns etc.). After about 5 minutes of hard running, the supporting square nut had actually managed to dig into the plastic enough to cause the wheel to free spin (22mm gearboxes and 1806 motors on 4S really are powerful!). This isn’t perfect, but I do feel better in the knowledge that:

    • They survived longer than the old wheels, and longer than a typical 2 minute BW fight

    • They were being pushed far harder than I would be driving normally, I’ve tended to use a driving style that “nurses” the wheels after my experiences with the Barróg’s fragile wheels

    • They had only three or four walls on the print before the gridded infill, since then I’ve made wheels with totally solid pulleys

    • This time I’m bringing spares, and lots of them. Even after losing this set, I’ve got four spare pairs of rear wheels, and a spare set of front wheels. This should give me enough scope for a deep run in the competition (provided I actually win fights this time, gotta break that 6 loss streak eventually)

    You can actually see where the right shaft-side nut dug into the plastic. Given the surface area of the square nut this is really quite remarkable!

    Hopefully these new wheels prove to be a success, if the design holds up better I may consider selling them in the future. My main reliability issues have been with the sheer power of the motors, but this should be mitigated with lower voltages or the more standard BBB brushed sets, though not without further redesign. I actually ended up purchasing a set of the BBB brushed sets with the intention of being replacements, and was surprised to find that the flat on the shaft was significantly smaller than on the Rotalin gearboxes (the flat starts roughly 0.5mm down from the diameter of the shaft on the BBB gearboxes, compared to 1mm on the Rotalin gearboxes. This is only really a concern for press fit wheels such as the design I use)

    The new horizontal config ready to go, along with the standard setup in the background.

    Bonus picture: this is how I've been adjusting my forks to be flush with the ground, using washers with base-mounted mounts. Keeping a flat edge on the floor reduces the chances of getting caught in seams on the floor.

  7. #7
    Ocracoke's Avatar
    Team Kaizen

    Nice work! Love the CNC machine with the adhoc setup, might invest in something similar (albeit beefier for the weight classes I typically play around in) for when I've moved house - was your one particularly expensive? I might invest a bit of time in setting up some forks along the lines that you've done.

    See you there!
    Team Kaizen - Build Diary for all the robots

    AW: Amai, Ikari, Lafiel, Osu, Ramu
    BW: Shu!, The Honey Badger
    FW: Azriel
    MW: Jibril, Kaizen

  8. #8
    Thanks! The machine I ended up getting was a Genmitsu 3018-PRO, which was surprisingly affordable at around €220, so certainly less than £200 (link here: For about €100 extra there exists the PROVer variant, with an easier assembly and safety features such as limit switches.

    The 3018 did take me a few weeks to get running, as there was a lot I needed to do first such as assembling it, making a spoilboard, purchasing the necessary surfacing and cutting bits, though a lot of these can be purchased on the Sainsmart site instead. It's also worth learning some Fusion 360 for its CAM software as well as a PC to CNC interface suce as Universal Gcode Sender. There were plenty of tutorials online available however, and once all the prep was done every plastic piece I've made has worked flawlessly.

    The most important tip I've been given for operating with HDPE was to use these bits here:, 1/8th single flute end bits. The single flute should prevent the HDPE from heating up compared to the dual flute cutters, and lead to better chip clearage and a smoother finish overall.

    Also finally if you were in the market for something bigger, the 3040 variant hovers around the £700-800 price range, but gives you twice the machining area, with room to upgrade should you wish to work with metals tougher than the softest aluminiums.
    Last edited by Shooty; 22nd February 2022 at 10:04.

  9. #9

  10. #10
    BBB Beetle Brawl 2022:

    Most of the work for the robot had been completed two weeks before the competition, it was just a matter of picking it all up along with printing some spare parts. I did end up forgetting to bring a few parts along however such as grub screws and certain nyloc nuts however, and while I was able to obtain all the necessary spares, reassembling the robot, along with helping with the arena and venue setup, meant that I only made the tech check with minutes to spare. I had assembled the horizontal setup, as it was faster to assemble, which proved timely considering my first round matchup…

    Fight 1 VS. Beetlejuice, Everything’s A Drum:

    Some very interesting designs in this fight. Everything’s A Drum for this event was actually a combination of two different cluster teams; EAD which was two drums, and Frenchiest Fries which were two wedges, so for this fight I was fighting against one drum and one wedge. Beetlejuice meanwhile was a melty brain spinner built by brushless wizard and gearbox despiser Gareth Barnaby, which had the potential to hit harder than any other opponent if he could get up to speed. On the basis of the horizontal threat, I figured the wedge config would be best, along with the static claw up top (able to withstand more punishment, but unable to grab things).

    Babróg ready to face off against its opponents in the opening melee.

    Fight starts at 15:20

    As the fight started, my main goal was to prevent Beetlejuice from spinning up, and after taking a few blows I was able to consistently stay in contact with him, the last thing any melty would want. I was concerned about the weapon on EAD, but unfortunately the drum half seemed to be having issues, and couldn’t spin up, while the wedge half seemed hesitant to go anywhere near the danger zone that was Beetlejuice (probably rightly so). Without the grabbing claw, I found it tricky to get a good grip on any of my opponents, though I did manage to hook Beetlejuice and hold them up for a while at one point. Eventually the pit button was hit, and I wasted no time in corralling the melty brain towards the pit. After that, I got a pretty lucky shove, and managed to pit both cluster bots simultaneously, winning me the fight!

    The bot after the match. Outside of some light scuffs on the wedge, the bot was effectively in perfect condition.

    Needless to say, I was delighted after that fight to finally end my 6-fight losing streak. I checked the wheels after the fight to see how they held up, and while they seemed to have a tiny bit of slip, they had held up far better than before, which was a massive improvement in my book. The wedge had survived the few hits Beetlejuice had managed to land, and I was able to keep him under my control about as effectively as you could hope. The worst part of that fight was that Beetlejuice was one of the machines I wanted to see working the most, and it pained me that it was against my best interest to let him spin up. It would have been great to see EAD working at full power as well, though sometimes these things just happen in the opening fights.

    Fight 2 VS. Igor:

    After a longer than usual wait for my second fight (not being in the redemptions was a pleasant surprise), my second opponent, Igor, promised me a good old fashioned control battle. Igor was a well driven, 4WD lifter, with good pushing power and a weapon that could win the ground game if I wasn’t careful. I put on the standard config for this match, hoping my work on my front forks would pay off, and that I could flip over Igor rendering their forks less useful.

    Fight starts at 49:06

    This fight was probably some of the best driving I have ever done in any event, and I chalk a lot of it up to changing the rates on my sticks for this event to 50% for forward/back, and 20% for turning. I spent most of the fight getting under Igor, and most of those opportunities came from getting around to the sides and rear of them. I remained cautious throughout the match; I didn’t want to burn or stall the servo out without a perfect lift, and I didn’t go too hard towards the pit for fear of putting myself in. A key advantage I had was that Igor’s forks had a tendency to get stuck under the arena walls, while mine were too steep to do the same. Right before the end of the fight, I managed to score the only good lift of the match, flipping Igor over, and guaranteeing me the win through a judges decision, though I feel confident that I’d have won the fight without that lift regardless.

    A shot of the bot after the fight with the front panel taken off. The rubber seems to be vulnerable to being torn off in certain conditions.

    The wheels after this fight had definitely become much looser, and I could feel it in the way the bot drove in the last 20 seconds of the match, so I made the decision to swap over for a pair of my spare wheels. The grip that they offered though really proved crucial in winning that one though; even with Igor’s four 22mm brushed motors and Banebots wheels, I was able to shove them around with just the two 1806/22mm motor/gearbox combos. It was also reassuring to see how effective the front of the machine was in out-wedging an opponent while also not compromising my driving, even as it was essentially the exact same design that I brought in November.

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