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Thread: Schnake - Beetleweight Grabber Build Diary

  1. #1
    This is Schnake, a four-bar grabber built for my Dad for the Robot Rebellion event at Rapture in July 2022. This is my fourth BW, my third four-bar build, my second robot to use CNCed parts, and the first bot built entirely for someone else to drive! This was a fast build compared to many of my other projects, so I'll just tear right into the design stage.

    I had tossed around the idea of making a four-bar lifter before (this was originally going to be for a potential Léim 3), but since my Dad wanted to do something different for his design I was interested to see if I could do something different. The idea for the four-bar grabber mechanism came from seeing some machines use their lifters in reverse to try and hold onto opponents. I saw a potential good idea in having a weapon capable of grabbing opponents, but also capable of being recessed into the robot. After experimenting with geometry for a while to see if the idea was viable, Schnake was born. The name of the robot comes from several places, even if it's been more of an afterthought than previous builds. The motion of the grabber closely mimics that of a snake, as do the teeth. Schnake is also a very Irish way of saying snake, and inspiration was taken from the accent of a famous Irish comedian, Francis "The Viper" Higgins (NOTE: Not pronounced like "Schnack").

    The mostly finished CAD for Schnake. The robot uses most of the same internals as Babróg, as well as the same wheels.

    Some of the fun that comes with owning a CNC machine (the fun is mostly sarcastic).

    A finished grabber piece. The gap in the middle was a decision to try and counter verts, the theory being that the robot could go head on with less of a chance of getting hit badly.

    For the weapon, I was very paranoid of taking a direct hit to the weapon, and that killing the servo gearbox as a result. To counter this, I decided to design in a clutch into the weapon, hopefully I can explain it well enough.

    Here's the first part: an M3 threaded bar, loctited into place. The nyloc nut holds the servo horn in place, similar to what a bolt would usually do. The servo arm would be sandwiched between two washers/spacers. They would pivot around the threaded rod, but crucially would not be directly attached to the rotation mechanism of the servo. Tape would be added to the washers later for more friction. The idea would be that the friction of the Nyloc against the weapon assembly would result in the arm wanting to rotate along with the servo horn, though with enough effort it would slip instead. This could be adjusted by tightening the servo arm to whatever I would see fit on the day. Perhaps a little conservative, but with a grabber instead of a lifter I could afford to be, and this can be tweaked during and after the event.

    The Nyloc clutch assembly.

    For the spacers for the wheels, I used these 35mm long M4 hex standoffs. I wasn't a big fan of the brass look however, so I printed these sleeves to press onto them to better blend in with the white HDPE.
    Last edited by Shooty; 29th May 2023 at 06:34.

  2. #2
    This robot is the first time the majority of plastic in one of my builds was CNCed, but there was still one piece that demanded good old fashioned hand-cutting and bending. The rear panel of the bot took the better part of the day getting right, and even now it still risks rubbing on the rear motors, but for the pressure that was on me to finish it I'm happy with the results!

    The new back piece, also containing a slot for a link at the back. I'd like to think I can still make really fun looking HDPE robots, even with CNC making me look at the stuff differently now.

    Babróg's wheels have proven themselves to be usable at a BW level, though still not exactly as reliable as I would prefer. The wheel on the left is our attempt at fixing this.

    For the hub, we're using a 12mm long M4 hex standoff, with a 7mm hex size across the flat. the M4 thread is drilled out with a 4mm drill, and a tapped M3 thread is done on top of the standoff using a specialised mount. From here, it's simply pressed into the 3D printed wheel, and presto! Homemade Banebots hubs with none of the fiddly thread shenanigans!

    The new wheels. What past me doesn't realise is that there were in fact fiddly thread shenanigans.

    Here is one of my favourite build photos: the internals of Schnake compared to Babróg. An interesting look at how most of the same components can be arranged in completely different ways. For Schnake I printed a two-storey electronics storage box, with the dual UBEC found below the two ESC's and the receiver.

    Babróg compared to Schnake.

    And here's the final robot, next to its sibling bot, Babróg. Schnake is a little wider, but much lower, and is several hundred grams lighter than Babróg despite using basically the same internals!

    The "glamour shots" of Schnake, as well as the robot next to Babróg.

  3. #3
    Robot Rebellion 2022 Event Report:

    Robot Rebellion 2022, also known to many of the competitors as “Rapture”, was a rather unique BW event for a few reasons. The first of those being that the format of the event involved robots in heats fighting in a round robin format, before the top scorers in each heat moved on to a single elimination best of 16 bracket, closer in style to a FW event such as those run by Robodojo or Robochallenge. The second was that along with me running Babróg, basically unchanged from Brawl 2022, this would be my dad's first ever BW event, running Schnake, a four-bar grabber robot that was only finished a few weeks before this event. He unfortunately didn’t have much time to get much practice with the far more sensitive drive required at BW level, and a lot of the first morning was spent trying to troubleshoot an incredibly frustrating problem with the robot not responding with the transmitter after a restart (the problem ended up being an issue with capacitors in the BEC requiring a longer time between turning on and off). With all of that out of the way though, both bots finally ended up passing their tech checks, and the tournament was underway.

    All fights are taken from the re-upload of the official Robot Rebellion stream, though there may be some video issues due to it not being the raw footage. Special thanks to Nick DSC for the Herculean task of timestamping all of the fights!

    Schnake: Fight 1 Vs. EMP

    Fight starts at 41:31

    Schnake’s debut fight was against EMP, a very unique four-bar electric flipper built by Felix Townsend. EMP actually managed to flip Schnake within the first few seconds of the fight and beached it on the wall, but through a mixture of sportsmanship and wanting to shake his own robot down more, EMP flipped Schnake back over, and so the fight continued. Schnake actually had some impressive drive power, and the forks at the front were able to consistently win the ground game, but what the robot really suffered from was control. All of the swapping of transmitters earlier gave me no time to properly adjust the trims on Schnake, and that combined with perhaps some issue with the chassis meant that the bot naturally turned to one side when going forward, and totally straight going backwards. I would struggle to drive this in the best of times, and my dad had far less experience at the class than I did, but all this meant Schnake really struggled with the ground game, and never really got to use its weapon. Both bots ultimately struggled with drive, but EMP ended up getting the win due to better control. Slightly disappointing, but this fight at least gave us a baseline on things to improve about the robot going forward.

    Schnake going into its first fight. Unfortunately I wasn't able to find too many images from this event, so photos may be sparse.

    Schnake: Fight 2 Vs. 7th Circle

    Fight starts at 2:22:44

    Schnake’s second match was against 7th Circle, a rather nasty vertical spinner by Dave Weston. Dave is an excellent driver, so we knew the danger going into this one, but fortunately he seemed to be struggling with drive on one side, and this gave my dad some time to pick when he wanted to engage. Considering Schnake’s continuing drive issues, my dad drove very well, getting around to the sides of 7th Circle, and generally able to push it around. Unfortunately, one nasty hit was all that was needed to send Schnake flying, upside down and near the pit. The robot was meant to be invertible, but manufacturing issues meant that I couldn’t get it to work reliably, and so 7th Circle took a well earned win.

    Schnake: Fight 3 Vs. Swag Demon

    Fight starts at 4:05:52

    Not too much to talk about with the third fight unfortunately. Swag Demon had the speed and excellent control to beat nearly anyone in the tournament, and unfortunately control issues were once again to blame, seemingly unable to drive straight easily. After a few chunky hits Schnake was beached and counted out. One positive to take from this fight however was Schnake’s durability; the side armour survived many direct hits, and nothing on the robot ever really seemed to break.

    Schnake: Fight 4 Vs. Step Up 3D

    Fight starts at 26:19

    Schnake’s final opponent would be Step Up 3D, a control bot that had basically been destroyed twice before this fight, and was certainly durable, if not a little past its peak. After some slow driving from Schnake to see how drivable the bot was, it seemed like we had both the ground game advantage and the mobility to control the fight. Unfortunately, Schnake ended up going into the walls at full force and ended up getting a wedgelet stuck. Being unable to move freely, the bot ended up getting counted out. A disappointing end for sure, but lots to learn from.

    Bonus Fights: “Grabber” Melee and “International” Melee

    Fights start at 4:51:38 and 5:50:57 respectively.

    Now that both bots were out of the main competition, we had a bit more time to get some more driving time and iron out any more bugs with whiteboard battles. The first whiteboard was going to be mainly a rematch between Step Up 3D and Schnake, but very rapidly evolved into a general grappler fight with a few lifters as well. Then right after, there was due to be a fight involving all of the “International” competitors, and as a result we barely removed our bots in between matches. These fights were great as a torture test for both bots, as we could see how they’d manage a variety of weapons with no real time to tweak or charge things in between fights. Schnake got some good charges in, and Babróg finally managed to actually land some suplexes!


    Schnake and Babróg both tech checked (with some panic) and ready to go!

    This was probably the most hectic event for us since the UK FW Champs in 2019, and there was a lot to learn for sure. Schnake was far more of a mixed bag than Babróg, as is to be expected from a bot at its first event. The robot certainly had the speed necessary, and its durability was fantastic, but this didn’t make up for its issues. The biggest issue was its driveability, it seemed impossible to re-do the mixing in such a way as to make it drive slowly in a straight line, something my dad struggled with greatly. The new wheel hubs promised a lot, but unfortunately they started to come loose very quickly after fights as the event went on, hurting control even more. Finally, the robot was not able to drive upside down at all, due to the tight tolerances everything was under. A lot to learn from though, and I’m already considering possibilities for a Schnake V2.

    This was another really fun event, and I’d like to congratulate all involved! Both robots should appear new and improved for Robot Rebellion 2023!

  4. #4
    Schnake was an experimental BW slapped together in record time for us to compete with for Robot Rebellion 2022, using mostly the same components as Babróg for convenience. The robot was novel and durable, but there were several issues that prevented it from meeting its full potential. Fortunately, Schnake was already severely underweight, so changes could be made with little concern. To address all of these issues, we decided to do a near-total redesign of the design, to arrive at what could basically be called a Schnake 2: similar in concept but different in many ways.

    The new (mostly finished) Schnake.

    By far Schnake’s worst issue was in how it handled. The robot was very twitchy, couldn’t drive properly upside down, the hubs kept coming loose, and seemed to constantly drift in one direction, with no seeming way to fix it. As it turns out, the drifting seemed to be a result of a twisted front piece that twisted the chassis in such a way as to keep one front wheel off the ground, but the other issues would need a good quality rethink.

    The new 3D printed hubs for the wheels.

    A productive tire creation session, complete with a new hubbed design for Babróg.

    My first call with the new robot was to change the drive from the 1806/22mm gearbox setup used in Babróg to a more conventional BBB 22mm brushed motor setup. I’d lose a bit of the speed and compactness that comes with the brushless drive, but the robot would become far easier to control at slower speeds, which would be critical when positioning the robot for a grab or trying to orbit an opponent. Schnake also no longer uses the 49mm wheels used in Babróg, but now custom wheels, 40mm at the front and 60mm at the back. The increased size at the back allows us to drive more reliably when upside down, and should grant a very slight boost in speed from that lost with the brushed drive. The new larger diameter rear wheels can now fit a proper Pololu hub, which should be far less likely to come loose in a fight.

    “Your three choices of tire compound for the weekend are the 60mm C1’s, the 49mm C1’s, and the 40mm C1’s.”

    Finding the right sized belt was tricky to ensure a decent wraparound, especially on the front wheels. Unfortunately, my previous belt supplier now charges £30 minimum in shipping for any orders, including two tiny HTD3 belts in a jiffy bag (thanks Brexiteers). After about an hour of searching, I finally found a supplier providing the belts in the right length, only to discover once I got them that I had ordered 9mm width belts, when I can only fit 6mm. Fortunately, within 10 minutes of letting Jack Tweedy know about this, he had sent over a custom .stl file for a belt cutting design, which I had printed in an hour and had the perfect belt for the job.

    That’s why he’s the GOAT!

    One big concern from last year was how Schnake managed to get stuck under the arena wall so often with its forks. As a result we have designed and ordered new forks with a less shallow angle at the front, which should allow us to drive head on to an arena wall with little chance of getting stuck. The new forks will likely not be as effective at getting under opponents as the old ones, but they will be able to make it harder for an opponent to drive off once grabbed.

    The new forks shown off in the CAD.

    The old servo never necessarily failed, but that was mainly because it was never actually used, and I still have major doubts as to its effectiveness. With this in mind, Schnake now uses a 37mm 80rpm 18kg-cm Pololu motor, similar to those used in other grabbers and lifters in the European scene. This allows me to do a few things. First: a motor setup that’s far less likely to self-destruct and far more likely to grab and hold something. Second: I can now use a simple brushed ESC for control, allowing me to move away from the bulky and complicated dual UBEC setup used before. A new much smaller voltage limiter provides power to the receivers. Third: I will now have the motor connected to a separate receiver, which I will control while my dad drives. This alone will allow the weapon to work much more easily in tandem with the rest of the bot, while my dad can fully focus on driving.

    The new electionics smushed in. The battery and electronics will swap places, but everything fits in snugly.

    One major issue I struggled with in this design was that my CNC machine started to wear and flex quite dramatically, to the point where I could’t really reliably pocket parts anymore. Most of the pieces were finished before the problem got really bad, but I still had to rely on some good old fashioned chiselling from time to time.

    The back pieces on my robot always seem to end up curved. A fiddly one to do, but happy with the results!

    All of these changes have resulted in a nearly total rebuild, with very few parts perfectly carried over (most notably are the grabbing panels, simply because they took a ton of time to make and I’m not doing that again in a hurry). All of this was written before Schnake V2’s debut at Robot Rebellion 2023, and while a lot of stuff could still go wrong, we were confident that this iteration of the design should perform much much better than before!

    Schnake from the back, now with a much cleaner action on the grabber.

    Schnake and Babróg, ready to take on the best of the UK!

  5. #5
    Robot Rebellion 2023:

    Robot Rebellion 2023 would see both of us returning in a very similar manner to 2022, with minor upgrades to Babróg and the entirely new Schnake to test. This year the format of the competition was slightly different: each of the 12 heats would contain four robots in a round robin format, with the only rule to the order being that the winners in the first round would fight each other in the second. Points were no longer being used to score a heat by the method of winning or losing, merely if the fight was one or lost. The robot with the best record would go through in each heat, with the second place robot going to a three way playoff to determine the final entrants to the top 16. There was also the potential for “lockdown” melees to determine heat order should three robots have the same W:L record by the end. Finally, each heat would have a seeded robot competing, where Schnake had Bby Shrekt as its seeded opponent.

    Here is the heat Schnake took part in, which has every fight it took part in except for the whiteboard rumble.

    Schnake: Fight 1 Vs. Aggro Wobba: Smidders Edition

    Schnake’s first match was actually against Babróg’s first opponent from last year, Aggro Wobba: Smidders Edition. This fight was definitely a match for teething issues: one of the teeth on the grabbing arm was getting caught on the plastic front, and prevented me from being able to use the grabber at all, meanwhile the new mixing I had done on Schnake made the robot less likely to be uncontrollable, but had the opposite issue for my dad in being too sluggish to handle, especially with turning. This left a fight where Schnake was never able to really get around Aggro Wobba, and when it could, it just didn’t seem to have the pushing power. Schnake was slowly making its way to the first loss of the competition, before a driving error from Aggro Wobba left it stuck in the arena wall, with Schnake literally too slow to free it, resulting in a rather undeserved KO to start things off. Nice to have a win, but definitely a lot to improve.

    Schnake: Fight 2 Vs. Bby Shrekt

    Schnake’s second fight was against Bby Shrekt, one of the favourites to win the competition, and a real test for the robots durability. Unfortunately there wasn’t too much to talk about with this match. Schnake drove straight into Bby Shrekt, before then reversing into it again. This combo of hits caused the robot to limp on one side, before another hit at the back knocked the link loose, leading to a nasty KO.
    This match was a nasty loss. In the few seconds it lasted, Bby Shrekt managed to mangle a gearbox, the threaded support of the armour, killed a drive motor, and snapped the rear bulkhead of the robot, twisting the entire chassis in the process. A lot would be needed to fix the robot going forward, but this fight also revealed just how weak the structure of Schnake actually was without enough bracing at the rear of the robot.

    Schnake: Fight 3 Vs. MOTHenator MKII: CODENAME LITHIUM

    Schnake’s final fight was one that would, thanks to how the group had gone so far, determine if it would finish its heat 2nd, and secure a spot in a playoff rumble for the top 16. In its way was MOTHenator MKII: CODENAME LITHIUM, an undercutter that had lost its weapon, and was now reduced to a 2WD pushbot. This should have been the type of fight where Schnake could have gotten one good bite and won it, but unfortunately things didn’t go our way thanks to a few factors. The wedgelets at either side of MOTHenator were perfectly positioned to prevent the grabber from getting a hold, and MOTHenator was driven very well to make the most of this. The real kicker however was how this was Schnake’s first real demonstration of pushing power, and boy howdy was it a stinker. I had expected some drop in performance from switching back to brushed motors, but I had massively overestimated how strong a pusher with only two 22mm motors was. Without a useful weapon, pushing power, and a seeming drop in power near the end, Schnake was finally pitted, ending with a 1-2 record.

    Heat G 2nd Place Playoff: Schnake Vs. MOTHenator MKII: CODENAME LITHIUM Vs. Aggro Wobba: Smidders Edition

    Due to the format of the competition, each of our robots ended up in different rumbles to remain in contention. While Bby Shrekt strolled away with a comfortable 3-0 record, Schnake managed to score a second chance due to both of the other robots in the heat also having a 1-2 record. Unfortunately Aggro Wobba had to pull out of the fight due to transmitter issues, and so the fight basically ended up being a repeat of the last match. For whatever reason, using the grabber seemed to be playing havoc with the electronics, so after a near scare early in the fight I decided not to use it any more. The fight was a near copy of the previous fight: MOTHenator had better control, a design that negated Schnake’s weapon, and crucially electronics that didn’t seem to be iffy, resulting in a win late into the match, leaving Schnake 3rd in its heat, knocking out of the competition.

    I really must apologise, but I took very few photos from this event, and if you can believe it, this is the only photo I have of Schnake while there.


    Robot Rebellion 2023 was certainly an event with a lot to teach us. Schnake’s redesign was a pretty big disappointment, and a lot of the errors with the design should have been spotted by myself way earlier. The most major issue was the drive power: I had expected some reduction in drive power by going from a brushless to a brushed drive system, but I did not expect the downturn in pushing power to be so dramatic. On top of that, the robot was just not as durable as I would have hoped it would be: I never really came to appreciate how well supported Babróg was until I noticed how little support Schnake had for the baseplate to flex outwards from the robot, and the machine payed the price as a result. I don’t believe that all the changes were bad, the weapon motor in particular seems to be a massive improvement. I can see this design being worth at least one more crack, though I’d like to take a break for a while before committing to anything major.
    So that was Robot Rebellion 2023! Apologies for the delay in posting this, it’s just been a challenge to find the time to sit down and properly write all of this down. I am unsure how much time I will have in July 2024 for what I’m assuming will be Robot Rebellion 2024, but I definitely intend to have both me and my dad competing at a BW event together at some point in the following year. Stay tuned in the coming days for some more event reports!

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