YAM! beetle build/cad

design for yam started a few months back, been wanting to make another 2wd vert of some kind for a while but didn’t want to make a standard vert, wouldn’t really fit my style, so wanted to do something silly, the main inspiration came after scouse showdown 2, where sion had a really awesome 500 gram drisc bot, really liked the idea of building a silly heavy vert but wanted to try and make it more driveable, it was about this time i also saw ripperoni with its really cool anti gyro flywheel and i figured i might be able to emulate that with a tilting frame instead, i also really liked how much of the bot was off the ground to prevent forks being a factor so wanted to do that too, as the weapon and tilting assembly is the most interesting part of yam ill talk about that in-depth with a little bit on the drive ect at the end

so with these two ideas in mind i then also set myself the challenge of having the heaviest vert beetle in the uk, naturally the best way to ensure this was to make half the weight of the robot a spinning weapon, which was the first thing i designed

i knew from the get go i wanted a hub motor, it gave me the most spinning mass as well as ensuring i could keep it running after even the biggest hits

the weapon itself is 85mm diameter, i those this to ensure it was about the same diameter as traditional verts so it would be harder for them to out tip speed me as well as ensuring i had more bite than they would with over 12mm of tooth, this also meant i could have a better shot at getting massive impacts without needing forks

the bearings we 10mm id by 30mm id and 11mm deep on a 10mm grade 5 ti shaft, i did this to ensure i had lots of strength to take big weapon to weapon shots, as part of my gameplan was to run upside down to deliver enough energy to hopefully break the other weapon in a impact

the motor itself is a old brushless motor i had for another hub motor that i never built, its a 3536 propdrive of unknown kv (somewhere between 960 and 1800) im 99% sure its 1400 kv as thats the cad model i had from years ago but decided to run on 3s to be safe to ensure i was well under the limit at around 170mph

the weapon was made by pcb way from 4140 and i decided to try getting it chrome plated, it was like another quid to try it out so figured even it its useless then ive not wasted anything in trying

the core of the drum is ali machined by myself, there are several reasons for this, firstly i wanted to keep the cost of the drum down. getting them to machine the bearings pockets and motors was Gunna be costy, it was also done to prevent pressing bearings into hard steel, talking to other builders this is a bad idea and can lead to cracking, so hopefully the ali should act as a “pillow” between the weapon shots and the bearings

next thing i designed was the tilting frame, i wanted to ensure it was as strong as possible so opted for 3mm reax construction and a 12mm pin for it to pivot around, its designed to give around 20 degrees of tilt either side, this was a totally random number but figured it would be a good first test, originally it was of bent construction but opted for welded due to time

the tilting is controlled by 2 m5 bolts that run in the slots pictured, captured by 2 locknuts on each bolt to ensure it wont vibrate off

it is mounted to the frame by 2x2mm by 16mm flanged bushings in 2mm 6082 aluminium plates, the shaft itself was 12mm silver steel with a m6 cap head bolt holding the whole thing together

i also wanted to ensure that i didnt need to play the ground game, the supports from the drum are swept back and even rounded off, and the large wheels ensure i have a massive around of ground clearance (close to 20mm on the front) to effectively drive over forks and delivery the weapon effectively

the body is a tpu unibody designed to be as light and durable as possible, although mainly just to save me from the odd hits it might take with owobotics brushless drive motors paired with bbb brushless drive escs which worked out well, the other small thing of note is the rounded ali back sections these are just to prevent it getting it stuck on its butt

finally its got 2.75 inch foam wheels to save weight and stop me breaking the gearboxes on weird landings

so yeah thats the deisgn idea for yam, the build process went well, most of the pain was getting my printer to print the tpu at all, ill spare you the hours of pain to get it running as its still not reliable haha

so yeah, yam!


So cool seeing this in action in Bognor! The tilting weapon looked really slick :smile:

thanks man! need to improve its stability and stuff but im pleased with it overall

Looks super tanky! I half wondered if it was going to be some kind of Gyrobot/Wrecks walker from the motion - maybe if you need to pack more weight into the weapon at a later date.

if it’s not too much of a rude question what was the ballpark cost of the 4140 drum and did you heat treat it?

its certainly got the gryo for a gyro walker but wanted to try and get more mobility out of it

ha nah its all cool, around 80 quid for the part and another 30 or so for shipping, i could of got it allot cheaper i think, i had some tricky geometry that if i were to get another made id redo it to make it a little easier to make

didn’t end up heat treating it, ari seemed to get decent results with a unhardened beater and i wanted to avoid it snapping, so its a little soft but so far seems to hold up

(edit converted dollars to pounds)

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Tilting weapon looks amazing in action. Love it Morgan, you consistently bring the most wild and chaotic energy to the arena!

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Great, that’s good to know. Yes I think I was part of the conversation with them about whether or not to harden as they were on the fence - will keep all in mind.

following its first event there was allot i learnt about the design so heres a bit of an update for it, with a small “what i learned” from each fight rather than a full event report, although i should say a special thanks to joe for bring my delivery (containing the all important wheels) with him after royal mail managed to loose it for the best part of 3 weeks lol,




  • having my only driving with the robot be in the arena is not ideal
  • the tilt didnt take as much of the gyro away as id of liked
  • the 4140 is pretty soft and got dinged pretty bad, nothing that effects the weapon but might prove problematic with the more chunks taken out



  • got its first knockout!
  • everything was still mechanically fine after the fight


  • it died, no room inside the bot for padding the receiver got crunched and got pretty lucky that lobster could self right
  • the unbound esc noise is pretty annoying

7th circle

  • it still didnt explode!
  • went weapon to weapon with a top level vert for 30 seconds and was mostly unharmed and opened up some pre-existing cracks in his weapon bulkheads
  • took body shots and survived
  • made it to the top 4 of the winners bracket, no 3rd place playoff due to time but still not bad
  • Dave was able to avoid my upside down attack potentially because i had to run the robot inverted making it pretty obvious what i was planning
  • was outdriven and hit in the rear lots of times
  • self ootad

as a general takeaway the mechanics of yam were solid, i never lost a side of drive and the weapon kept hitting hard deep into fights and the tilting system didnt explode off the robot first hit, despite constant pressure, so mostly smaller changes but i think some of them are interesting solutions so i wrote them up anyway,

so to solve these issues i first knew i had to increase the space in the robot, there’s compact and then there’s killing expensive electrical parts by landing weirdly

picture is without the battery and motor covers, as you can imagine it gets pretty snug

so i changed to a more rounded rear to give me a little more space as well as increasing the length of the wires to the drive escs, removing some of the tension in the cables, if it persists as a problem i also now have space and a little spare weight for foam

overall mechanically i was very happy but also changed the bolts that control the extremes of the tilt to some proper grade 8 bolts rather than stainless bolts, and also put on a thinner washer to help move the weight a pinch further back

next i wanted to address the running in reverse stratergy, it worked a treat and am now very confident in the weapon assembly to be able to take those shots, however having to run upside was not ideal, driving was backwards and i lost the element of surpise, ideally id like to run a reversible weapon esc, but not sure if theres on that could take it, and it would also need to be without a break, to avoid a massive front flip

so my solution is a little jank but i found these really neat 3 way connectors on ebay after a few people suggested them in the beetle ground chat, i found that if you use a hack saw you can get the connector to go in the “wrong way” allowing me to switch weapon directions minutes before a fight with a simple disconnect, and will also make servicing the weapon assembly allot easier as i can remove it from the rest of the electrical system

finally i added some silicon to the wheels, however im trying a few diffirent ideas for that, one is gunna have patches of grip kinda like a tractor tire, to hopefully deal with dust better on the dojo floor, one is solid latex for pure grip and the other will remain just foam, incase its too much for the drive motors for it to actually grip

theres a few bigger changes i have in mind if/when it gets wrecked, namely a 2mm hardox from rather than 3mm reax, save weight and likely be stronger anyway that way i could put more weight into a suitable reversible weapon esc or magnets to make it drive better, as well as a move to 4s high voltage as i now know the kv of the weapon motor and could be at 240~ on a higher voltage battery for bigger hits at its currently at the 170 ish mark, which does mean i cant out tipspeed drums atm

with that done Yam! is ready for june dojo, hopefully it can break some more vert