🦀 Grab Crab v4 - turning the suplexing to yeeting!

I’ve finally made a new solo build video, I am not a huge fan of talking solo to camera… I used to do this more often, I think it was more useful when I used to do builds by hand with much less CAD, but still good to share the process I guess… enjoy! It’s got a good summary of my last few years of builds and what kinda thing I try go for :slight_smile:

To summarise the build in text form:

Firstly, here’s grab crab v3 before rapture 2022:

And after:


I had an onslaught of spinners and was super happy to come off ok against most of them until I got very stratus’d.

So for v4, I decided to keep most of the same chassis design with a few tweaks, but try out a new beefy motor - the ‘strangbox’ - @Strang_H’s set up on bonbonbonbon’s lifter - a 2836 on 100:1 28mm gearbox - BEANS!

The chassis was my usual CNC’d boxy red HDPE PE500 interlocking 5 and 10mm:
image

Now upgraded to repeat max drive (had been great on :lobster: Lob-ster earlier in the year, and repeat AM32 ESCs which seemed very responsive… so responsive in-fact I ran one on the weapon too. I decided toothed belts had caused me enough pain so stuck with trusty PU belt on drive and fun lego tyres, with TPU cores printed by the excellent Joe M!

I’d initially mounted the weapon motor for direct drive as in my innocence 37D motors happily stall out this way


I’ve now used barrel nuts and HDPE spacers for the wheel guards, these held up sooo much better than the puny aluminium standoffs in v3

But in my testing, this had way more power and was going to tear the D-hole into a… well hole I guess. So I tried a series of 3D printed gears, see the video for the full run down on that, the summary was the gear teeth were too small and shatterable whatever the material (PLA, TPU, Taulman 910, ABS…) so wouldn’t really work without a pretty major redesign, which I at this point did not have the time for!


Using 3mm hardox forks and claws, now reused from both v2 and v3, one here a bit bent from Stratus but still very usable!

So day of the flight to Burgh (cutting it very fine…) taking influence from the excellent Tosser electric flipper by THE @Gareth, I went for as chonky as I could fit 20mm wide HDPE CNC’d gears

And these worked well enough in a quick test, no teeth exploding, no crunching noises. Still had to be careful to not stall out too much! So finished bot, ready to head to Battle in the Burgh!

Full run down of fights in the video above, but due to some good yeeting and quite a nice draw managed to somehow come out on top?!

with an all control bot final with the excellent Boom Zoom getting some air miles!

Gonna whack this weapon motor on :lobster: lob-ster next with a lot of HDPE gears, because chonk plastic gears are fun. GG, thanks for reading. See y’all in 2024. :crab:

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man that thing is super impressive!
and congrats on the trophy :slight_smile:

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wonder how much it would help with the tipping forward if you moved the weapon assembly right to back

good shout, I used to have the pivot point further back on v3, but yeah could try having weapon the motor at the back.

just thinking the likes of Nyx has it much more reward and you look to have plenty of space plus could also move the CoM closer to middle

Hi Joe. Well done on the win!

How did the HDPE spur gears hold up in the end post event? Also are they MOD2 or 3?

Hey Sam, thanks!

They’re just under MOD3 (MOD2.9 or something so they’d not hit the baseplate on the last minute redesign) They held up really well for 7 fights worth - a couple teeth have started to bend along about half the length presumably from when the arm is stalling on the chassis, but it’s still would be usable as is. I did make a spare pair of gears though just in case!

I think the 20mm thickness really helped, particularly with the hub being pocketed within the input gear

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Very impressive machine! Echoing Mark, moving the pivot further back should help with the face planting - it’s something that Déjà Two and my ant grab-and-lift used to do a lot!

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Grab Crab has been revived for Rapture this weekend!

Have just given it a quick once over from Burgh and made some chonky TPU toes for my 3 spinner fights!

Thanks as always to the amazing @Liquid for his great prints :slight_smile: Lob-ster’s coming along for whiteboards or as crab spares if it gets pasted!

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Rapture was a spicy weekend! Crab fought 5 spinners in 6 fights and managed to go 4-2, getting knocked in the quarter finals by judges decision to a very well driven Boom Zoom, I’m happy with how it went.

Had to pillage Lob-ster for parts after the weapon motor sheared it’s shaft clean off! Thanks to all involved in organising, it was a great if very tiring event! :slight_smile:

Couple pics of crab doing the thing!


Thanks Stuart Camp for the bangin photos as always! :crab:

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A rebuild but not a total re-do of Grab Crab for pub this weekend! Very similar on the outside (apart from all plastic forks/claws because pub rules!) but on the inside there’s upgrades because i like numbers that go brrr:

  • 4S to 6S lipo
  • moved from repeat max to repeat pro (silly 2207 drive motors)
  • moved from chinesium gearbox (shaft shear-er 9000) to repeat ultra gearbox with a hardened hex shaft for weapon.
  • everything AM32 with current limiting set so hopefully nothing burns out…

Less reduction in the gearbox, but lower kv motor plus more external HDPE reduction should still do the thing!

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Looks solid!
Did you have to reduce the MOD of the gears due to the reduction?

I havent, I’ve moved the rotation point back (aiming for less faceplanting) and dedicated the whole left side to just gears so it’s still mod3 20mm hdpe

Had a great time with the new grab crab last weekend at BBB’s pub beetles, gonna make a few tweaks before taking it to Capital Punishment next month! A few ‘mob rule’ judgings that should have definitely gone to more fun bots than mine, but the crowd was in a crabby mood :crab: Highlight trick:

ezgif-24429f2d286200

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We just need epic music in the background with the words “CRAB FLIP!” flashing in black outlined white text, all whilst in super slow motion.

It definitely looked like a lot of fun out there though, even through the sweltering heat… hope y’all had sunscreen and plenty of water to drink haha.

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Some images of a typical Grab Crab encounter. 10/10 experience, would fly Crab Airlines again. My favourite flight was the one at 26:40 where Fatal Deviation disappears totally out of frame for a little bit. Very pleased to have built a robot that slots so neatly into Grab Crab’s forks for optimal yeeting performance.

I felt a little sorry for you with the way a microphone kept getting stuck in your face mid-fight, but only a little bit because without that distraction I’d have ended up in the ball pit immediately. Two minutes of yeeting was much more enjoyable.

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Yes that was a chaotic match! Was trying to have full 2 min fights where poss for pub beetles, thanks for pointing out 26:40, I’m hoping with hardox claws I’ll get more throws like that, I think bots slip off the HDPE ones too early to get much airtime but unsure.

Did you burn out some motors in the end or what was the issue? Didn’t get a chance to catch up later.

I only skipped through my own yeets frame by frame looking for fun stills, but it looks like FD can slide all the way to the back of the lifter and is retained by the top forks, I bet a lot of larger bots are resting on the points of the top fork and sliding off early - maybe different heights for the top fork, or some flex would help account for different size bots? Some spiky hardox bits sound good too, I’ve been thinking of going the same way and it seems to work great on bots like Boom Zoom.

I actually shredded a couple of gearboxes (I think I killed four or five that day), I specced them when I had less space and way less traction, and then bought a dozen spares to chew my way through when I upgraded to lego tyres… Any chance you’d sell naked BBB gearboxes for me to put the spicy nerf motors on? :smiley:

(I’m hoping for a gif of that 26:40 flip btw but no pressure!)

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Ah fair play! Unfortunately the gearbox is the expensive bit, the motor is the cheap bit I have spares of so can only do whole gearmotors for the 22mms, would only save ya a few quid.

yeet

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Fantastic gif, thank you! I really enjoy the minibot coming in for some action afterwards.

No worries, I’ll start digging down the back of the sofa for pennies for a full set of gearboxes + spares…