Time 400 Crab! Under the Sunk Cost falliSea

I’ve committed myself to a Featherweight version of my antweight Time for Crab! so its time for build log.

First up, my excuse for the name: It’s (rounding up) 100x the weight of Time for Crab! and I’ve sunk cost fallacied myself into building it after picking up a couple of second hand drill motors. :stuck_out_tongue:

The current plan is to make this as close as possible to a scaled up version of the antweight, but we’ll see if that survives through to the final robot. I probably won’t make a giant transmitter and tell everyone around me it’s us who have shrunk, but the temptation is there.

I’m in love with the idea of scaling up the 34mm wheels to featherweight sizes. These will either have a rubber overmold or if time and cost get in the way have some bike tyre screwed to them. There will be an imitation D shaft sticking out somehow.

Inside there’s the aforementioned drill motors, with the plan being to add a belt drive and some reduction so they have a chance against the giant wheels.

The claw mechanism is currently based around a big linear actuator that @McMullet had lying around. It’s rather slow (the full 20cm stroke takes about a minute, though I was giving it 18v and it wants 24), but might be okay if I mount it close to the claw pivots and use a limited amount of range.

The backup plan if the speed becomes a problem is to add a second motor that rotates the ram of the linac. Since that acts as the ‘nut’ on its leadscrew you can spin it and it screws itself along the leadscrew, normally it relies on the mounting bolt to stop it from just spinning freely. Hopefully that will give me a fast mode, but I might need some way to stop it spinning when more force is needed.

I’m still trying to calibrate myself to featherweights so right now there’s a lot of wrestling with material thicknesses and how big things should be.

The current version is scaled up 5x from the antweight, making it about 550mm wide and 500 long, with about 150mm up to 650mm gap between the claws.


Nice! You don’t see many FWs on the forum, so this is a change. Also questioning why you posted this at 10 PM…

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We love a good crab.

Good plan trying to save the drill drives. Honestly a lot of what kills them is the axial load too so taking that away is a solid idea. My concern is the wheels are awfully far back without much weight over them. Doesn’t strike me as handling very well at.

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The wheels are pretty much copied from the antweight right now. On the antweight the claws are very light so it tends to get flipped over, and I tried to make sure the wheels could be in contact all the way around.

I might need to revisit for this version, but I’m aiming for the claws to be fairly light again. I haven’t modelled it in the CAD, but there will almost certainly be some kind of casters on the claws to get it driving well, especially in the BEVs arena.

Antweight crab has some tricky curves in the claw profile so when it grabs an opponent the side nearest me gets lifted, which means the crabs wheels stay on the ground. I’m wondering if combined with the casters in the claws I can come up with a clever mechanism so this works both ways up.

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As my red-featherweight-horizontal-grabber-crab is very much retired and on a wall as if it’s been hunted or something (pictured below), I very much welcome this excellent addition to the scene and I’m very excited to see this fella in action at August BEVs!

Definitely look at swapping out the linac motor for a faster/beefier brushed or brushless one down the line if you’re looking for more speed :slight_smile:

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the world needs more horizontal grabbers! really loving the upscale design with the little D shaft additions will be a very fun visual

i think that claw gap should be about right too. most feathers are between 300-500mm wide. anymore than a meter and its almost too wide

on timingila i have little side forks to help pick other bots off the floor when i grab them, might be worth looking into for you bot. helps a huge amount with winning a shoving match

looking forward to a grab off with timingila!

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