Crux

For a while I've wanted a machine that is very destructive. Bitza MKI, MK II and Splinter didn't really strike fear into opponents hearts and should Crux come into being that's what I'm hoping it'll do. For a while now I've been toying with the design for a large diameter disk similar to the heavy weight Nightmare, but with a couple of variations. I'm thinking of have a disk around 500mm in dia spinning at 3,000RPM (if it was just over 12,000 it would break the sound barrier ;) ). Realistically it'll be about a year until it's built so I'm putting the designs out there in the hope that I'll be able to refine it and troubleshoot some of the problems before it enters the arena.

Here's my initial, very rough idea:

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Right off the bat I've got 2 problems I could do with some solutions to firstly how do I fix a relatively thin disk (working on it being 5mm ali) to a large shaft.

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My first thought was to cut a square hole in the disk and make some sort of flange like the one above. 4 x M10 bolts would clamp the 2 flange halves onto the disk and a keywayd silver steel shaft would locate into the flange. I want the shaft to be chunky, I was advised 10% of the disk dia works well but a 50mm shaft seems a lot, the one in this model is 25mm

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I'm considering using some extruded ali section for the frame. I've watch the Nightmare Warhead fight a couple of times and clearly this sort of design is vulnerable to horizontal spinners so if I can source some large dia tubing I'd like to make some simple wheel guards. I was considering cutting into the leg supports and swapping a section out for springs from a garden gate so the leg could be knocked away by the horizontals then return. If I was going to do this I'd have to have supports either side of the disk like Backlash had as the legs would fold out of the way under impact. This would rely on the centrifugal force of the the disk spinning to prevent it toppling over. Not sure this is the best way around that problem, but I've got a year to nail the design down.

If you've not seen the Warhead / Nightmare fight it's well worth watching

http://www.youtube.com/watch?v=58j1MypGJDA

I particularly like the insightful commentary at 1:14 :P

The second issue is with weapon drive. I'd like it to be direct drive to remove the inherent weakness of using belts and chains but there's some concern the motors would get trashed.

http://www.youtube.com/watch?v=V0LYpIekDxE

My idea for the weapon drive is to use 2 fan motors directly keywayd into the shaft. They're really torquey and the local scrap yard sells them to us at £2 a piece!

The disk is connected to the silver steel shaft, the shaft spins freely inside 2 pillow block bearing carriers which are bolted to the frame. On the other side of the frame is a support to hold the fan motors. The shafts on these motors would have flats ground on them which would locate into a keyway cut into the ends of the 25mm silver steel shaft.

As the forces of any impact would travel through the frame via the bearing and the motors although connected are effectively resting inside the shaft, do you think they would be damaged by this set up?


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This looks like it will be a really interesting robot, just make sure that if you put the wheels on springs that they can't be knocked into your own weapon by a hit from a horizontal!
Also 5mm aluminium I imagine would warp or bend, especially if anything hits it from the side, even a ram bot. I'd make it from thicker aluminium then 'mill' out pockets towards the centre to keep weight down.

Agreed, 5mm of Hardox would possibly still be pushing it in terms of sideways-strength, let alone aluminium. I don't know about the high grades of ally, but the lower grades you'd probably be able to bend by hand, let alone with NST's help.

You may need to look into a thick outer ring, something as bend-resistant as Hardox, then you may get away with a high grade aluminium "core", assuming the attachment of the two pieces is up to it. In that case you would have a massive moment of inertia compared to an equal weight solid disc.

Obviously listen to someone who has big spinner experience before heeding my advice, though!

How will you self-right it?

Alu box section for the chassis isn't out of the question (When you double the thickness of something you quadruple its stiffness) but I still think the material is inherently to soft for combat with that construction style.

4mm Hardox welded to make box section with holes in it to keep the weight down would do it nicely.

Like Nightmare it would be a one hit wonder against flippers or lifters. The Battle box was so big that Jim could get the disc up to speed before his opponents got to him. in the RC arena you just don't have time.

For the weapon itself I would use 8mm or 10mm Hardox then do weight saving similar to that of nightmare. Bolt each tooth on with two M8 bolts and that should make it plenty strong enough.

If you are going to have wheel guards have them bevelled or slanted, I can see the cylinders getting crushed with flat sides like that.

But with proper refinement this could be utterly lethal.

Thought if I started now I might get time to test before GSL 2015!

A few changes to the design and the thinking behind this bot. Hornet is my robot this year and although I really enjoyed making a bot using CNC machines, its just not very Bitza. If Crux does come into being it's going to be back to our old mantra, recycling as much as possible. This box section was getting chucked by school so I cut out some really rough lengths before the scrappy collected it, currently 3.5kg of steel there.

Design changes:

I'm thinking of having the suspension in the wheels rather than the frame. The down force will be huge, so I hoping the frame will bottom out after the wheel compress a bit.

Something like this
http://www.societyofrobots.com/image...sion_wheel.jpg

Probably going to go for a bar over a disk. I'm sure there are advantages to a disk over bar but I can't really think of them. Also and a bar would be cheaper / easier to scrounge.

I'm ditching the control box for conventional electronics

It'll probably be shorter than the original CAD image I put up


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