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Sand casting a robot chassis
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chunkulator



Joined: 27 Jul 2016
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Seems like gasless MIG hardfacing is also a possibility:
http://www.proweldwelding.com.au/product/proweld-gasless-wire-55fco/

Post Fri Jan 06, 2017 6:59 pm 
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Glen
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Every process uses hard facing and its very common in earth moving for buckets, chutes and so on. The TIG welding hard face is called Stellite and it's really brittle, for abrasion resistance not impact toughness. Would likely just shatter off very fast if welded onto blade teeth Smile

Decimators first disk was 12mm Everhard 400, the spokes were super thin on it tho Razz lol crap design! The later blade is 16mm hardox 500, definitely stronger.

Ring spinner would be awesome to see as a featherweight - the hardox itself is reasonably priced but the cutting adds up depending on the part. The bars which are simple were $48 to have waterjet cut and the original disk was nearly $200. Send a DXF for a quote to action laser in perth, definitely my favourite mob so far Smile

Laser is good for under 16mm hardox parts, and typically much cheaper. The heat affected zone according to the datasheet is sub mm thick with laser and realistically probably of no consequence. My waterjet weapons wear the same as the plasma cut ones and laser is much better than plasma for containing the heat affected zone! YMMV on that one.

Good luck with building it Exclamation
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Post Fri Jan 06, 2017 7:30 pm 
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chunkulator



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Thanks for all the tips folks. Much appreciated. Have you got a preferred place to buy 16mm hardox glen?

Post Fri Jan 06, 2017 8:52 pm 
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Glen
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That was from precision oxycut. Action have it on hand and can laser it.
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Post Fri Jan 06, 2017 8:54 pm 
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marto
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Getting stuff from Action cut was actually cheaper than we could get material for the big bot.

Steve
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Post Sun Jan 08, 2017 5:13 pm 
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chunkulator



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Here's where I got to after a couple of evenings' CAD work on this concept:


And without the lid so you can see what's happening inside:


red: laser-cut 16mm Hardox 450 ring. ID 300mm, OD 348mm, 3 teeth protruding 20mm, mass 3.8kg. I will work on getting this as low to the ground as possible.

green: 6200 bearings (10x30x9mm), 8 for radial support, 8 for axial support

pink: 2.4kW 1400kV brushless outrunner https://hobbyking.com/en_us/turnigy-t600-brushless-outrunner-for-600-heli-1400kv.html , 1:1 #25 chain and sprocket drive to friction drive wheel (34mm black rubber on steel hubs), TZ85A ESC running SimonK

yellow: 2x BaneBots P60 gearboxes, 1:1 #25 chain and sprocket drive to wheels, BotBitz TZ85A ESCs (or maybe a pair of brushless 540 motors and TZ85as running SimonK)

dark grey: 2x Colson wheels 5x1 1/4" on BaneBots clamping hubs, 1/2" axles running in R8 bearings

blue: 2xLiPo 3S 3Ah 65C. Weapon runs off both in series. Locomotion runs off one of them.

light grey: chassis from 10mm 6061-T6 aluminium plate, top and bottom from 6mm 6061-T6 plate

Total mass (not including fasteners, wiring or polycarbonate shielding around the sides): 12.3 kg
Weapon: around 3500 RPM delivering about 25kJ hits (baby grand piano dropped from 10m)
Ground clearance: around 8mm at wheels

Perhaps some of the experienced spinner whisperers can please give me their suggestions on whether this seems on-target before I go working out more of the details. In particular:
- Will my rubber drive wheel evaporate?
- Is this support bearing configuration up to the job?
- Do I need ball castors front and back or just let the edge ride on the floor?
- How to defend against wedges?

Post Mon Jan 09, 2017 10:20 pm 
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Nick
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That looks really good! The only major issue I see are the small ring support bearings; they will take a real beating.
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Post Mon Jan 09, 2017 10:44 pm 
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maddox



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I would go for single tooth (not easy in this design) and a V shaped inner edge on the ring, so you can work with only 2 bearings for support in both axis.

Post Mon Jan 09, 2017 11:23 pm 
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chunkulator



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Any suggestions how to achieve a V on the inner edge of the ring maddox? I guess I would need either 3D waterjet or some kind of monster lathe for this?

Post Tue Jan 10, 2017 5:59 am 
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chunkulator



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Nick, instead of 8x 6200 bearings for radial support, do you think I should be looking at 4 or 6 significantly larger bearings?

I did consider whether it might be possible to start with a bag of steel balls and machine my own race, but quickly discounted this as impractical.

Post Tue Jan 10, 2017 6:08 am 
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maddox



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Not that big a lathe and hardmetal cutting tools. My old light combo machine could do it.


The only thing you'll have to think about is to have holes cut in the ring to clamp it on a support so you can turn the V 1 one setup.

Post Tue Jan 10, 2017 6:57 am 
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chunkulator



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I'm not set up with a lathe (not yet anyway). Can anyone suggest a way to turn a V onto the inside edge of a 16mm hardox disc ID 300mm OD 368mm? Perhaps someone local has the relevant tooling or can recommend a shop that can do this commercially? I'm in Sydney.

It would be really nice to put the weight into one large set of V bearings if I can find a way to do the machining.

Post Tue Jan 10, 2017 7:36 am 
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Nick
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Those 6200 bearings are light duty but its hard to know what will work - there are so few successful ring spinners to compare your design to. Because the bearings need the smallest OD possible, perhaps a double row or roller bearing can be found.

With all due respect to Mario, I don't think a V shape on the ID of the ring is the best way to go. It does reduce the number of bearings but the bearing mounts will be angled and can't be made of flat stock like the current design. That means a chunky milled part that will eat up some of the saved weight & space.

Cutting a perfect V on the ring could be difficult. It would be someone else's problem but it will probably cost quite a bit.

The final problem with almost all the bearing mounts for ring spinners is that the bearings are mounted on studs and supported on only one side. On a bearing with a small ID, that can make a big difference.

Here is an alternative design I thought up for a UK heavyweight. It could easily be downsized to fit your design:



The advantages to this design are the simple bearing mount ( just a length of steel rod tapped at both ends. and the ring guides that are easy & cheap to turn from steel are stock. This design still need some work; if you are interested, I can downsize it and make some improvements.
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Post Tue Jan 10, 2017 8:31 am 
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chunkulator



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Actually in my design I had the bearings supported top and bottom. There is a 10mm plate above and a 10mm plate below (both ali). I hid the upper plate on the second screenshot so as not to obscure the internals. I was going to put a 10mm high tensile bolt through the lot. I could probably upgrade this to something like a 6202-16 bearing.

Some help on machining some bits along the way would be gratefully received thanks Nick.

Post Tue Jan 10, 2017 8:57 am 
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Nick
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No problems - I have a new lathe arriving soon that will make turning large steel parts a breeze. Those 6202 bearings should be up to the job and still not too large.

BTW: another advantage of that bearing design above is that by lying the bearings down, the ring can be much closer to the ground - handy for defending against wedges.
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Post Tue Jan 10, 2017 9:15 am 
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