*** THREE YEARS LATER ***

Loving the proposed changes, those skateboard bearings are cheap, tough, proven and come in a variety of useful flavours.

I vote a steel shaft through them though.

Definately try to support the motors toward the end caps, they seem to fail either there or at the brass bush on the gearbox most often (as evidenced by Glen's thorough addressing of that issue in Killer)
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<Patrician|Away> what does your robot do, sam
<bovril> it collects data about the surrounding environment, then discards it and drives into walls

Yep they are great little bearings we just bought 2 pairs of roller blades from the cheap shop for $2 a pair and each roller blade wheel has 2 bearings in em….so thats 32 bearings in todays haul….however I noticed one set of roller blades the bearings are only 6mm ID and the adult sized ones were 8mm ID.
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Miles Blow - Julie Pitts
www.mulesfilm.com.au
www.wombokforest.com.au

-Pickasso- Vivid Sportsman champion 2015

so the drawing is getting closer, everything done as nice clean curves so the CAM doesn't barf on it.

I may have gone a little nuts and put an isogrid base in it.
http://i.imgur.com/nCEXz7B.jpg

Its all the little crap that takes the time, ridges for the bearings to mount off, keys for the halves to join together, ensuring all the countersinks have enough room to actually fit into.
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Mechanical engineers build weapons, civil engineers build targets

The joys of not having to pay based on cutting time So much millage!

Starting making bits out of my 7075 last night, by gawd it cuts so nice. I reckon it'll come out amazing in the cnc.
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www.demon50s.com - Minimoto parts
http://www.youtube.com/user/HyzerGlen - Videoooozzz

You sir, are a total CAD geek
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Checking the bearing dimensions was handy, 7mm ID not 6 that was lucky.

Tossing up what to make the shafts out of, I'm thinking either drill rod (but I'm worried it'll be too brittle) or 4140.
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Mechanical engineers build weapons, civil engineers build targets

Screwdriver shaft

CADing that in Rhino must be hell.
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https://www.halfdonethings.com/

I have been very happy with drill rod for motor shafts - if you are supporting it at both ends its not likely going to crack.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

quote:

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Originally posted by Knightrous:
Screwdriver shaft

CADing that in Rhino must be hell.

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The stuff I use is thru-hardened M42 steel. Most of the other grades I found (O1, W1, D2 etc) were sold annealed and are probably not much harder than 4140. Other vendors might be different but if the rods are really tool steel, they can be hardened. One thing I like about drill rod is that its usually accurately ground to size and is rated for straightness.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

wasn't that hard really, made 2 triangles, copy paste into a pentagram and a half, add the central holes, copy, paste repeat a few times and make a sheet of isogrid.

The hard (time consuming) part was filleting all the curves to fit the cutout areas and leaving the 1mm band.
So I just did an offset from that curve, exploded the curve, copy the curve segment that goes over the triangles in question, then fillet, fillet, paste the curve segment back, do the next triangle.

How would you do it in solidworks?

I think I don't want to harden the shaft, mostly because without an oven I probably lack the skill to do it with a torch and by eye. My concern getting stuff that's already hardened is 1 brittleness, and 2 if it needs to be reduced at all to take the bearing.
I think I'm after a sliding fit on the bearings, not too tight.
Any further suggestions?
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Mechanical engineers build weapons, civil engineers build targets

The hardened rod I bought was slightly over the specified diameter, so I put it in the lathe and used the die grinder like a hand held toolpost grinder. For your sized shafts, a Dremmel would be large enough. The same trick would work even better on unhardened drill rod.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Calculation puts it at 236 grams vs the last one at 113 grams (just the aluminium)

Should be much stronger though.
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Mechanical engineers build weapons, civil engineers build targets

To do the triangle pattern in Solidworks I would draw your grid, probably using the pattern tool at some point, then on another drawing copy the lines and trim them to size before Extruding Thin Feature and then using a macro to fillet all the corners. any that are missed due to geometry difference you can do manually after that.

Looks incredible though. I have been looking for someone to help me with a ring spinner project and I may have to ask you lots of questions, along with whyachi; how did they get Warrior SKF's ring to work!

not really polished but https://www.dropbox.com/s/lv8lqdmkmqb5svt/shredder2.rar?dl=0
has the cads in it for those interested.
Rhino 4 format.

I'd be interested in any suggestions people have too ;->

no ring yet, I'll weigh it all up when its finished, bolts and all then cut the ring to fit that weight.
The new one is ~100grams heavier than the old one.

I'm thinking I'll make the ring a H shape (or probably a C facing down) to try and keep the inside round when the outside deforms.
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Mechanical engineers build weapons, civil engineers build targets