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 Camden's confoundations

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Evan Steeves
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PostSubject: Re: Camden's confoundations   Sun May 22, 2011 10:44 pm

lol I see some mega blocks snuck in there Very Happy

and heres the rough idea of the hub pulley shell mount




the light purple and red object on the left is the outrunner motor with a pulley the black line going across both objects is the belt

the green represents the hub it captures two bearings and has a flange ontop that the shell will bolt onto through the four red verticle lines because the hub is indexed as long as the shell was made correctly it would be balanced everytime it was taken off or put back on the purple on the right represents the nonrotating deadshaft and the red represents the base that holds the deadshaft to the base of your chassis by whatever means you choose the two light blue objects inside the green hub are the bearings
hope this makes some more sense -evan
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Camden W
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PostSubject: Re: Camden's confoundations   Sun May 22, 2011 11:59 pm

ok, i see how that would work. the only problem with the hub would be the added weight. if i were to use this, keep in mind i would still have the top plate. i added bearings in lighter blue to show where they would intersect the top.




and on another note, my completed lego-bot. it is 1/2" taller than actual size, and the bottom of the weapon grazes the ground lightly, about 1/128" off the ground. i have rounded bottom pieces to act like casters, the wheels giving me 1/8" clearance (they're only 1" on this), the casters planting the bot firmly flat. (this thing seriously runs exactly like i want my metal counterpart to)

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Camden W
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PostSubject: Re: Camden's confoundations   Wed May 25, 2011 6:12 pm

I did another sketch today, this time a side view of the parts i'm struggling to visualize success with. Neutral mainly because i have never attempted to look at these areas in detail yet.
This one includes a deadshaft. i found a 1/8" x 2 1/4" steel rod in my legos, (no idea why it was there) and tried unsuccessfully to bend it. i have thus decreased the size of the main shaft by 1/16" Also, that lego i'm holding is going to be one of the casters, unless i can find something better.



What I want to know, is where the heck i am going to get bearings, nuts, and bolts that small, total dimensions of the Axi motor, how i should attach the deadshaft to the bottom of the bot, if 1/32" garolite is what i should use for the bottom, and what should my weapon be made out of? (Aluminum would weigh 95g, Ti 158g, and Steel 276g)

and on an unrelated note, is it just me, or do i seem to be getting more mature as i post more?
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PostSubject: Re: Camden's confoundations   Wed May 25, 2011 8:15 pm

You could use 1/16th Garolite for the baseplate. It would weigh pretty much the same as the 1/8th uhmw you were going to use. the density of Garolite is around .065 lbs/in3 and Uhmw is .033 lbs/in3. I'm using 1/16th garolite on the Ant I'm building. It's worked well so far.
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Evan Steeves
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PostSubject: Re: Camden's confoundations   Wed May 25, 2011 9:54 pm

nusts and bolts ... www.mcmaster.com
bearings www.bocabearings.com

the nuts and bolts people will have thier own opinion on I prefer the metric side of the spectrum because I like things based on 10 instead of 12 they all do the same thing cheers
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Evan Steeves
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PostSubject: Re: Camden's confoundations   Wed May 25, 2011 11:06 pm

as for your shell if you want longterm it should be titanium, aluminum shells can get chewed up after one tough competetion although alumnium would be the most cheap option if you are having it lathed from a solid rod.

steel seems too heavy buy if you can pull it off it would be very strong if it was thick enough, i would stay away from stainless though its too bendy.
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Camden W
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PostSubject: Re: Camden's confoundations   Thu May 26, 2011 5:54 pm

I did some redimensioning on my bot's weapon today. i came up with some nice numbers, and i think this shell could make weight if it's made of steel. (241g now, @ .2836 lb/in^3)
Are these acceptable thicknesses to suit battles vs. beaters? for example the CF one that alex has trouble beating. (no pun intended)

Or will having a thicker shell made of TI be better?

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Camden W
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PostSubject: Re: Camden's confoundations   Thu May 26, 2011 6:20 pm

and for the boca bearings, these things are freaking expensive!!
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Don Doerfler
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PostSubject: Re: Camden's confoundations   Thu May 26, 2011 6:47 pm

if i was doing a fbs i would go with a thicker Ti shell... but thats me
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Camden W
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PostSubject: Re: Camden's confoundations   Thu May 26, 2011 7:25 pm

i'll take that into consideration. also, i found the inner bearings if i'm going to use the hub tactic: http://www.bocabearings.com/bearing-inventory/Radial-Bearings/517/MR85UU-5x8x25

and here is the perfect bearing for the central rotating shaft:
http://www.bocabearings.com/bearing-inventory/Radial-Bearings/8200/SMR685UU3-5x11x5

Also! Thank you to whoever added the edit function for me! it's soooo helpful! cheers
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Evan Steeves
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PostSubject: Re: Camden's confoundations   Thu May 26, 2011 10:27 pm

that would be alex cheers

and that shell is pretty thin right now even for steel.

After my first fbs I found that even with an extremely simplistic design I was still far overweight for just the robot than I had calculated I would recomend subtracting some weight for stuff that sneaks in such as unforseen fastners and teeth of the shell itself unless you are 100% positive that is how it will weigh in.

as for the shell don is right a thicker titanium would be a much more sturdy option than thin steel although pricy. Also consider how it will be fabricated in your final design as a solid rod of titanium that thick to be turned down will be in the hundreds of dollars whereas a sheet that is welded would be in the less of the tripple digits. Or cheapest a 7075 shell would run about 30$ for the rod and about 50-75$ for the machining if you find the right place. and of course you have to figure out teeth and how they will be mounted.

if you are having trouble with metal weight calculations( or if youre not) I recomend this website it has helped me a whole bunch http://mdmetric.com/tech/metalwtcalc.htm
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PostSubject: Re: Camden's confoundations   Thu May 26, 2011 11:59 pm

for the milling, i will be using the one my school is getting this summer in its brand-new not-even-constructed-yet $1 million dollar community-wide tech lab. (seriously this is so awesome)

for the weight, i'm giving the teeth and fasteners 50g max.
for the whole robot, i count
38 bolts (35 if rotating shaft design)
6 spacers
22 nuts (19 if rotating shaft design)
20 washers
5g of superglue (or shoe glue)
bottom and top shells
the hub, the pulley
the shaft holder
the shaft
the pulley tensioner
the main shell
the wheels
the electronics/wires/battery/motors
...am I missing anything?
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PostSubject: Re: Camden's confoundations   Fri May 27, 2011 12:05 am

looks pretty well covered tongue

Iwould avoid milling the shell unless you have a super duper accurate rotary table or maby youre awesome unlike me and remeber backlash before you mill a perfect apogee into something you want round.Very Happy
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Camden W
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PostSubject: Re: Camden's confoundations   Fri May 27, 2011 12:20 am

Ya i was thinking about that...how much can the shell actually bend while milling, even if the sides are clamped?
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PostSubject: Re: Camden's confoundations   Fri May 27, 2011 12:48 am

Im not a machinist by any means I come from a woodworking backround in technical theater but it all depends on how well built the rotarty table is and how well you can account for backlash.
For me on my friends harbor frieght mill with a really nice shim kit we get about one thousands on the x and y with proper setup but it takes forever.
With a nice mill it goes alot faster but the rotary table really adds in a strange variable with the harbor freight mill with an off brand rotary table im lucky to hold an 1/8th inch on a 3 inch circle cutting delrin I could just be a tard with the backlash but I wouldent ever use it to make something to spin true.

for something to spin as true as a shell on a fbs I would only use a lathe or have someone very skilled weld it then balance it.
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Camden W
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PostSubject: Re: Camden's confoundations   Fri May 27, 2011 1:17 am

I just don't like the aspect of welding for something this small...and if by 'forever' to machine it you mean a few hours, i can live with that. i can wait a few days, even. It's not like i'm going to need a replacement shell every match. maybe every season.
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PostSubject: Re: Camden's confoundations   Fri May 27, 2011 1:27 am

im going to speculate that since its for a school you wont be getting a crap mill so your setup wont be so painfull lol

still you will still need a rotary table for the mill base though. and thats where holding a tolerance gets tricky.


you should just sway them to get a lathe Very Happy
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Camden W
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PostSubject: Re: Camden's confoundations   Fri May 27, 2011 1:38 am

the tech lab will be getting a lot of high end machinery...i was told it's THE best in the world for a high school. I'm sure there will be a lathe in there somewhere ^_^ I'm gonna call dibs on the stuff to use when i get my materials pirat

also, i came up with some names already! Category V, Cyclone, Spindoom, Washing machine of hell, Twister, Turnpike, Torq, and Thwack.

I think imma name it Whirlwind.
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PostSubject: Re: Camden's confoundations   Sat May 28, 2011 1:15 am

From the looks of your shell size, I think a lathe would probably be best for a balanced machining job. However, if your Tech Lab ends up with a good CNC mill, an indicator (aka Dial Indicators) and a Collet Block you can probably mill the interior out with a good deal of accuracy. Collet blocks allow you to mount a collet into a vice to get a good grip on cylindrical objects (often small ones), and indicators can be used to zero cylindrical objects for milling. My only warning is that this part may be too large for a collet block, so double check with someone familiar with the equipment you have on hand before trying it.

PS - With a collet block, milling the exterior of the part is possible. This would allow you to either have teeth integrated as a part of the shell, or let you make nice mounting surfaces for the teeth.

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Camden W
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PostSubject: Re: Camden's confoundations   Mon May 30, 2011 10:45 pm

definitely going to make mounting holes. that way it's easier to repair a damaged blade
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PostSubject: Re: Camden's confoundations   Mon May 30, 2011 10:58 pm

Camden W wrote:
definitely going to make mounting holes. that way it's easier to repair a damaged blade

then you can use s7 teeth Twisted Evil
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PostSubject: Re: Camden's confoundations   Mon May 30, 2011 11:06 pm

that's actually what i was planning to use ^^ hence the hefty sum given to the teeth (12.5g per tooth). though, it may be more like 3g lol
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PostSubject: Re: Camden's confoundations   Mon May 30, 2011 11:31 pm

3g is realllyyyy small to have enough surface area for bolts to hold the tooth secure and be thick enough to not sheer
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PostSubject: Re: Camden's confoundations   Mon May 30, 2011 11:45 pm

Ooh! relevant question! bolt and nut and washer sizes!! I haven't a clue! help:!: Crying or Very sad

Specifically, most likely something with a 2mm (5/64") dia. x3 is what i'm thinking for weapon tooth mounting. and probably 2 or 3 mm for the spacer mounts.

Suggestions and personal usage?
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PostSubject: Re: Camden's confoundations   Mon May 30, 2011 11:55 pm

2mm is way to small i wouldent use anything smaller than an m3 you can get away with about 3 m3 screws and nuts provided the tooth has some support so the bolts dont take all of the sheer load

also if you order them dont get rc car brand m3 screws they are either soft as butter stainless or brittle black oxide i would recomend the mcmaster grade 10.9 m3 hardware its incredibly strong when used in the right application
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