diy/2591466.txt

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--- 2591466
I'm hoping there are one or two materials science austists here that can help me out. What sort of plastic has properties most closely aligned to the following:
-very tough, specifically shock and abrasion resistance
-good (at least decent) dimensional stability 
-fairly rigid/stiff, max rigidity while maintaining high impact resistance is preferred

I'm considering UHMWPE, it's probably the toughest plastic out there, but it doesn't have great dimensional stability and is less rigid than i would prefer, although it's not too bad. 
Lexan is great right up until it shatters under higher energy impacts.. 
Nylon family stuff seems like a solid contender, it's stiffer than UHMWPE, but I wonder how shock/abrasion resistant it is. 
I've also been looking into delrin, various glass fiber impregnated stuff, givory, zytel and even micarta. 
The application will be the shell for a 3lb shell spinner combat "robot".
Metal shells are far more common with this sort of design, but I was inspired to try something different by picrel, which uses UHMWPE I believe, but I can find almost no information on how well it preforms and holds up to abuse. 
Wall thickness would be around 6-8mm, and unlike the picture, the bottom edge will have a steel ring mounted to reduce flexing on impact. 
In theory, full height impactors/teeth should help protect the polymer while spinning. 
I'm not sure how well various plastics hold fastoners without stripping out.
 This will not be 3d printed, instead would either be machined from a solid puck if rigid enough to not twist at the mounting point, or a short section of large dia poly tube with either carbon fiber or 7 series aluminum top if the plastic isn't rigid enough. 
Please help me bros, i am out of my depth with so many options.
--- 2591468
If you're not going to say what you're trying to do with it you're going to get half-baked answers. I'm also 72% sure you're retarded.
--- 2591469
>>2591466 (OP)
>-fairly rigid/stiff, max rigidity while maintaining high impact resistance is preferred

OP is designing dildos.
--- 2591470
>>2591468
he said it's for some gay robot shit
--- 2591471
>>2591470
My bad, I got lost in the wall of womanly whining and missed it. Fuck you OP.
--- 2591483
>>2591468
>>2591470
>>2591471
I bet when you guys sit down, you go YEEERRUUYYAAHHHhhhhhh. You're right though it was written like a needy pussy.
--- 2591508
>>2591466 (OP)
peek or glass / carbon filled nylon

hope youre loaded op

also
>fasteners
Look into threaded inserts, be it heat-set or stuff like helicoils
--- 2591620
>>2591466 (OP)
IN THE RED SQUARE...
--- 2591625
>>2591466 (OP)
You're gonna want some of these
https://en.wikipedia.org/wiki/Belleville_washer
--- 2591663
>>2591508
Noted and will do, thank you brother anon.
>>2591625
I had no idea.
--- 2591683
>>2591466 (OP)
DELRIN
E
L
R
I
N
--- 2591690
>>2591466 (OP)
Can’t say I understand the design but here’s some thoughts. 
Both Teflon and uhmpwe come to mind because they’re used in applications where they see a lot of impact abuse (trucks, plane cargo bays, warehouse logistics).

> Wall thickness would be around 6-8mm
That’s pretty thin if there’s no structural support on the inside. Wondering why you want it to be so rigid instead of a hard rubber though 

> I'm not sure how well various plastics hold fastoners without stripping out.
Usually not amazing but there are many types of threaded inserts available depending on application. Some are press/form fit, others glued or thermally bonded depending on application
--- 2591724
https://www.riobotz.com/riobotz-combot-tutorial
Lots of information put together by some battlebots champions.
Also friendly reminder that a torque wrench is to make sure fasteners aren't on too tight.
People tend to tighten things up too much, one big hit and the bolts snap.
--- 2593283
>>2591466 (OP)

>-very tough, specifically shock and abrasion resistance
>-good (at least decent) dimensional stability
>-fairly rigid/stiff, max rigidity while maintaining high impact resistance is preferred

In general, impact resistance is a direct tradeoff with rigidity. People love steel because it's an exception. Amongst plastics, CF-filled nylon is kind-of an exception, though nylon has its own weird drawbacks. For 'cheap/easy', racemic PLA is surprisingly good, and nearly as stiff by itself as CF nylon.

>I'm considering UHMWPE, 

I can think of few things less dimensionally stable or stiff than UHMWPE. OTOH, if that's almost good enough for you, then your requirements aren't as strict as you think.

>Lexan is great right up until it shatters under higher energy impacts.

Yes, and it crazes/accumulates stress damage.

>Nylon family stuff seems like a solid contender

*very* shock/abrasion resistant. God-tier. OTOH, static stress will crack it over long periods, and it absorbs moisture (and swells) like a sponge. So.... not as dimensionally stable as many things, but it's probably not an issue for your use.

>I've also been looking into delrin, various glass fiber impregnated stuff, givory, zytel and even micarta.

Pricey.

>The application will be the shell for a 3lb shell spinner combat "robot".

In this application, *nothing* will perform better than steel. Even just mild steel.

>In theory, full height impactors/teeth should help protect the polymer while spinning.
>I'm not sure how well various plastics hold fastoners without stripping out.

They hold fasteners well. They may not stand up to repeated insertion/removal, and very tight / stressed connections will cause most (not all) polymers to creep and loosen over time to a degree. But--- I wouldn't worry about the creep on your time scale.

>carbon fiber or 7 series aluminum top if the plastic isn't rigid enough.

CF is stiff. Most Al alloys you'd use really aren't.
--- 2593284
>>2593283
Forgot to mention--
High stiffness urethane/polyurethane may be interesting. Very wear/shock resistant. *and* you can cast it easily for cheap.
--- 2593505
I would say POM.

There's a reason machine workshops love working with it.
--- 2593739
Just melt down a bunch of milk jugs and cast it out of that.
--- 2593752
>>2591466 (OP)
The shell acts as a flywheel so metal is better and you have no reason to want plastic stop being retarded. More weight towards the rim is better than a thicc center. 

A healthy spindle (not a motor shaft) will avoid damage when smashing shit. Consider how front wheel drive spindles are built and copy that.

Just machine the spinner on a large manual lathe or even turn down a car flywheel to suit. Art doesn't matter. Winning matters.
--- 2594439
why don't we have a combat robotics general?
--- 2594443
>>2593505
Based POM, King of plastics
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>>2591466 (OP)
>I'm not sure how well various plastics hold fastoners without stripping out.
Use Chicago screws.
--- 2594487
>>2591683
>burns, releasing poisonous formaldehyde gas
learned this the hard way. dont use fucking delrin
t. lung cancer
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>>2593752
I bet a dead axel would do him better
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>>2594487
>dont use fucking delrin
More like don't burn delrin. The little bit of formaldehyde smell you get while machining it is just part of its charm.
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>>2596015
Machines sweetly tho and ventilation is an option.
--- 2596985
>>2591690
>That’s pretty thin if there’s no structural support on the inside. Wondering why you want it to be so rigid instead of a hard rubber though
The bottom edge will be reenforced by a waterjet steel ring. I'm also throwing around the idea of using a short section of large diameter poly tube for the sidewall so I could use a stiffer material like 6061 or cf for the top
If it's too soft/flexible, there will be twisting and out of plane forces at the mounting point upon impact.
Thank you, I will read into Teflon.
>>2591724
I have the robots tutorial, its a fantastic resource.
Thanks for the reminder anon.
>>2593283
Yes, for sure, that's the difficulty of finding one that's just right.
I heard about Nylons affinity for water, will it slowly absorb humidity from the air?
I appreciate the info.
>>2593505
Will look into it, thanks.
>>2593752
Heat treated steel shells are generally fine, grade 5 ti is probably the best metal, but 6061t6 Al can work as well.
I want to try something different, and believe this could work passably well. Its also nice to keep machining and material cost down.
I admire your klingon brutalist mindset, QA PLAH!
>>2594447
Ive heard this before, I know they also make screws specificly for plastics. Will look into it, thanks.
>>2594487
Thanks for the heads up, praying for you man.
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>>2591466 (OP)
Delrin.
--- 2597272
>>2591466 (OP)
uhmw is brittle. a softer plastic would be a better option it will be able to absorb much harder blows. built up ABS with kevlar mesh would be extremely strong
--- 2597283
>>2596985
>Its also nice to keep machining and material cost down.

That's a key reason for steel along with simplicity. Suitable "drops"/cut offs can be found at machine shops left over from jobs (the customer already paid for it) and are often for sale. Friday is a good time to visit.

Car and truck flywheels are dirt cheap from salvage yards and are already drilled and bored for a central hub or shaft of your choice. You can turn them down and if you want to make a cup you can use sections of heavy wall pipe or cut up more flywheels. No need to buy the heavy parts new. 

Battlebots are supposed to be brutal. You just want to add production complexity for its own sake not actual performance which is fine but never lie to yourself.
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>>2597272
>uhmw is brittle
I made skateboard rails out of it. It is one of the few things tough enough to survive. What was your use case that destroyed it?
--- 2597330
OP be sure to post here when you're on TV.

Poor Chris Rose, by the way ... he used to co-host his own show on MLB Network, now he's giving the "play by play" on Beyblades battles.
--- 2597548
>>2591471
There's no womanly whinibg in there.
He simply lays out his considerations while you try to cover up your inability to read.
--- 2598576
not a materials expert, but isn't "shock resistant" and "rigid" at odds with one-another? usually the more hard something is, the more brittle it is, you get better impact resistance if you use something that has a bit of flex
i design mining equipment, and for material impact surfaces we use sheets of HDPE, now that's not to say that's the best for your case, weight isn't a concern for me, but cost is, so i don't use fancy materials, but i don't use a stiffer material because i want it to wear away slowly, and not just crack and disintegrate
--- 2598594
>>2591483
kek
--- 2598810
>>2598576
Well partially, but absolute strength also plays a part. A sheet of carbon fibre reinforced plastic is both more shock resistant and stiffer than a sheet of glass, but only because CFRP is so much stronger.
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>>2597272
--- 2599719
>>2591620
fucking lol
--- 2600132
>>2591466 (OP)
Polycarbonate I'm using is meant for an 8mm thick panel. Incredibly tough and scratch resistant once coated. Jump on the thinner PC parts like a trampoline. Met up with a sales rep for Triton material, think Nalgene uses that now, seems pretty great and no Bisephenol A?
--- 2600135
>>2598576
Milk jug PCR. The melt on that shit is like .3 compared to normal 5 or 8 melt consumer hdpe. Cheap as dirt too.
--- 2600158
>>2600132
Is that the same as lexan?