HDPE vs Polypropelene

Hi guys,

In my next featherweight, I was planning on using 12mm HDPE for bulkheads/side armour as I had read on here in numerous different posts that it makes great armour against spinners etc. Id also heard similar things about polypropelene and for a while I thought that HDPE and polypropelene were the same but just realised when looking at materials earlier that they were different.

Is there much difference between HDPE and poloypro when it comes to robots? In particular, I remember reading in one of the posts that polypro isnt very good for tapping/screwing into - is HDPE any better in terms of tapping? As thats how I plan to fix it all together in my bot.

The bot Im referring to is going to be a vertical crusher generating at most 400kg of crush. The point at which the actuator attaches to the base is obviously going to undergo pulling forces when the claw is crsuhing. At the moment Ive designed for a 4mm ali base (6082 T6 grade) with several HDPE (or polypro) bulkheads running parallel and perpendicular to the mouting point of the actuator. Reckon this will be strong enough to cope with the forces?

Any info/tips appreciated.

Cheers guys,
Jamie

(Message edited by K_C_R on May 28, 2007)

HDPE is a bit softer and lighter than Polyprop.
But is virtualy unbreakable, compared to the harder, but still difficult to break PP.

Non of both materials are good for high strength needing bulkheads. Both lack the stiffness especialy HDPE. This makes also the strength of this stuff, it just gets aside.

Jamie,
If you are looking for an engineering plastic then consider nylon6 or nylon66 (66 being a little harder, but more brittle) I have used nylon6 in all of my feathers without any problems.
It is very easy to drill, tap, and machine plus it is only a fraction heavier than Pollyprop.

So its Nylon6 you use in Pain in the Asp too? Cool - cos I had been looking at pics of it (http://s46.photobucket.com/albums/f1...C0220.jpg>this

Yep, its all 12mm nylon6, the top pannel fixings are M5 threaded AVX inserts (from RS, part no. 206-0155) that are forced into the nylon under heat (100W soldering iron!) I only use them for the top pannel because of the need to frequently remove the screws. Constant use would eventualy wear out the threads if the screws were directly into the nylon. All other fixings are either tapped into or bolted through the nylon.

i was thinking of using HDPE as armour, on the advice of other people, would this nylon 66 be bettter?

does anyone have any links to stores stocking nylon 66?

thanks alex

http://www.directplasticsonline.co.u...?cat=4468>This

this is where i was planning to buy my hdpe anyway!

Alex,
Nylon66 being that much harder than nylon6 is too brittle for high impact armour, but would be fine for internal bulkheads.

cool, my picture came in useful :)

I use HDPE for armour, good enough for me, but dont use it for heavy load bearing parts (IE: the base), because it will bend (so will nylon - ask Tony (Team Dragon))

i now have lots of hdpe off cuts of varying thicknesses, whats the best way to cut it to shape? jigsaw?

Skink is entirely made from hdpe, (apart from the small,outer side tops and link access panel which are polycarb).
The sides and back are tongue and grooved into the base then tapped and held with m5 allen screws.
Skink has been thrown up into the netting twice, bounced around dozens of times, hit by Little Spinner, Dizzy Tilley and wacked by Little Hitter
many times over the last 14 months and is still unbent!
We have replaced 1 side panel that Little Spinner Chewed up at Godmanchester.
Like most materials its how its used that counts.

wear a mask dude i had an ashma attack the other day cutting mdf without a mask

that wasnt clever, should et the fibres get into your breathing system

will a jigsaw do to cut it?

I would imagine a jigsaw would be perfectly fine on a slow speed setting. If you have it too fast the friction will melt it. (Never worked with the stuff myself yet)

jigsaw is fine. You dont have to worry about melting it. I let it go as fast as it will and its fine.

what ever tool you use to cut hdpe make sure its sharp, high cutting speeds will increase the risk of melting.
I sometimes apply a little water, it helps cool and lubricate (watch the electrical bits though!)

cut the front, back and top for psycho ram, looking good might need to turn the speed down as it did start to melt


alex

thinking of using 6mm / 8mm hdpe for my feather base and armour and using 16mm mdf for the bulkheads what you guys think, it must have alot of strength as my axe is quite powerful and also must be able to compete agaisnt some spinner occasoinally, and also be cheap lol

Sounds OK for starters - if you possibly can Id look at something like Nylon for the bulkheads, MDF is likely to split if subject to impacts especially with screws in the wood. If you build the rest around it sturdy enough it might be able to stand a few shocks though.