Polycarbonate vs HDPE

Please post all questions and answers in here. This way people can easily see if someone else has the same problem.

Moderators: administrator, BeligerAnt, petec

User avatar
Rhys
Posts: 992
Joined: Tue Oct 29, 2002 12:00 am
Location: Caerphilly, South Wales

Polycarbonate vs HDPE

Post by Rhys » Tue Feb 05, 2013 8:39 pm

Hi all,

I was out of ants when HDPE became one of the more popular materials, so never used it. I've stuck with polycarbonate since I've been back, but I was wondering which you guys thought was better? Currently my ants are 3d printed chassis with polycarb armour, but would HDPE do a better job? The only reason I ask is that someone posted today on the FRA forum that polycarb isn't really used in heavies and feather anymore, as it's a bit crap. Is this the case with ants too? I've bought some HDPE of different thicknesses to try out, but there's no substitute for first hand experience. Are there any other advanantages/disadvantages aparts from impact absorption? Is it true it's less brittle than polycarb?

Cheers,

Rhys
Image

User avatar
joey_picus
Posts: 1137
Joined: Tue Jan 13, 2009 1:51 pm
Location: Lancaster, Lancashire
Contact:

Re: Polycarbonate vs HDPE

Post by joey_picus » Tue Feb 05, 2013 9:33 pm

In my experience HDPE is less stiff and feels 'softer' - i.e. it's more likely to be chewed by spinners, spikes, and pick up surface scratches - but at the same time I find it much less likely to crack or break rather than bend as polycarbonate has a tendency to do. It seems to depend on your construction methods and what you use it for, really - I don't use it much, I prefer polycarbonate as I tend to make a chassis out of plastic with metal armour (and HDPE at ant thicknesses would make a poor chassis unless welded) but as spinner-absorbing armour HDPE would be very good if mounted right.

The other main advantage of HDPE is weight, it's roughly two thirds the weight by volume of polycarb if I remember right?

DISCLAIMER: I may or may not have any clue what I am talking about at all :D
Joey McConnell-Farber - Team Picus Telerobotics - http://picus.org.uk/ - @joey_picus
"These dreams go on when I close my eyes...every second of the night, I live another life"

razerdave
Posts: 1531
Joined: Mon Jan 02, 2006 9:40 pm
Location: Carterton, Oxfordshire
Contact:

Re: Polycarbonate vs HDPE

Post by razerdave » Tue Feb 05, 2013 10:01 pm

I use HDPE on a lot of robots, in its thicker forms its very good (I use 6mm thick as side armour). Its much easier to work with than polycarb, although for flat armour plates, 1mm would be better than HDPE of the same thickness. As for making chassis out of the stuff, 2 would be absoluteminimum due to the flexibility of 1mm. It should be noted that HDPE does not tap as well as polycarb.

Joey is correct on the weight difference, HDPE = 2/3's Polycarb equivilent.

Remote-Controlled Dave
Posts: 3716
Joined: Sun Apr 03, 2005 5:30 pm
Location: Antrim, Northern Ireland
Contact:

Re: Polycarbonate vs HDPE

Post by Remote-Controlled Dave » Wed Feb 06, 2013 8:21 am

2 would be absolute minimum due to the flexibility of 1mm
I've used 1mm fine as a chasis. :D
Die Gracefully Robotics
Winner - AWS 39

User avatar
Rhys
Posts: 992
Joined: Tue Oct 29, 2002 12:00 am
Location: Caerphilly, South Wales

Re: Polycarbonate vs HDPE

Post by Rhys » Wed Feb 06, 2013 2:22 pm

Spoken like a true champ Dave. ;)

Cheers for the info guys, I didn't realise it was that much lighter. Looks like I'll replace the 2mm poly on Duff and Cosmos with HDPE. I'm also planning on using some 6mm HDPE as side armour on my new 4wd pusher, and hopefully can put together a 2mm welded chassis for Warhorses (they've been destroyed at the last 2 events!).

Any tips for welding? Do you just get a soldering iron and run it along the seam? Also, does it bend easily? I was considering a heat gun to try and bend my poly. Will I need this for HDPE? Or will it cold bend?
Image

razerdave
Posts: 1531
Joined: Mon Jan 02, 2006 9:40 pm
Location: Carterton, Oxfordshire
Contact:

Re: Polycarbonate vs HDPE

Post by razerdave » Wed Feb 06, 2013 3:22 pm

It will cold bend up to 3mm, I used the barrel of a soldering iron to bend a 4mm piece.

As for welding it, I would recommend some 1mm HDPE slivers as welding rod.

josh
Posts: 1115
Joined: Thu Apr 28, 2005 6:56 pm
Location: Uxbridge, London
Contact:

Re: Polycarbonate vs HDPE

Post by josh » Wed Feb 06, 2013 7:33 pm

I saw somewhere somebody used copper wire between two pieces and ran a current through it. The heat of the wire created an evenly welded joint. You could do the same thing using thin fuse wire potentially.

Possibly somebody will know where I saw it? I think it could have been the FRA forum...

EDIT: Here
RPD International
www.RPDintl.com

User avatar
BeligerAnt
Posts: 2464
Joined: Wed May 15, 2002 12:00 am
Location: Brighton
Contact:

Re: Polycarbonate vs HDPE

Post by BeligerAnt » Wed Feb 06, 2013 8:39 pm

HDPE is *much* softer and more flexible than Polycarb. Also, cold-formed HDPE has a tendency to try to return to its original shape. You think you've made the perfect shape, then a week later it's all pulled itself out of shape :(

To make a decent stiff HDPE chassis shape is important, folding and welding fillets in the corners works well.

To make successful welds you need to ensure the heat gets right through the thickness of the material, and of course HDPE is an insulator! A pointy soldering iron tip poked into the joint at regular intervals works well. As Dave said, some thin pieces of 1mm used as welding rods do help.

And forget trying to tap it. Self-tapping screws should be OK.
Gary, Team BeligerAnt

daliad100
Posts: 229
Joined: Thu Apr 08, 2010 8:18 pm
Location: Milton Keynes
Contact:

Re: Polycarbonate vs HDPE

Post by daliad100 » Wed Feb 06, 2013 11:39 pm

I've cold bent acrylic to the right shape then used a heat gun to get it close to melting to relieve the stress. The closer to melting you get it the less it springs back.

HDPE should work better than acrylic because it cold bends better and has a lower melting point (you could dunk it in boiling water if you're willing over bend it by a few extra degrees)
Team Imperial - What is that, metric?

User avatar
joey_picus
Posts: 1137
Joined: Tue Jan 13, 2009 1:51 pm
Location: Lancaster, Lancashire
Contact:

Re: Polycarbonate vs HDPE

Post by joey_picus » Sun Mar 10, 2013 4:45 am

Bringing this thread back up for relevance:

I've been looking at Jigsaw with the intention of getting it running again to keep my driving half-decent (I didn't dare take LiPos in my luggage!) and noticed that the polycarbonate chassis has a lot of stress cracks, mainly around the mounting tabs for the bodyshell where there's a very acute bend. I'm trying to design most of the stress out for Jigsaw 64, but was wondering if other plastics coped better under long-term stress, or if there's a better solution than bending?

I've tried a few things in the past - polypropylene snaps too easily and/or doesn't keep a bend, sheet HDPE seems far too soft and also doesn't keep a bend, and injection moulded HDPE/UHMW from old VHS cases seems to work better, but need a large bend radius (and also it's getting increasingly hard to find Fawlty Towers on VHS...)

Any ideas?
Joey McConnell-Farber - Team Picus Telerobotics - http://picus.org.uk/ - @joey_picus
"These dreams go on when I close my eyes...every second of the night, I live another life"

Post Reply