Armour

[gravity]

Armour

@ Julian:

Gravity 5 will pack 4 of them... so thats quite a lot of Fire extuinguisher indeed... I just dont think the event organisers would be so happy if I put them on the outside of the robot... would be neat though

[Guest]

Armour

If you take a hit, instant cloak of invisibility

[talulah]

Armour

For a compromise, and still very cheap, you could use much thinner steel (say 2mm or even 1mm) and mount it onto 6mm or 8mm plywood backing. The steel acts as armour against cutting tools and flames, and the plywood behind supports the steel against impact weapons. The result is significantly lighter than 6mm steel.

It would be interesting to do some tests on a composite like this, and obtain hardness & strength values. Ive got hardness and strength values for lots of other materials ona page of my site here: http://homepages.which.net/~paul.hills/Materials/Materials.htmlhttp://homepages.which.net/~paul.hil...Materials.html

[Guest]

Armour

Maybe UHMW Polyethelyne would be better then using ply wood as it has better impact properties. You just need a thin layer of steel or other high hardness material to stop cutting blades as UHMW is rather easy to cut (yet I get it from chopping boards, hmmmmm).

[talulah]

Armour

Im not sure Daniel, UHMW Polyethelyne is heavier (941 kg/m^3 compared with about 615 kg/m^3.

Im not sure how to compare the impact properties. It is there to support the steel, so I guess something like the Flexural Modulus (0.75GPa compared with 9.3GPa for plywood) shows that the plywood is a lot more resistant to bending, although the polyethylene has a slightly higher ultimate tensile strength.

Im no expert in materials science so I wouldnt like to say really.

[fluppet]

Armour

Just to bring up a random thought, are you talking about just resting the metal against the wood/polyethylene to support it against impact perpendicular to the metal, or are you thinking of gluing them together as a laminate (which would work better against shearing forces likely to buckle the metal)?

Speaking from absolutely no personal experience, I was wondering if the ability to repair armour is considered a factor these days. Obviously if you get a gash in solid steel, youve got a good chance of fixing it (given a while with a MIG and a big hammer). It strikes me that repairing a laminate is pretty much a throw-it-out-and-start-again job - although I guess if you used a hot glue gun to stick the parts together it might be possible to heat them and re-separate them.

Neither a new sheet of thin steel nor a new lump of wood is going to break the bank, and obviously repairing the wood (to its original strength) is getting on for a non-starter anyway, but I guess its relevant with thicker and more expensive (e.g. titanium) armour.

On the topic of strengthening wood, some model builders on Discovery Home & Leisure were swearing by the idea of liberally coating wood (especially balsa, to be fair) with superglue as a way of strengthening it without adding much weight. Gluing on a thin strip of carbon fibre seemed to help, too. I dont know how well model aircraft techniques translate to combat robotics, but it might be worth an experiment. :-)

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Fluppet

[big_nipper]

Armour

I tired that with balsa wood & wood glue on an antweight. It did increase its strengh but warped the wood in the process. Dont think it will work on a bigger scale but you never know. Try asking WJ if he has strengthened the MDF Armour on Gravity 4 . Well thats what it looked like on Arthers Pics.

As for easily fixing armour. Never damaged a panel enough to warrent replacing/fixing it yet. Repairing armour for us means making a new piece. Its not been designed to be fixed in a hurry

[richard_morris]

Armour

A few points :
Coating something in superglue is a bit pointless - cyanoacrylate adhesives are intended to bond surfaces together, with the minimum glue volume. If you want to and mechanical strength using a coating, you are better off with an epoxy - like Araldite.

From experience, you do not want to put carbon fibre on as an outer skin on a combat robat. Sure it is strong - but also brittle, has poor abrasion resistance and if damaged, looks horrible (big damage points against you). Sure, use carbon for stiffness, out of sight (on the inner face of your armour), better to use kevlar on the outside - tougher and better abrasion resistance (but bad UV stability, so paint it!)

Richard

[fluppet]

Armour

Richard: I should have phrased that better, I guess. Im only reporting what was mentioned on the telly, but my understanding was that their cyanoacrylate soaked into the wood, and added substantially to its strength - but they were using a fairly porous wood (balsa) so it may not make as much of a difference with another material. My knowledge of materials science is limited, but I could quite understand that its effect purely as a coating would be next to useless - although I suppose it might gum up a saw blade, if anyone still used them. Still, we were talking about a wooden backing to metal armour, so it might have had some value there (even if the glue was just used to laminate the steel and wood together).

As for carbon fibre, I quite agree (said from my authoritative position as a spectator :-) ). As with fibreglass, Id be wary of breathing in the area after someone had been attacking carbon fibre with a circular saw. Im sure kevlar would be better, if a good bit more pricey; hopefully the suggested thin layer of steel would be decent resistance against abrasion too - I guess a decently smooth surface is the best start. I was certainly thinking only in terms of reinforcing the wooden inner layer.

Interesting about the UV stability of kevlar, though. I learn something new every day. :-) (And now I know that if ever I want to shoot someone, I should do it in a tanning booth.)

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Fluppet

[Guest]

Armour

Well looking at the mechanical properties of a material in a text book is a bit different then looking at how the material would perform on a robot. The mechanical properties for Perspex and Polycarb are almost identical in the text books I have at home but I know for a fact, since my first robot had Perspex panels riveted to an Ali frame and my second was completly Polycarb (both feather weights), that the material handle completly different when impacted.
What I was going on about with the UHMW backing up the metal was if you just bolted the metal over the UHMW. If the combanation took an impact from an axe, spike, fly-wheel toothed spinner or other simalar weapon it would strik the metal which would deform, pressing into the UHMW, which would absorb the energy. Because the UHMW can deform well over 100% it would be able to absorb the impact and because the metal would then have planar loading it wouldnt be punched though unless the impact pushes deep enough into the UHMW. If wood was substituted for the UHMW the wood would absoub the impact, but wouldnt deform as much as the UHMW and would then splinter. Once that happens the metal covering would have to take more of the load and would split.
Of corse this would all be different if it was glued together. Carbon Fibre panels glued onto a foam core would make good structure materials, so would Perspex glued onto a balsa wood core. Actually the Perspex/Balsa composite seemed stronger when we were shown it a uni.
Oh and the technical term for the stuff that coat Blasa Wood with when making model planes it Dope. I got weird looks when I first tried buying the stuff for my planes when I asked for it in a craft shop.

[fluppet]

Armour

:-) That would explain why the bloke on Discovery H&L said what Ive got here is some industrial cyanoacrylate (slop, slop, stick fingers together). I remember dope from something (other than semiconductors, obviously); maybe its paper mache or something.

Interesting to have heard someone trying it. Id be interested to see whether anyones thought about repairing damage to this stuff - earlier comments would indicate not, but Im curious whether my hot melt idea is worth a try. If layers are only bolted together, its obviously not a problem.

As for deformation of materials, Ripper being squeezed by Kan Opener (in the RW7 Annihilator) really showed what titanium can do for you. Oh for the money! (I think Ill be buying some motors first, though.)

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Fluppet

[Guest]

Armour

A tip working with wooden armour.

A historcal fact you can fire harden wood. which first done around the time of the caveman/neandthal.

For sheet wood (a hard wood ply is best)use a blow torch to blacken the surface, have a fire safty cloth/blanket on stand by in case you set it alight, dont use water to put out any fires as you will have to start all over again when it has natural dried.

Once harden apply the dope let that soak in that a plly a thin layer of apoxy resin to seal it all in.

For a top layed use between 1 to 2mm of case harden steel, stainless steel, titamium make sure the wood is glued on good.

When using this in bolt on to frame format the use of edging renforcement is recomended as this will add structal strenght to the whole of the case.

For people who would like to test this. Simply get 2 small bits of metal the same size glue one to any bit of wood you have around the place but both pieces and a off cut of the wood that you used, on some sand or grass and then hit them with a hammer untill they brake.

In stead of glueing the metal to the wood you culd use some small screews and screew the wood to the metal

[typhoon_driver]

Armour

In stead of glueing the metal to the wood you culd use some small screews and screew the wood to the metal

or you could do both

[maddox]

Armour

Plywood , weight 0.8kg dm³.
Polycarb 1.2 dm³
Hardox 8kg dm³
Mild steel 7.8 kg dm³

1 m² 18mm plywood=14.4 kg
1 m² 12mm polycarb=14.4
I know what I want to glue under the 1mm steel(7.8 kg) plate. Both things give me 22.2 kg armour

Nothing, I will use a little more wight to use the 3mm thick Hardox.That goes 24 kg. Less hassel, cheaper ,easely as strong and easier to fix. Just reweld the damaged parts.

[ewan]

Armour

Yeah, Ive got to agree really... those weight figures really give you an easily visable comparison between the different materials, if you were to use a steel+x laminate, then the x might as well be polycarbonate, as it is very comparable in weight to the wood.

A solid panel of one material is obviosly stronger than most (if not all laminates) so I guess a wood+steel or polycarb+steel laminate would probably only be for teams on a very low budget from the start of the build.

We still havent gone over kelvar, or carbon fibre etc in much detail yet (I dont think), so that might be something to cover next, also softer plastics (which can be VERY cheap) like HDPE could be used for armour in many robots, I know that Dominic (http://www.ukrobotics.comwww.ukrobotics.com) uses HDPE in his heavyweight.