Lid/Baseplate materials

[Max]

Hi,
I'm curently planning what's next for me and robotics, one possible option is a full combat feather weight. I'm trying to figure out what sort of design I wouid go with so I can think about costings and where/when/how I would build it.

What I was wondering was what material people recomended as a non-structural lid/baseplate? I wouldn't want anything mega expensive but want something decent, hardox would be too heavy. Each plate would be roughly 250x200mm, well supported around the edges but not really anything in the middle although I guess I could have say and aluminium column in the centre between the 2 plates but this could well do more harm than good?

Some options I was thinking about:
-Titanium: not sure what thickness is necessary but would imagine 1-2mm but fear this would be cost prohibitive
-3-5mm Glass Fibre sheet: I use this material in antweighs and it is very easy to work and machine and easy to get off eBay but not sure how it would hold up against featherweight axes and crushers, I'm guessing not well!
-5mm Aluminium: I'm imagining some decent grade Aluminium alloy like Aero grade rather than the regular soft stuff, but not sure what sort of grades are decent or how much they would I cost
-6mm polycarbonate: this is obviously fairly cheap and easy to get hold of but again not sure how it would hold up against modern feathers

So can anyone offer any advice as to which one they would recommend or recommend anything else?

Thanks
Max

[daveimi]

Titanium is your best bet, ally is ok but gets beaten up quick with being soft. Ideally you want thick steel but it gets heavy. HDPE is always an option as well but I imagine you'd need 10mm+ thickness wise.

[RogueTwoRobots]

6mm poly will protect you against all the axes out there, never had anything go through it. Little Hitter will make nice marks in it but that's about it. Cobalt put a hole in mine back in 2012 but considering that was a hydraulic crusher, it's not surprising.

Used 5mm as a baseplate on Onyx and it worked well, although it eventually developed large crack in it, but that originated from one of the countersunk holes I'd drilled, so it wasn't entirely unexpected.

[overkill]

Glass fibre (AKA Garolite) and other composites will not stand up against impacts or crushing - I have tried it several times with poor results. Composites are great for internal parts, but not armour. Titanium will work well but for full combat you will need at least 3mm; 1mm sheet is surprisingly bendy and will not provide much protection. Even 3mm Ti will fare badly against spinners if they catch an edge so recess the top and bottom behind your side armour.

[mrsam]

Agree with Jamie, for a lid 6mm Polycarb will be absolutely fine. Hatchet caught Reavers polycarb top a good few times at this years champs and it made a few dents and scratches but not much else, and LH doesn't really do anything spectacular either.

Spinners have no problems with it as i learned with Hatchet 1 ( 12mm baseplate, shattered into 3 pieces from 1 Mr Mangle hit) but as Nick said if you recess it so the edges can't be caught you should be fine.

[Flag Captured]

I used 5mm 6082 alu (from Aluminium Warehouse) in Overdrive/Banana Overdrive and that's not even slightly budged. It's nice but thick, and a lid wouldn't be nice from it. if you can get 5mm ti in, I doubt anything will crack that - even 3mm won't, but Nipper is scary and I'm told it's gone through 3mm ti so... yeah.

My best advice would be something like that with a HDPE over-layer, doesn't have to be thick but does provide a bit more protection than just a sheet of something on its own but it's totally dependant on your design. Also +1 to what Nick says, Shard turned HW2's top plate into a banana (2.5mm stainless) just because it wasn't recessed behind the back panel...

The key thing I'd say is you want enough flex to absorb the impact, but enough strength to not be damaged by it if that makes any sense whatsoever

[maddox10]

Hannibalito 3 uses 5mm HDPE as a bottom dust cover, and it survives wonderfully well.

[Max]

So sounds like 6mm polycarb would probably be my best bet unless I can afford 3-5mm titanium.
I wondered about the high grade aluminium alloys like 7075 grade, I can't remember where but thought I read its strengh approached that of titanium, has anyone had any experience with this?

[Eventorizon]

The problem with Polycarb is it will shatter if you hit it to hard, Hatchet suffered that fate during its first or second fight to its poly base plate. That said, I agree with the others, 5-6mm Poly for the top should be fine, but HDPE would be better. You could put in some rubber washers so its shock mounted in some way if you are worried.

On a more technical node, Titanium is used because not only is it much lighter and stronger than Aluminium and steel for the same weight its also much tougher, ie: it can absorb lots of energy in an impact. However, because once Titanium is bent you cant bend it back without risking it breaking (Anything made of grade 5 and up anyway) it needs to be much thicker to prevent that happening all together, else you risk ruining a very expensive panel.

Even more technical, Grade 5 Ti has about double the fracture toughness of 7075 Alu at 44-66Kic and around double the UTS at 1000MPa. At 4.43g/cc Ti 5 is basically double the strength and toughness of 7075 for only a ~50% increase in weight; 7075 is 2.81g/cc. This is where the 4 times stronger saying comes in, but its very rough.

PS: I will probably have got something in there wrong knowing my luck but you get the idea :P

[Ellis]

Don't use polycarb, it'll crack. I would use 1-3mm ti if you can get it, but stick to Grade 5 if you go thin. I would prefer 10mm HDPE over ~5mm alu, you want a baseplate to have some flex and not permanently deform and aluminium deforms more easily than the others. It's damn near impossible to deform 10mm HDPE significantly in a baseplate role.

As for top panels the same is true although 5-6mm HDPE (if grade 500 or 1000, not sure about 300) will keep most things out. Obviously nipper and a good pointy axe will go through but that's true for materials weighing 3x more, so it's a balance. Perhaps leave weight to beef up depending on your opponent.

In all cases I would recommend making the base as unnecessary structurally as possible, save preventing a box from collapsing diagonally. You want strength to come from chassis bulkheads.