Chassis Materials

[higgeh]

Wonder if anyone can give me a bit of guidelines here.

Working on designing a featherweight at the moment and looking at what I can use as good chassis material.

I was thinking of having a baseplate for everything to mount on (motors, ESC, Batteries) that would be made of 10mm aluminium but I'm unsure if its up to the job and whether a thinner steel would be a better idea. obviously weight is going to be an issue but I can address that.

[Eventorizon]

Hi there :-)

10mm Alu is a good starting point, as in most people totally underestimate the power of modern machines, and that might be a good option depending on the type of machine you want to build. There are many grades of aluminium so make sure you choose a good quality grade such as 6061 or 6082. There is also 7075 but its much more expensive, though much stiffer, so save that for when you do version 2.

The alternative is to use a wear steel like Hardox, about 3-4mm thick. Mild Steel is no good these days, but Stainless 314 is an option though very expensive. Calling up your local waterjet/plasma cutting company and having a chat and you should be able to source a sheet to suit your needs; K-Cut seems to be the go-too for many builders. Unless you have an angle grinder you won;t be able to cut or machine the Hardox yourself (unless you have the right tools) so most people have their base CNC'd from Hardox, with all the mounting holes for the other components done at the same time, and work from there.

[maddox10]

10mm Ali is thick and heavy for a feather and is about the same weight as a 3.2mm thick sheet of Hardox.

I would know what to use.

[higgeh]

cheers thanks for that.

was thinking it might be a better idea to have all the components placed before I send it away and get it all cutted. Now to just negotiate with the cutting companies as I reckon through modelling I can use a lot of the cut outs from the metal to make other parts.

Any good suggestions on CNC cutters or plasma cutters. Im in Scotland.

[higgeh]

kinda liking the thought of using the aluminium for number 1. its a material im used to working with and then will move onto something else at a later stage. At the moment the 3d models I have been working on have me in about 200g below weight with the layout im planning. Hope it stays that way.

[Eventorizon]

Ignore the CAD. Even with 7+ years of working in solidworks, nothing I design is ever as the CAD says. I have taken to designing to roughly 5% under the limit. This seems to get me close once you include wiring lights, bolts, all the cable ties and electrical tape you use to lock things down. Even when the finished pieces weigh exactly what the CAD says they should somehow when its all together its always heavier than it should be.

Maddox is right BTW about the Alu and Hardox. However, if you feel better with Alu, go for that and then move to Hardox at a later stage.

[higgeh]

CAD just gives me a bit of re-assurance when it comes to the chassis etc but yeah will consider what you say. I just dropped the power in my batteries so hopefully that gives me a bit more breathing room.

I think the aluminium is mainly due to the way im planning on putting it together. I will get it modelled up and see how it looks. Also due to lack of tooling and equipment my plan would be to get everything plasma cut then hopefully just have a simple assembly that just needs some tapping and drilling to put it together.

[RogueTwoRobots]

Yeah if you're used to aluminium and can work with it, go for that. Hardox is great and all, but if you haven't got the right equipment to work with it, it can be a pain. And building a first robot will be a big enough pain as it is without adding more unnecessarily.

Whereabouts in Scotland are you based? I don't know many CNC or plasma cutter places up here but then it's not something I've really investigated much.

[R9000]

Yep, I made the mistake of having to tap Hardox - it's not easy to work with from my hours of trying to file bits down. Thankfully I know a guy who might be able to help, but if you're planning on metalworking without some serious tools, I'd go with Aluminium.

[higgeh]

Whereabouts in Scotland are you based? I don't know many CNC or plasma cutter places up here but then it's not something I've really investigated much.

I'm central belt but will probably just find an internet supplier to use. I'm pretty confident I can supply them with the drawings exactly as I need them.

[Graw]

Not trying to hijack your thread mate but rather than spam the forum with another one, I've read about HDPE sometimes warping is there any way to avoid this? Also would say 12mm of HDPE hold up well as a base and what else could I use for the same kind of weight, I guess 3.2mm of hardox would be a fair bit heavier for say a 300mmx200mm size base? Alu?

[higgeh]

Aluminium seems to be around 3 times the density of HDPE and Hardox 3 times the density of Aluminium roughly

so a 12mm sheet of hdpe weighs the same as a 4mm sheet of aluminium
a 4mm sheet of aluminium weighs about the same as a 1.3mm sheet of Hardox.

(I think that's correct)

[Graw]

Righto cheers.

1.3mm of hardox seems very thin.. im guessing I should go a bit thicker if I go with HDPE, maybe 16mm?

[maddox10]

Density
HDPE 0.95kg dm³
Aluminium. Between 2.7 and 2.9 kg dm³, depending on alloy. (better to err on the heavy side, Always pleasant to have some weight left after building)
Steel (hardox is low alloy steel) 7.9kg dm³

HDPE warping? Yes, it will always try to get into the original shape.
Very surprising to see a crooked wheel go straigth after a few days of rest.


1.3mm Hardox is rare as hens teeth. 3.2 is not rare , and 4mm is easely sourced.

You could do what we did for Perun. Take a big, thick sheet and mill it out to fit everything in.

[higgeh]

Just to say I was only giving you relative densities. Hardness has more variables than you can explain on an internet forum. Usually you need some pretty swanky software to analyse stress.