Wall thickness

[afterdark]

ok, so after much deliberation I have taken the decision to redo the design I was pulling together. It was my first proper attempt at using Blender in anger and lets just say that there were a few issues...

One of the design considerations I am a little stuck on is what thickness should I print the outer shell? There body will be around 1400mm in length and I am thinking somewhere between 3 - 5mm?

I don't want to over cook it as it will extend print times, PLA costs, weight, etch, but I am also mindful that the drive motors have quite a formidable torque so it needs a reasonable structural strength!

The body is currently designed to be comprised of 7 segments, each segment having three 'tiles' on the upper shell and 3 tiles on the lower which will be bolted together

I will likely be running some steel rods I have the length of the body to increase overall stiffness
Any advice you guys can offer would be much appreciated as I am quite new to the wold of 3D printing and still near the bottom of the learning curve. If it matters, I am using a Prusa i3 Mk3 and was plannign to print in PLA unless there are better alternatives?

Any advice or pointers on what to look out for much appreciated!

cheers

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[AlwynTurner]

Rather than printing a thick skin, I would suggest designing a structural frame and add a thinner skin over that. This will keep the weight and print time down and in turn mean that the structural frame can also be lighter. It could also depending on the design mean you can print the frame and skin separately breaking the printing into more manageable sessions.

Might be worth sketching it out in cad to see how it might work. Have you considered using Openscad for design, I find it easy to work with?

Alwyn

[afterdark]

Rather than printing a thick skin, I would suggest designing a structural frame and add a thinner skin over that. This will keep the weight and print time down and in turn mean that the structural frame can also be lighter. It could also depending on the design mean you can print the frame and skin separately breaking the printing into more manageable sessions.

Might be worth sketching it out in cad to see how it might work. Have you considered using Openscad for design, I find it easy to work with?

Alwyn

Hi Alwyn

I am using a stress structure to distribute the load (as much as I can), this is what will also be carrying the steel rods

I really want the lower hull at least to be waterproof (If possible) - we have a large lake near us which is calling out for some amphibious action LOL - so I don't really want to be poking hulls through the outer skin for bolts etc (cant use glue as I want to be able to dismantle it if need be for servicing / upgrades)

Once I have redrafted it, I will upload some images

Do you think 3mm would be too thin for an outer skin (over the top of a stress frame)? it will need to be able to withstand a few knocks and scrapes I suspect

[jarndice]

The Taigen Panzer 4 Metal Hull along its unstressed side is just under 3.0mm thick over a distance of 31 cms.

[AlwynTurner]

Hi, 3mm of pla will be pretty tough provided you specify a thick skin or high infill percentage. If you use a 1.5mm wall for a 3mm hull you will get a solid skin. Another factor is to use decent quality filament, I use AMZ3D filament from Amazon and it is very strong whilst being quite cheap (£15.99 per kg), plus the surface finish is very good even at .2mm layer height.

Try designing and printing 1 section and test the result for sturdiness. If you can stand on it and it doesn't break then its strong enough . If you plan on going waterproof then try and design a small inset to fit a rubber gasket between the sections.

I'm sorry if I'm teaching granny to suck eggs here. Its difficult to offer advice without more detail of the actual design. One thing to be very conscious of is that the strength in your print is along the deposition layer not between layers. An example would be to print your hull sections on their end, not flat. The longitudinal body strength would have to be provided by your metal connectors. It might be an idea to have an aluminium floor pan that you bolt everything to, possibly with aluminium section along the body for extra strength.

I hope some of this is useful. I'm sure when we see your section designs will all make more sense.

Alwyn

[Vertigo]

IMHO its easy to get carried away with 3D when other techniques can be used. This is particularly true with large items.
I have thought of making a large scale model like this.
I would be more inclined to make the basic structure from plywood etc and use the 3D for detailed dress panels and smaller features.
Another potential issue with 3D is that you are tempted to use an infill of less than 100%. But if you have to attache new items or modify something you will only have this for support. The plywood has the same section all over so it provides consistent support.
Don't forget that PLA is biodegradable. Im not sure what its durability is but i wouldn't feel comfortable investing time and money on something that is not durable.
If your worried about getting the dimensions right on a large piece of plywood you can use your 3D to print thin templates tiles

[Tiger6]

PLA is only really Biodegradeable if its heated up to 150 Deg C in an industrial composter - if its left to its own devices it will last a lot longer than you or I.
In terms of its structural durability, it is really up to the designer to make their part suitably ridged, wall thickness and infill density is only part of the equasion.

[AlwynTurner]

I must admit I agree with both vertigo and tiger6, personally for something of the size you are planning I would use ply and skin it with fibreglass for the chassis, this gives a strong base unto which you can mount your 3d superstructure. I am planning to do something similar with a 1/6 scale universal carrier which will be much smaller than what you are planning.

The advantage of using ply is that it is strong in all directions, it is light, it is very cheap, and you can build quickly, scrapping prototypes if they don't work as desired. You can also bolt components to it and fibreglass over it to give a waterproof finish. With proper design of the pla components then can be screwed or bolted to the ply.

Alwyn

[midlife306]

This may blow your minds, on my fully 3D printed 1/6 scale T35-A the 1700mm long hull walls & floor are 18mm thick, I used a wall thickness of 2mm & 30% infill.
I knew that the weakness would be around the bonded edges of the 20 odd segments so having nice thick bonded edges helped the strength lots.
With the hull above the floor due to the suspension bogies bolted to the hull I accidentally stood in it, I’m 16 stone & it didn’t even creak.
I don’t 3D print everything because I think it’s better, I do it because I can. It keeps me off the streets Lol
If you get concerned about the speed of 3D printing then perhaps 1/35 is more your scale, I couldn’t let my Anet A8’s run over night because of the noise so I had to cut everything up into manageable chunks, now with the creality printers I can run 24/7 and I do lol

Cheers
Wayne


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[afterdark]

This may blow your minds, on my fully 3D printed 1/6 scale T35-A the 1700mm long hull walls & floor are 18mm thick, I used a wall thickness of 2mm & 30% infill.
I knew that the weakness would be around the bonded edges of the 20 odd segments so having nice thick bonded edges helped the strength lots.
With the hull above the floor due to the suspension bogies bolted to the hull I accidentally stood in it, I’m 16 stone & it didn’t even creak.
I don’t 3D print everything because I think it’s better, I do it because I can. It keeps me off the streets Lol
If you get concerned about the speed of 3D printing then perhaps 1/35 is more your scale, I couldn’t let my Anet A8’s run over night because of the noise so I had to cut everything up into manageable chunks, now with the creality printers I can run 24/7 and I do lol

Cheers
Wayne


Sent from my iPhone using Tapatalk

I think for me, this hits the nail on the head - the whole reason I am doing this is a) because I can and b) to lear as much as possible about modelling, 3D printing, electronics and software development

I love the flexability I get with 3D printing but as I am still fairly new at this, just want to make sure i am making the right choices about my approach. Realistically, I will be supprised if this thing is operational until the Autum at best but wheres the fun in finishin git a I would then need to come up with something else! LOL!

Thanks for all the input - much experimenationis in my future me thinks...