Replies to This Discussion

3D RoboticsPermalink Reply by Chris Anderson on August 21, 2009 at 4:36pm

Looks good. Just a FYI--it's more effective if you embed images in your post, rather than attaching them, to save people from having to click. Use the little camera icon.

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Permalink Reply by Nigel C on August 23, 2009 at 10:57pm

Nice drawing! What software did you use?
Manufacturing of CNC components you speak of could be achieved within DIY drones community: Differences in foreign exchange rates could make it cheaper for some members.
I use CAD (Microstation) every day, as an Architect, and don't have first-hand knowledge with CNC technology (although we've recently used it to model parts of a project I'm working on).
I'm aware .dwg format is the international standard for Architecture & Engineering, but can anyone tell me if there is an "international" file format for CNC tech?

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Permalink Reply by Oliver on August 25, 2009 at 11:39pm

Hi Nigel thanks for the response. I used solidworks for the CAD modelling. The manufacturing process would be an aditive one rather then CNC. The advantage of this is that you can make the wing in one piece with all the internal features you need in one operation.

The largest machines can currently make wing sizes 900mm long by 800mm wide. The material I have selected is a polycarbonate, ideal for high impact applications, crucially none of the currently available materials have the required strength/stiffness so they would need some kind of carbon fibre spar to give them the required strength.

The CAD model I have shown doesn't really take advantage of some of the unique properties of this manufacturing process so the next concept will have a skinned honeycombe structure and a central spar box.



Regards





Oliver

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Permalink Reply by Jordan Smith on August 26, 2009 at 10:23am

Hi Oliver

First, I really like your idea for using RP to manufacture planes. My primary concern with the idea is the surface finish that your wing will have. How much sanding (if any) is involved in finishing these parts?

Are the ribs you have in your CAD model going to be made from polycarbonate also? I would think one way to reduce weight would be to create the ribs out of something lighter, like balsa, rather than the polycarbonate. What's the density of the material you're planning to use? That will help determine whether it's worth making it all out of polycarbonate or making the ribs out of something else.

As for your 500 gram weight, that sound a bit high. There is no easy answer though, it all depends on how much payload you need the plane to carry. You might be able to get away with this weight, but you wont be able to carry as much in electronics. The airfoil you choose will also impact whether or not this weight is acceptable. What have you chosen?

Anyway, it's an interesting project. Please keep updating on how it's going.

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Permalink Reply by Oliver on August 26, 2009 at 3:45pm

Hi Jordan

The finish you get from the RP process would require a paint finish to make it smooth and possibly to seal the surface, the additive manufacturing process gives a stepped finish usually in 0.010 slices. (Could this be a useful aerodynamic feature like the corrugated wings on a Junkers?).

The build process of the RP machine doesnt really allow us to use seperate materials, the idea is to build all the structure in one go. However one idea I came up with was bonding a box section wing spar to seperately built leading and trailing edges. My aim has always been to try and build a wing which has simplicity and ease of build as the main criteria rather then ultimate performance.

I understand what you say about the density of the material (polycarbonate 1.2 grams/cubic centimetre versus balsa 0.155 grams/cubic centimetre) but the tensile strength of the Polycarb is between 5 and 9 times stronger depending on the fillers used in the plastic.

The wing profile I have used is an E205 Naca form, I am sure its not ideal for what I want but it was a convenient place to start. I started out just looking at the feasibility of using this manufacturing process on a conventional wing, I am wondering if it works better on larger scale wings as the material weight is less critical.

Regards





Oliver

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Permalink Reply by bGatti on August 27, 2009 at 8:41am

No one uses RP for production due to the costs. A wire-cut styrofoam wing is far more cost effective and broadly attainable.

RP is really only cost effective when the parts being produced are expected to change significantly on a daily basis.

I believe Boeing already made and flew a fully RP drone, not sure if a market emerged.

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Permalink Reply by Oliver on August 27, 2009 at 3:40pm

Hi there thanks for your reply,


RP has moved on from one off parts to "digital production" which is seen by industry pundits as the big growth area for the future.......see this link for a company offering (low volume) production parts: http://eu.redeyeondemand.com

I'd love to get any information on the Boeing drone you mentioned, RP can be a bit of a misnomer as its a generic term and is sometimes used to describe anything from high speed CNC machines, additive fabrication ( what I'm talking about) and just doing things quicker!

Just to make a point about how the cost of RP will continue to become cheaper, the cheapest machine available now is just £ 750 .....http://www.bitsfrombytes.com

I understand what you say about the wire cut foam foam, I am really exploring the concept of what may be possible in the future, perhaps looking for a method of production that doesn't need the kind of model making skills found in the RC community. My concept is design, print, fly or perhaps download files, print, fly.


Regards



Oliver

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Permalink Reply by Jordan Smith on August 28, 2009 at 5:39pm

The reason I asked about making the ribs out of another material is because they don't need the higher strength that the polycarbonate provides. One way to reduce weight would then be to make the top and bottom half of the plane shell as two separate pieces and place balsa ribs in between the halves before gluing it all together.

It sounds like that defeats your purpose though. If you would rather be able to print the plane as one complete piece, you're going to have to add some weight. With the right wing design, this shouldn't be a problem. I have a plane that I've designed and am currently building which could accommodate this additional weight without much trouble.

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Permalink Reply by Oliver on August 30, 2009 at 1:34pm

Hi Jordan,

What kind of plane have you designed? did you do it on cad or do you have drawings for it?


Regards


Oliver

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Permalink Reply by Ken Boone on September 1, 2009 at 7:03pm

Have you attenpted to print a single section rib to rib? It seems to me that the wing covering (skin) would be difficult to print since it is not supported in the middle.

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Permalink Reply by Oliver on September 2, 2009 at 4:23pm

Hi Ken,

I have spent some time looking at this. The best ( I think at the moment with what I know!) way to build an exterior wing profile is to build it vertically rather then to lie it down. This is because all the additive RP processes slice up the cad file to create 2 d slices which are then built layer by layer on top of each other until the part is finished. If you lie the wing down horizontally the slices run through the wing giving you pronounces stair-casing on the part. Most RP processes use support structures to hold the part in place, I think your assumption is correct in that building 2 seperate parts could prove difficult if they warp during the build especially if your part transitions from thick to thin sections.

When I have built large RP parts in the past I have added dowel or step features on the cad model to help align the part and make it easier to join parts.

If you are trying to build the "core" of a wing (I think!) the above does not apply because any surface stepping should be lost when the surface skin is applied, ie if you covered it in fibreglass or CF.....Although I have to say I havent tried this yet!


Regards






Oliver

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Permalink Reply by Scott Plunkett on September 1, 2009 at 7:41pm

What if you printed just the ribs, essentially everything in your picture above except the skin, then had an easy covering method like a shrink wrap bag of some sort...it may not be as quick, but it could be lighter. Additionally, if you were going to go that route you could make all of the ribs thinner and maybe even go to something like a thin walled honeycomb internally - significant strength, less material. Just some thoughts.

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