Can I scan my model ?

[duluthboats]

If you are interested in our effort here is the link. This project is still moving but at a much reduced pace.

http://www.cnczone.com/forums/showthread.php?t=4424

Gary

[Tim B]

True Gary, but we're still talking factors of 50 times the amount but anyway... I think we ruled out the commercial option some time ago.

I will post my general thoughts on the subject at the end of this ramble. They include interfacing and a little to get you started on the programming.

I am going to make a few massive assumptions now. Firstly that you are using a PC, secondly, that you do in fact have a parallel port. and I will assume that you are using Windows XP. Firstly you need to find either a copy of Q-Basic, or a free C compiler. Alternatively install a distribution of Linux (Mandrake 10.1 with KDE 3.2 is good) and welcome the free C compiler and all the appropriate header files. If you have not done much programming before it would be easier to use Q-Basic, but probably more interesting to learn C.

A good book for C is "C programming in easy steps" by Mike McGrath. C allows you to do some rather nice tricks with I/O systems and values. It also bolts into the X windows system in Linux quite well.

This is copied from an e-mail I just sent on the matter:
Many years ago I remember that my father built a 2-axis digitiser which interfaced into a BBC Micro. There was no special electronics involved because of the BBC's Analogue input port. The voltages from the resistors were simply fed into the computer and that was that.

However, these days, analogue ports are rather expensive, and so if we only need to measure a position a 555 astable is useful, then by timing the pulses we can work out the position of the variable resistor.

I have included the electronic design in the PDF file. You may have to try different capacitor sizes to get a usable frequency. I have thus-far only dealt with the parallel port at low speeds. So I cannot tell you what the maximum speed is (though I do intend to find out in the near future).

I can supply the code I have been writing if necessary, though my code has been used more for output purposes than input purposes.

The mechanical details are a suggested solution, the actual size and shape of the parts will depend on what you have available. There are two different types of end given and the use of either will depend on the complexity of the object being digitised and your budget/available time.

I would suggest using aluminium for the working parts as it is easy to work with. The retaining blocks on either side of VR1 could be plastic though. It will pay to make the 'arms' reasonably wide, certainly around the variable resistors as these will induce stress concentrations.

If you have any questions please don't hesitate to
e-mail me,

Tim B.

Tim@MarineDesign.tk

nb. The PDF file is rather large about 1.7Mb

[wet feet]

I have a little experience with a laser scanner attached to a FARO arm.If you can find the hardware and an operator,it will produce a point cloud of the model.You can create sections(or for that matter,buttocks and waterlines) and save a dxf file to be used in your favourite application. It is unlikely to be cheap but it will give you a result in less time than it is likely to take to build your own scanning system.You could use the FARO arm itself to take sections.Or you might be able to find a large enough CNC machine with probing capability and some time available.
I suspect though,that the fastest,easiest and cheapest solution is to follow the suggestion above regarding the construction of a movable bridge and a sliding stick to trace the sections directly onto paper.If you secure the model well and align the bridge carefully you can lift all the sections.With this information,there should be no reason why you cannot use a flatbed scanner to scan the paper on which the sections lie.You may need a larger scanner than the usual home/small office type but you will have the information.I have an old version of Corel Draw which will permit the saving of scanned objects as dxf files.There are other types of software that have the same capability.Once you have the dxf file,some time spent seperating,cleaning up and moving the sections around in space should give you what you are after.

[Chris Krumm]

The reality is buying a ready-to-run mill drill or router table already set up for 3 axis CNC and a digitizing probe would probably cost the same or less as a Microscribe or Faro arm, and you'd have a tool to cut parts with, too. Since it would be a 3-axis Cartesian coordinate machine, you couldn't read undercut surfaces.

Tim - we'd love to have an accurate, easy to use digitizing arm for under $500, but I'm not seeing it on the market (yet). Gary aptly pointed out the need for quality encoders, precision machining, and electronics. To that I'd add software development. Is Simone's goal to get his hull model dumped into CAD or to R&D a digitizing arm? Gotta pick your projects, and I wish you the best of luck with yours.

Chris Krumm

[Tim B]

I was just saying that it isn't that difficult. Actually writing the code yourself isn't too hard either. Building the digitiser shouldn't take that long. As an example I am currently working on a 3m span Slingsby T65 Vega. I plan to mould it from foam/carbon/glass throughout. However, I plan to get the model as accurate as possible. Thus I'm milling moulds, which needs a milling machine, which needs a controller, and software. All done for as little cost as possible.

Thus far I have a surface definition, and I'm building the controller and writing the software at the same time.

I am well aware of the size a project can become, and in the case of the Vega that's absolutely huge. Sure, you get what you pay for, but it should be possible to build your own well enough for your own purposes if you are careful and take some time over it.

When I've finished the milling machine controller I may well build a 2 axis digitiser for A0 size lines plans but that will be for interest only.

Cheers,

Tim B.