Can I scan my model ?

[simone]

Hello. My first visit to this forum ! I am working on a hopefully seaworthy runabout (and hopefully seeworthy), working only with pencils, copenhagen curves, lots of sheets and lots of coffee. This has produced a model at approx. 1 meter, scale 1/7, to run some tests with R/C and to confirm the usability of my drawings. Of course, some alterations had to be made, and some of these where hard to document, as it`s a bit difficult to place a halfbuilt model back on the drawingtable (although some templates were made). My question, finally; Is there a tool out there to scan my smooth hull (built in plywood stations and beech strips) back into stations, to enlarge them to a full scale mold for my coldbaked lady (without spending a fortune, that is) ? Best regards Simone

[D'ARTOIS]

I know a software company in Holland that do as you subscribe. I don't know the process exactly, but I have a drawing table that can do it in 2D and this software co has a similar device that handles 3D.
I'll look up their coordinates and come back on this topic.
Have some patience.

[D'ARTOIS]

Apparently they do not exist anymore - not to be found on the net either,
sorry.....

[simone]

Thank You. Best regards Simone

[RThompson]

If you were to approach a company that supplies measuring equipment, they could put you in touch with a contractor, or they may even scan the model for you.
Measuring equipment I have used is from: www.faro.com
you may even find your local reseller will scan it for free (or maybe a few beer's)
good luck.

Rob

[Tim B]

It seems to me that there are two ways to do this...

Firstly, you could 'scan' the model itself with a laser (or non-contact) measuring device supported from a carriage moving in two axis. If you have a milling machine this is possible... It's not cheap.

Secondly, you can find a couple of bits of aluminium (15mm x 6mm) bar (must be straight), a few variable resistors and basically build yourself a digitizer. you can do this with as many axis as you're heart desires but 2 axis are needed for plans and at least three are needed for taking points from models. Please see:

Paper plans to computer-plotted?

particularly my posts which tell you how to build such a machine... to add a third axis, just mount the variable resistor currently next to the counter-weight on a platform connected to another variable resistor. (so one gives angle and the other gives direction). Connect the variable resistors to a few cheap multimeters (one side and centre pin to the meter) and measure the resistance as you move the arm. The angle is then defined as R/range. With a little bit of maths you can work out the position of the end of the needle.

Of course, you could be really clever and feed the resistance into an 555 astable (check web for details), thus producing a position dependant pulse. This can be fed into a home computer via the parallel port and all the maths may be done internal to the computer. I can supply circuit diagrams or more detailed mechanical diagrams if necessary. I can also help with programming in BBC Basic (for RiscOS), QBasic (for PC), or C (PC/Linux/Mac).

If you want more information on this please e-mail me at Tim@MarineDesign.tk and I will do what I can to help.
at it's simplest it should not cost more than 25euros (including multi-meters).

All the best,

Tim Brocklehurst.

nb. you can, of course, use a 3 axis digitiser to digitise 2d plans. Also, if you run the system on computer, you can use it to tell you the current needle position in any scaling. so you can use it to work in real/model/drawing units.

[Tim B]

Ok, I just did a quick pricing from the Maplin catalogue. and the full PC version (electronics only) comes to £12.38 (+ signal wire).
The price of the aluminium parts will depend on where you get them or who you know.This pricing assumes that power can be taken from the parallel port itself. This is ok for a signal level project like this but should not be used otherwise. You could always use a normal plug-type power supply like you get for portable CD players. and use a preset variable resistor to reduce the input voltage to 5volts.

Of course, this will take time to build and write the software for, but it might be useful.

Cheers,

Tim Brocklehurst

[duluthboats]

The Faro arm would be a good choice. The company will be able to tell you who has one in your area. Also most large machine shops and some factories have coordinate measuring machines, (CMM’s) large enough to do the job. Both will give you digital information you can use to draw the stations in some CAD software.

Gary

[Chris Krumm]

SInce you've drawn the whole thing by hand, and have built the model by hand, why not stick with simialr technology? Flip the model over, level it to a reference waterline and make a little fixture with a tracing arm and a pencil to transcribe section cuts to paper. You'd have it built and the job done before you could finish researching available resources for a 3d digitizer.

And then if you still need a digital fix, take offsets from your paper drawings and run the design through a boat design program to fair the hull and run hydrostatics.

Chris Krumm

[ludesign]

Originally Posted by simone

My question, finally; Is there a tool out there to scan my smooth hull (built in plywood stations and beech strips) back into stations, to enlarge them to a full scale mold for my coldbaked lady (without spending a fortune, that is) ? Best regards Simone

An alternative method may be to use background images and a set of marker lines on the skin. In TouchCAD you can import in-scale high resolution background images that follows the model when you zoom and pan and you can have separate images for the Front, Top and Side views. It does generate a certain degree of error caused by the perspective but I have still found it to very useful. The image shows how to model based on two or three background images, using the built in image processing features to reduce the perspective effect, and a practical example where I needed to cross check the displacement of a boat relative to the drawings.

More info at: www.touchcad.com

[simone]

Yes, Chris. I`ve though of that oldfashion option, but I reccon that in the end I need a pc-program to do the math to upscale it anyway, so I don`t end up with stations with 5mm pensil-lines, and then the inaccuracy of that. Partly the idea of spending so much time on my model (except for it beeing a trophy in the end and the love of sawdust), is to be nearly done with the lofting. The pc program will off course also assist me when I get to the interior and the making of all curved panels for it. Up to this point I`ve been old-fashion, but I guess its time for some numbercrunshing to upscale the model, and also to run some hydrostatics as You point out. If I go for the manual option, how many stations would be optimum to run in a program (bear in mind that the hull look very smooth on the model, with progressively changing curvature everywhere). Best regards Simone

[Chris Krumm]

Simone -
I'm not implying you shouldn't use a computer to fair your lines, run hydrostatics, and ultimately to create templates and detailed construcution drawings. I would do that as well.

I prefer to start with a deck plan, profile, and a couple sections with pencil and vellum at a generous scale (typically 1/8 full scale for a hull in the 18'-24' range). After that it's into New Wave Systems ProBasic for fairing and hydrostatics, and then exported as IGES to CADKEY for detailed modeling and layout drawing. Templates for moulds, bulkheads, and all sorts of parts are plotted full size right from Cadkey during construction. I've used this approach for several sea kayaks, a 20' inboard electric launch, a 20' inboard electric proa, and am using it for a 24' trailerable trimaran design.

It looks like you are a careful worker. I daresay you could pull manual templates from your 1/7 scale model using a .3mm lead, scale offsets from them, and get all that into the computer with sufficient accuracy to make a quick job of fairing. For about $3000 - $15,000 less than the cost of a 3D digitizing arm. The number of stations you pick up probably could be on order of 7-9, inclusive of transom and stem profile. Remember the simpler your NURBS net can be to accurately capture the shape of your model, the better. Generally, you'll need more points in areas of greater curvature, and for sure you need to get points at any knuckles (cusps).

Points for a NURBS net shouldn't necessarily be taken at the regular waterline, station, and buttock intervals typical for traditional yacht design and lofting - you'll get a better net if the points allow you to form a nicely proportioned net of isoparms. Play with just about any NURBS hull design program and you'll se what I mean. I'm sure others in this forum have experience with this and could describe the process better.

Good luck with your design - it looks like a fun project.

Chris Krumm

[Tim B]

just out of interest... how do you make a digitising arm cost in excess of $15,000 ? I can believe maybe $500 tops plus a profit margin.

Tim B

[simone]

Thank You for sharing, Tim. You are probably correct on the price if one build it by oneself. I reccon some precise maching for the joints are required to keep it true and reliable ?! I would like to make one, but then I need help with plans for the wiring and also a program to run the math ! (My experience with gadgets are solely as a user, not as a constructor!) But I need one, and would always like to learn how. Could You assist further ? Best regards Simone
PS. I only need a digitalizer to read this model, not to start compeeting with Faro !

[duluthboats]

As one who attempted to design and build an inexpensive digitizing arm with a group, I can tell you the expensive part is high resolution encoders. The smallest of errors is multiplied by the length of the arm, and compounded by the number of joints. The Faro arm has 5 or 6 joints, some with a reach of 10 feet and accuracy of .0005 of an inch. The arm I was working on would have had 4 joints a 3 foot reach and an accuracy of about .020 of an inch. This would have required some custom machining and electronics.

Gary