Monday, February 11, 2013

CAD to real life - Part 4

The build is progressing well, an I apologise for getting behind on the blog, but I thought it might be neat to sum up some of the tricks I've been playing with in an attempt to keep the project on schedule. With a detailed Rhino model as a reference, it's been amazingly efficient to print or CNC cut templates for all sorts of jobs at 1:1, eliminating the need for double-handling of measurements and reducing the potential for certainty of operator error. If only you could make buildings this way, it would save all that time making 2d drawings from the 3d model, only to have them poorly re-interpreted back into a 3d building! Here we go from 3D model to 3D boat.

For a start, it has been fortunate that the Alpha hull is incredibly close to the original digital shape. John Gilmour did a nice job with the mould, and I guess would have used CNC to cut out the stations from his initial model. I'm benefiting from his hard work now, with the female moulded deck, foredeck and wing fairings mating onto it with only minor swearing and banging.

All the internal bulkheads were hand cut from carbon flat panel, guided by templates that I created in rhino using the 'section' command. I made an allowance in the drawing for the thickness of the shell, and just followed the line with the jigsaw. They all fitted perfectly first go after an  hour's work, a big time saver compared to the last boat.

To align the wingbars, a traditionally painful job, I cut a couple of templates from some scrap MDF on the CNC. They eliminated all the guess work in setting up the wings, it was almost too easy. You can see how perfectly the template mated to the CNC cut deck. In the end though when I eyeballed the wings, I decided that they needed to be a bit steeper, so I propped up the templates off the deck a bit to get that to work.  I guess it's always a bit of a surprise when you see the real thing having 'understood' it on the screen, and you have to trust that you can make judgements in real life too. I had to then adjust the CAD model to reflect those changes so that the tramps would still fit!

Another job that was painful last time was doing all the tube copings. There are coping calculators around that would have helped me before with the round tubes, but with a few foil sections in the mix, that becomes a bit problematic as well. The solution was to model the exact sections in Rhino, intersect them and the use the 'smash' command to unwrap the surface into a flat piece. Then you have a template that you can just print out, wrap around the tube and cut.

A few assorted pics below:









8 comments:

n4rkla said...

"Smash" should only be a last resort for unrolling surfaces. Better to use "Unrollsrf", particularly if the surface is developable.

n4rkla said...

Looking really good though. Can't wait to see you on the water again. Any dates set yet?

nick flutter said...

Cool, cheers Nick I'll give that a go. I have been using another one called 'squish' for non-developable surfaces, have you had any experience with that? It's a plugin. Seems to do an ok job, im counting on it because I have 'squished' my tramps, and those shapes will go straight to the sail plotter!

On the water in a month I reckon. I'm a couple of days off paint, but there are a few fiddly details still to do.

Bora Gulari said...

Why is there such a downward angle in the wingbars towards the back.?

nick flutter said...

Hey Bora,
in short it's an experiment in aerodynamics. It's supposed to reduce the angle of attack of the leeward wing when sailing upwind - to the apparent wind - and get the airflow to attach at lower side of the tramp. It's a bit of an experiment, but the CFD said (if you believe the results) that it should reduce the hull drag a bit. You have to look at it from the wind's eye view for it to make sense I think.

Unknown said...
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Simon Liddington said...

Hey Nick, the new boat looks great. Just saw this photo here (http://www.internationalmoth.co.uk/moth-news/mothies-at-the-bloody-mary/) and it seems the Mcguire Exocet has quite a bit of downward wing angle though I think its exaggerated in the photo byt the trim of the 2 boats.

intercad said...

What CAD software/Engineering software is used at University?

Solidworks 2012