Hunting the Zero: 123D

Hello, and welcome to the chronicle of my first attempt to model anything seriously using Autodesk 123D, done while Bioshock Infinite is installing (ty James!).

123D has proven to be a steeper learning curve than expected - The model I chose features several complex prisms in it's construction, something that extrusions cannot effectively do in this package.  Then again, you need to select a reasonably challenging model to really test something like this. 

After what initially felt like coming adrift from that lovely £1m yacht called Solidworks in the Caribbean Sea, I have had some success modelling the bicycle rack outside my block of flats at Swansea University:

This is what the new age of model building looks like :)

This is just the part where the bikes are locked to, the roof is to follow.


I'll try to describe the method I use to get my curves correct:  First, have a picture handy of the side of your subject; mine wasn't straight so some perspective issues did happen, but the important thing is to measure at least part of the subject and use it to draw up a grid like so:

The base was 1000mm in length (thick black line), so I drew up a 3x3 grid using it in the indispensable Paint.NET

Set a zoom level for all the grid to be shown simultaneously (in my case 66%), and measure the grid line on your screen (73.5mm on my 1080p screen).  From this you can obtain measurements relative to the grid or otherwise by measuring the on screen subject, dividing by the measurement per-grid-line (as luck would have it for me, 1 metre irl = 73.5mm on screen); this will give you it's irl length, an approximation perhaps, but suitable for modelling.

If this still confuses you, I will give you a pictorial guide has to how I made a single support for the roof of the bike rack.

Tutorial:  How to obtain measurements using a photo and one measurement

We start by obtaining a length in whichever axis, x or y, is most suitable; for me this is a vertical component so I use the y axis coming from the baseplate up to where it joins the roof strut:

The lime-green box is the measurement tool, and the support in question is bounded by the box

Measuring on my screen, I get 134mm, so 134/73.5 = 1.823m = 1823.13mm irl.  I should mention at this time that I am modelling to O gauge, or 1:43 scale, so dividing by 43 gives a value of 42.40mm for use in my model:

Now we need to measure the distance from the bottom-left of the lime-green box to the centre of the support, since it does not start there.  Again, measurements on the screen give me 2.5mm, so 2.5/73.5 = 0.034m = 34.01mm irl; again this is divided by 43 to give 0.79mm.

Finally, we measure the line from the top-left of the lime-green...  you know what, I think you know the drill by now :)

Ready to receive arc...

Luckily, I know that the arc the support follows begins perpendicular to the support so I need not measure a middle point for a 3-point arc, I simply adjust my aim until the start of the arc is at a right angle to the grid.

Now we delete the right angled Construction lines to leave our arc; since the support has a circular cross-section of 0.93mm radius, we need to draw that and orient it to be perpendicular to the arc, use the "Sweep" Tool under construct to do this.

Final Verdict:  The MS Paint of 3d CAD

I eventually failed at making the roof of the bike shed, it could have been perspective issues in my photography, but I think the major reason is that precision is god-damn hard in this package.  In Solidworks, you have access to 3 planes right off the bat, that is to say you can start working vertically or horizontally both ways; additionally, solidworks creates a flow-chart of all your moves similar to Photoshop or Paint.NET, so error correction is a cinch - neither of these things are present in 123D, you have to model vertically and orient it when you are done, plus it really drags when you have to begin again all because you failed to measure accurately, causing systematic error which is something which should be easily correctable given how it has a cascading and predictable effect on your work.

So I feel my comparison to MS Paint is very apt:  it's fine if you just want to save a screen-cap from a program to post on facebook, just like 123D is fine for making a custom phone casing or a simple functional item you wish existed; but you try to paint "Fireworks at Chilcompton" with MS paint or make a scale model with 123D for that matter and things will get messy very quickly.

In closing, for anyone wanting to 'sperge out on your models, like I do, get Solidworks.  It will not leave you "Hunting the Zero".