Ariane 5 launch table

[Hobbes-22]

To complement my Ariane 5 models, I'm building the launch table.

My starting point was the 1/96 paper kit, scaled to 1/125 to match the Heller Ariane 5 kit. I started converting this so I could build it in styrene:
- paper has no thickness, so a 1x1x1 cm cube consists of six 1x1 cm squares. If I build a cube from 1 mm thick styrene, I have to use two 10x10mm squares, two 8x10mm rectangles and two 8x8mm squares.
- the tabs used to glue the paper model together are not necessary.

This is fairly straightforward, so I soon had part of the design done and I could start cutting plastic for the base. 

The second part I tackled was the wheels. The launch table runs on rails, using 32 axles in a complex bogie arrangement. The paper model wasn't usable for this, so I started drawing new parts using photos as a reference.

I'm using photos like attachment 2 (found at capcomespace.net). I've got a known dimension (height of the Ariane 5 first stage). I scaled the photo until it matches this known dimension, and then anything else I measure is 1:1 with my model - if the photo is not distorted. The best photos for this techniques are the ones taken from far away. I usually use several photos and average the results.

Unfortunately, I soon found out that the paper model is inaccurate. The width of the launch table (left to right in this photo) was off by 20%. Heights were closer. This meant restarting from scratch, and discarding most of the work based on the paper model.

I've done most of the design for the base now, see Attachment 3 . These parts will be lasercut. Other parts (simple rectangles) will be cut manually.

For the rails and wheels I'm using TT scale (1:120) railway stuff.
I'm also building the truck that tows the launch table. This will not be to the same scale: I'm doing this in 1:87, H0 scale. Truck kits are readily available in H0, not so much in TT scale.

[Hobbes-22]

I'm working on the wheel sets at the moment. This is perhaps the most complex part of the project:
- parts of the structure are hidden in all of the photos I have, so I have to do some guesswork
- the scale of the model is small enough that the thickness of the material can get in the way. For structural parts I tend to use 1 mm thick styrene: that's 125 mm in the original. Most of the steel plates used are far thinner than that. For lasercutting, the lower limit at my supplier is 0.5 mm, but styrene gets rather flexible when it's that thin.
- it all has to fit the TT-scale railway axles I bought, and the rest of the model.

I haven't decided what to do about those springs. Each spring is 4 mm high and 2 mm in diameter in this scale. There are 4 rows of 4 springs in each of the 16 bogies, 256 in total, far too many to do by hand. Maybe I can 3D print them.

I'm drawing this in Adobe Illustrator. I started with a single bogie, got the side view done now. The front view is in progress, as is the yoke that connects 2 bogies.

The PDF is a file I sent out for lasercutting earlier this year, with the first iteration of the design, plus parts for another project. Black lines were cut, red markings were engraved.

[Hobbes-22]

I ran into an issue with the wheel sets: the measurements aren't adding up. I have to fit 4 bogies between the corners of the platform. When I create a bogie with the data I have available (set a scaled photo as the background, draw the design on top), it ends up far too wide (26 mm, when I have only 21 mm of space available). If I scale it down to 21 mm, the proportions are all off.
Part of the problem is that basically every photo is distorted: they're all made using wide-angle lenses to get the entire rocket in view, or they're taken from 1 km away and the wheel sets are so small you can't measure them reliably.

So now I'm trying to fettle the dimensions to make something that looks right, and fits in the space available. I'm also constrained by the wheels I have. I may resort to putting those on the lathe to reduce their diameter a bit, but at 64 wheels that's something I'd like to avoid.

I was able to confirm the major dimensions of the launch pad. In the Ariane 5 user guide, I found two top views of the launch table. These agree with the dimensions I measured on photos, so that raises confidence in the data.

[Hobbes-22]

I took a good look at the wheels. The flanges on the TT scale railway wheels are much higher than I need. So I can remove most of the flange and get wheels that look better, and I reduce the size of 4 bogies by about 4 mm. With some other fudges in the design I now have a workable compromise.

To take off those flanges, I made a jig that fits on the axle, between the wheels. This can be clamped in the lathe. I had to work very close to the chuck (about 1 mm of room between the chuck and the tool), but it works ok.
These wheel sets have one wheel sitting on a plastic spacer (to prevent shorting out the rails). This spacer was a bit loose on a few of the wheels: the tool pressure was enough to stop the wheel rotating, which meant I couldn't turn this wheel all the way down.