# [bouLED] A proto-demonstrator

## Early demonstrator

Since last post, all triangles have been soldered, including their power supplies. Getting them to work was a bit of a pain, since some LEDs got fried, so Alexis spent a lot of time replacing LEDs. Last Friday, we had to do a demo of our progress, and here’s a video of it:

There were five triangles we couldn’t use because they were missing a connector, but Alexis finished them this week-end.

The board Lucas is moving (far left) is the main board, with the AHRS array. The image is supposed to move to “counteract” the main board’s rotation: when it is inside, it would make the image static even when rotating the icosahedron.

Lucas used the projection algorithm he describes in this post, which works really well in my opinion. There’s still room for improvement, though: for instance, we haven’t figured the axes out yet. We’re also thinking about what to do in the final demo.

## Mechanical design

### Ranting time

There are holes in the triangles that allow us to bolt them to 3D-printed pieces. Hichem designed pieces for this in OpenSCAD to join triangles together at a shared corner, but the angles were off. We also tried using FreeCAD, but it was a huge pain to use, even for simple stuff like drawing pyramids. The problem was that when using OpenSCAD, there’s a lot of calculations to do, which are easy to get wrong, and in this case, it’s way simpler to use a constraint-based CAD package. Next, we tried FreeCAD, which was somewhere between “huge pain” and “nightmare” on the user-experience scale. Even for simple stuff like drawing pyramids, it was really unpleasant to work with, although I do concede that a) we’re not mechanical engineering students, b) we’re not familiar with mechanical CAD packages, and c) we didn’t have the time to learn FreeCAD properly (didn’t take it, either).

Enter SolveSpace. This one was a bit of a surprise: it’s a TINY (5.46MiB for the Arch package !) open-source constraint-based CAD package, as opposed to OpenSCAD which uses constructive solid geometry. Even though its UI doesn’t look very modern, SolveSpace very simple and intuitive to use, and what’s more, it doesn’t try to be as featureful as <proprietary CAD package everyone knows>: its simplicity is its best asset. There are some quirks (no loft operations, for instance) but there are often ways around them. All in all, I’m very impressed by SolveSpace: it’s a lesson in minimalism.

## A simple structure

I redesigned Hichem’s corner-piece using SolveSpace. It’s meant to join five triangles together at a corner. Here’s what it looks like:

There are hexagonal wells for the nuts. To house the electronics, I designed a plate and supports (yes, also bolted to the triangles). The supports will be glued on the plate. Here they are:

The notches in the plate are there to let the bolts protrude from the supports.

Finally, here’s a view of the whole structure:

The corner pieces have all been 3D printed as hollow pieces, which made them way faster to print, and they feel strong enough. We’ll have to laser-cut the plate once I finish its design (mostly figuring out where to put holes for velcro straps for the LiPo battery), print the supports (~20 minutes each, from my early experiments), and finally glue the supports and the plate together.

The insides look like this so far:

Way messier than the screenshots, huh ? The grey ribbons are for the SPI connections to the LEDs, and the other wires are for power. Soldering the wires to a proper power distribution board (i.e, a two-sided un-etched PCB) and shortening them will probably make this a bit more manageable.

## 2 Replies to “[bouLED] A proto-demonstrator”

1. Loki says:

Good job on the demo, it looks really cool!

About the cad package i’ve grown fan of https://www.onshape.com/, it has the same workflow as solidworks but it’s a web based tool (so no install required) and has an account model a bit like github, you can have a free account with public projects and also some private ones.

1. mrabault says:

Cheers !

i’ll keep Onshape in mind. I try to avoid non-free software though, but if open-source tools don’t do the trick for my next projects, I’ll check it out. Thanks for the tip !