A false sense of symmetry

Although our initial plan to light the petals was to put waveguides between the petals and LEDs placed on a flat rigid PCB (see “About LEDs“), Alexis recently told us using flexible PCBs might be possible.

Flexible PCBs could be placed directly on the inside of the demi-sphere of the sculpture, thus avoiding the use of waveguides and ensuring a good luminosity. Their drawbacks however includes a high cost and the fact that Alexis hasn’t yet used them for previous projects.

Using flexible PCBs, our idea would be to take advantage of the symmetry of the sculpture and place identical PCBs along each of the 13 spirals. On each PCB, we put LEDs corresponding each to a petal. There is one catch though: the spirals are all slightly different… Indeed, it is an important property of John Edmark’s sculpture to have each petal placed at a unique height and angle on the sphere, with a unique size. While this is great for fluid animations (see Generating 3D Models), it makes the placement of the LEDs on the PCB a bit of a headache…

LEDs placement

We decided to use a smaller version of our sculpture, with only 8 clockwise spirals and 13 anti-clockwise spirals (The previous images we showed you were of a 13 and 21 spiral model)

Ideally, we want each LED to be placed at the center of each petal. But using an identical LED placement on 13 different spirals will obviously introduce off-centered LEDs: our goal is to minimize this. In order to do this, I first aligned all of the spirals in the same orientation, and sorted them according to their lowest petal height:

The petals are getting in our way here, what we want is to just see the quadrilateral surrounding each petal.

We then need to flatten everything, it will makes things even clearer, and the PCB schematics needs to be done in 2D anyway.

The floor you see on this image is the actual floor of the pedestal on which the sculpture lies. You can see some petals are partly buried under the floor: they still need to be lighted for a fluid animation, but some are unfortunately too small to have LEDs placed underneath them. With this additional constraint in mind, I spent some time in blender figuring out the best LED placement, and this is the result:

LEDs are in red, their size is around 5mm on this image

Here is a superposition of the worst case spirals, which was also very helpful to design the placement:

Frustrating, isn’t it ?

Alexis is currently gathering information to assess the feasibility of flexible PCBs for our project, we will make sure to keep you updated on our final choice.

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