Going all out on the 3D

As mentionned here, we will use 62 LED mounted small “Petal-PCBs” and 12 “processor PCBs” to drive groups of 4 to 7 Petal PCBs. Now you might be asking “how on earth will you assemble all these PCBs and solder all the wires involved on a structure rotating at 30 rotations per second ?”, and that would be a fair question…

Along our reflexion we had multiple ideas:

  • Add structure to our 3D printed shell on which to stick the PCB: we had to drop that idea after all the problems we encountered printing our shell
  • Make the axis go all the way up and have arms stretching from the axis to hold the PCBs: this would’ve made the structure quite heavy, and we were not sure how to design this
  • Make the PCB hold by using rigide wires to link them: This was initially proposed only for the PCB-petals, but even for them we were not convinced it would hold
  • Print another solid shell with structure to hold all the PCBs: this was problematic since it might delay or block the IR emitted by the IR LEDs we wanted to place inside the shell

Finally, we decided on the latter option, as we will probably have the IR LEDs emit in a gap between the PVC plate and the large aluminum top platform.

Designing a structure to hold all the PCBs is far from an easy task, especially since we will have many wires between the PCBs : 6 wires from each PCB petal to it’s processor PCB, SPI buses between the PCB processors, and VCC and mass wires coming from the rotating PCB at the middle.

The difficulty also lies in the irregular placing of the PCBs : the phyllotaxic geometry of the shell meant we had to place the PCBs in an irregular way in orderd to maximize their size.

However, printing it shouldn’t be too much of a problem since the structure can be thick, and we don’t really care about the aesthetics (these two factors were the main problem with printing the shell).

I first design a structure on which we could insert the processor PCBs:

The final structure will have a hole at the top since there is a top PCB, and maybe on the sides

The idea here is to solder all the wired need on each processor PCB, and then insert the wires in the holes made for them, and then insert the PCB in the structure. As you can see, the structure has a place for each PCB which perfectly fits its shape.

For each PCB petals, I plan to add a structure mounted with 4 legs on the above structure so we can have space to move the wires around:

All of this will be part of the same structure, and printed all at once. The idea is to grab with pliers the 6 wires hanging out of the holes close to the processor PCB and make them go through the hole made for the PCB petal. The wires will be longer than needed, so that we can have a gap between the 3D structure and the PCB petals to make the soldering easier. Once the soldering is done we can just fit the PCB petal in it’s designed spot, as with the processor PCB, and let the wires toss themselves in the large gap there is.

We will probably add glue or blu tack to the PCBs once they are fitted in their spot, this should make everything hold quite tightly.

Here is what it should look, with the PCBs in green, and the shell in transparent white:

The circles you see on the PCB Petals correspond to the positions of the pads (although the pads are of course on the other side), and the blocks correspond to the LE RTDUW LEDs.

As usual for all the 3D work, this was done using Blender, making mainly use of the boolean modifier, the python API to place the petal PCB and structures in a phyllotaxic way, and the remesh modifier to have a clean model at the end since the boolean modifier can make things quite messy.

There is still a lot of work left before printing it, but I will keep you updated.

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