To Qi, or not to Qi, that is the question (that was actually)

About Wireless Power Transmission

Because we wanted to create a design centered around aesthetic for our device, we chose to implement wireless charging for our battery.

There are plenty of ways to implement WPT. First of all there is near-field power transmission and far-field power transmission.

For our project, we will focus on a near-field power transmission. In this field, one of the most common technique is inductive coupling. But it is not the only one : capacitive coupling is an interesting technique for our project.

Capacitive coupling VS inductive coupling

Because inductive coupling is based on converting AC current to a magnetic field, there is a high risk that it will cause strong interferences and perturbations with the magnetic fields of the marbles, thus complicating our control over our device.… Read more

Weird flex but okay

The issue of centrifugal force

When you try to rotate at a relatively high speed, centrifugal force comes with the territory. The issue is that PCBs are not the most robust pieces in a mechanical system. We need to find a way to make them stronger to hold them in place so they don’t fly away and/or break and find their way into a bystander’s face.

We tried to figure out how much the PCBs would flex. Thankfully, Wikipedia exists and our problem is a classic strength of material case. We have an issue similar to beam theory’s cantilever beam case with a spread out force.… Read more

A first look at the FPGA architecture

In order to synchronize the LEDs and create a persistence of vision image, we use a CycloneV SOC.

Here is a first idea of the architecture we might use :

The ARM processor fills a buffer with the next image to be displayed, that is then swapped with the second buffer. It can pull this image from the SD card, or from another source such as the text printing function we plan on adding.

The full buffer is then accessed by a Direct Memory Access (DMA) IP that then sends the relevant cylinder (32 * 128 pixels) to each LED band controller that is then stored in their memory.… Read more

Going back and forth the H-Bridge

We need to be able to drive our little magnet marbles and flip them according to a magnetic field direction or the opposite one. To do so current must be able to flow both ways through our self-inductances. Moreover we’re going to need current’s intensity of a much higher value than what is able to flow out of or flow in the GPIO.

One way to do so, is to use a H-Bridge as we can see on this site that we’ve already mentionned in an earlier post.

What’s an H-Bridge

Basically an H-Bridge is a electronic circuit built with drivable switches in a way that allows us to flip the voltage on a load and thus allows us to flip current polarity.… Read more

Wireless power transmission and Motor choice

Power Transmission choices and explanation

As referenced in a previous post we need a way to wirelessly transfer power from the static part to the rotating part of our system. We found a 200W dev kit from Würth Elektronik but it seemed over-powered for our needs. Another integrated solution exists but is only good for 60W. Therefore we needed to estimate how much power our rotating system would need.

The bulk of our needs is in the LEDs. Considering 1280 LEDs and a multiplexing factor of 1:4, we would consume at most the power of 320 LEDs at a time. According to the specifications, an LED could use 60mA@3.3V… Read more

LitSimulate

LitSimulate is a simulator which simulates what LitSpin will display. We developed the first versions with PyOpenGL and PyGame.

Image Format

Each 3D image is represented by a classical image. If we note r the radial resolution (total number of columns), h the number of LEDs by column and n the number of steps by rotation, our image dimensions are rh x n. In our case r=20, h=32 and n=128. So we have 640×128. One line represents the n points one led will display. And each block of h lines represents the 360° image of a column from the outermost to the innermost (from 1 to r).… Read more

Choosing our components: “We are dwarfs on the shoulders of giants”

For our project, we need to test our components in order to find the best way to control our marble. Good news, our project has been done in other ways before. That’s why we take a look at this webpage: https://wiki.fuz.re/doku.php?id=projets:datapaulette:1bit_textile (in French)

Diameter of the marbles

Our first idea was to choose the smaller marbles, which have a diameter of 5mm. I have some of these marbles at home, so I tried to make a prototype with some cardboard.

Conclusion: my biggest fear was that a marble would move the other marbles when we rolled it (because of a too big magnetic field), but with my prototype, they don’t.… Read more

Gobal architecture for LitSpin

In order to better understand how to make LitSpin a coherent and functionnal device, we created a diagram of its architecture .

The following represents how the different modules will communicate and work together. Technical details will come later as choices in components and communication buses are made. This is not supposed to be a drawing so it is not representative of how LitSpin will look but it should give an idea of how it will work.

Basically, there will be two main systems. A static system that will have an electric motor and what is needed to control it : a control board that will communicate with an Electronic Speed Controller, the accompanying BLDC motor, an IR receiver that will get information from the rotating system and the induction power transmitter.… Read more

About LEDs

First ideas

Our original idea was to place LEDs on the inner sphere of the sculpture, either with flex PCB, or by drilling the sphere, placing the LED in the holes and connecting them with wires to a rotating PCB contained into the sphere. To facilitate the positioning of the LEDs, we could have modified the design so that we can pin the petals one by one on the inner sphere rather than print everything in one block.

But these designs are not easily achievable. First, Alexis does not know how to design flex PCBs. Second, to have a satisfactory visual impression, we would like to have at least 100 petals.… Read more

Generating 3D Models

TL;DR

  • We need to generate 3D models of phyllotactic patterns.
  • We give an explanation of how to generate phyllotactic patterns on a sphere.
  • We present an issue we encountered, and the solution we found.

Why 3D Models ?

When we first started thinking about the project, we quickly realized we would need to generate 3D models of the sculpture ourselves.

First because we need to have full control on the model, to try various configurations for the future 3D printed sculpture. And second because it will greatly help us visualize all the kinds of animations we are imagining.

Accordingly, Vlaya wrote a script using the blender python API to generate a 3D model, following John Edmark’s online explanation.Read more