Live wire

Yesterday evening, the whole groupe work together to test the power transmission through the ball bearings. Those tests are significant to determine if we need to add a 5V-regulator on the main board, and which regulator we choose for the bottom PCB  to account for the tension drop.

Electrical setup

We had ordered the resistors (two 0.5Ohms/25W resistors and one 0.1Ohm, 30W)  described in this article and used them to build the following electrical setup:

The generator supplies 5V because we plan to use a 5V regulator on the bottom PCB and send 5V to the main board through the ball bearings. 

On the rotating part of the Phyllo, we need approximately 5A in average. 

By measuring the voltage over the 0.1 Ohm resistor, we can determine the current passing through the ball bearings.

We really had a hard time yesterday with the soldering : a few amps were enough to make the resistors really hot, which makes the tin fixating them melt, as well as burn the tape keeping them against the PVC plate. When we tried to hand-turn the PVC plate to ventilate and cool them, the VCC wire, soldered on a copper tube inside the ball bearing, kept disconnecting. 

We improved the setup this morning with Xavier, and we could finally run some proper tests without having to repair solderings every two minutes. We used some copper plates to better evacuate the heat of the resistors and a plastic collar to reduce the stress on the VCC wire soldering: 

Please keep in mind that the fixation of the black wire in the second picture is temporary: we will drill another hole in the PVC plate to avoid twisting it so much.

Results

With a 5V voltage source, only approximately 3.3A were circulating inside the circuit. 

By measuring the resistance of the different parts of the circuit with an ohm-meter, we got about 1.3Ohms for the entire setup (between A and E on the drawing at the beginning of the article), between 0.2Ohms and 0.5Ohms for the GND transmission (between B and C) and about 0.1 Ohms for VCC transmission (between D and E).

Here is a video of what we obtain on the oscilloscope, with the maximum, minimum and average voltage over the 0.1 Ohms resistor: 

Then, we tried to rise the voltage to reach a 5A transmission. At 7V, we had 5A transmitted in average :

Consequences

Regarding those results, we plan to use a voltage regulator able to deliver 8V on the bottom PCB, instead of the 5V-regulator in our initial idea. That means we’d need a 5V-regulator on the main board. However, merely using a 7V regulator on the bottom pcb (which according to our tests results in an average of 5A on the rotating part) in conjunction with the big capacitors on the main board might be enough.

We will discuss this with Alexis as soon as possible and keep you posted 🙂

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