Blog:Almabraxas

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Almabraxas blog and engineering notes.

2017-05-01 resulting PCB

I added a TMP 36 probe in the process to have the on-board (capsule) temperature, as opposed to the BMP 180 giving the OAT (Outside Air Temperature).

Almabraxas-2-10-v2 pcb.png

2017-04-16 Designing the PCB

I'm using Fritzing by the way. I like its ability to describe physically the breadboard, so when capturing schematics, I first capture the breadboard, and then arrange the schematics. This is one more step than capturing schematics (or say half a step, since components and relations between them are captured already), but I found it less error prone than going directly from the breadboard to the schematics. Furthermore, laying out the schematics is an additional chance to catch a missing resistor or two.

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2017-02-11 RockBlock 1 wiring with an eye on RockBlock 2

A comparison of RockBlock 1 and RockBlock 2 wirings.

Signal Description Rockblock 1 RockBlock 2 RB 2, separate connectors
- Do not connect 1
5V 5V Power supply 2 4 A4 (as Vcc)
8 B2 (as 5v In)
TX Iridium 9602 TX 3 3 A3
RX Iridium 9602 RX 4 2 A2
CTS Iridium 9602 CTS 5 5 A5
RTS Iridium 9602 RTS 6 1 A1
SLEEP Iridium 9602 On/Off control 7 12 B6 (as OnOff)
RING Ring Indicator 8 10 B4 (as RI)
NET Network available 9 11 B5 (as NetAv)
GND Ground 10 6 A6
7 B1
14 B8
5v Out 5V regulated output, for powering external Arduino host 9 B3
LiIon 3.7V Li-Ion power supply 13 B7

2016-11-12 back to Afro ESC (for 22V operations) + feedback frequency

The basic Afro ESC doesn't support enough voltage for my needs (the solar panel can deliver as much as 22V). I tried the Spider ESC, but it doesn't support reverse and I can't flash it (furthermore, it's a bit too hot for my taste). Luckily, there's a "high voltage" (8s) version of the afro ESC, astutely named afro_hv. I got one of these, but it ships without reverse_pulse, that is the ability to go forward and backward, enabled. So I had to flash it, which was very easy using RapidFlash and the AfroESC USB programmer.

On a totally different matter, I tried several frequency for the power sampling loop, and after a few problems and Fourier transforms, I settled on a 1kHz frequency: I'm using an ACS 712 based breakout for current measurement and a voltage divider vor voltage measurement. I had a very unstable measurement with the motor running, that I first thought was provoked by uncontrolled noise (magnetic ?) around the ACS 712. However, when calibrating with a resistor, I had a very stable measurement, thus leading to the evidence that the "noise" is actually the commutation of power inside the ESC / motor pair. I sampled at different frequencies, and got something stable around 1kHz (initially, I was using 10Hz...), which coincidentally is the sampling frequency of the ESC.


2016-08-02 They did it !

Seacharger crossed the Pacific Ocean from California to Hawai. Clic here to read everything about this great achievement.

2016-07-16 30cm linear servo (actuator) driven by arduino nano + H-bridge

Video: https://www.youtube.com/watch?v=ibmTeS0C4S4

For the Almabraxas boat, I dropped the idea of using a rudder in favor of a differential thruster system, because I think the rudder control mecanism is too complex, both from the mechanical and waterproofing point of view. However, since I had selected some components, I built a control card, just for training. We can see the result is quite simple.

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2016-07-06 1st solar powered test

Video: https://youtu.be/DCFKpQhoYAs

Some thoughts and observations after a first run

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2016-06-26 T200 thruster run video

2016-05-19 Need for a UVLO

I gave a first shot at prototyping with a teensy, R78 for power regulation, an Attopilot voltage + current sensor and an Olimex LCD display, everything powered by a 100W polycrystalline solar panel (some pictures to come).

I had first naively assumed that I wouldn't need a UVLO (remember that the whole idea is to have no battery, no sun = no power), but I realize this is not a realistic proposition, since each circuit has a different undervoltage sensitivity, I can't assume they would shut down and (mainly) reboot gracefully when power is restored if this isn't done in a controlled way.

For the same reason, most likely, some circuits will be reset on a regular basis.

2015-10-31 One of the solar panels

It's about 100x70 cm, weight about 9 kg (although it feels lighter when I carry it). It's a polycristallin one, and graded 100Wc for a cost of 99 €. Connectors are MC4. It's encased in aluminium, and the box is "bad weather" grade, although I doubt very much it's "underwater" grade, so something will have to be done here.

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2015-10-11 We got a T200

20151011 110743 2.jpg

2015-08-10 description of the computer

The on-board computer as of 2015, July the 20th (click to get a full-size image).

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2015-08-09 More on the boat:: thrusters and solar power


For now, I'm looking at Blue Robotics T200 thrusters.

The thruster should reverse its sense of rotation on a regular basis.

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2015-08-09 More on the boat:: the hull

My thoughts have oscillated between two shapes / materials: a styrofoam torpedo shaped boat, or a catamaran.

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2015-07-27 GPS altitude bug solved

The altitude is taken from the GPGGA GPS message, and the on-board computer was using field 10 (altitude of geoid above mean sea level) instead of device altitude (field 8).


2015-07-21 In-flight field test

I've taken advantage of my training flight yesterday (I try to fly once a week) to take the on-board computer with me. Here's the run.

And yet another lesson learned from this test (the more you test, the more you get something): the GPS altitude doesn't make its way to the data server ! I haven't found the bug yet, the code seems ok in the MCU.


2015-07-20 First field test

The run can be seen here.

I took a tour from my house to the office, through bus, railway and so on.

Two lessons learned:

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2015-07-07 More on the telemetry center

Although I haven't posted anything here for several weeks, that doesn't mean that nothing happened. Much has been done on the telemetry panel. Most of the data are displayed. Time series are pulled (so you can start at any time and get all the history). Some work is still needed so that several "missions" can be displayed. The display is done using google maps javascript API, canvasJS for the time-series data, and handcrafted javascript to glue everything (there's a bit of jquery also).

Speed and vertical speed are computed on the web server side using the GPS coordinates, time and python geopy for the distance computation (which implements the Vincenty formulae).

2015-07-04 Long outside battery running test

On the on-board computer side, almost everyhting is ready, but the resilient-to-something-stop-working is still to do. I'm still considering using ChibiOS (the alternative being using various libraries with timeout in all the serial / I2C / SPI communications). But then, I would rather compile from the command line, and although having tried many (arscons, sonsduino, ino), I still haven't found a make or scons approach that allows the easy compilation of the zillions of files necessary.

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2015-06-23 Fixed GPS value encoding for telemetry transmission

I had stupidly assumed the values from the GPS were decimal while they really are DDmm.


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