Author Topic: Nyx marine robot and his solar challenges  (Read 2477 times)

SlipperySeal

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Nyx marine robot and his solar challenges
« on: October 29, 2015, 05:08:25 AM »
I have really been enjoying the videos. Iv been refreshing my electronics knowledge (with lots of ďgee, i didnít know thatĒ and ďso thatís why that happensĒ moments).  I wanted to share a little project of mine an ask if anyone had any advise about the solar system.

This is my marine robot, Nyx.  Nyx 1 was a solar panel on wheels. Nyx 2 is my prototype of a marine exploration robot and Nyx 3 will be a bigger better version which will hopefully be able to swim long distances.

https://twitter.com/NyxRobot

https://www.youtube.com/watch?v=nUwcMUmB27I



The electronics are a Raspberry Pi A+, GPS module, compass, 4G internet and HD camera. This all uses very little power, measured in the hundreds of milliamps. But the propulsion is from 2 Blue Robotics T100 marine thrusters.  They are rated up to about 130 watts each (admittedly, this is where they are least efficient).  Iím looking to build a solar system which is as efficient as i can make it.  The system on Nyx 2 is a 40 watt marine panel, a small simple charge controller and a very small battery. In fact, Iím surprised iv been able to drive the thrusters as fast as I have with this. In the video they are at about 50% power and the ESC claims they draw about 5 amps each.  But at the end of the day, Iím trying to build a small system that delivers as much power as possible. And then Nyx will regulate his thruster speeds to accommodate that.

Iím thinking i need to build all the electronics under the panel and use a 80-100 watt panel on a board which is perhaps a little longer - up to the length of a surfboard.

The electronics require a 5 volt supply. I was thinking a simple regulator, perhaps with a large capacitor to help protect against brown out of the thrusters spike the load.

Iíll need a MPPT charge controller and it would be as small as possible. My concern with running the load directly across the battery is, how would thrusters drawing lots of current effect voltage and battery charging, if voltage drops below 14 volts? Iv noticed that some charge controllers have the separate load connection, but will cut the load to protect the battery. Thatís the worst case scenario for me. If the CPU loses power itís game over :)  I could use a voltage divider and an ADC so the software can keen an eye on the panel and battery voltages.

And then thereís the batteries. The lighter and more compact they are the more i can use. But on the other side of that, Nyx 3 will need a keel - to keep it upright and to help it maintain forward momentum. So i was thinking of building the batteries into a keel. So they weight would be useful, up to a point.

The thrusters are rated to 30 volts. Iím using 12 volts, but maybe there is a case for a 24 volt system?

The goal would be that it could remain constantly in motion, traveling at speed during the day. Slower overnight, based on battery levels, or just hold position if power it too low.

Anyway, lots of challenges. But lots of fun. :)

SeanB

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Re: Nyx marine robot and his solar challenges
« Reply #1 on: October 29, 2015, 12:18:46 PM »
Very nice video there, and a nice thought as well. Batteries you probably will want to use lithium cells, and use a BMS that will look after the batteries. A good start is to look up Electrodacus on the forum, as he has designed his own open source BMS which will handle those cells and run off solar power, while also having low standby power use as well. You probably could fit the board into your system with ease.

http://mjlorton.com/forum/index.php?topic=598.msg4133#msg4133

His solar controller is very nice, and will handle the cell charging and balancing as well, along with giving you a load terminal which will drive the motors, and you can even power the other stuff off the board itself, as it is low power and there is on board voltage supplies for that.

http://electrodacus.com/

That will allow you to see his design, and as it is open source it is very nice. While it is massive the basic design will show you what is possible, and this can easily be scaled down smaller and lower power ( though you can keep the existing MOSFETS and use a smaller heatsink or just the bare board at 200W of motor) and the MCU can interface to your existing setup.

SlipperySeal

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Re: Nyx marine robot and his solar challenges
« Reply #2 on: October 29, 2015, 09:45:13 PM »
Thanks for your response Sean. This is exactly the kind of insight i was hoping to receive. :) I suspected that lithium batteries would be the way to go but knew they required special care.