SPOT Hack files

There is a PDF for the schematic but the board design will need to be brought up in Kicad.

Everything supplied is as-is.  No guarantees, no responsibility if it burns your house down, no apologies for missing documentation.

For those of you who use Google Earth, you can see the Elk Lake Course
here.

2 pieces of 3/16″ (5mm) acrylic getting mounted on SolarCrawler^® -  22″ x 13″ ’semi-circle’ over the bow, and 22″ x 18″ piece over the stern.  I’m concerned about the weight of all this acrylic (feels like maybe 3-4 pounds) but I wouldn’t want to risk anything thinner in terms of durability.

8 of the Pitsco solar panels will be mounted on the stern portion of the acrylic.  the 9th will be on the bow, this still leaves enough space for the GPS and SPOT device to have a clear view of the sky.  In fact I may try and sneak a few more solar panels around the bow, I saw some decent 3v 60mm square panels for sale in the latest issue of “Nuts and Volts” from allelectronics.com that I think I’ll order up — every little bit of power helps!!

1. Because GPS is CPU intensive and critical to what we’re doing, we encapsulated the GPS navigation onto a separate board.  This handles everything including reading the NMEA stream and calculating the destination bearing and distance to destination.  It’s got an I2C interface and was recently used in the Sparkfun Autonomous Vehicle Competition for our modified RC car.  Unfortunately we did not win, but it wasn’t because of the GPS navigation.  What’s that?  Can you buy one of these?  Well in fact, yes.  We had a bunch made and you buy them here.
2. Due to an unfortunate accident (I would like to say it’s not my fault, but you can judge for yourself (click)) I lost my laptop in the name of GPS research.
3. Most recently, we’ve taken the brushless motor driver that we built from scratch (see below) and have built an I2C interface to it.  Each modified CD ROM motor will have its own controller and a distinct I2C address.  We will be able to give each motor its own address and RPM feedback.  That will let us implement the redundancy that we want (4 motors in case 1 or 2 go belly up).

The kits are made from CDROM motors and customized parts. Usually, these are used for home-built RC planes so we had to experiment quite a bit using thin wire and lots of winds. It was then that we found out that commercial brushless motor controllers wouldn’t work at low current draw so we built our own.

The magic formula is (and this is the result of easily a month of investigation so please at least pretend like you’re excited) 100 turns of 38 gauge magnet wire. That’s specific and tuned to our purpose: high pitch, 2 bladed, 2 inch prop underwater running at 100% duty cycle. 38 gauge wire is about twice as thick as human hair (Science Nerd measured it).

I would post a picture, it would look a lot like any other failed attempt (blog Aug 6th entry).

We have tried about 30 different motor / prop configurations and we still haven’t gotten better than about 15 grams of thrust.   Ever hear that expression, “you just can’t buy that”?  Well when it comes to GPS guided, autonomous, solar powered boats, you just can’t buy that.  You also can’t buy the parts that go in them.  Try it.  Go down to a hobby place, or Ebay or whatever and try to purchase a motor that will push a prop under water at over 15 grams of thrust with 200 mA.  You won’t find it.

 We figure our best option is to wind our own brushless motors with a very low KV value (thin wire, lots of turns).  We thought we could use off-the-shelf brushless motor controllers, but no, they are built to control RC airplanes, not low current water props.  So, we need to design our own brushless motor controllers to drive these low current brushless motors efficiently.

I never thought we’d get this deep.  Also, I burned my thumb today really badly on a mosfet that got super hot trying one of the configurations.  Try winding a 500 turn brushless motor with a blister on your thumb.