6. September 2009 by Sean.

After trying many combinations of commercial brushed and brushless motors, we resorted to winding our own. I didn’t think this was feasible but came across this site: http://www.strongrcmotors.com/ Don, the proprietor, was very helpful and gave us some tips on winding a motor around our needs (as you’ve read many times, 200 mA draw, as much thrust as possible).

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).

Posted in Uncategorized | 8 Comments »

3. September 2009 by Sean.

because we’ve been busy winding brushless motors and designing motor controllers. 

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.

Posted in Electronics | 34 Comments »

3. September 2009 by gmoney.

I don’t know what my next project will be after the solar boat, but I do know it won’t involve fiberglass

Posted in Uncategorized | 3 Comments »