3D Robotics Comment by Chris Anderson on August 28, 2011 at 7:35am

Brad: Many thanks for the background information and explanations, which really helps to put the project in context. My respect for you only grows!

(Just wear a proper full-face helmet next time, and you'll be my hero)

Comment by Nigel Conliffe on August 28, 2011 at 8:59am

But the important question is:  Will the kit be available through diydrones.com/store ?

 

I have to tell you Brad, I'd take it up for a flight.  Well done indeed :)

Comment by Denny Rowland on August 28, 2011 at 9:05am

I expect he renamed it POS-1 shortly afterwards.

Comment by Brad Hughey on August 28, 2011 at 9:54am

To address the technical questions popping up:

The MOSFETs were IR 1405s and 3907zs, which are being replaced by 4030s, all of which were obtained from reputable sources.  Technically, I am not employing "best practices" running the gate lines out that far without opto isolators and having as much as 12 feet of wire between the power source and the MOSFET drains.  But it was a compromise of using N-channel devices in a low-side controller while keeping complexity to a minimum...and yes, they are BRUSHED motors.  The venerable DeWalt 319080 cordless hammerdrill motors can take a beating like no hobby-class polyphase motor can at a price that's reasonable (that's why the combat robot guys swear by them).  I am on a budget here.:-) 

 

The APM is driving 4 standard brushed motor ESCs for the control zones (hey, why redesign the wheel?) and the PWM output is taken right off the gates of the ESCs and distributed to the thrust unit MOSFETs via IR 4427 gate drive chips, with each MOSFET gate having its own channel. 

 

The power source is comprised of 36 matching individual 3800 mAh 18C lithium polymer batteries of 10 cells each, yielding a 34 volt supply rail under load.  Given this capacity, I am estimating an out of ground effect hover (the least efficient flight mode) time of approximately 6 minutes.  And no, this is not a commercially-acceptable duration.  Production units will most certainly have a Rotax-like motor-generator set with a battery backup.  Lithium phosphate cells are a likely candidate for this application because they can dump their charge very quickly.

 

The rotors themselves are entirely my doing.  Each blade is 23 inches long.  The lower, counter-clockwise blades were hand-made using carbon fiber layups with a balsa filler.  They are the originals, and their Clark-Y airfoil section, chosen because of the flat, easy-to-fabricate underside, work the best IGE for some reason I have yet to fully understand.  The upper, clockwise blades are Martin Hepperle's MH-114 profile fabricated from polystyrene sections on an aluminum spar.  They are the 4th generation of blades used, and should be markedly superior to the Clark-Y blades just on lift vs. drag coefficients alone...but they're not, offering quite frustratingly similar performance (although much more consistent from unit to unit by virtue of not being hand-fabricated). 

The ground effect aerodynamics are both extremely complex and totally uncharted territory.  Regular helicopter pilots merely drop a little collective pitch IGE to take advantage of the increase in virtual angle of attack.  For reasons of minimal complexity and concomitant expense, I have avoided the temptation to incorporate variable pitch blades.

 

Thank you all for your support.

Comment by Brent on August 28, 2011 at 10:08am

Thanks for the writeup Brad, very interesting.
I read that Burt Rutan has also decide brushed motors will be on his electric design, less probability of catastrophic failures.

Moderator Comment by Morli on August 28, 2011 at 11:50am

Good Luck Brad,   I guess coming/hovering out of the home/car garage was part of the deal else you would have tested it else were :).  Keep it posted and Helmet pls , we want to hear about flight/s from you ..  Tnx for the feed backs too,

Comment by Sebastian Jensen on August 28, 2011 at 12:22pm

Too cool, your video reminds me of this: http://www.youtube.com/watch?v=-XpHE-tXFEc Sikorsky himself never wore any protection when test flying his rigs, only his hat.
Keep 'em coming.

Comment by ramboky on August 28, 2011 at 3:14pm

Thanks for the additional context Brad. I still think you're insane, though you clearly know what you're doing and are not reckless as I originally concluded.

 

Truly impressive work! 

Comment by Chuck on August 28, 2011 at 3:28pm

Good thing the Wright Brothers didn't have to listen to some of the comments in this thread.

 

 

 

Comment by ramboky on August 28, 2011 at 3:46pm

@Chuck the thread seems largely positive and supportive to me. With a few tongue-in-cheek wisecracks thrown in.

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