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[DPRG] Autonomous Flying Robots

Subject: [DPRG] Autonomous Flying Robots
From: Ed Okerson ed at okerson.com
Date: Thu Sep 20 19:42:06 CDT 2007

Yes, the fans are independently controlled, and it can hover.  The real
aircraft used a rotary engine mounted in the back, so it had to have
variable pitch props.  The model will have a brushless DC motor in each
duct.

Ed

> I have never seen that unique aircraft before, thanks for sharing.
> Do the fans articulate independently?  (I imagine that would be
> needed for hovering yaw control, assuming hovering is a capability.)
>
> !!Dean
>
> On Sep 20, 2007, at 17:26 , Ed Okerson wrote:
>
>> The one I am building is a 1/5th scale model of this aircraft:
>>
>> http://en.wikipedia.org/wiki/Trek_Aerospace_Dragonfly
>>
>> It is nearly complete, and hopefully will be flying soon.
>>
>> Ed Okerson
>>
>>> Saw this today:
>>> http://blog.wired.com/defense/2007/09/british-polices.html
>>>
>>> There's a whole sub-industry out there building these things.  I'd
>>> be up
>>> for trying one as well.  Silicon Sensing has a nice IMU out that
>>> looks
>>> promising for stability control.
>>>
>>> Though, I've long thought of doing it something like this:
>>> http://en.wikipedia.org/wiki/Avrocar_(aircraft) or this:
>>> http://en.wikipedia.org/wiki/M200G_Volantor
>>>
>>>
>>> -----Original Message-----
>>> From: dpa [mailto:dpa at io.isem.smu.edu]
>>> Sent: Sunday, September 09, 2007 1:38 PM
>>> To: dprglist at dprg.org
>>> Subject: [DPRG] Autonomous Flying Robots
>>>
>>> Howdy,
>>>
>>> Last March I bought my oldest son Stephen a small R/C helicopter
>>> for his
>>> birthday.  It is a Blade CX, which features a pair of counter-
>>> rotating
>>> blades that cancel out the torque on the airframe:
>>>
>>> <http://www.e-fliterc.com/Products/Default.aspx?ProdID=EFLH1200>
>>>
>>> and we had a lot of fun learning to fly it.  Then he went back to
>>> college
>>> and took it with him, so I bought one for myself and flew it
>>> around the
>>> hallways at SMU for a few months.
>>>
>>> The counter-rotating coaxial blades make the heli very stable, but
>>> that
>>> turns out to be a disadvantage once you learn how to fly, as it
>>> greatly
>>> limits maneuverability.
>>>
>>> So last June I bought a TREX-450 for my own birthday, with a Spektrum
>>> DX7
>>> 2.4 GHz radio, and have spent the summer learning how to fly it:
>>>
>>> <http://www.rcuniverse.com/magazine/article_display.cfm?
>>> article_id=572>
>>>
>>> There are several interesting pieces of technology for robot builders
>>> here.
>>> It uses a brushless DC motor and speed controller with 2200 mAh 11.1v
>>> Lipo
>>> batteries.  These are extremely powerful motors with speed
>>> controllers
>>> that
>>> are somewhat like stepper controllers, some of which also have
>>> built in
>>> "governors" and some of which can also be reversed (see the ones
>>> used by
>>> the
>>> R/C boat people).  The governors evidently measure the motor's
>>> back EMF
>>> in
>>> order to maintain constant RPMs.  Nice.
>>>
>>> The 2.4 GHz radio is also very nice, little stumpy antenna and up
>>> to 40
>>> R/C
>>> devices can operate simultaneously, each using a pair of
>>> frequencies for
>>> data redundancy.  The radio actually has two receivers that are
>>> mounted
>>> orthogonally a few inches apart, each with two antennae.  (Which
>>> means
>>> no
>>> more "frequency pins," for those R/C'ers among us.)
>>>
>>> Another interesting feature is the use of the motor itself for audio
>>> feedback
>>> during the programming sequence of the speed controller.  The normal
>>> high-
>>> frequency PWM signal is modulated down in the audio range, around 200
>>> Hz,
>>> to produce beeps and melodic sequences without a speaker or piezo
>>> buzzer,
>>> using the motor itself as the "speaker."  Very clever.
>>>
>>> The heli uses 3 microprocessors, one in the speed controller, one for
>>> mixing the
>>> R/C signals, and one for the gyro that controls the tail rotor
>>> pitch --
>>> which they
>>> call a "heading hold" gyro -- that sits between the R/C receiver
>>> and the
>>> tail
>>> rotor servo.
>>>
>>> Here's a video of me learning to hover last June:
>>>
>>> <http://www.geology.smu.edu/~dpa-www/heli/
>>> first_hover_outdoors_m1.mpg>
>>>
>>> I'm a lot better than that now, and the "training gear" has come off
>>> since
>>> then.  Turns out that the hard part is learning to hover, to hold the
>>> heli
>>> in one place, and to do that in all orienations (especially "nose in"
>>> hovering
>>> with the nose of the heli pointed toward you --- I've gotten quite
>>> good
>>> at that this summer ;)
>>>
>>> Which brings me to the point of this post.  It appears that
>>> hovering the
>>> helicopter is very much analogous to the problem of balancing a
>>> two-wheel
>>> robot like nbot:
>>>
>>> <http://geology.heroy.smu.edu/~dpa-www/robo/nbot/>
>>>
>>> except in 3D, rather than 2D.  Here's the alogorithm for nBot's 2D
>>> balance:
>>>
>>> <http://geology.heroy.smu.edu/~dpa-www/robo/nbot/bal2.txt>
>>>
>>> Doing the same for an autonomous helicopter will require a 3D sensor
>>> rather
>>> than the sensor that nBot uses:
>>>
>>> <http://www.microstrain.com/fas-g.aspx>
>>>
>>> more like the 3D IMU that jBot uses for it's navigation:
>>>
>>> <http://www.microstrain.com/3dm-gx1.aspx>
>>>
>>> and the balance algorithm needs to be expanded to include 3 axis.
>>>
>>> For those familiar with the sourceforge autopilot project, this
>>> was the
>>> goal of
>>> that autonomous robot project and their home-brew IMU.  Those people
>>> went off and
>>> founded Rotomotion LLC, and now have several working prototypes.  Ed
>>> Okerson has some
>>> friends who also have developed a home-brew multi-axis IMU which they
>>> are currently
>>> flying on an experimental autonomous helicopter at Stanford, and have
>>> agreed to share
>>> the design and data with us if we will do the same for them.
>>>
>>> Here is one of Rotomotion's helis flying autonomously:
>>>
>>> <http://www.geology.smu.edu/~dpa-www/heli/SR20_R34_small.mov>
>>>
>>> The $16,000 seems a bit steep, but maybe I am underestimating the
>>> difficulty of the
>>> project (again!).  If my skill level continues to improve then
>>> maybe by
>>> Spring
>>> I'll feel confident enough to begin thinking about throwing a
>>> switch on
>>> the
>>> transmitter and letting the heli fly itself, confident that I can
>>> "catch" it
>>> when the software doesn't work.  That will be a little harder than it
>>> was with
>>> nBot, and a few rubber bumpers like on nBot will not be much use in a
>>> crash.  Still,
>>> I think I can do it... :)
>>>
>>> As you may remember, our friends out in Seattle (Larry Barello) have
>>> done some
>>> interesting work on autonomous flight with autonomous guided para
>>> sails:
>>>
>>> <http://www.paraflite.com/>
>>>
>>> which must solve some of the same problems, but not the specific
>>> hovering/balance
>>> problem.  There are also some infrared devices that attempt to
>>> balance
>>> the heli
>>> my measuring the differential radiation from the ground and the
>>> sky, but
>>> these
>>> suffer from a number of problems for a more general purpose robot.
>>>
>>> So, is anybody else in this debating society <grin> working on a
>>> flying
>>> robot,
>>> or interested in doing so?
>>>
>>> cheers,
>>> dpa
>>>
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>>
>>
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