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Gustav Jansson wrote:
> I'm working on a Lugnet page with more information on my helicopter but in
> the mean time, here are the photos:
>
> http://www.brickshelf.com/cgi-bin/gallery.cgi?f=28783
Ah - *many* thanks!
THe thing we couldn't understand was how you'd managed to make the
helicopter fly forwards and backwards. We'd assumed you had
some amazingly clever cyclic pitch adjustment in the rotor head
(which looks complicated enough to maybe do something like that
in the original photos). Now I realise that you are simply rotating
the support beam - we'd thought of that as a measure of last resort
but were hoping to find that you'd done something much cleverer.
> As you can see, I use a low-torque, hi-rpm motor with a non-lego rotor. The
> rotor, by the way, came from a cheap helicopter pull-toy.
My son has managed to make one (along similar lines to yours) that
uses only Lego parts. The motor is a standard geared Mindstorms motor
(we don't own one of the older style motors) with a 40t gear on the
motor and an 8t on the rotor shaft. The blades are the blue
translucent "insect wings" from the RDS set. We experimented with
two, three and four rotor designs and with different gear ratios -
but the more blades it has, the slower it spins because of the
increased load on the motor. In the end, it doesn't seem to matter
much - you get the same amount of lift with two faster spinning blades
as with three or four slower blades - so we settled on two to keep
things light and to simplify the rotor head. The 40:8 gearing is
also optimal.
The extra weight (compared to your non-lego solution) is something we
can deal with using appropriate counter-balance weights - but we are
rather tight on load carrying - if the helicopter is balanced
correctly so it'll take off *and* come back down again, there isn't
enough thrust left to lift much of a load. We can fix that by making
it 'neutrally' balanced - and throw the rotor into reverse to go down
but that's an ugly solution.
One 'feature' of using the insect wing rotors is that their pitch
angle is adjustable - we've been thinking about whether we could
build a swash-plate and drive the collective pitch of the rotors
instead of (or as well as) the RPM of the motor. Controlling the
cyclic pitch would also be cool - but I don't see how to do that
easily.
The counter-balance arrangements are similar to yours and the RCX is
driven with a Lego remote instead of a second RCX.
> Let me know if you have more questions about how it works, either I will
> answer them directly or I will include them in my eventual lugnet page.
What you have there explains a lot. Thanks!
---------------------------- Steve Baker -------------------------
HomeEmail: <sjbaker1@airmail.net> WorkEmail: <sjbaker@link.com>
HomePage : http://web2.airmail.net/sjbaker1
Projects : http://plib.sf.net http://tuxaqfh.sf.net
http://tuxkart.sf.net http://prettypoly.sf.net
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In lugnet.robotics, Steve Baker <sjbaker1@airmail.net> writes:
>
> Ah - *many* thanks!
You are welcome.
> My son has managed to make one (along similar lines to yours) that
> uses only Lego parts. The motor is a standard geared Mindstorms motor
> (we don't own one of the older style motors) with a 40t gear on the
> motor and an 8t on the rotor shaft. The blades are the blue
> translucent "insect wings" from the RDS set. We experimented with
> two, three and four rotor designs and with different gear ratios -
> but the more blades it has, the slower it spins because of the
> increased load on the motor. In the end, it doesn't seem to matter
> much - you get the same amount of lift with two faster spinning blades
> as with three or four slower blades - so we settled on two to keep
> things light and to simplify the rotor head. The 40:8 gearing is
> also optimal.
I did a fair amount of experimenting on the rotor blades. I also tried the
RDS insect wings (though I only had two) and I did have limited success. I
couldn't think up a way of mounting them that will keep them at a fixed
pitch and in the proper position. With my high rpm motor, if the blades
were not perfectly adjusted, it would shake horribly and produce very little
lift. If I managed to get the blades perfectly positioned they worked okay,
though not as well as the pull-toy rotor. I also tried fixed blades made
out of large 6x16 plates that worked about as well as the RDS insect wings.
I also tried blades made out of soft foam sheets. These had the advantage
that kids could touch the blades without getting hurt though again, the lift
was not very good.
>
> The extra weight (compared to your non-lego solution) is something we
> can deal with using appropriate counter-balance weights - but we are
> rather tight on load carrying - if the helicopter is balanced
> correctly so it'll take off *and* come back down again, there isn't
> enough thrust left to lift much of a load. We can fix that by making
> it 'neutrally' balanced - and throw the rotor into reverse to go down
> but that's an ugly solution.
That is no good, the helicopter should drop if the rotor power is too low.
You should also be able to control the robot position while hovering. If
you hover under no power, you can't move the robot by adjusting the pitch.
> The counter-balance arrangements are similar to yours and the RCX is
> driven with a Lego remote instead of a second RCX.
I started out using the Lego remote but the second RCX controller is much
more satisfying. One of the pictures
http://www.brickshelf.com/gallery/GJansson/Helicopter/controller3.jpg
shows the controller partially disassembled. To detect the position of the
levers, I use gray-scales that I printed onto label paper and stuck onto
Lego disks (like the disk brakes that came with some of car models). This
works very well and gives me more then a 100 step resolution on 90 degrees
of movement.
Gus
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