Subject:
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Re: Helicopter was Re: Newbie has an idea
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 26 Nov 2002 23:32:28 GMT
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Viewed:
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1321 times
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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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Message is in Reply To:
 | | Re: Helicopter was Re: Newbie has an idea
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| (...) 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 (...) (21 years ago, 26-Nov-02, to lugnet.robotics)
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