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Dear All
Wow, thanks for the interest. I have taken some pictures of the RCX in flight today -- I have
not had them developed yet, so don't know how they look. Anyway, I'll keep shooting until I
get some decent ones and post them on the web somewhere. I have posted a dat to the CAD/Dat
files/Models goup # 749.
* On the micromotor --
Yes, the micromotor is plenty strong enough to shift the RCX and change the flight path. I
tested this with the kite suspended on a static line to the center spar before I flew it. The
only problem was that that the micromotor kept tearing itself off, so I have tacked it in
place with hot-melt adhesive.
* Why do I enter a spiral after 1 second? --
Two reasons. First, I didn;'t want the RCX to be just a payload -- I wanted it to do
something under power. Second, my launch point is the rear balcony of my third floor
apartment into the garden. The garden is short and has a wire mesh fence at the back. I
wanted to avoid the kite and RCX smashing into fence, and I thought a spiral would do the
trick.
* Could you do more advanced control of the kite this way?
The max flying time so far has been 4.5 seconds -- that's not much of a window for stunting.
I have thought that you could maybe use two homebrew bend sensors, one either side, sticking
out into the air and maybe have the RCX shift left-right to keep the bend value the same on
both sides as a way to keep the glider heading into wind. However, I probably won't get round
to trying it. I'm so nervous each time the RCX flies, I'm only going to keep doing it until I
have a good enough set of photos to post and then I will stop. To go much further would
require a very different kite with an aspect ratio more suitable for gliding (long skinny
wings).
* On the kite --
The kite is a Tori Tako (Icarex sail, CF spars). My setup for the RCX glider is a real lash
up, but the Tako doesn't glide worth a damn without some modifications. I took out the front
spreader and used it to elongate the rear spreader to get the sail profile flatter -- the two
"scoops" in the regular delta setup made for lousy gliding performance. There are four
standoff whiskers in the regular Tako setup -- two on each side of the center spine, which
attach between sockets in the trailing edge of the sail and connectors on the rear spreader to
give the sail a nice scoop for stunting. In this modified setup, I taped the two inner
whiskers to the rear spreader (again, to try and keep the sail profile as wide and flat as
possible) and left the outer two whiskers in trailing. I would have loved to have removed the
outer whiskers, but I superglued them into the sockets in the sail last year because they kept
popping out when the kite was flying in high winds.
* On the bridle/attachment of the RCX --
The standard Tako bridle setup has, on either side of the kite,
a. one pigtail from the rear spreader/wing spar connector, and
b. one long loop either side from the front spreader/wing spar conenctor to the center spine,
c. one thin line with a loop in it from the wing spar, midway between the two spreaders.
Here's what I did --
1. take off the pigtails
2. The long loop starts at the nose spreader spar. I led this up, over the top of the sail to
the nose, and taped it to the nose. The rest of the loop hangs free under the kite (back its
usual attachment point at the rear spreader/cetner spine connector) and the RCX "sits" in
these two loops. Each loop is run under one of the 1x16 Technic beams and is tied off front
and back to the triple-length Technic pegs with elastic bands. The elastic bands are looped
figure eight fashion between the ends of the Technic pegs, over the top of the beams, to clamp
the line in place against the peg. This allows you to fine tune the position of the RCX
without having to keep tying and untying knots in the bridle lines.
3. The thin lines with loops are connected with a third piece of line which runs through the
third-from-the-back holes in 1x8 Technic beams and is tied off to the ball peg on the cam with
a small elastic band. Turning the cam 45° shifts the RCX just enough to start the spiral
(unless there's any wind, in which case the spiral may well start as soon as you launch the
kite).
* If you try this at home --
I strongly recommend that you make a "test pilot" with a Lego weight brick and some 1x16
Tecnnic beams. The test pilot was very useful for optimising the bridle setup (my first
"flight" was actually an immediate stall followed by a plummet -- I'm not sure the RCX would
have survived). Like I said, I will keep flying until I have put some decent pictures to put
up on the web and you can be sure that I will post the URL to the robotics group when they are
up. Then I am going to stop... so anyone who wants to run with this idea, please feel free.
Cheers
JP
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Message is in Reply To:
 | | Re: LEGO RCX Skydivers
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| Hi Marco The RCX is slung underneath the "glider" (actually a 2 meter delta stunt kite). It has one micromotor plugged into OUT_B (i.e., the micromotor contacts are fitted directly onto the OUT_B contacts so the center of the motor's rotation is (...) (25 years ago, 6-Nov-99, to lugnet.general, lugnet.robotics)
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