Oleg, I have used RDS in my scratch built 1/4 scale Woodstock
for more than a year and they have performed flawlessly.
I have also installed them on flaps and ailerons in my tow plane,
and can get 90 deg. flap with no trouble. They move smoothly
all the way down and up even when moved by hand.
Certainly the positioning of the shaft must be correct to make it work,
all I did was to put it together and do some trial and error then ground
some flats on the shaft, nipped up the screws, hey presto, works great.
Dennis
----- Original Message -----
From: "Oleg Golovidov" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Cc: <[EMAIL PROTECTED]>
Sent: Saturday, May 26, 2001 7:56 AM
Subject: [RCSE] Why RDS did not work for me... long
> Content-MD5: /blEUAcXFpZL42aHYxpCnQ==
>
> Sorry for sending a negative post about this great gadget, but I can't
hold this
> to myself any more :-) I may be the only sore looser with negative
experience
> with RDS, but I still want to share it.
> Harley, please, do not consider this as a disrespect to your invention - I
truly
> admire your ingenuity and thank you for all you've done for our hobby!
>
> My claim is that RDS are not a truly correct mechanical design and if all
> components are done correctly (stiff shaft, no slop in the support
bearing,
> servo mounted absolutely firmly, control surface hinge infinitely strong)
will
> not work. There are some ASCII diagrams below that require a fixed width
font
> text editor (mail reader) to display correctly, so all of you using
'wonderful'
> HTML browsers for reading e-mail will need to set them to use fixed-width
fonts
> or read my message in a text editor (notepad).
>
> Here is the proof. The two lines on the diagrams below are: 1) RDS shaft,
o -
> shows the bend location; 2) control/wing surface, o - shows the hinge
axis.
>
>
> First, let's look at the flap RDS installation. As Harley mentioned, to
get 90
> deg down deflection, you have to position the bend of the shaft behind the
hinge
> line a little (more precisely, by the distance between the hinge and the
shaft
> axis), so that when deflected 90 deg the shaft goes 'around' the flap/wing
> surface corner, keeping the shaft equal distance from the surface.
>
>
> distance due to RDS pocket thickness and half shaft diameter
> |
> |
> |
> `|'
> --------o--------------------------------servo
> -----------------o--------------------------
>
>
> o-------------------------------servo
> | o---------------------
> | |
> | |
> same | |
> distance -------> |
> |
> |
> |
> |
>
>
> Now, look at an intermediate flap position, say 45 deg down. The distance
> between the shaft and the control surface is now greater by the factor of
> 1/sin(45deg) = 1.414. The shaft will be pulling the control surface away
from
> the wing. If the servo is mounted firmly and the shaft doesn't bend, the
hinge
> tape will be pulled off the wing surface (which is exactly what I expected
AND
> observed when I tried RDS). Depending on how stronly you glued the servo
into
> the wing or just taped it, the servo will either move towards the flap,
or/and
> rotate a little horizontally if the shaft is allowed to shift horizontally
at
> the hinge line (recall that for flaps RDS shaft is placed at 45 deg angle
when
> looking from the top, so it will want to move sidewise). If the shaft is
thin
> and the servo mount doesn't give at all, the shaft will bend. If you used
a
> support bearing at the hinge for the shaft, and the servo is mounted
reasonably
> well, the hinge is the only thing that can give up, and so it does...
>
>
> o-------------------------------servo
> / o--------------------
> / /
> / /
> / /
> increased /
> distance---> /
> /
> /
>
>
> Now look at the up flap deflection (reflex). The picture is reversed - the
> separation distance between the shaft and the flap surface is decreased
down to
> zero at 45 deg deflection. The servo will be jammed away from the flap,
and/or
> the shaft will bend in the opposite direction.
>
>
> \
> \
> \
> \
> \
> \
> o----------------------------servo
> o--------------------
>
>
>
>
> Now let's see how it looks for ailerons. For simplicity, imagine that
ailerons
> are hinged on the bottom surface. To get some up deflection, say 45 deg,
the
> bend in the shaft must be positioned a little forward of the hinge line.
Then at
> a 45 deg angle the distance from the shaft axis to the aileron surface
will be
> the same as for 0 deg deflection:
>
>
>
> ---------o----------------------------servo
> -----------------o--------------------------
>
>
> \
> \
> \
> \ \
> \ \
> \ \
> \ o-----------------------------servo
> o-------------------------
>
>
> But when aileron is deflected down, the distance will decrease down to
zero at
> 45 deg deflection angle. In any position but the two shown above (zero and
45
> deg up), the distance between the shaft and the aileron surface is either
> greater or smaller than the original distance (determined by the RDS
pocket
> material thickness and 1/2 shaft diameter). Again, if the shaft and servo
are
> mounted firmly, the hinge will separate.
>
> o---------------------
> o--------------------
> /
> /
> /
> /
> /
> /
> /
>
>
>
> I know RDS worked for thousands of people now (judging by the amount of
couplers
> that Harley has sold) and a lot of people are happy using them. I am not
one of
> them, unfortunately. I did my diligence and tried installing them in my
> unlimited ship long ago, but soon gave up and converted it back to regular
> control horns. Not only the hinge tape was separating immediately, but the
> servos were trying to break loose from the wells (or at least tilted back
and
> forth when moving the control surface, which I really didn't like). Not to
> mention that if you make an error and the flap or aileron end up being off
> neutral, you MUST use your computer radio to adjust the neutral, or
disassemble
> the whole system (remove the hinge tape), trash the RDS shaft (I had to
make
> flats on the shaft, otherwise it was slipping), make another one with the
> correct angle, and assemble it all again for another iteration.
>
> Once again, RDS is a neat gadget and it may work (and have worked) under
certain
> conditions, but it didn't for me... So am I the only one like this, and
does the
> above make sense to ya'll?
>
> Regards,
> Oleg.
>
> ________________________________________________________________________
> _____ _____ __
> / ___/| / ___/| / /|
> Oleg Golovidov / /__ |/ / /__ |/ / / /
> Engineous Software Inc. / ___/| /__ /| / / /
> www.engineous.com / /__ |/ ___/ / / / / /
> (919)677-6700 x107 /____/| /____/ / /_/ /
> |___ |/ |____|/ |_|/
>
>
>
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