r.m.r FAQ Part 6 of 8: Guidance and Control (Repost)

r.m.r FAQ Part 6 of 8: Guidance and Control (Repost)

Post by Buzz McDermo » Fri, 27 Oct 1995 04:00:00



Archive-name: rockets-faq/part6
Posting-Frequency: monthly
Last-modified: 10 October 1994

*** PART 6: Payloads


Any additions or corrections should be sent to that address]

Updates
-------------
October '94: Updated AstroCam section with "Sticky Shutter" discussion. Updated
             "Adept" section with new products. Updated "Transolve" section with
                 review from recent "Sprocketry".
August '94:  Added "Night Flying" section. Updated hombrew still camera section
             based on NARAM 36 inputs.
June '94:    Added reference to "Microbats" project. Added "Alternative Boosters"
             to Astrocam section. Updated some camera references.
April '94:   Re-wrote section headings into "Q&A" format, minor editing throught.
             Split off "Guidance Systems" into separate (new) Part.
             Renumbered to "Part 5" as part of FAQ reorg.
             Added table of motor "theoretical performance" in Astrocam Section.
Jan '94:     Minor addition to camera introduction
-------------

Introduction - Flying sport rockets is fun. Flying competition rockets can
be exciting in the heat of battle. Scale models (my favorite) can be as much
of a challenge to research and build as they are to fly.  But if you want to
do something "real" with your rocket, you've got to fly a payload. This also
provides you with a good response to the perpetual question from the great
unwashed masses when they ask "so, what's it do?"

6.1 Camera Payloads

   Cameras are the most often flown payloads (after eggs and bugs :-) because
   they hit us where we live. No other payload lets us see the flight from our
   rocket's point of view. The intensity of interest in camera payloads can be
   seen by how early they were flown: Goddard flew them, the VfR (the German
   rocket society which gave Von Braun his start) flew them and, of course,
   dozens of post war sounding rockets carried camera payloads. In fact, the
   very first operational (as opposed to experimental) rocket system was Alfred
   Maul's photoreconnaissance rocket built for the German Army which was used
   from 1912 until airplanes became more reliable.

   Some of the products and techniques that have been tried and/or are still
   available are:

6.1.1 Can I just go out and buy a camera for my rocket? What cameras will work?

Some commercial camera products produced over the years:

6.1.1.1 Camroc - The first purpose-designed rocket camera. Designed by Estes
   and sold from 1965 to 1974. A marvel of simplicity, it was patterned after
   several homebrew cameras of the early '60s (see 5.1.2). It was simply a
   cylindrical body that held the film topped by a hemispherical nose that
   was flattened off to accept the optical window which the forward facing
   lens looked through. One shot per flight on "Astropan 400" (Kodak Tri-X)
   cut into a 1 1/2" dia. round negative. Easy to process at home. The film
   had to be push processed to 1200 ASA (officially, though most home
   developers went to 1600). Extremely valuable on the collector market.
   [Note: Don't write me asking how much your old Camroc's worth. Bob


   of the Camroc: "At one time there were quite a few homebrew modifications to
   the Camroc floating around. Most popular was substituting a 3-element glass
   lens from Edmund Scientific for the standard plastic lens; it gave much
   sharper and better color-corrected results. I have also seen a wide-angle
   variation with yet another Edmund lens that required cutting the forward body
   section of the Camroc down to a much shorter length. As someone pointed out
   at the time, the Camroc lens was a short telephoto relative to its film
   format. It doesn't make sense to send a rocket up as high as possible and
   then use a telephoto lens to get a SMALLER angle of view; it's a wide angle
   you really want, so you can get more in the picture from a lower, easier-to-
   aim flight with a smaller motor and less risk of losing the camera. Several
   people flew color slide film in the Camroc, but high-speed color films were
   pretty terrible at the time; the ASA 1600 print films available today would
   probably work very well in it."

6.1.1.2 Cineroc - Estes' second foray into camera payloads, the Cineroc was
   *much* more sophisticated than the Camroc. This was a full bore 8mm movie
   camera crammed into a package not much bigger than it's predecessor (although
   more aerodynamic). Introduced with much fanfare in 1969, it lasted only 5
   years before its plug was pulled in 1974. The lens looked aft via a hooded
   mirror and it shot ~15 sec worth of flight time at 2X speed (30 sec projec-
   tion time). At least that's what the spec says. In reality, most Cinerocs ran
   in the 18 - 20 fps range which is more-or-less normal speed. The film was
   a Kodak ASA 160 instrumentation film on a polyester base which was probably
   adopted because it was the only daylight-balanced Super 8 film available.
   The Cineroc used a custom film cartridge meaning that you either used the
   Estes processing service or went to a custom lab.  It could be developed
   at home using a Kodak E-4 developing kit, but this was *much* more trouble
   than most modelers would want to go.

   Gary Rosenfield, now president of Aerotech/ISP, made a name for himself
   by coming up with a significant hack on the Cineroc that both reduced its
   diameter and increased the film capacity. As detailed (somewhat sketchily)
   in the V 14, N 1 (July 1974) issue of the _Model Rocket News_, Gary took
   the basic guts of the camera (lens/film gate/geneva transport plus motor
   and batteries) and put them in a BT-55 tube with the mirror hood outside
   as usual. He extended the tube fore and aft enough to hold 50' of film (a
   full cassette worth) in random storage, i.e. no spools. The film simply ran
   from one compartment, through the gate and into the other compartment.
   While this made the system much more difficult to reload in the field, you
   could now have the film developed anywhere, provided you bothered to
   rewind it back into the standard cassette afterwards. The photo of "Wild
   Man Rosenfield" that accompanies the article is probably suitable for
   blackmail :-)

   The official reason for its early demise, still lamented to this day, was
   that the small electric motor it used went out of production. However,
   in a conversation with Mike Dorffler (the designer) he revealed that the
   product was killed by a combination of events that occurred over a very
   short (2 month) period in early '74: the motor went out of production,
   Eveready stopped making the tiny "N" batteries, Kodak changed the formula
   of the film which couldn't be accommodated by the custom lab doing their
   processing and, the coup de' gras, a technician dropped the mold for
   making the custom lens.

   Some Cinerocs are still flown today 20 years later. The size "N" alkaline
   batteries, much better than the original carbon-zinc ones that Estes
   supplied, are widely available now; and the new film stock (which is
   available off the shelf, not special order like the one Estes originally
   chose) is sharper and less grainy than the old stuff. Both of these actually
   make for easier and better Cineroc results today than when it was first
   introduced.  You do still need a custom film lab to deal with the nonstandard
   lengths of 8mm film, however.

6.1.1.3 AstroCam 110 - Another Estes product and something of a combination of
   the previous two. Reverting to the still format, the AstroCam was designed
   around a stock 110 cartridge. It took multiple shots per roll of 400 speed
   color print film, but still only one frame per flight. The lens looked out
   through a hooded mirror (like the Cineroc) but this time looking forward
   (like the Camroc). Image quality was marginal due to the plastic lens and
   small format, but the film can be developed anywhere (although the prints are
   reversed). A very long lived product, it lasted from it's 1979 introduction
   until early 1992 when, for reasons known only to themselves, Estes canceled
   it. Public demand was great enough that they re-introduced an "improved"
   version in early 1993. Said improvements consisted of a better lens for a
   sharper image, a one stop increase in aperture (so it can use the much more
   available 200 speed film) and pre-assembly of the lens and sprocket. Perhaps
   the biggest improvement of all was that they dropped the price by $10 :-)

6.1.1.4 AstroCam building and flying tips - The AstroCam is the source of
   continual threads on r.m.r. The following is a distillation of nearly half
   a megabyte worth of AstroCam discussions I've archived:

GENERAL TIPS



* The film is quite grainy, hence a lot of people move on to 35mm cameras.

* Underexposure is a problem - the pictures are lousy if you launch in
    anything other than bright sun.  Of course, there's also the usual problem
    of forgetting to open the safety shutter before launch.

* Overexposure is a problem several ways:
   - The shutter cord can get tangled in the shroud lines, taking multiple
     exposures or one long exposure.
   - A hard impact can take another shot.  At the least, landing impact will
     close the safety shutter making you wonder if you forgot to open it
     before launch.
   - Problems with sun and heat on the pad make some folks drape it with
     aluminum foil until final countdown.
   - Adjustments on the pad are always a source of causing the shutter
     to go off on the pad.

*  Chris suggests advancing the film before take off and advancing it after
...

read more »

 
 
 

r.m.r FAQ Part 6 of 8: Guidance and Control (Repost)

Post by Bob Mill » Thu, 02 Nov 1995 04:00:00


Probably not FAQ material for guidance, but I have a co-worker who
worked on Stinger missile guidance systems. There is only one pair
of control surfaces -- not one for each axis. The rocket is designed
to spin and the control surfaces are deflected at just the right
moments in the spin (one way at one point, then the other way 180
degrees later) to steer the rocket toward the target. Cuts the
control fins and actuator ***in half. If you needed less steerability,
you could correct once per revolution with a control surface which
only deflected one way, reducing the HW again...

Bob (who wishes we had two suns so that they could be used as a
     vertical reference)Miller