Rocket Launch Camera Triggers

From: johnd (John DuBois)
Newsgroups: rec.models.rockets
Subject: Re: Launch Photographs
Date: Fri, 03 Aug 90 17:02:54 PDT

     I've used two methods to electrically sense a rocket launch to trigger
a camera.  The first thing I tried was a normally-closed circuit created by
clipping an alligator clip to the top of the metal launch rod.  When the rocket
reaches the top of the rod the launch lug knocks the clip off, opening the
circuit, which is sensed by a device which triggers the camera.  This worked
reliably, and has the virtue of simplicity.  But, it had two problems.  First,
there was always a flying cable in the picture, and second, the trigger point
is not adjustable.  It always occurs at the top of the rod, which is a bit late
for a nice picture.
    Because of those disadvantages, I came up with a second method which I
still use.  The best incarnation of this method I've come up with is this:
I found an alligator clip with a long "mouth".  I filed down the teeth and
squeezed the top and bottom parts of the mouth into roughly circular
shapes with pliers.  I slipped a piece of brass tubing over the top part of the 
mouth to make it very smooth.  Over the bottom half, I put a piece of rigid
plastic tubing (as sold in hobby shops), and over the plastic put a piece of
brass tubing which exactly fit over it.  Before putting the brass tubing over
the plastic, an insulated wire was soldered to it.  So, when the clip is open,
there is an open circuit between the (metal) clip and the wire because the
brass tube over the bottom half is insulated from the clip by the plastic tube.
     When the clip is closed, the metal of the piece of tubing over the top
half (directly connected to the metal of the clip) contacts the brass tube and
closes the circuit.  The brass tube over the top half of th clip may be
squeezed so that the part that will touch the rocket is flat, to get a better
contact.  A second wire is soldered/crimped/screwed onto the base end of the
clip; the two wires are part of a cable.
     To sense a rocket launch, this clip is simply clipped onto one of the fins
of the rocket.  The cable is taped or tied to a leg or other part of the launch
pad, with the length of cable after the tie point being adjusted to cause the
clip to pull off the rocket fin at whatever height is desired.  
     I've been getting great pictures with this method for 5+ years.  The
first camera I used it with (a Mamiya ZE) did not have an electronic release, 
so I made a solenoid trigger.  I bought a cable release and cut off the camera
end of it.  I drilled a hole in the end of the case of a small soleniod (the
end that the plunger pulls *toward* when the solenoid is activated) that was
large enough for the release cable to pass through.  Then, I soldered the part
of the release that I had cut off (the part that screws into the camera shutter
release button) onto the end of the solenoid case.  I drilled a hole in the end
of a solenoid plunger, and after making sure I had the correct length of cable,
soldered the cable (which ends in the bit of solid metal that pushes the
shutter release down) into the plunger.  After feeding the cable though the
hole drilled in the solenoid case, activating the solenoid would push it out,
triggering the camera.
     Since I couldn't get a solenoid of the right type that would operate on
battery voltage, I rewound it to get the impedance I wanted, built a device to
briefly trigger it after a circuit opened or closed, and used it with the sense
systems described above.  This system would trigger in a few 10's of
milliseconds, which I attributed to the time the solenoid needed to pull in.
     The ZE was eventually damaged.  I bought an SF-1 to replace it.  This
camera has an electronic remote release.  I interfaced the sense system to
it, expecting a much faster release.  Unfortunately, it seems significantly
*slower*!  It may be that the input circuitry has some delay built in to
debounce the switch on the remote release.  And, there is no cable release
capability on the shutter release button.  Oh well.  I adjust the cable to
trigger lower, which sort of works, but makes the system more sensitive to
differences in launch accelertion.  I still get some good pics.

	John DuBois
Newsgroups: sci.electronics,,rec.models.rockets
Subject: Re: Remote triggering a camera
Organization: The Armory

In article <1992Apr30.172526.11611@anasaz> bobm@anasaz.uucp (Bob Maccione) writes:
+  Has anyone out there ever built a remote trigger for a manual camera,
+I want to be able to trigger a cheap point&shoot autowinder ( cheap cause
+the camera will probably be broken on the first couple of attempts, I'm
+attaching it to the lower surface of a wing ).  I havn't been able to 
+find a < $50 camera with a remote so I have to build one myself.
+  The main questions are: 
+  1: mounting of the solenoid ( or even where to buy the solenoid ), I'm
+     not past using epoxy, etc.
+  2: vibration problems from the solenoid triggering ( or releasing ), do
+     I need a RC network to hold the solenoid in past the initial triggering.

     I made a soleniod trigger for my Mamiya ZE about 8 years ago (I
couldn't afford the ZE-X which had an electronic trigger).  I bought a
remote release cable and cut the end that attaches to the camera off right
where the flexible sheath connected to it.  I found a small solenoid and
rewound it so that it would produce sufficient force when operated on 9V. 
I drilled a hole in the end of the solenoid that the armature pulls
*toward* big enough for the trigger cable to fit through and then soldered
the release connector onto it.  I cut the release "pusher" off at an
appropriate length, drilled a hole in the solenoid armature just big
enough for the cable, and soldered it in.  Then I put the armature back in
with the pusher sticking out of the release connector.  Since the solenoid
was originally a "puller", the armature extended out of the solenoid on
the "pull" side.  I cut off the excess and put a cap over that end of the
     Pictures might help... even ASCII graphics...

Original solenoid
+--------------+   |
|   Armature   |   |
+--------------+   |
   Armature pulls this way -->

Original cable release
Cable sheath        Release connector
==================-------O-----------\ <-- Release connector threads
================================oooooo  <- Cable (=) & solid pusher (o)
                         ^-- Bearing to let connector rotate
Solenoid Release
Cap   Solendoid
+--+-------------+  Release connector
|+-----------+   |------O------------\ <-- Release connector threads
||Armature  ====================oooooo  <- Cable (=) & solid pusher (o)
|+-----------+   |------O------------/
+--+-------------+      ^-- Bearing to let connector rotate
Armature pulls this way -->

     The whole thing didn't weigh very much, and the shutter release on the
ZE wasn't "wobbly", so I just screwed it in and let the shutter release
support it.  It worked well.  I built a little controller for it which
included an ultrasonic remote and a jack that a hardwired NC or NO circuit
trigger could be plugged into.  I used it mainly for taking pictures of
rockets lifting off.  
     At first I used a NC trigger made by putting clips at the top and
bottom of the launch rod.  When the rocket lifted off it knocked the top
clip off.  But, it turned out that the delays of the trigger, solenoid,
and shutter release were enough that if I used that method, the rocket was
moving so fast by the time the circuit was broken (having accellerated to
the top of the launch rod) that only a very wide shot would catch it.  I
didn't have much success trying to guess where the rocket would be by the
time the shutter released.  
     So, I made a NO trigger by putting an insulated pad on one of the
jaws of a clip, with the pad and the other (uninsulated) jaw forming the
contacts.  The clip went on one of the fins of the rocket.  I could tie
the cable to the launch pad with the amount of free cable determining the
height at which the camera was triggered.  I usually set it to six or
eight inches off the pad so that I was pretty sure to get the rocket
within a range of a few feet.  I got lots of nice shots this way.  
     Unfortunately I later damaged the ZE.  I bought a Pentax SF-1 to
replace it.  It had an electronic release, but had *no* provision for a
manual release.  Of course, it had a unique jack for the electronic
release.  I spent the $30 or so they wanted for the release :-( and cut it
in two and put a mini stereo phone connector between them so I could
connect whatever I wanted to it.  I thought it would be faster than the
solenoid release, but it turned out to be slower!  I doubt that the
electromechanical release in the camera is really that slow; more likely
the debouncing on the remote release is just overenthusiastic.  But it is
still fast enough that I can catch rockets by using a bit shorter cable on
the clip.

This web page maintained by John DuBois