After contemplating this design and even digging out a geared DC motor for it, I realized that the KK5.5 board I've been fiddling with could do the job with just a single servo and a 4cell NiCD pack for power. I did a bit of sketching and came up with a mechanical scheme I thought would work. But first, I spent some time on the software to make sure it would work as I intended. I am using a mechanical button press since my camera does not have any kind of electronic interface to the shutter button.
Here is the board and servo under test. The LED comes on when the servo moves.
The 'roll' 'pitch' and 'yaw' pots are used to adjust timing. In this application, the gyros are not used at all.
In this image you can see the basic mechanical construction. I built this from a sketch and some TLAR measurements
of the camera. All the aluminum bits were cut from scrap sheet about 2mm thick. I was careful to make sure that
the holes in the vertical bits lined up. The horizontal lever is drilled for a 2:1 (in use) and a 3:1 ratio.
After testing, I think I am going to move to the 3:1 ratio so the servo can move further with more precision,
while retaining the short throw on the button press foot. As you can see I have used some old clevises but
of course you can use Z bends or some other method of securing the push rod ends (even ball links).
The presser foot has had some self-adhesive sponge tape added so that it does not slip off the camera button, which is
at a slight angle.
Here is the entire rig. Had to take the photo with my cellphone so not very clear.
Bottom: showing the tripod mounting hole. The screw that holds the camera to the rig is a 1/4-20 nylon bolt
more commonly used to hold wings. The hole in the wood is tapped 1/4-20 for the tripod screw.
The YAW pot is used to set the time interval from 5 to 30 seconds
PITCH pot is used to set the dwell delay length. The servo is moved about half it's travel and then delays this long before moving to the end of travel. This was an attempt to allow it to focus butin practise it is better to simply move the servo slowly in one continuous motion.
ROLL pot is used to set the servo traverse time, ie the total time it takes to travel from end to end.
g_pot = (1023-analogRead(POT_YAW));
nmseconds = map(g_pot,0,1023,5,30) * 1000;
The servo motion time is read from the ROLL pot using similar code except that the pot value isused directly as the delay in milliseconds.
The dwell delay time is not really required>
Make the minimum delay less than 5 seconds.
The source interval.ino
The header for the KK board pin definitions: kk.hI put the kk.h in the Arduino libraries folder so that it can be added to any sketch by using the usual library add menu item. I created this header file from the code at RCHacker
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