Whoo
hoo! Another shot in focus. For now on, I'm calling it
the 'selective focus' feature on my camera. This is the
top of the basket and the other arm that creates the 4-link
system. In theory it doesn't hold any weight, but it's
important that it doesn't bend because then it'll change
the properties of the 4-link and the camera will no longer
be level. The idea behind a 4-link is if you have two
poles standing vertically with one mounted and one movable.
And you connecting them with two other orthogonal poles
that are exactly the same length and attached exactly
the same distance from each other, no matter how you pivot
the movable pole, it will always be parallel with the
vertical fixed pole. Enough physics, so the second arm
is connected with a rod end found at an auto store or
grangers type industrial supply store. I welded a stud
into the end of the arm so the rod end just screws on.
The nut is to lock it in place so it doesn't move. It's
also great for fine-tuning the setup to get the two arms
exactly the same length.
So
what is the piece of metal with all the holes drilled
in it? Well, it's a way to relocate the second arm, which
also controls the tilt of the camera basket. When I want
to do bird-eye shots that I wouldn't be able to do with
the arm connected in its normal position, I bolt it in
one of those holes.
So
lets move back a little to the other side of the 4-link.
Hopefully
this is all starting to make sense. You see that the two
arms–which are the same length bolt-to-bolt–are attached
to the tripod the exact same distance apart as they are
on the camera basket. For the main, larger arm, I've used
the same bearing set as on the other end. For the second
arm, I've used the same welded stud and tie rod end system
with a bolt going through. Now, it's tough to see, but
the second arm is attached to a pivoting arm of its own
(the large hex bolt is where the pivot is–bearings are
behind the bolt). By undoing the wing nut shown, I can
tilt the camera up and down by moving the bar forward
and back. To get more exaggerated tilting motion, I unbolt
the second arm and bolt it through the hole in the very
top of the bar. I'm told by friends smarter than I, that
this is all basic physics ... mechanical advantage stuff
we're supposed to learn in high school. What is that arch
on the back of the setup? It's a way to lock the arm in
place. A bolt and washer go through the hole in the arm
(you can barely see it) and lock to the plate. I cheated
and used a plasma cutter, but you could cut an arc with
a jigsaw or other common tools. Building this entire jib
only needs basic tools.
