25
Looking good!
Spinning a bit wobbly.
We put the rig in dynamic balance by
first choosing the monitor position and
then placing the camera close to its final
position. By trial-and-error, we then
discover the one-and-only ideal position
for the battery.
First, set up your sled at the proper
length for the shot and place the monitor
where you want it for proper viewing
and inertial control. Typically with the
Flyer-LE, the monitor will be horizontal,
for maximum pan inertia. Position the
camera so that its c.g. is about .5 inches
(12mm) behind the center post. The
center post is 28mm in diameter, so you
can use the back of the post as a guide.
Next, static balance by rotating the
battery down from horizontal (your
only choice) so the sled hangs perfectly
vertical fore and aft. Make sure the top-
to-bottom balance is set with a drop time
of 2 seconds.
Trim side to side with the camera, using
the knobs on the stage. Fine-tune the
fore-aft balance with the camera. You
want the sled perfectly vertical.
Give the sled several careful test spins.
Very important: do not spin the rig very
fast – certainly not much faster than a
normal panning speed (3 – 6 rpm). Note
the results. Is it good or bad, i.e., panning
flat or wobbly? Is it your technique or is
the sled out of dynamic balance?
If your Flyer-LE is not in dynamic
balance, do not move the monitor!
Instead, move (rotate) the battery a little
bit first, then rebalance statically with the
camera. There are only two directions to
move the battery, out or in (which is also
up and down). You have a 50% chance
of choosing the right direction, so stop
worrying about it and give one direction a
test. Just be sure to make a note of which
direction you move the battery.
After you lock the battery in place, you
must rebalance the sled statically with the
camera. Do not move the monitor! Once
you are in static balance, spin the sled
again. Is it better or worse? Again, you
have two choices for moving the battery.
Re-rack, rebalance, and spin again (and
again!) until the sled pans flat. This
should not take a lot of time.
When the battery is within about 1/4
inch (6mm) of ideal, the sled will behave
nicely – pan flat – and feel “sweet.” We
suggest you do not attempt to do this for
the first time on set!
Adding any accessory to the sled will
affect both static and dynamic balance.
Changing the length of the sled, and/or
moving the monitor in, out, up, or down
will change both static and dynamic
balance.
How much will dynamic balance change?
It depends on the mass and position of the
new object, and the masses and positions
of everything else on the sled.
You will discover that as the monitor is
placed higher towards the camera (and
inwards), the closer the battery c.g. gets
to the center post, and the more the
camera c.g. moves away from the post to
the rear.
With both batteries installed for 24 volts,
it may be impossible to raise the monitor
from horizontal — unless you add some
weight to the monitor. Adding weight
to the monitor (about a pound) will also
increase the inertia and give your Flyer-
LE a more stable feel.
In practice, it’s a lot easier than it sounds
on the page, and luckily, there’s one
great gift in all this: it doesn’t matter for
dynamic balance what weight camera you
are using or if you change lenses, filters,
etc. Really!
So if you make any changes with the
camera – or use a different camera –
there are no worries about getting back
in dynamic balance! You only need to
rebalance statically and you will be in
dynamic balance again. Honest.
Put the other way around: you can set up
your rig in various ways with a practice
camera at home, making it long or
short, monitor high or low, with an extra
weight, etc. Note the positions of the
monitor and batteries, and you will be
able to get into dynamic balance quickly
on set, regardless of the camera you
carry. Really. Honest. No fooling.
For the complete story, see the Dynamic
Balance Primer and play with the
Dynamic Balance Spreadsheet, available
online at www.steadicam.com.
Dynamic balance spin test with an Ultra
2™