Tom Ramcigam (magicmarmot) wrote,
Tom Ramcigam


AIM crashed on me last night in mid-chat with Tony, and it crashed hard.
I ended up uninstalling and reinstalling and it couldn't find a way to
log in, even though everything else was working fine. Ran a virus scan
last night just in case.

Got a set of skateboard wheels & bearings for the dolly trucks. These
are pretty low-key, but it's the first prototype so it can be low-key.
Discovered that the inner diameter of a skate wheel bearing fits a 5/16"
shaft perfectly. Did the preliminary assembly of the wheel structures
last night. I still need to weld the truck base, cut the individual
trucks, drill and tap them. And I still need a solution to my lateral
sliding issue. I have a couple of thoughts, but nothing is screaming
elegance to me yet. What I need is something like a short linear thrust
bearing-- I could make one if necessary, but I'm thinking that somebody
must make something like this already.
A quick perusal of the McMaster-Carr website shows a lot of expensive
solutions. I don't want expensive, I want cheap and good.

The wheels that I got are 53 and 54mm diameter, shore 100a which is
really pretty hard for what I want to do. The ideal wheels that I found
are 76mm and much much softer (like shore 80), but they're also much
more expensive and can wait for the second prototype build. I can also
get them a lot cheaper if I buy in bulk, but it's a minimum $400 order.
If I ever go into manufacturing dollies, it's perfect. :)

Then there's the camera crane/jib arm concept. There are a lot of
designs for things to enable you to move the camera around on the end of
an arm that make for some wonderful shots, and I don't think there is a
movie made anymore without a dolly, crane, jib, or steadicam rig (maybe
with the exception of ultra-no-budget indies).
I have a couple of ideas here. I suppose that's not exactly surprising.

One is an electric camera lift. The mechanism goes from nearly flat to
fully extended with about a three-foot height gain, and the camera rises
in a perfect vertical axis. That's important when you're dealing with
tightly focused shots. I have a couple of lift designs, but I have an
instinctual feeling that one of them is more mechanically sound than the

Another idea is a long crane with a remote head. The idea here is to be
able to move the camera in as many axes as possible at the end of the
crane without being able to touch the camera. The remote head is a
project in and of itself, as it deals with some pretty spectacular
servocontrol and mechanical issues. There is a simpler version that has
only one axis of motion of the camera (tilt), and it's a lot easier to
build, but there are some funky issues when you start dealing with
different cameras-- for instance, the center of rotation of such a
device should be located at the center of the imaging plane of
the camera, which is most likely not it's center of mass (i.e. center of
free-body rotation). This means that I have to take some load-bearing
stresses into account in the design, and it starts to get funky when you
talk about multiple axes of rotation.
But it's really cool.

Third idea is a jib arm, which doesn't really do anything except move
the camera up and down while keeping it level. Pretty simple design,
probably the simplest of all with no electromechanics-- it's fully
manual. It's also a right bitch to use for one person.

Ideally, I'd like to be able to mount any of these on the dolly frame.

The frame itself I'm trying to make 32" x 46". The first prototype will
probably be steel tubing, since I can weld that directly. Aluminum would
be nicer and lighter, but I have yet to actually weld aluminum, and I'd
rather not bust my cherry on this piece. Besides, aluminum is freaking
expensive-- although steel isn't cheap either, as I'm finding out.

Ah, well. My brain is full of little 3-D mechanical puzzles

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