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-   -   Microcrane?? For Skater Dolly (https://www.dvinfo.net/forum/dolly-track-cable/116127-microcrane-skater-dolly.html)

Bob Hart March 1st, 2008 07:46 PM

Microcrane?? For Skater Dolly
Does anyone have a design for one of these things.

Vertical travel approximately 2 ft or 600mm.

Adjustable vertical parallel upper control arm for auto tilt of camera on approach to groundlevel, optional adjustable horizontal lateral control arm for auto parallax correction on small arc lateral swings.

Paul Mailath March 1st, 2008 09:09 PM

sounds like fun!

I build one out of sq alumimium tubing with vertical travel of around 2m from bits I got from Bunnings Hardware - If we reduce the size of everything we should get to the size you want.

Let me first understand what you're asking

Adjustable vertical parallel upper control arm for auto tilt of camera on approach to groundlevel

I'm assuming you mean that the camera stays level as you raise and lower the arm? or do you mean that you want to be able to adjust the camera level 'on the fly'?

optional adjustable horizontal lateral control arm for auto parallax correction on small arc lateral swings.

yea.. I've got no idea what you mean by this - can you explain it in simple terms for me, what do you want the camera to be able to do?

of course if someone comes up with a real design, forget I mentioned it - we'll both steal the real one.

Giroud Francois March 2nd, 2008 06:41 AM

for such design, a micro elevator will be more efficient.
crane requerie a very stable stand, i do not thing a rolling platform would fit.
a simple vertical rail would do the job

Bob Hart March 2nd, 2008 08:55 PM

Paul and Giroud.

Thanks for the feedback.

The adjustable arm can be seen on small studio cranes, the one which gets bent because the designers failed to build in a limit stop.

I built a 14ft one about 25yrs ago and had the upper control arm arranged like the track rod of a truck steering system and used automotive parts to be assured of adequate strength.

I found that if I was cunning enough, I could set the thing up to be centred on the horizon, dip to an approaching subject halfway down the descent then centre on the horizon again at bottom of descent.

It was a bit of a disconcerting ride for the camera operator though. The countermass tray has to be securely packed against movement of the contents or things get a bit exciting.

I also had this crane set up so that there was a slight pendulum effect. The point of balance could be adjusted to come to rest high or low by fine-tuning the countermass. That is what I would like to do with the skater, as hands-free an operation as possible to avoid bumps and knocks.

My design was set up like a beam balance with load centres directly above the main support beam end pivots, not outboard of them as is the conventional practice.

Conventional is the more competent design in that there are no alternating tension and compression loads and consequent bending force applied to the control arm, which could end badly if the control arm fails by bending and dumps the operator or leaves him hanging in his safety harness upside-down.

I found I did not have the confidence to ride the thing and it required a second assistant. Instead I found it handy to send the camera up on its own, pre-positioned on the tripod head, the control arm set up to tilt upward at groundlevel with the balance biased upwards and haul it down with a light rope and follow the approaching subject by operating the camera conventionally at groundlevel.

The lateral arm for a skater version would be for control of the pan movement of the camera.

It could be set up to be truly equal length arm with the loadbearing arm or to be shorter to provoke the reversing panning movements over the half-arc of available swing or to provide a full arc panning movement if the arm is adjusted longer.

Horizontal full arc movments are not really necessary as the Skater can be set up to do these anyway, but it cannot reverse an arc movment in one direction of travel except by the wheels being ridden in "C" section rails which defeats the convenience of the Skater system.

With a fluid head on the end of the arm, there would be a tendency for the operator to pull the whole thing over.

A fixed vertical movement is very worth looking at. Adjustable counterforce would have to be designed in and that could be a bit difficult to control. Would probably have to be something like the steadycam arms and their compression spring and cable systems.

It would be difficult however to bring the base of the camera as close to groundlevel as the crane arrangement could be made to do.

Paul Mailath March 3rd, 2008 10:44 PM

Woah! - after considering the pendulum effect of the countermass tray and the horizontal full arc movements of the main support beam end pivots I realised I have no idea what you're talking about.

It may just be that my engineering skills (lego based) are not sufficient for this particular problem.

Good luck with it.

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