A HD Camcorder flying through the air metres above the ground, you're either very rich or have a lot of faith in your system. 

For starters I'd have a fail safe in case a wheel goes, cos if one goes the other will probably follow soon after, so a loop of rope going over the cable and firmly fastened to the rig. Also attach the camcorder into the loop in case its mount fails.

Other things to consider are the sort of slope you plan to use it on? and how long will it be?

I wouldn't think fishing line would be suitable, rope of some sort would probably be better, I'm looking at using climbing rope for my next one as its more springy and easier to tension. The longer the length the more tension you'll need so it doesn't sag in the middle.

From what I know of skiing it will be a fair slope, think of what gravity will do to a 1-2kg weight on that slope, the only way of stopping it without complicate the design is to put jumpers and towels etc on the rope, so that it has to push in front of it that will add friction and gradually slow it down. Presumably you will be tying it onto trees?, you'll need to be sure it will stop in time, cos trees and camcorders don't get on well.

Looking at your design it might take a while to get it balanced so its platform is level.

If your camcorder records to HDD or DVD be aware that vibrations could cause write errors and disc errors or damage the camcorder.

Make sure you are confident your camcorder will be safe, and that you are aware of the risks of damaging it, and can afford to replace it if it cos wrong. 

Let us know how it goes. 
Jeff

you need some way of regulating the speed of the camera, or if the rider is staying at one speed a way of stopping the camera before it smashes against the end of the line,
a rope attached may be a good idea,
but this may be in view of the camera and get tangled up with the rider below.
i am tempted to build one of these! so tell me what you come up with as it will help with my ideas!

If you mount the camera on the "base plate" or bottom board of your Cad design then have a bolt going though the upright into base plate with a wingnut so the whole thing is completely adjustable.
 You can then send it down a few runs and adjust the angle of the base plate/board according to the steepness of wire, hill etc.

i hope that makes sense??

I almost finished the cable cam today, following a new design I found on the internet. I just have to paint it now (black) and get the pulleys and rope and straps to tighten the rope.

Yeah, I'll definately take some pics when I get back home. I'm on holiday at the moment.

Thanks for the tip, mattyh222, I'll definately keep that in mind. You could have avoided a potential catastrophe by saying that. 

I looked at building a cable cam system similar to the one you are talking about, but cme across a lot of potential problems;  the main one being that the camera is fixed pointing in one direction (which in itself is a challenge), but the nature o downhill means that the track will vary alot in gradient, even over a short period, so it is very difficult to keep the rider centered in the shot.  As well s this adjusting the speed of the camera is very difficult to control
       Instead I have built one to take me and my camera.  This avoids almost all of the problems associated with your design as you can control the direction and zoom of the camera thus keeping the rider centered at all times.  Obviously there are logistical difficulties but my design works very well and was less expensive than you would think.
      Basically I have a 50m 10mm climbing rope, 2 ratchet straps to tension the rope, a pitzl tanem pulley, a harness, some carabiners, and a thin 50m additional line.  The hardest part of the design is slowing yourself down.  I ruled out any friction based system such as towel due to the extreme heat buid up and damage to the rope that it will cause.  You can run another rope round the starting point and use a belay device to basically absail down the line, but that requires a 100m length of rope which is cumbersome.  In the end I used the secondary line.  This is thin and has a knot in it about 5m from the end.  A pulley runs along this and is connected to me by 4 bungee chords.  I start down the zip wire, if I get ahead of the rider I zoom in, the when the pulley on the additional line hits the knot it jams and the bungees slow me down over a distance of around 3 meters (to avoid whiplash!). 

I will get some pictures up soon if you want, sorry abou the essay but I thought I might as well suggest a different design, plus its a lott more fun when your on it!

Callum