Projector update

Just a very quick update today. I’ve continued to work on the projector gantry, as it was obvious from my testing that neither projector was actually mounted perpendicular to the middle of each half of the screen.

To make sure they were, I placed two wooden beams running from above the centre-point of each half of the screen, offset by about 22mm to the left – which is the offset of the projector lens to the right – and ran this out to where it crosses over the gantry and beyond. This gave me a physical mounting line along which each projector could be mounted and be square on to the middle of each half of the screen.

Some experimenting showed that my original calculations for the gantry depth were actually about right – perhaps a little generous, but not by much. The effect I had seen, which led me to shorten the gantry, was due to the projectors being at an angle to the screen centres.

The original Icarus design does away with this problem by having a full circular frame at the top so that the mounting points for the projector are on that circle. Since I don’t have the capability to cut decent circles, I decided against that method, but it has led to these recent problems. Oh well, you win and you lose 🙂

Having found the right place on each crossbeam to mount the projector, I then did so using roofing blots, which keep the mount in place securely. Then I powered them both up, adjusted, and the result is below – a nicely even pair of pictures with an area of blend in the middle. There is still a little vertical keystoning, but this is unavoidable without adjusting the gantry height again. It’s not enough to care about.


Although the projectors are now effectively hanging in space behind the gantry, in reality the overhang and the stiffness of the wood + bracket combo keeps them from sagging, and it’s only the flexing of the gantry itself that lets them move about. The extra crossbeams actually give the whole structure more stiffness than before. I’m going to look at ways of supporting the gantry more, but this can’t be at the expense of the seating position.


Now that I’ve got the whole thing assembled, I know how much of my room this contraption is going to take up. The answer is – quite a lot. About 60% of the floor area, I reckon. Plus I’ll have to avoid the low-hanging projectors while I’m walking about. Oh well.

(I’ve had a look at the Icarus Avenger design again, and it looks like they put their projectors up higher and angle them down – this would work but would introduce significant vertical keystoning. I’m happier with my current solution – or at least, I will be until the first time I bang my head on one of the projectors!)

On the software front I’ve decided to try out NTHUSIM, which is both the most modestly priced warping software (these things are expensive and have to be licensed per-projector) but also the friendliest from what I can see. I’ll be playing with that during the week. More on that when I have something useful to say.