So that took longer than I had expected…
I got the new hardboard for my screen update a few weeks back and it sat there for a few days while I got ready and pulled down the existing screen. But then I was ill for a bit, and then I had work stuff to do, and one thing and another meant it was a while before I got round the new screen.
There’s been a mild setback in the curved screen department. In an attempt to improve the finish of the screen and get rid of the oval-shaped ‘dip’ in the centre where the two halves join, I pasted a layer of thermal lining paper over the screen. This seemed to be working well, but upon painting over that paper, all kinds of nasty sagging and distortions appeared. The lining paper is all but impossible to get off, too.
So I’ve decided to remove all the hardboard from the frame, and do it again. This time I’ll use three segments rather than two – I still can’t get a single piece of hardboard big enough – so the joins will be to the left and right rather than in the middle. I will also take the opportunity to improve the frame so those joins can be better made.
That’ll all happen this week, after which I’ll have to re-paint and re-warp the image. Annoying, but not the end of the world, and I’ll have a better screen for it.
Pictures later this week…
Just another quick update.
I made a few more adjustments to the projector frame and gantry over the last few days. The first major thing I did was move the projectors higher up. As I observed last time, in the Icarus Avenger 180,which is my inspiration for this project, the projectors are placed rather higher than mine. Mine are placed level with the top of the screen, whereas the Avengers’ were placed at least 200mm above it, maybe more. They are then angled down to direct the light towards the screen. This has the disadvantage that horizontal keystoning occurs – that is, the bottom of the projected image is wider than the top – but the degree of keystoning is small at low angles and can be corrected for quite easily. So I raised the gantry by about 200mm and then angled the projectors down to compensate. This has one immediate advantage: I no longer have to duck to walk around any more. Taller people may find their mileage varies, but I’m not moving them any higher.
The horizontal keystoning is not at all bad
Because the gantry brackets were now much higher up than they were designed to be, the gantry itself was starting to ‘lean back’ as the brackets bent a little – the attachment part is made of 18mm pine baton which is not rigid. So I purchased a couple of metal shelving brackets from B&Q and used these upside-down to brace the gantry.
Lastly, I ran some power and HDMI cabling up to the gantry. I placed a 4-way adapter socket on the gantry itself in the middle, and ran the power cables for the projectors to this. This gives me two more sockets which will come in handy when I put in place the overhead monitor that I’m intending to mount – of which more later. See, I do think ahead sometimes! I might cut down and re-make the power cables for the projectors to custom lengths to avoid having to coil them round the wood like that.
Power wired up – HDMI was added. The shelf bracket is just visible on the right
I need to clean up the build area. Then I can set up a workstation to begin the screen warping configuration. For this I will resurrect my previous Sandy Bridge gaming rig – into which I’ll place a newly-purchased GeForce GTX 980 Ti – as this is close enough in horsepower to my new rig to enable me to set up and test without losing my ability to go on simming in the other room.
I’m mostly stuck working at the weekends still, so progress is slower than over Christmas, but look forward to some warp action maybe this weekend, if not then next week at some point!
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.
I did a very quick vlog to show you the projectors being tested… I promise future vlogs will be more interesting!
Construction on my 180 degree curved projection screen is complete, at least for now – there’s stuff to finish later, but only once I’m happy that everything is working as it should.
Now I’m moving on to placing and configuring the projectors. This will be a relatively lengthy process, so I thought I’d document a few of the pitfalls first, before I really get started.
So I’m still working on my curved projector screen. Last time I updated you I had gotten the hardboard onto the frame in a semi-circular shape (roughly) and had gotten the whole contraption up on tripod legs.
Since then, I’ve adjusted the legs slightly for the uneven floor in the room, and firmly attached the left side of the frame to the wall. I’m thinking about doing the same on the right using some baton as a bridge. But it certainly isn’t going anywhere now, not without taking a chunk of wall with it.
Holes and bumps filled
Over the last few days I have been filling and sanding. This is harder than it looks on a curved surface, since you can’t use the usual filling knife to make a flat surface. In the end, I used my fingers a lot, which was messy. I had to give particular attention to the split between the two sheets of hardboard, as this will be in the middle of the screen and needs to disappear altogether. This will be a big challenge. Several rounds of filling and sanding later, I had a reasonably smooth surface to paint. Today, I put on the first layer of undercoat. This is going on before the Screen Goo base coat – indeed, putting on the Goo will be almost the last things I do, I want to be sure that everything else is good before I apply paint that costs hundreds of pounds a tin!
I’m using an undercoat intended for ceilings and masonry, because this will soak into holes and defects and will stretch and resist cracks, and cover blemishes well. But after a single coat, there are still very obvious problems – a clear dividing line down the middle where there is heavy filler and the surface accepts paint differently. Also, now it’s painted, I’ve revealed a few surface imperfections that will need to be further filled. So I expect I’ll need to do maybe another 3 coats of this paint before I’m happy that there’s a flat white surface I can apply the Screen Goo to.
After first coat of paint – note the obvious middle seam
Once I have that initial flat white surface I will mount the projectors and get their positions fixed. Then I may do some initial tests on the image warping software – of which more in a future post – to see how it all works. Once I’m happy it will work as constructed, the Screen Goo goes on. I’m a bit nervous about that 🙂
I’m hoping for some form of demo by New Year – not complete, by any means, but a working, warped image. We’ll see…
Another quick update. Today I fixed the hardboard sheets that will act as my curved screen to the frame, and then mounted the frame on tripod legs to get the screen to the right height. Pictures below.
Half the screen surface in place, frame on the floor
The completed screen up on its tripod legs
This was difficult work to do on my own, given the scale of the frame. I cut the hardboard in-situ downstairs where it was delivered into the smaller pieces I needed – I couldn’t get a single piece, so it had to be done in two halves, about 1570mm x 970mm each. I overcut the length to give myself room to fiddle with the curvature.
I placed the hardboard up against the middle vertical member of the frame, used a clamp to hold it flat in place, and then put in a number of screws down the length of the baton. I moved to the next baton left / right, pushed the hardboard into a curve, adjusted the curve until it appeared circular, and then did the same again, and so on. This left me with a curved screen, a join in the middle (not ideal, but it’s the only way I could do it with the frame as designed), and some overspill on the left and right which I trimmed off.
Then I needed to add the legs. Ordinarily I would just have laid the frame flat on its face, added the legs, and then stood the frame back up again onto the tripod of legs and bingo. But the room I’m building in is just too small for that. I was able to add the middle leg of the tripod, at the very rear of the frame, and still get the frame back to the vertical, but the legs either side were a different question. Eventually, I hit on the answer of screwing the side legs in with a single loose screw, so they could move, and then moved them out of the way to lift the frame, and then moved them back, kickstand-style, once it was up. Then I simply added the second screw and tightened the first, and there you are… one screen, 800mm from the floor, as requested.
Finally, a single bracket was driven into the wall stud and the bottom of the frame, to keep it anchored in place along the wall. I’ll do another along the top later on.
Next steps – add the hangers for the gantry, and the gantry itself. Then filling and painting, then a coat of white primer, and I can start testing the projectors before I finally add the Screen Goo!
Just a really quick update… I’ve started on the build of the frame for my projection screen. Current progress shown below.
This is a pretty simple construction. It’s basically half of an octagon – although for various reasons the odd and even sides are not exactly of equal length – and will force the hardboard I’m using for the screen to adopt the semi-circular shape that I need. The board will be tacked to the vertical frame members which are designed to be flat against that point of the curve.
The frame is pine baton, 44m x 44m, mostly joined together with 120mm x 7mm concrete screws – which have proven excellent for building frames provided I drill proper pilot holes. The angle joints were all cut on my trusty mitre saw and are joined with multiple 3.5mm screws. This holds them together but does allow them to move a bit and since the frame needs to be stiff, they needed re-inforcing, so each joint is backed up by a strong steel plate that braces it. Now it only moves as far as the wood itself will bend.
Next, I have to put on the hardboard itself. This is likely to be tricky so I will test-fit everything first and trim to size. And once this is in place I will add a tripod of supporting legs to hold the screen the correct distance from the floor, and the side of the frame that contacts the wall – only one can do this, because there’s a radiator on the wall on the other side, unfortunately – will also be screwed into the wall battens using brackets. This should keep the whole assembly rigidly in place.
Finally, I will mount a gantry to the rear of the frame to hold the projectors. I need to do some tests to measure the picture displacement distance for my projectors, so I won’t know exactly where to fit the gantry until I’ve done that test. So that’s probably a job for after Christmas.
Oh, and speaking of which, Merry Christmas to all my reader 🙂
Just a very quick update – today I finally got around to printing and adding labels to the magneto and switch panel on my temporary simpit.
This is not quite as easy as you’d think, at least not without the proper tools – Adobe InDesign or similar. But you can achieve good results with Paint.NET, provided you measure things carefully and take note of your printer’s DPI setting.
In my case, my printer does 600DPI and so I created an image at 600DPI and sized it to fit, then put labels on as text and adjusted them until they were in the right places.
For the magneto, I pasted a piece of paper onto the top of the plastic panel, marked off the switch positions with a pencil, then scanned that in and put it under my image, scaled correctly, so I could position the text labels.
Then it was a matter of firing up my trusty colour laser printer, printing onto A4-sized sticky labels, cutting out the relevant parts with a scalpel, and then sticking them to the console. Results are below. They’re good enough, although some of the labels are a little off-centre. Never mind!
backbedroompilot.com 