Building our Pixel Tree

This is a re-creation of our original page on the building of our video pixel tree, which was lost during a software upgrade.

Introduction:

Pixels are individually controlled LEDs. Out tree is composed of 1344 of these pixels. Each of these can be turned on or off, fade, etc. and change colors, with over 16 million color combinations possible. Moving images, still pictures, and video can therefore be “projected” by this tree. Pixels are not foreign to any of you. Every time you look at a television, or monitor you are looking at pixels, but they are much smaller than the ones that make up our tree. So think of our tree as being built using pixels on steroids!

Design considerations:

The first consideration was where to locate the tree in our display. We decided on an area in the yard that up to that point had not been used for any decorating. We also considered the option of being able change the location, should we wish to make changes to the display at some point in the future. To allow that option we decided to go with a portable base, designed by our good friend Walter Monkhouse. Walter calls this a portable hole, which is a good descriptor of its function! The base is built using 2 x 6 and plywood construction, following Walter’s plans which are here: portable hole ii

Here is the assembled base, with the rebar and center pipe flange installed. You will notice the eyebolts loosely positioned in the corners of the frame. They will be permanently anchored in the concrete:

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2 bags of 60 pounds of Sakrete were to be used. Given the weight of the base once the concrete was added I decided to mix it on site:

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I brought out a bucket, for better control of the amount of water to be added to the mix to ensure a relatively dry mix, and began the mixing process:

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Once the mix was to my satisfaction I added it to the base. You will notice the plastic cap threaded onto the pipe flange. That was a temporary measure to assure no concrete found its way into the open pipe:

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It was compacted as it was more cement added to make sure the form could accommodate the 120 pounds of mix:

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Special attention was given to compacting the corners where the 4 eye bolts would be added:

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Once the compaction was accomplished, it was time to smooth the surface:

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The last step was to add the eye bolts, and then let it cure:

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The next step was to design the bottom “hoop” to which the strings of pixels would be attached. I did not want the strings to come all the way down to the ground, as that looks like a maypole. I wanted to design something that would resemble the base of the tree, just as I did for our megatree.

Once again I followed a design that Walter had engineered which he called his ColorMotion tree: Building_A_ColorMotions_Tree_sm

I picked up 4 sections of 1 inch diameter EMT metal conduit at Lowes. I marked each one at 1 inch increments to guide me in bending the conduit to the circular shape I wanted. Although 4 conduit sections were more than I needed I wanted to make sure I had extra as I had never bent pipe before. I borrowed a pipe bender which worked out fine.

I was so focused on not messing this step up, I never thought to ask my wife to take pictures of the process!

Here is the conduit after the bending showing the 1 inch markings:

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Here are the conduit sections after bending. As you can see I had some extra length to remove:

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I took a pipe cutter and then removed the excess length, taking off the excess from both ends of each section, as the ends did not have the same degree of curve to them the body of the sections had:

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I wound up with a nicely formed circle:

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If I decided to go with  360 degree tree I was all set. I made the decision to not go with a 360 degree tree, as I did not want pixels from the backside of the tree to show through when I was “projecting” video effects, pictures, etc. on the tree. Additionally, I already had a megatree that gives a 360 degree view.

After considerable thought I went with a 210 degree arc, which gives the illusion of a full 360 degree tree from all possible viewing angles in our display. I cut the conduit down to the length needed for the partial (210 degree) circle.

The next decision was how to support the hoop above the ground to avoid the maypole appearance, and provide enough height to clear the usual amount of snow that we get. Based on that I went with 24 inches above ground.

To support the hoop against the pull of the pixels it would be anchoring I made the decision to employ 1 inch diameter rebar. Given the 2 foot height above ground for the hoop I went with 4 foot long pieces, to allow 2 feet below ground to serve as a solid anchor. Based on my 210 degree hoop I would need with 8, plus 2 more which would be located behind the tree to serve as a counterpoise. More on that later.

Knowing our soil is heavy clay which contains a fair amount of buried rocks, it would be a challenge to pound 1 inch diameter rebar into the ground, so I decided to grind the ends to a 1/4 inch diameter point:

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Once the rebar was ground to a point it was time to decide how best to mount the conduit to the rebar. I liked Walter’s idea of using galvanized pipe fittings, so I purchased 10 one inch diameter galvanized T’s, and 10 one inch diameter by 4 inch long pipe nipples.

Since the 1 inch conduit was now curved, it would no longer slide through the T’s without some modification to them. This was accomplished using a hacksaw to cut both arms of the T off as close as I could to the main body of the T .

Even after cutting the arms off I found the conduit would still bind when I tried passing it through the T, so I took a drill with a small 3/4 diameter inch grinding bit attached to it and ground out all the inside threads. This allowed the conduit to easily slip through the T without any binding whatsoever:

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Finally I drilled a 1/4 inch hole in the side of the nipple, through the 1 inch rebar, and out the other side of the nipple, to allow me to place a bolt and nut through, which will anchor the T (and therefore the conduit passing through it) to the ground. When all attached it looks like this:

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Now it was time to go out to the site, taking the conduit sections, joining them with couplers, and then centering them around the now cured base unit. I used a length of string to be sure the center of the pipe fitting installed in the concrete base was in the exact center of the conduit hoop that went in a 210 degree arc around it. Once I was assured everything was centered I sprayed white yard marker around the conduit to enable me to know where to drive the 1 inch rebar into the ground:

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Then began the process of driving in the one inch rebar, with the help of my son-in-law Aaron. Even with the rebar ground down to a 1/4 diameter point, it was a chore, given our soil conditions, but we knew once it was pounded in, it would stay:

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After pounding in all rebar, I had to grind down the ends of a couple as there was some flattening of the ends after we drove them through some buried rock:

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During the process of anchoring the rebar we used a long level to ensure each one was level with the next rebar, so the hoop would be perfectly level. We then lowered the conduit with its galvanized Ts onto the anchored rebar and rechecked for level:

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Here are some pictures of the final assembly of the base and surrounding conduit hoop:

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In the picture above, on the left hand side, you will note the 2 rebar with T’s designed to be a counterpoise to the tree once the pixels strips are mounted. More on that later….

The vertical pipe that would form the “trunk” for our tree was composed of a ten foot section 2 inch metal conduit, which would through a coupler and reducing section (see Walter’s plans for details), support an 8 foot section of 1.5 inch conduit.

The most engineered part of the tree would need to be the “topper”, the metal top piece that all of the pixel strips would attach to. I spent some time with Walter on the phone, as I wanted to re-engineer his original design to develop as small of a topper as possible, so the tree would have more of a taper resembling my mega tree.

That worked out to be a round disk a little shy of 16 inches in diameter, instead of the original 20 inch in diameter disk. With the proper sized star on top that would look fine. To give you a size comparison most conventional mega tree toppers are about 8 inches in diameter.

This was a task I was not able to undertake, so I relied on a commercial shop to fabricate it for me.

The question was how many strings? I went with 32 (half of what is on my conventional mega tree), figuring this tree is only 210 degrees instead of 360. Doing some math I realized I could take a string of 85 pixels, run them 42 up from the hoop to the top, and then 42 down from the top back to the hoop, with one pixel left over that would be left turned off. Bottom line I would need 16 strings of 85 pixels (8 universes worth) to make the 32 strings I was looking for.

I went back to Lowes and picked up 32 J hooks that are 1/4 inch in diameter and 4 inches in length, along with associated hardware, and began to attach them to the topper, which had been drilled for 360 degree placement if needed, allowing me for future changes if I ever decide to go for a different look. I doubt I’ll change the tree to go beyond 210 degrees, but I can if needed:

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With the topper prepared (everything was painted flat black to help hide it at night) I added a ropelight 3 D star. I designed it to be 30 inches to ensure it was not dwarfed by the tree, nor too large for tree either. That is a subjective decision, one the reader should make for him/herself. It is installed on a small section of one inch pipe that screws to the top flange on the topper:

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I then turned my attention to the actual straps that would hold the pixels. I went with 5/8 inch wide banding material which is used to tighten and secure packages for transport. It has exceptional tensile strength. It can not however be drilled through (as others have found out), as it significantly weakens it, causing it to split.

The best way to secure it is to fold the ends over, using rings/hooks, and securing them with tape or zip ties. Here is a pictures of the strapping, along with the 2 different connectors used to attach the strips to our tree. One connector is a standard D ring, that can be purchased from clothing/fabric stores. The other is an eye bolt that can be purchased from any hardware store:

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You will notice the eyebolt looks almost like a J hook, as it is open. Unfortunately they are not sold that way. They need to be modified, which I accomplished  with the use of a large screwdriver, a vise, and a lock grip:

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Once the eye bolt was opened, just enough to allow the 5/8 strapping to fit I folded over the end of the strapping and secured it with four 80 pound zip ties. The other end of the strapping was secured to a D-ring, which fortunately needed no modifications, with 3 zip ties:

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This process was followed for all 32 bands. Here are a few:

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Once the bands were ready I had to figure out a way to stretch the bands out to full length, to be able to attach the pixels at precisely the same distances. Unlike a conventional mega tree where the distances don’t matter all that much, this needed to be extremely precise, as we were in essence making a video screen in the shape of a tree. Even 1/4 inch differences would be readily apparent!

Fortunately in the basement I was able to use my yet to be finished train tables to provide the distances needed to stretch these bands out to length and attach the pixels. Given I was using one pixel string to first go up one band, and then come back down the other I secured the banding in pairs, using their opened eye bolts at one end:

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and chains with turnbuckles at the other end:

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To make sure spacing was correct the bands were each measured and marked off at 3.5 inch intervals, which is the spacing I decided to go with. Now it was time to begin the slow, and laborious process of attaching the pixels.

The first step was to test the pixels, “burning them in” for a few hours to make sure there were no failures:

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Once that was done it was time to attach them to the banding material. I considered using zip ties, but the tension of the zip ties slightly deformed the sides of the banding (unless it was folded over as it is on its ends), and I didn’t want to weaken them. Clips were out, as they would tend to slide unless fastened to the banding, which would also require zip ties.

I settled on using tape, cutting 6 inch long strips to wrap the wire above and below each pixel. I picked up 30 rolls of Scotch 88 industrial electrical tape, and wound up using all 30 rolls!! This was the most time consuming aspect of the entire project, but once taped in place, these pixels don’t move, and the tape stays on! At the time I am re-writing this how-to the tape has been on 2 seasons, with the banding with attached pixels being rolled and unrolled each season for storage, without any shift of pixels or unraveling of tape.

Here is a picture of the pixels being applied. Unfortunately 3 years ago after these were first installed we ran into issues with pixel failures, so the entire lot had to be returned to the distributor. They were replaced with better quality pixels which have been in use for the last 2 season without a single failure.

That process was painful, as I had to unwrap the old pixels, and then attach the news ones, using another 30 rolls of 3M tape, but the end results are better, with pixels that have 16 bit dimming, as opposed to the originals, shown here, that were 12 bit. The first picture show both strings fully attached with the 85th (extra) pixel loose projecting beyond the end of the banding:

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Tis picture shows some rulers I stuck under the wiring in between pixels to keep the banding from twisting while attaching the pixels:

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This shows the cross over of the pixels from one band to the second. This is at the top of the tree.

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After all 16 strings of pixels were secured to the 32 bands, the strings were rolled up, ready to be taken outside and installed on the tree:

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Once the vertical main pole was installed in the concrete base, the topper was added and it was time to take 3 strings out and attach them to the topper to far right, center and far-left J hooks. They were then stretched out and where they touched the bottom hoop their positions were marked.

I then measured and equally divided the spaces between those 3 points of reference, in preparation for drilling the 32 holes 1/4 inch in diameter in the conduit necessary for the eye bolts attached to the end of the pixel banding to pass through and be secured. I drilled each hole with a slight angle to line up with the angle the banding intersected the conduit with:

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Once that was completed, I reattached the 3 pixel bands, securing them, and then loosened the slip connector between the 2 vertical conduit sections, sliding the inner 1.5 inch diameter conduit up, until all 3 bands were tight. A mark was made at that point, the upper section lowered, the bands removed, and the conduit was then raised again a few inches beyond the mark.

I clamped the 1.5 inch conduit just above the connector, drilled a 1/4 hole at the mark made earlier, and put through a bolt through the conduit it, to prevent the 1.5 inch conduit from sliding back down into the 2 inch conduit. The slip connector was then re-tightened:

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Once that was done all 32 pixel containing bands were then installed, with their d-rings  being hooked over the J hooks on the topper, and their bottom eye bolts being inserted through the 32 holes in the conduit, where they were secured with double nuts, to allow any adjustment of tension as needed.

Two 1/4 inch aircraft cables were attached to the topper on the backside, equidistant from the back left and back right sided pixels, to provide back tension on the topper, which receives a lot of forward pull by the tensioned 32 pixel bands on the opposite (front) side. They were attached to the 2 rebar in back, passing through the attached galvanized T’s and a turnbuckle for tensioning. The tree was essentially now complete, except for one issue.

There was slight rotation of the banding the pixels were attached too. Fortunately Jackie Monkhouse had figured a way around that, by weaving extra banding behind one strip, in front of the next strip, behind the third, in front of the fourth, etc. horizontally across the tree, in a basket weave pattern!

I liked the concept , so I expanded it a little to weave a band every 6 pixels vertically, requiring a total of 7 straps. It worked like a charm, and in even in very high wind (we received a record breaking 72 mph gust the first year) nothing moved!

Here is the finished tree:

 

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How well did all the measurements work in designing what amounts to a tree shaped video projection grid? Forgive the underexposed cell phone picture, but you be the judge of this projected picture of Rudolph:

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My thanks go out to Walter and Jackie Monkhouse for the original design and engineering tips, and my son-in-law Aaron for helping to install this remarkable display item!

Greg