I now have some target numbers for designing a new power system for Glow Flow, and whatever system I design will need a big battery to enable long run times. The most capable batteries on hand (*) are those I purchased for Sawppy rover. These batteries are designed to deliver high amperage (~150A) by trading off raw capacity. They are not ideal batteries for Glow Flow, which would draw low amperage over a longer duration, but they’ll work and they’re already here.

I started designing the battery tray first because it is a simpler problem to solve as I start figuring out how to apply tool-less construction techniques for components inside the cylinder core. They will be clipped to the grooves in top and bottom end pieces. Batteries are also expected to be the largest and bulkiest component, so installing one will help me gauge how much volume remains to work with.

A velcro strap holds the two pieces of this battery tray together. This strap was a free gift the battery manufacturer conveniently packaged alongside the battery.

Previously the USB power bank was held in the center of the cylinder. This time around the battery is held against the inner side surface of Glow Flow core cylinder, leaving a few millimeters of space behind for wire routing. There appears to be plenty of space left for additional components. Next up: the power regulator board.

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(*) Disclosure: As an Amazon Associate I earn from qualifying purchases.

Even with the help of a few test pieces, it was not a surprise that the first full sized prints of a Glow Flow flexible diffuser panel and associated rigid support rib still required a few final adjustments. But once done, I printed out a set of three ribs, three panels, and assembled them together. Each of the ribs also function as one leg of a tripod for supporting Glow Flow. Not as subtle as the previous iteration, but the same general idea.

The completed assembly was more rigid than I had anticipated. The ribs worked well and, when supported by ribs on either side, the panels could actually take some stress. Enough to allow someone to handle Glow Flow by grabbing the sides without risk of everything falling apart. This is a pleasant surprise. I started with the minimum of 3 ribs 120 degrees apart, just to see how well it worked before I increase the number of ribs. Apparently 3 ribs are sufficient so we can stop here.

But the most important part is to see how well it does its primary job of diffusing LED lights and it’s very satisfying to see that job done well.

This design has a few issues: Because of its flexible snap-together nature, the ribs are free to slide out of position no longer exactly 120 degrees from each other. When this happens some panels will bulge out more than others. A related but different problem is the panel vertically shifting within their slot. I cut the slot taller than a panel needs to be as a provision for some sort of top & bottom border pieces. But right now those slots mean a panel has room to shift, which could also result in an unsightly bulge.

Those are problems I could tackle later. For now, attention turns to restoring Glow Flow to battery-powered portable operation.

Limited by my 3D printer’s usable print volume, the 3D-printed thin translucent diffuser panels for Glow Flow must be printed in multiple pieces and joined together with rigid support ribs. When I experimented with snap-together construction for thin panels, I tested a simple design for joining two of these panels together. However, I’ve since found that design could not be used to join a thin diffuser panel to a rigid rib. I will need a different design better suited for the task.

The characteristics for this problem were:

• It needs to join two parts, one rigid (support rib) and one flexible (diffuser panel)
• Flexible portion will be printed vertically in vase mode as part of the diffuser.
• Rigid portion will be printed printing horizontally as part of the rib.
• No supports as I don’t want to cleaning up supports inside the slot!
• Rigid portion must be printable both right side up or upside down so a rib can accommodate a panel on both sides.
• The joint does not need to be equally strong in both directions. These panels are more likely to experience inward force as when someone is grabbing and handling Glow Flow by the panels. In contrast, outward force is far less likely.

To test these constraints, I printed small samples to see how small tweaks to geometry impacted performance. Each of these small samples consisted of two symmetric pieces. A rigid one representing the rib, printed the way a rib would. Plus a flexible one representing the diffuser, printed in vase mode.

Getting the pieces to fit correctly were a challenge. If the pieces are too loose, a diffuser panel might pop out at inconvenient times. If the pieces are too tight, I would not be able to insert them. The rib section is designed to be symmetric, but the center of the rib depends on 3D printer’s bridging capabilities to work without supports. A bridged surface isn’t as smooth, so there’s some asymmetry between the two slots. There’s also some asymmetry introduced by the interface with the heated print bed also sometimes called “Elephant’s Foot“. And finally, there are imperfections introduced by the 3D printer that cause parts to collide because the two pieces are printed in different orientations. Test sample #1 in the picture above shows print bed orientation of each piece.

These test pieces were useful to explore both CAD dimensions and 3D printer settings before returning to the challenge of building actual pieces for Glow Flow.

3D printed in vase mode, Glow Flow diffuser panels can be held together without tools using flexible tabs. However, keeping them thin to be translucent also means they are very soft and could not hold their own weight. They will need support structures to hold them at correct distance from LEDs. At the very minimum we’ll need 3 support ribs, spaced 120 degrees apart, to support panels small enough to be printed. This first pass will install three ribs and associated panels. Once they’re up and running, we’ll evaluate the results for future iteration.

The diffuser panels re-awakened an interest in designing for tool-less construction, individual pieces that snap together. So the diffuser support rib is designed to be printed in one single piece and, through flexibility of plastic, clips onto grooves in the new top and bottom end pieces. The cross-section of this rib is an I-beam, with slots on either side for installing diffuser panels. However, the first iteration did not fit.

Even though all dimensions matched the earlier diffuser panel tests, it didn’t work here because the new rib is rigid and its slots did not flex. This design only worked if both ends are flexible to accommodate each other on insertion, as was the case earlier when I had two flexible diffuser pieces fitting in each other. Now, the rib is rigid and the diffuser panel tab could not compress enough to fit within the slot. In order to proceed, I will need to put time into designing a better mechanism.

Once I started thinking about building my diffuser panels to snap together without fasteners, I started thinking about designing other parts of Glow Flow for tool-less construction. It is appealing to be able to perform field repairs without requiring access to a tool box. I’ve done a few other projects with this kind of thinking in mind, like the panning camera base for my Supercon 2017 badge hack. But as I started incorporating aluminum extrusions for my projects (Luggable PC both Mark I and II, and Sawppy rover) I had to use fasteners for those larger and heavier projects.

In terms of size and weight, Glow Flow sat in between those extremes, so would be a fun new frontier to explore tool-less snap together construction. The project did not start with that in mind, so my central LED cylinder core was printed with holes for M3 screws. But that is no barrier, as the cylinder was always intended to allow exploring different end pieces top and bottom without having to reprint the large core cylinder, a flexibility that I shall now take advantage of because there’s little to lose.

My current top and bottom end pieces were designed to support a USB power bank, which could not deliver enough power to run the 300 LEDs at full power. So it was never intended to be the permanent solution and those pieces were slated to be replaced eventually. I would have to find another home for the Pixelblaze circuit board, but that is a minor thing.

Replacement top and bottom end pieces were drawn up and printed, each with a central groove for modules to grip on to. They are fastened to the core cylinder using its existing provision of M3 screws but, if all goes well, there would be very few other fasteners on Glow Flow.

With removal of the USB battery bank, Glow Flow is no longer portable and is tied to my bench power supply until a new power solution is online. That is a problem to be solved later. In the near term, attention returns to the LED diffusers which had awakened my interest in designing for snap-together construction.

After exploring a few ways to make 3D-printed diffusers for Glow Flow, I decided to proceed with no surface features and instead relying on raw distance to obtain diffusion. Not putting in surface features is easy, but how would I go about keeping these panels at a distance from LEDs?

If they could have been close to the LEDs and thin, there was a chance I could print one continuous cylinder to put around these lights. But the ambition to hold them 1 cm away, and have two layers 1 cm apart, pushed overall size beyond what my printer volume could handle. I will need to move to a multi-piece system.

Going multi-piece means I have to start thinking about how the pieces would join together. And given the nature of the diffuser, anything I do will be clearly visible and backlit by Glow Flow LEDs. This makes aesthetics of the solution a much larger concern. I didn’t want to have a row of screws or really any fasteners, so I started thinking about minimalist snap-together joints for these diffuser panels.

The first experiment seemed to work well, these pieces They fit together with a satisfying click and held up well to moderate mechanical stress. The resulting seam is visible as a plain shadow without details to distract. No black circular shadows of fasteners. The downside is that these panels are not nearly strong enough to support themselves. I’ll have to add some rigid support ribs to hold them up. And since these panels got my mind going on tool-less construction, I’m going to continue on that theme.

After playing with the magnitude of a diamond pattern as LED diffuser for Glow Flow, it looked like the easiest thing to do for a good blend is put more distance between the LEDs and their diffuser. Which led to the next question: where should that distance be? Because these diffusers were printed in vase mode, they actually have two surfaces to help with diffusion: an inner layer and an outer layer. It looks like the outer layer needs to be about 2cm away from the LEDs, but where should the inner layer be?

If we put the inner layer close to the LEDs, it would get first stab at diffusing light early, hopefully increasing its impact on outer layer diffusion. If we put the inner layer further away, it would receive a more diffuse input to begin with. Which would end up looking better?

To test which of the two might be better, a quick test was printed up with two different separation distances between inner and outer layers. Putting them up against Glow Flow LED core, the winner was… neither. It was basically a tie.

When we held the outer layer at the same distance from LEDs, visual output is nearly indistinguishable up close. From further away, they were identical. It appears for this 3D printed diffuser approach, the position of inner layer does not matter. It is the position of outer layer that will determine diffusion.

Based on these experiments with 3D printed diffusers, neither a surface texture nor texture magnitude nor layer separation made a significant improvement in appearance. The variable with most impact is distance of outer surface from LEDs.

In commercial product development, devoting such distance for diffusers is problematic because that is empty space not productive for whatever the product is supposed to do. One example: LED taillights in cars have a very limited space budget, because any volume consumed for good diffusion means less trunk space.

But for a hobbyist project like Glow Flow, where the whole point is appearance, we can freely devote volume to allow LED diffusion with a simple 3D printed mechanism. The next step is to think about how this diffuser will be installed.

Using a diamond pattern to diffuse LED light for my Glow Project had interesting results but the first iteration wasn’t quite to my liking. But it showed enough promise that I thought maybe it’ll just be a matter of tuning. The first parameter for experimentation was the magnitude of diamond peaks, how does it look to have a subtle diamond pattern versus a strong one?

Holding them up close to the LED, the subtle pattern was preferred. A strong diamond pattern added itself into the conversation and, while that’s a valid approach to a project, it’s not the goal for this specific one.

This difference only got more pronounced as they were moved further away from the bank of LEDs. A strong diamond pattern started shouting its presence where the subtle one stayed quiet.

So far the best blending effects were accomplished just by holding the diffuser further away from the LEDs, and exterior pattern structure doesn’t do enough to mitigate the bright points of LED. But there’s another variable we can play with: these are vase prints, with an inner and outer wall. If we changed the distance between these walls, would that make a difference in distance required for a good diffusion?

Experiment continues to create a LED diffuser for my Glow Flow project. I started cheap with some paper towels from the kitchen, moved on to a featureless 3D printed sheet, which I then added horizontal ribs for strength. The downside of 3D printed diffusers are their layers, which interact with light resulting in uneven brightness across layers.

After observing this behavior, I decided to try using a diamond pattern overlaid at 45 degrees to printed layers. The hope is that, by changing how layers stack on top of each other, I can break up the vertical streaks of brightness. Doing this experiment meant taking my horizontal rib and, instead of revolving around a center axis, I would loft it along two helical path instead. One helix goes up, the other goes down, and the intersection of those two gave me the diamond pattern I wanted. This turned out to be a nontrivial shape to compute in Onshape CAD. I could probably do it more efficiently, but this is good enough for my experiment.

Once printed, I held it up to Glow Flow and… well, not a complete success. The diamond pattern succeeded in breaking up the pattern of vertical glare, but just by its nature it also introduced other distortions. When Glow Flow is turned off, the diamonds introduce a pretty pattern of light and shadow relative to ambient light. But with Glow Flow turned on, that pattern also interacted with light emitted by LEDs and the results are not to my liking.

When we pull the sheets further from LEDs, the diamond pattern becomes just a distraction no better than the featureless sheet.

There’s potential here, perhaps it just requires some tuning. Let me experiment with a few variables starting with diamond surface height.

A 3D-printed curved sheet of plastic showed promise as LED diffusion layer, but it was very flexible and I worry about its suitability to be the outermost layer of Glow Flow. The flexibility means people who try to handle Glow Flow by grabbing this outside layer may damage the sheet, and the flexibility also means it might be difficult to control its distance and therefore diffusion.

As an experiment to increase rigidity, the next print added a wave texture to the outer surface, giving it appearance of horizontal ribs. This shape should resist bending more than a texture-free sheet of plastic. It would also diffuse light differently, which may or may not look better. At the very least it is worth exploring and a vase mode print is a quick experiment to find out.

On the front of structural strength, the ribbed version is indeed noticeably more rigid than the featureless sheet. It still doesn’t feel rigid enough to withstand handling, but enough that I think it can maintain a particular distance (and therefore diffusion) without worry. Certainly good enough to be worth further experimentation down the line.

On the topic of visual appearance, the varying angles of these ribs picked up light from both above and below, presenting a blending of lights that correspond to the ribs themselves. On the downside, the print layer direction seems to magnify a problem where the light is focused into a vertical line that is extremely visible from certain angles. The featureless sheet also had this problem but not as serious.

The ribbed sheet is more interesting than a featureless sheet, and this opens the door to additional experiments on how we might use physical strengthening geometry to aid diffusion. The next experiment: introduce bending along more than one axis for a diamond-like pattern.

Experimenting with different ways I could implement a light diffuser, there’s no reason to overlook 3D printed plastic. One problem is that 3D printed structure typically has infill that is never seen, so their placement aren’t calculated with the goal of controlling light transmitted through the structure. There are some fancy tricks we could use to control infill pattern, but the easy way out is to skip infill entirely and use a hollow plastic structure.

The other potential problem is the Z-axis seam. A fused-deposition modeling 3D printer (most popular affordable hobbyist 3D printers) puts down plastic one layer at a time. When it shifts from one layer to the next, there is a brief pause that also manifests as a little bump in plastic. Good slicers will bury this somewhere invisible, either inside infill or on one of the inner layers, but if we’re printing something to transmit light there’s no escape.

The solution to both problems is to use a single-wall print that continuously spirals upwards in Z axis, also referred to as “vase mode”. This will give us a no-infill print without Z-movement seam and sounds the most promising way to print a light diffusion layer. This first test piece is 2mm in thickness, printed with 0.4mm nozzle in vase mode it means there’s 1.2mm gap in between the inner and outer layers.

Held right up against the LEDs at a distance of less than 1mm, we have a decent amount of diffusion while leaving individual LEDs clearly visible. This might be a good choice if we want to display graphical patterns that need separation from one dot to another.

Holding the test piece a little further away at 5mm, we see a much smoother blend. Individual pixels are still visible, so any graphics (or text) will still be somewhat legible.

Going a bit further, at approximately 10mm, the pixels can no longer be differentiated. While this may be bad for things like marquee text, it is an excellent property for projects with abstract gradual color changes like Glow Flow. This is promising, but this thin walled object was very flexible and felt too fragile to be used as the outermost layer for a project meant to be handled by people. Perhaps it can be made more rigid with a little structure?

With Glow Flow sitting stable on three stubby feet, I am out of excuses and must confront an important but very challenging topic that I’ve been putting off: light diffusion.

LEDs are very bright point sources by nature, which is very useful for some applications. But most lighting applications would prefer to diffuse light across a larger surface. Unfortunately there is no single best way to do so, one method which is ideal in one application won’t necessarily be ideal on another. Getting perfect LED diffusion on a cost constrained, mass produced, real world product, is an art form sitting at the intersection of engineering, design, and black magic.

Fortunately, as an one-off hobby project, I don’t need to perfectly balance appearance with manufacturing cost and complexity. I just need “looks pretty good” and that’s an easier bar to meet. I’ll obtain a few experimental data points to guide my design, starting with some cheap and easy diffusers. And there’s nothing easier and cheaper than going in the kitchen to grab some white paper towels for installation with masking tape.

Paper towels give better diffusion than standard copy paper due to their fibrous construction lending to greater thickness. This helps with their primary purpose of absorbing liquids, but in this off-label application it also helps with absorbing and redistributing light energy.

Wrapping a layer of paper towels around this LED helix had a surprisingly large benefit to making Glow Flow better looking. This was the first data point: I probably won’t need anything terribly fancy to achieve good enough diffusion. The second point came from pieces of paper towel that weren’t sitting flat against the surface: when they bulge away, the diffusion improves, so a little distance helps.

This was the state of the project when I brought it to show off at Hackaday Los Angeles July 2019 meetup. People seemed to like it, and I’m only just getting started on the exterior design.

 

With my Pixelblaze pattern for implementing Glow Flow in good shape, attention turns from software back to hardware. First on the list is another iteration for the bottom end piece. Earlier I had installed a surplus handle on the bottom for experiment’s sake. It was a fun way to test some ideas using an already-printed piece that would otherwise have gone into the trash. But having taken the results around to show a few people, it was clear the lack of an obvious bottom to set it down was disorienting. Confused users are never good from a user experience design standpoint, so I’ll back off to a more conventional base.

With the extraneous bottom handle removed, Glow Flow sat on four screws used to fasten my existing end unit holding the USB power bank. As anyone knows, four points of contact are rarely on the same plane, resulting in a Glow Flow that rocks back and forth on three of the four screws. This had the risk of damaging the four screw heads, as well as damaging soft surfaces that the metal screw heads might scratch up.

To address this in the short term (and possibly long term) a base was designed with three blobs of contact, printed, and installed. Intending to be subtle, not calling attention to itself very much, but now it is obvious to people how they should set down Glow Flow on a tabletop. And once placed, it will stay level.

With that little annoyance out of the way, I’ll have to face a big challenge that I’ve been dreading ever since the start of this project: find a good way to diffuse my 300 LEDs so they blend together well.