Luggable PC Drive Bay Revisions

Here’s the 2.5″ drive bay in the initial iteration of the threaded-box Luggable PC design. It is a simple, basic place to hold one laptop-sized drive, but not a very efficient use of space.

IMG_20170228_090310 - Copy

The most obvious thing to do is to vertically stack another drives adjacent to the existing drive. Easy to do in CAD, but has problems in the real world.

Problem 1: How do you access the fasteners? The laptop storage market have mostly settled around two basic fastener schemes: four screws on the bottom of the drive, or four screws along the sides. If we use the side fasteners, they would not be accessible for drive replacement without taking the whole case apart. The bottom fasteners would be accessible, except that bracket would be impossible to print on a FDM 3D printer.

Problem 2: How do you connect the wires? While at first glance there is enough space to physically accommodate the drive and its plugs, it fails to take into account the wires. The wires for the existing drive barely clear the edge in the picture. Stacking another drive into that space (even if moving it another cm or two to the right) would demand wires make relatively sharp right-angle turns. This would place strain on the connectors including the fragile unsupported SATA connectors on the drive itself.

After some experimentation with the available space, keeping in mind the requirements above, I decided to angle the two stacked drives:

IMG_20170228_091421 - Copy

Now the Luggable PC has two independent drives: One for Windows 10, and another for Ubuntu Linux 16.10.

This design solves the fastener issue: in this arrangement, it is possible to 3D print the drive bay so both drives are held in place by the shape without use of any screws on the sides or on the bottom. Both drives are held in place by a single 3D printed clamp that is secured with just two screws. The downside is that the design only works when both drives are present. It is unable to hold a single drive in place.

This also solves the initial wiring issue: By angling both drives, the wires do not have to make sharp turns and would not place unreasonable strain on the connectors. However, this comes at a cost of usable interior volume. By angling the connectors, and avoiding sharp turns, the cables consumed more precious interior volume than the previous design.

Going back to the idea of drives stacked in the available volume, we revisit the problem of forcing wires to make sharp turns. The turns can be relaxed if we can find more room for the wires without angling it into precious interior volume. The solution turned out to be… turning the drives instead! By rotating 90 degrees a drive can be positioned to make room for the cables’ turns. It also allows two drives to exist side-by-side, allowing the bay to work with a single drive or dual drives.

This design was incorporated into the following iteration of the chassis, built using aluminum extrusions instead of threaded rods as the metal structure.

DriveBayV3

 

Luggable PC Feet Design Considerations

After some time using the assembled Luggable PC prototype, I wanted to adjust the screen ergonomics. While the screen has been raised to a height much more comfortable compared to a laptop, after a few hours of use I wished I could tilt the screen upwards a few degrees.

At first glance this would have been impractical – the screen hinge design is already complicated and adding a tilt adjustment mechanism would only make it more so. So instead of tilting the screen, let’s achieve the goal by tilting the entire Luggable PC by adding 3D printed feet that can be bolted to the bottom of the machine.

The easiest approach would have been to print a simple solid wedge with the desired angle, but I decided to be a little more experimental. I played with Fusion 360’s spline tool to sketch out feet that are designed to move and flex a tiny bit. The flexibility adds two features:

  1. Shock absorption: We still need to be careful setting it down on a surface, but the minute bit of flexibility we gain will help cushion the harshest part of initial impact and make it feel less like we’re breaking the machine every time we set it down.
  2. Flatness compensation: With a bit of flexibility in the feet, the Luggable PC can now conform to surfaces that are not perfectly flat. Previously, the solid bottom means it will rock on 3 out of 4 feet on any surface that isn’t perfectly flat (which is most of them.)

Here is the first iteration, which accomplishes the desired goals:

IMG_20170228_173547 - Copy

Unfortunately it also has a problem: by moving the contact points inward, the front feet are now uncomfortably close to the center of gravity. A slight push from the rear will send the whole thing toppling forward. The design needs to be adjusted to have a wider stance… but we are constrained by the fact the fastening nuts still need to be accessible.

In this case, the short-term fix is to move the feet as far front as possible while still allowing wrench access to fasteners.

IMG_20170228_174620 - Copy

The real solution is to redesign the bottom of the case to accommodate the feet while maintaining a sufficiently wide stance. This idea was incorporated into the following iteration of the Luggable PC. As it used aluminum extrusions for backbone instead of threaded rods, the new wider feet were installed on the bottom extrusion.

FeetV3

A Tale of Three Corners: Design Evolution

The use of threaded rods to hold the Luggable PC case together was borne out of necessity: The print volume of the 3D printer is much smaller than the volume of a PC case so it must be printed in pieces then fastened together. A threaded rod provides strength along its length, but how do we best handle the inevitable corners?

The key constraint is the strength of a 3D printed part, especially the adhesion between layers. This is an unavoidable fact of life for FDM-type printers: the part is weakest between layers, so designing for 3D printers must consider the layers similar to how designing for wood must consider the grain.

Version 1: basic asymmetric

In this design (as used in the “Easel PC” iteration) two of the rod axis are aligned with the direction of the layer. Stress along those two axis would mostly be held in check by the strength within each layer, but a fraction of the force would try to push the layers apart. To guard against this, the third axis is orthogonal so its fastening nuts would also try to hold the layers together.

Corner 1 B
Two of the rods are co-planar with the print layer. (Rod pointing left, and rod pointing down.) The nuts fastening the third rod (Rod pointing away) also exerts a clamping force on the layers.
Corner 1 A
Same hinge viewed from a different angle.

The problem with this design is that the corners are asymmetric by nature. Not just in appearance, the loads it can tolerate are also asymmetric.

Version 2: symmetric but space consuming

The goal of a corner that handle loads symmetrically across the plastic layers means finding a way to make sure the plastic grain is equally strong across all three axis. The solution is to print at an orientation that lies at the same angle to all three axis.

CornerCura
The corner laid flat on the print bed for slicing in Cura.
Corner 2 B
Results in a corner that is equally strong across all three axis.

While this design solved the problem of symmetric appearance and strength, it introduced a new problem: by printing this way, the hinge consumes a lot of the enclosed volume making it unusable. When the goal is to pack the computer components inside a minimalist PC case, every cubic centimeter counts!

Corner 2 A
Angle showing the problem with this design – it consumes a lot of space inside the enclosed volume.

This hinge was used in the “Threaded Rod Box V1” and the space it consumed severely hampered the packaging of that layout. It is definitely not the optimal solution so the search continues.

Version 3: Let’s All Huddle Close!

The previous two designs both depended on the plastic to take some part of the load and hold on to a few steel rods. These rods were a few centimeters apart because we needed room for a wrench to tighten the nuts. We needed the nuts to sit inside the corner because…

… um, why do we need them inside? The key for version 3 is the realization that we don’t need that. By offsetting the rods slightly, we can extend the rods past the corner so the fastening nuts are outside of the enclosed volume and not competing for space with the components inside the box.

When the nuts (and the required wrench clearance) are no longer inside the volume, it allows the rods to sit much closer to each other. Now the closest distance between rods are measured in millimeters instead of centimeters. It also means the three sets of fastening nuts help exert a clamping force across all three axis, compressing everything together. This compression means the alignment of the print layers become much less critical allowing significantly more freedom in designing the rest of the case.

This corner design was used successfully in Threaded Rod Box V2 as shown. (In these pictures, some of the threaded rods have yet to be trimmed to length.)

Corner 3 BCorner 3 A

Luggable PC Screen Hinge

In the previous post we have established all the desired traits of the ideal screen layout, and how it’s impossible to meet them all simultaneously. The only solution is to design a mechanism allowing us to convert between two different configurations, each designed to provide the traits desirable for its corresponding condition.

  • Closed: the travel configuration.
    • Compact: We want to be able to lug this around without too much worry of catching on things, so the screen should align with the rest of the case (vertical or portrait orientation.)
    • Protected: To protect the screen, it should be facing inward so the glass surface is less vulnerable to damage.
  • Open: the computing configuration
    • Landscape: Unlike phones and tablets, desktop computer applications are not designed for the possibility of vertical/portrait orientation, so the screen needs to be in horizontal/landscape orientation.
    • Ergonomic: Unlike laptop screens that sit at table height, we can turn our extra heft into an advantage as support to hold the screen up to eye height. Ergonomically superior to the tabletop height of laptop screens.

To transition between these two states, we need movement along at least two axis:

  • Flip: The screen needs to move from facing inward (protected) to facing outward (visible)
  • Rotate: The screen needs to move from vertical/portrait orientation to horizontal/landscape orientation.

My ideal was to devise a mechanism that can execute both of these movements in parallel, so the user sees a single continuous movement from one configuration to another. After quite some thought and experimentation without success, I decided to postpone this ideal for later. For now, I’ll implement a hinge that has two separate degrees of freedom so the two desired axis of movement can be accommodated.

front-open
The open in-use configuration, with the screen offset to the left instead of centered

Originally the open configuration would have the screen up and centered relative to the rest of the body, and I had a few overly complex mechanical linkages attempting to make this happen. But then I realized it isn’t really necessary: the body has enough heft to hold up the screen even if it is not centered left-right. If we accept that the screen can be offset to the left, the rotation axis becomes a very simple hinge, leaving plenty of room to implement the flip axis.

front-closed
The closed travel configuration

This “ah-ha!” moment of realization, letting the screen be offset, greatly simplified the design. With the side bonus of reliability as simpler designs tend to be more reliable.

 

closelid
Demonstrating the open-to-closed transition. (Animated GIF by Shulie)

In the back of my mind, I will continue to dream of a continuous single degree-of-freedom unambiguous movement between open and closed. Maybe I’ll have another “Ah-ha!” moment to make it happen. I’m happy with this as the first draft.

Luggable PC Screen Layout: Challenges

The previous two posts discussed the design reasoning behind the positioning for the power supply unit and the motherboard. Now we get to the most interesting problem: Where do we want to position the screen?

The easiest approach is to line the screen up with the existing components, so I tried that first. A 17″ screen is almost the same length and width as the ATX motherboard plus PSU. But that means the screen would be at a vertical (portrait) orientation. While common for phones and tablets, it is not a typical layout for a desktop PC. (Historical trivia: The Alto by XEROX PARC, recognized to be one of the first computers with a graphical user interface, uses a portrait orientation.)

threadrodboxisoThe easiest solution to that problem is to rotate the whole works 90 degrees. I tried it for a while and the upright screen sitting at table height level was ergonomically poor.

Laptops also have their screens at table height (one of my peeves against laptops) but at least their screens can tilt. I wanted to do even better than merely tilting: I aim for the OSHA ergonomic recommendation raising the top of the screen to eye height.

spaceThe wasted volume between the screen and the motherboard was another problem exposed by this prototype. The space looked small in CAD because the CAD model blocked out all the volume allocated by ATX spec. Since the actual motherboard consumed only a fraction of the allocated volume, the real world example had far more wasted space.

screenwingsI had the idea to solve both issues by raising the screen high to eye level, oriented horizontally, and tilt it into the empty volume. I never got as far as building it. Looking at the CAD layout, it is quite clear that the horizontally-oriented screen sticks out on either side of the case. This makes for a shape awkward to transport and also leaves the screen extremely vulnerable to damage. The screen height was good, but everything else was bad.

Plus, there was one more problem not addressed by any of these ideas: The screen glass surface is exposed while in transit. Laptops fold closed to protect the glass while travelling, but all these designs leave the glass exposed.

It became clear that no single static arrangement will have all of the desired qualities. Similar to a laptop, we will need some kind of mechanism to switch between two states.

  • Closed: A compact configuration for easy transport while protecting the screen from damage.
  • Open: An ergonomically desirable screen position.

Next post: The mechanism to address these challenges.

Luggable PC Motherboard Layout

a360mobopsu2The previous post described how I decided to position the PSU (Power Supply Unit). Once the position was decided, the next task is to determine the motherboard position.

The first challenge is my desire to accept a full-sized ATX motherboard. Full-sized boards are the easiest to work on and has the best feature set. They also have highest sales volume, which usually mean less expensive. I knew my project would be easier with a smaller microATX or Mini-ITX motherboard, but I wanted to accept full-size.

However, accepting the full size board doesn’t necessarily mean I intend to use all the expansion slots. In fact, I am happy to block the majority of them, leaving just the primary PCI-Express slot available to the GPU.

selectcardsThe GPU itself is the next challenge. The primary slot is close to the CPU, which means it is going to stick up in the middle of the board, making the whole assembly awkward to fit. Again, I have an escape if I want it: there are PCIe extension ribbons available for purchase that allows more positioning flexibility for the GPU. They range from $89 well-regarded units from Digi-Key to $7 roll-of-the-dice units via mystery retailers on Amazon. I want to make this idea work without use of an extension, and avoid the variable that introduces to the system.

While researching the layout, I learned the primary slot is not in the same position across all motherboards, adding to the challenge. While most boards position them in the slot closest to the CPU (all of the Mini-ITX boards have to by necessity) some of the boards place it in the second position. And since high-powered GPUs are two slots wide, that means I need to allow for three expansion slots worth of space.

selectcomponentsThe GPU in the middle of the board leaves two rectangular volumes on either side: Both volume are candidates for use. One volume sits over the remaining expansion slots, and the other volume sits over the CPU.

The volume over the expansion slots are predictable. ATX spec restricts height of motherboard components in order to maintain clearance for expansion cards. If I’m OK with the absence of cards, that entire volume can be reclaimed.

In contrast, the volume over the CPU is less predictable. While the ATX spec allocated volume to CPU and accessories (most significantly, the CPU cooler) that volume is highly variable. Stock CPU coolers typically take much less volume than allocated, and many fancy CPU coolers exceed the volume.

Given those two choices, it was an easy choice to snug the PSU up against the motherboard in the volume allocated to expansion cards that won’t be there.

The last factor in positioning the motherboard is which direction I wanted the ports to be accessed. Pointing down is inconvenient to access. Pointing up makes ports vulnerable to damage from dropped items. So that leaves pointing left or right. Since the PSU power cable port is already on the right, I decided to face all the ports that way as well so everything the user needs to plug in is facing the same way.

All of the above considerations resulted in the PSU+motherboard layout I used.

Next post: Positioning the screen.

Luggable PC PSU Layout

To help optimize arrangement of Luggable PC components, I sketched them out in Fusion 360 so I can experiment with layout in CAD space. I was able to find the specification for the ATX motherboard and power supply, which allowed me to use official dimensions. Unfortunately I wasn’t able to do the same for the PCI-Express cards, because I needed to be a member of the PCI SIG to access the official specs. So I measured and guessed dimensions from the specific implementation I have on hand.

Power Supply Unit (PSU)

As the heaviest single component, I wanted the PSU at the bottom so the overall system is not top-heavy. The question is then: which way to orient the PSU? There were two considerations:

  1. PSU cooling intake: The standard ATX case layout places the PSU at the top of the case, drawing air from beneath. I can’t do that with the PSU at the bottom since a downward-facing intake would be blocked by the table surface. I tried the upward-facing intake once, in the Mini-ITX “Easel Frame 2.0” design. That turned out to be a bad idea because every time I dropped something (usually a screw) it would fall inside the PSU and I have to retrieve it to avoid short-circuiting the internals.
  2. PSU wiring: One side of the PSU takes the standard IEC AC cable. The opposite side is where all the DC wires go to the rest of the components. The decision is then whether to point them front-back or left-right. I didn’t want either of them to point towards the user, so I went with a left-right orientation for the wiring.

Taking care of those two considerations leave two good orientation for the PSU. One with the cooling intake facing front towards the user, or facing away from the user. In the current design, facing backwards allows an unobstructed air path so that’s the preferred position today.

Next post: Positioning the motherboard.

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Luggable PC Gets Fancy Screen

closelidThe latest iteration of the home built luggable computer gets a fancy rotating screen to protect the screen while in transit and hold the screen up while in use.

The time pressure of making it ready for show-and-tell at the February Hackaday LA meet meant I hadn’t been documenting my lessons learned here.

Which is a shame, because there were quite a few 3D printing lessons learned while building this thing. I briefly mentioned a few of them on the project log update up on Hackaday.io but I intend to find the time to expand on those ideas as future posts on this blog. I just hope I can get them all written down before I forget.

Homebuilt Computer now “Luggable PC” on Hackaday.io

hackadayioprojectI’ve known about Hackaday for a while, both the professionally curated site hackaday.com and the public participation site hackaday.io. Some of the people behind the site are nearby which allowed me to easily attend some of their local events.

Most of the project pages I browsed through dealt with Arduino boards, Raspberry Pi boards, or even lower-level hardware. I wasn’t sure if a home built PC is the right kind of topic for the site until I brought my current prototype to one of these local meets. The staffers present assured me that it’d be a great project to document on hackaday.io.

All right then! I’ve created a project page to document my work so far, and I’ll continue documenting future iterations over there instead of here.

One of the Hackaday staffers took an interest in the project, wrote up a short blurb and posted it on the curated hackaday.com. I am very flattered by the attention and it was a great opportunity to see how other Hackaday users viewed the project.

The best comments are from people who appreciate the project and had constructive ideas and suggestions – this is what the site promised for project builders and I’m happy to see it working as intended.

There were a few variants of “This isn’t what I want. I want to see…” and while they are good project ideas, they’re not what I’m trying to accomplish here. Maybe they’ll feel inspired by my project to bring their own ideas to life!

And finally, the comments that dismissed the project. Pointing out shortcomings (some fair, some not) as criticisms without offering anything constructive to address the alleged issues. I just shrug off such criticism and focus on my work.

Positive or negative, the overall quality of the comments are far more articulate and intelligent than your average comment on YouTube.

I call that a win for Hackaday.

Homebuilt ATX All-In-One Computer

Scaling upwards from the previous project, I’m moved up from the Mini-ITX board to a (nearly) full sized ATX motherboard. The larger motherboard required a few more fastener locations but was not a significant challenge. The new challenge in this version was the addition of the GPU and properly securing it to the case.

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Given the triangular profile of the frame, it took a little effort to design the triangular frame to fasten the GPU metal bracket against. At least, as compared to the normal rectangular computer cases. Thankfully CAD software like Onshape have no fear of trigonometry calculations.

side

It all works together but I’ve lost most of the size advantage over the standard mid-tower case. Here it is standing in front of the case that used to contain these components.

sizecompare

While the overall volume is still smaller than the generic PC case, it isn’t smaller by a whole lot. Yes, I do incorporate a screen while the standard case does not, but like the standard case I have a lot of unused empty space in my volume. Even though this made cable management easier and neater, a lot of waste is left over.

I decided the previous Mini-ITX version was on the “too small” side, and we’ve overshot into “too large”. The next iteration of this experiment will try to shrink the design and work towards “just right”


The small 3D printed brackets seen on this page were designed in the OnShape project “Easel PC“, which is available as an OnShape Public Document.

Homebuilt All-In-One Mini-ITX Computer

The previous experiment 3D printed just an enclosure for the Mini-ITX motherboard itself, it didn’t have much of a computer around. This project expands on the idea by building something to hold the rest of the computer components.

The physical size is larger than the build volume of the 3D printer so additional hardware were brought into the equation. Emulating the design for some early RepRap 3D printers, I started using commodity hardware store threaded rods as building structure.

The power supply unit is the heaviest single element and employed to provide the stable base. The new addition to the project is the screen built out of the LCD panel salvaged from an old broken laptop. I used a controller board that translated standard VGA/DVI signal to the panel’s proprietary signal to connect the panel to the rest of this system. Such controller boards can be purchased from one of several vendors on eBay.

The cable management is better than the previous effort, which admittedly set a low bar. The PSU is nice and heavy providing a stable base. Compared to the commodity Mini-ITX case: the overall package takes less desktop space (especially considering the screen) and overall roughly the same volume of space.

easel-back
A better-managed but still a tangle mass of cables.
easel-front
3D printed all-in-one “Easel PC” with a commodity Mini-ITX case.

This is a perfectly usable (if not very neat or pretty) PC. If this were the final goal, I would take a Dremel cutting wheel to cut off the extraneous ends on the threaded rods. Since I have no real need for a Mini-ITX AIO PC at the moment, though, I’m taking the lessons learned and recycling the metal bits for the next project.

Enclosure for Mini-ITX board

Customized computer cases are an interesting area to explore for 3D printing. The home-built desktop PC market is blessed with the luxury of choice, with a wide selection of components a builder can choose from. As a result of this, most desktop PC cases are wide-open designs capable of taking most combinations of components. This directly proves the old adage: “Jack of all trades, master of none.” In contrast, someone with a home 3D printer can custom design for a specific need built around specific components on hand. The result would be a master of one.

Before I can embark on some grandiose vision, I started with a small project built around the MSI AM1I motherboard. It is an inexpensive and highly integrated PC motherboard on the Mini-ITX standard. It had been installed in a Mini-ITX case that, though smaller than most desktop PC cases, still had a lot of wasted volume present to accommodate for components that I never installed.

fullcase
Mini-ITX computer with a great deal of wasted volume.

The Mini-ITX standard restricted the motherboard size to 17cm squared, which is convenient because my 3D printer can print up to 20cm squared. This meant I could print something encompassing the ITX dimension in one piece. I pushed for full minimalism resulting in this design available as OnShape public document “Mini-ITX enclosure“.

emptycase
3D printed Mini-ITX enclosure.

It has screw holes for only the mainboard and the power supply. The large hole on top is tailored for the specific power supply I had on hand, positioning its fan immediately above the motherboard. This allowed removal of the noisy CPU fan as the large power supply fan can pull double duty cooling the whole works resulting in a small neat compact setup.

When I assembled the parts, though, things didn’t look as neat as I imagined:

minimalist
My, what a tangled nest you have.

I had underestimated the chaotic bundle of wires coming out of the power supply. Most of the wires were completely unnecessary and could be cut if this were the final product, but I didn’t want to do that just for an experiment. The remaining wires could be shortened for such a compact layout, but again I didn’t want to break out the wire clipper and soldering iron for sake of the experiment.

The other item I didn’t account for was the storage device, in this case an old SSD in 2.5″ form factor, awkwardly wedged into a slot. (See the red SATA cable in the picture.) I justified this oversight by the fact that most modern ITX boards have on-board M.2 SSD slots, making a separate mounting bracket unnecessary. Truthfully, though, I forgot.

I had fun building this proof-of-concept with old expendable components in case something went wrong. Next custom PC project will be bigger, with more powerful components, and hopefully the wires will be better managed as well!

Delta Robot: First Draft

The first attempt at a delta robot has come and gone, a fun experience with valuable lessons. This design used a central spine that locates the axis for each of the three arms. The servos were mounted to a bracket that was in turn mounted to the spine. The arms themselves were mounted on bearings then mounted on the spine. A long machine screw holds the arms and the servo brackets together.

dr1-onshape
Design in OnShape
deltarobotv1-small
3D printed and assembled

The main motivation behind this design is to isolate the servo motor from load bearing duties. The load on the arm goes to the bearings, which then go directly to the spine. The servo is only responsible for the movement.

The linkage from servo horn to arm, combined with the servo mount bracket to spine connection, added significant play to the entire assembly. It is possible to move the arm freely across around 10 degrees of range. I decided this was unacceptably poor accuracy to trade off against bearing the load, which turned out to be very light and not a concern like I feared.

jointassembly
Closeup of the unnecessarily complex assembly.

Each of the arms also featured a mounting point for a counterweight. The idea is to balance out the mass of the workload, but everything was light enough that the servos can easily keep things in place without counterweight assistance. The arm for the counterweight took away from the length of the working arm, which reduced the working volume of the robot assembly. So that wasn’t a good trade off, either.

It was an easy decision to scrap this version and move on. I’ll try again with a different design incorporating lessons from the first draft.

Ball Jointed Parallelogram

ball-joint-parallelgramAnd now another entry in the “3D printer is not the solution to everything” file.

I’ve had ambitions to build my own delta robot ever since I watched an YouTube video of ABB FlexPicker industrial robots at work. Key part of the robot geometry is a set of parallel links and I thought I’d try printing my own.

The reason why I thought this exercise might be interesting is that 3D printer offers the unique possibility of printing objects in place. This means the socket can be designed purely to hold the ball in place, without any provision for the ball to be inserted or removed because there’s no assembly.

Drawing the test piece up in OnShape was fairly straightforward. A few prints were required to dial in the precise gap needed between the ball and socket so they print as tight to each other as possible without fusing together. Once that was figured out, I had a set of parallel links that moved very poorly.

On the upside, the theory was correct. The ball was printed inside the socket and was held tightly. It’s never coming out, because it never had to be inserted in the first place.

On the downside, 3D printers can’t (yet) print very smooth surfaces. Which resulted in rough movement as the printed layers moved past each other. Far inferior to standard polished metal joints, except maybe when they have sand and dirt inside.

img_20161026_175726
Close up of ball joint, showing the printed layers that give it a rough surface.

Ah well, it was worth a try. If I want to build my delta robot, I will go buy some mass-produced ball-and-socket joints that’ll be much smoother than anything I can print with the 3D printer I have. Small projects can use joints from the remote-control hobby world, big projects can draw from the McMaster-Carr catalog.

Caliper Battery

caliper-batteryI had been using an inexpensive digital caliper to take measurements feeding into my Onshape CAD projects. It has proved sufficiently precise for my hobbyist level work but I’d definitely recommend paying for higher quality caliper for professional level work.

One annoying aspect of this caliper is that pushing the on/off button doesn’t really turn it on/off. It’s more akin to on/standby, where the display turns off but some part of the electronics are still on. This is clearly visible by turning the caliper “off” then moving the caliper – it detects the movement and displays comes back to life showing the new reading, which is impossible if the device actually turned off.

The consequence of this feature is that the device is constantly draining the little LR44 battery, which lasts only a few weeks no matter how little the caliper is used.

I decided to solve this problem with a bigger battery. I had set my eyes on the AA battery, which has significantly more capacity and far less expensive than a LR44. When the dimensions didn’t work out, I downsized to AAA battery size.

I didn’t want to make any permanent changes to the original caliper, so no drilling, gluing, or soldering. This meant that I had to:

  1. Find an attachment point: I settled on the thumb wheel, which is held in place by a plastic hook screwed into the main assembly. My project will displace this hook, taking over the thumb wheel retention duty. This allowed a solid connection conveying movement force parallel to the axis of caliper movement. Unfortunately, it doesn’t help hold things in place perpendicular to the axis of caliper movement, which led to…
  2. Grasp the rail: The battery tray needed to grasp the rail both above and below the rail in order to remain aligned to the slide at all times.
  3. Clear the rail end: The tray necessarily reduce the travel range and thus the maximum value I could read on the caliper. An early draft reduced the usable length by the length of the battery, which was unacceptable. Redesigning the battery case reduced the loss to roughly 1cm of range.
  4. Emulate a LR44: Since I didn’t want to solder, something would have to pretend to be a LR44 battery. This took the form of a cylinder with strategically placed wires exposed to make contact with the battery terminals inside the caliper.

AAA batteries are far more plentiful and far less costly than LR44 batteries. The reduced measurement range hasn’t proven to be terribly annoying. Certainly far less annoying than replacing an expensive LR44 battery all the time!

caliper-aaa

This was the most geometrically complex shape I’ve created to date. The dimension requirements were to hold the thumb wheel in place, grasp the rail tightly enough yet still allow sliding motion, and present the cylinder pretending to be a LR44 battery. It took quite a few iterations to get all the pieces positioned relative to each other.

It was also too complex of a shape to be printed directly on the flat bed of a 3D printer. All of my previous projects avoided any need for printed supports by creative positioning, but I couldn’t circumvent the need this time. The support requirements were complex and the automated support generation in Cura proved insufficient. I needed a way to adjust the support to fit the requirements of the project and the capabilities of my specific 3D printer.

Eventually I gave up on Cura and switched to Simplify3D as my slicing software, mostly for the ability to customize the generated supports.

That’s a story for another post.

Cardboard VR Tapper

utopia-tapAnd now, a story of failure not the fault of the 3D printer. The previous project allowed my Nexus 5X phone to sit correctly in the Utopia 360 VR viewer. This project addresses the next problem: the need to tap the screen during use of the VR app.

The first step is to buy a “touchscreen stylus” available everywhere (marginally useful) electronics accessories are sold. I planned to design and 3D print a small contraption to put inside the headset to hold the stylus and press it against the screen on demand.

The holder part was a tube whose dimension needed to match the stylus so it can be held tightly. That took a few trials and errors. Then the problem is how to mount it and how to control it from outside the viewer. After a failed design using rotation motion and a small spring, I switched to a linear motion design with a rubber band.

The rubber band’s role is to keep the stylus at a particular location. Then I can use a length of string to pull the stylus away from that position, against the screen. Once tension is released from the string, the rubber band will pull the stylus back to standby position.

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Touchscreen stylus widget inside the VR viewer.

Mechanically, this screen tapper contraption worked – I could pull the screen and the stylus would push against the screen, but nothing happened!

After a bit of research, I learned that the stylus is not enough to trigger the capacitive touchscreen by itself. To trigger the necessary capacitance effects, the stylus needed to be in electrical contact with a person’s finger, so it only works when held by hand, not when held by a plastic rubber band widget.

Darn.

At this point I got frustrated with the whole thing and didn’t feel like designing a new V3 tapper mechanism. I went even lower tech – drill a hole so I can hold the stylus by hand and tap the screen from outside the viewer.

Sometimes, the solution doesn’t involve a 3D printer.

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Ultra low-tech solution: Drill a hole for the stylus. Now it can be manipulated from outside the viewer and tap the screen inside the viewer.

 

Nexus 5X in Utopia 360 (Google Cardboard VR)

5x-in-utopiaEarlier this week Google officially released details about their upcoming Daydream VR. And we know what that means – massive discounts on the old Google Cardboard VR headsets!

Google Cardboard was launched with some fanfare two years ago. But with impending Daydream VR they are old news and retailers are clearing their inventory. I picked up one example of the breed, Utopia 360, as a Deal of the Day from Best Buy. This viewer allowed the lenses to adjust both for distance between eye and distance to screen. Much better than the fixed-lenses devices like the Mattel View-Master VR.

There are a few problems with the Utopia 360, though. The first I tackled was the phone mount mechanism. It was a sprint-loaded set of plastic clamps that has the unfortunate property of pressing and holding down the power button on the Nexus 5X, turning the phone off. Another mounting solution will be needed.

Since I had measured the dimensions of my Nexus 5X for the car holder project, the data easily translated into a project to make a replacement phone mount. The Utopia 360 bracket had to be two pieces as the phone mount area is too large for my little 3D printer to print all in one piece.

Since I’m customizing to a specific phone, there’s no need for sprint-loaded adjustability. The bracket precisely fits and grasps a Nexus 5X, with a cutout to stay clear of the power and volume buttons on the side. The end is also open, so I can plug in headphones and power if I needed to. And a little final touch: circular cutout to clear the phone’s camera bump, allowing the phone to sit flush.

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Utopia 360 VR viewer with new custom mounting bracket for Nexus 5X

Now I can enjoy Google Cardboard VR experiences on my Nexus 5X in the Utopia 360 viewer without being rudely interrupted by the phone powering off or changing the sound volume. I am, however, unable to interact with the VR app. While more recent Cardboard VR viewers like the View-Master included a lever for the user to tap the screen, Utopia 360 did not.

That’ll be the next project.

 

3D Printer, Fix Thyself.

fan-adapterI’ve enjoyed using my 3D printer to solve little problems around the house. This project was extra amusing: I wanted to solve a problem I had with my 3D printer that I wanted to solve with the 3D printer.

My Monoprice Select Mini 3D Printer is a basic unit built to a low cost, and I’m probably using it a lot more than it was designed for. The first component to show serious wear was the tiny 30mm cooling fan, a simple unit with a cheap sleeve bearing that wore out. As a result the fan started vibrating and making quite a racket.

I could easily buy a direct replacement fan online, but where’s the fun in that? I have a 40mm fan just lying around anyway. Let’s make an adapter!

For a while I was stymied by the fact that the two fans were mounted in opposite and inconvenient directions. The original 30mm fan screws were pointed in the direction of airflow, and the original 40mm fan screws were pointed against the airflow. This meant that when one set of fasteners were mounted on an adapter, holes for the other set would be blocked.

I spent approximately an hour tearing my hair out trying to design something clever, to no avail. Then clumsiness came to the rescue: I held the cooling duct (which the fan would be mounted on) in my hand, trying to think, when I accidentally dropped it. When it hit the floor, it fell apart into two pieces.

The duct was actually two pieces fit snugly against each other. All this time I had thought it was a single piece! With the two pieces apart, the interior of the duct became accessible. This meant I could use the 30mm fan screws opposite of the original direction (pointed against the airflow) where it is no longer blocked by the 40mm fan.

Suddenly the adapter project became trivial.

“Oops” moment for the win!

Nexus 5X holder for Mazda RX-8

nexus-5x-holderGiven how popular it is to have mapping and navigation on the phone, there are a lot of phone mount products on the market. Unfortunately, given the diversity of phones and of cars, it isn’t feasible for product manufacturers to custom make individual design for every car + phone combination, so every mount is a generalized trade-off of some sort.

Which is, of course, the ideal situation for a 3D printer. Making an unique product to solve an unique problem. In my specific case, I wanted to mount a Nexus 5X phone in my Mazda RX-8 vehicle. This was the result.

The base of the phone slides in to the holder, and fortunately its position and basic friction is enough to hold the phone in place. I didn’t have to add any kind of clasp or snap to hold the phone in place.

The two slots in the base are for the two cables I wish to plug into the phone. The center slot is made to precisely fit a Monoprice USB-C cable. The side slot is made to precisely fit the plug of the Kensington audio cable I am using, one with ground loop isolation.

I didn’t want to do anything permanent to the car such as drilling holes for mounting. So I shaped the base to fit in the ashtray. I originally intended to print a large block so it fills the whole ashtray cavity but changed my mind when I realized the extra space is useful for coiling up the extra length of cable and make things tidier. Using the ashtray had the bonus side effect of placing it adjacent to the cigarette lighter power socket.

The entire design is too large for my little 3D printer to print all at once, so it has been divided up into three parts that can each be printed without support.

  1. The ashtray insert
  2. The phone holder
  3. A cylinder to connect them, one face truncated at the appropriate angle to hold the phone for display.

I printed this design in ABS plastic because of its higher melting temperature. The interior of a car gets hot and I wasn’t sure if 3D-printed plastic would melt in the heat. Printing in ABS also had the additional benefit of letting me use acetone as glue, melting the ABS pieces together results in a very strong bond.

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