Pogo pins + laser cutter = test fixture

Eric Gunnerson made this DIY pogo-pin test jig:

I decided to build a pogo-pin test jig, and since the approach I came up with was different than the other approaches I’ve seen I thought it would be worth sharing. I’m going to be targeting my laser cutter for fabrication, though I could have chosen to use my 3D printer instead.

See the full post on Eric’s Arcana and RiderX blog.

Check out the video after the break.

New 2.5D pen/laser ESP32 controller


Bdring published a new build:

I have done several pen and laser machines lately, so I decided to create a custom PCB for Grbl_ESP32 for these types of machines. This is a small (70mm x 60mm) PCB with all the features a pen plotter or laser cutter/engraver would need.
These typically use stepper motors for the X and Y axes. On pen plotters, the Z axis is controlled by a servo or solenoid. On lasers you need an accurate PWM for laser power control.

Project info at Buildlog.Net blog and the library GitHub repository here. It’s also up on Tindie.

Getting control over a 50 watt CO2 laser cutter from China


Unboxing laser cutter Co2 50 watt from China:

There are people around me who think I’m crazy. And they are probably right. Who else would buy a machine from someone he does not know. I have to pay upfront. It is not clear how things will get delivered, what gets delivered, or if it gets delivered at all. Up to the point I can lose the money I have spent. Best of all: that machine is dangerous enough to potentially kill me. And it has the potential to put my home on fire too. Well, that sounds like an exciting weekend project, or not?

See the full post at MCU on Eclipse homepage.

Breathe Easy with a Laser Cutter Air Filter

A laser cutter is a great tool to have in the shop, but like other CNC machines it can make a lousy neighbor. Vaporizing your stock means you end up breathing stuff you might rather not. If you’re going to be around these fumes all day, you’ll want good fume extraction, and you might just consider a DIY fume and particulate filter to polish the exhausted air.

15203365_644939182347358_619032134291602214_nWhile there’s no build log per se, [ZbLab]’s Facebook page has a gallery of photos that show the design and build in enough detail to get the gist. The main element of the filter is 25 kg of activated charcoal to trap the volatile organic compounds in the laser exhaust. The charcoal is packed into an IKEA garbage can around a prefilter made from a canister-style automotive air cleaner – [ZbLab] uses a Filtron filter that crosses to the more commonly available Fram CA3281. Another air cleaner element (Fram CA3333) makes sure no loose charcoal dust is expelled from the filter. The frame is built of birch ply and the plumbing is simple PVC. With a 125mm inlet it looks like this filter can really breathe, and it would easily scale up or down in size according to your needs.

No laser cutter in your shop to justify this filter, you say? Why not build one? Or, if you do any soldering, this downdraft fume extractor is a good way to clear the air.

Filed under: cnc hacks, green hacks, laser hacks

90+ Videos Take you from Laser Chump to Laser Champ

Few of us document the progression of our side projects. For those who do, those docs have the chance at becoming a tome of insight, a spaceman’s “mission log” found on a faraway planet that can tell us how to tame an otherwise cruel and hostile world. With the arrival of the RDWorks Learning Lab Series, Chinese laser cutters have finally received the treatment of a thorough in-depth guide to bringing them into professional working order.

In two series, totalling just over 90 videos (and counting!) retired sheet-metal machinist [Russ] takes us on a grand tour of retrofitting, characterizing, and getting the most out of your recent Chinese laser cutter purchase.

Curious about laser physics? Look no further than part 2. Wonder how lens size affects power output? Have a go at part 39. Need a supplemental video for beam alignment? Check out part 31. For every undocumented quirk about these machines, [Russ] approaches each problem with the analytic discipline of a data-driven scientist, measuring and characterizing each quirk with his suite of tools and then engineering a solution to that quirk. In some cases, these are just minor screw adjustments. In other cases, [Russ] shows us his mechanical wizardry with a custom hardware solution (also usually laser cut). [Russ] also brings us the technical insight of a seasoned machinist, implementing classic machinist solutions like a pin table to produce parts that have a clean edge that doesn’t suffer from scatter laser marks from cutting parts on a conventional honeycomb bed.

Solid build logs are gems that are hard to come by, and [Russ’s] Chinese laser cutter introduction shines out as a reference that will stand the test of time. Don’t have the space for a laser cutter? For the micromachinists, have a look at The Guerrilla Guide to CNC Machining, Mold Making, and Resin Casting.

Filed under: laser hacks

Hackit: Laser Cut Your Own Jigsaw Puzzle

If you have a laser printer, you’ve got your Christmas presents sorted out. At least if your family likes jigsaw puzzles. The idea is very simple, laminate a photograph onto some laser-cuttable board, and then run the laser over the outline of the pieces. Bam! Instant puzzle.

The trick is generating the puzzle outline, and of course there’s an online application for that. It’s got options that let you customize the piece count and shapes, and then download the result as an SVG image.

Unfortunately, it’s closed-source and makes the pieces a little bit too uniform for our liking — many of the pieces have exactly the same shape as each other. Are you up to the challenge of writing a better one? We’d love to see it, because the idea of a simple puzzle overlay for laser cutters is too good. Help us get started with some brainstorming in the comments below. How do you go about generating meaningfully unique jigsaw edges algorithmically?

Once you’ve got the puzzle cut out, you can seal up the surface nicely, toss it in a box, and then you’ve got a personalized present. To put it together, we suggest an accompanying DIY pick-and-place tool. (And kudos to [Kristina] for the best headline of 2015 on that one!)

Thanks to Hackaday alum [George Graves] for the tip!

Filed under: HackIt, laser hacks

Two-Stage Tentacle Mechanisms Part III: Putting it All Together

Welcome back to the final chapter in our journey exploring two-stage tentacle mechanisms. This is where we arm you with the tools and techniques to get one of these cretins alive-and-kicking in your livingroom. In this last installment, I’ll guide us through the steps of building our very own tentacle and controller identical to one we’ve been discussing in the last few weeks. As promised, this post comes with a few bonuses:

Nothing like a fresh batch o’ parts.

Design Files

  1. The Almighty Bill-o’-Materials
  2. Vector Drawings for laser cutting
    1. DXF files pre-offset (0.003″)
    2. DXF files original
  3. STL Models for 3D Printing
  4. Original Tentacle CAD Model Files
  5. Original Controller CAD Model Files

Depending on your situation, some design files may be more important than others. If you just want to get parts made, odds are good that you can simply cut the pre-offset DXFs from the right plate thicknesses and get rolling. Of course, if you need to tune the files for a laser with a slightly different beam diameter, I’ve included the original DXFs for good measure. For the heavy-hitters, I’ve also included the original files if there’s something about this design that just deserves a tweak or two. Have at it! (And, of course, let us know how you improve it!)

Ok, now that we’ve got the parts on-hand in a pile of pieces,let’s walk through the last-mile tweaks to making this puppet work: assembly and tuning. At this point, we’ve got a collection of parts, some laser-cut, some off the shelf. Now it’s time to string them together.

Tipping our Hats to the Hallmark of How-Tos

In the last year, both the Crazyflie assembly instructions and the Formlabs printer maintenance docs have done something novel with their step-by-step instructions. They’ve mixed video clips into their instructions to better showcase a process. Whether that’s sliding a motor onto a quadcopter frame or sliding the build platform out of the printer for cleaning, these clips nail exactly one thing: the specific steps of a short process. In writing these docs, I’m tipping my hat to these folks who showed me just how informative a well-timed video clip can be.

All right–let’s get started!

Controller Assembly

Each Controller is basically two pulleys rotated and stacked on top of each other. We’re assembling everything ourselves here, but don’t fret–I’ll highlight the details to get you feeling comfortable enough to build one at home. (Curious to know why I opted for a mechanical solution? Check out Part II in this series.)

1. Assemble 4x Pulleys

To get the order-of-operations right, have a look at the quick clip on the right. Unfortunately, those parts won’t just install themselves! Getting those parts installed is a matter of using the right tool.



  • qty 2:  4-40 threaded heat-set inserts
  • qty 16: M2 threaded heat-set inserts
  • qty 44: 9/16-in long 0.125-in diameter semitubular rivets
  • qty 8: outer_pulley_plate
  • qty 8: inner_pulley_plate
  • qty 16: 612K-ND angle brackets
  • qty 16: 3/16-in 4-40 buttonhead socket cap screw
  • qty 16: small washers


  • rivet press (or handheld riveting tool) for semitubular rivets
  • soldering iron

Detail: Rivets

I’m using a miniature rivet press in my home shop, but you may be able to score some time on one at your local hackerspace.

Detail: Heat-Set Inserts

Getting the heat-set inserts into your part may seem a bit daunting, but it’s actually fairly straightforward. With the soldering iron set to 250 C, gently work the inserts into the part. Don’t press down on the iron! Instead, gently wiggle the tip, and let the weight of the iron work the insert into the part. Each insert takes about 15-20 seconds to set, so don’t feel too hasty!


Detail: Wire Clamps

To get the order of operations right on this feature, have a quick look at the assembly video. Keep in mind that the wire rope will slide between the washers and the upper angle bracket in a later step.

2. Install Inserts in 3x Pulley Plates

Heads-up! Three of our plates have several insert features. Warm up that soldering iron again; it’s time to get a few more satisfying thrills whilst melting brass into plastic. I’ve called out each “screw-thread-insert” (STI) location in the diagram below. These holes have been sized to specifically accommodate the heat-set inserts.



  • qty 40:   4-40 Heat-Set Inserts
  • qty 2: top_pulley_plate_insert_side
  • qty 2: top_pulley_plate_screw_side
  • qty 2: bottom_pulley_base_plate_insert_side

Installing these inserts is just like we did previously for the pulleys. Give yourself a few minutes to complete these, but be gentle as before.

3. Countersink Bracket Plates

These plates will be the main junction between a controller’s upper and lower pulley. Create countersinks in the following locations.countersink_callouts


  • qty 4: handle plates
  • qty 4: joint_connector_outer plates


  • Countersink + Countersink Cage and hand drill (or drill press) OR
  • Countersink with drill press that has a hard-stop feature

countersinking_delrinDetail: Countersink Depth Tolerances

The screws that slide through the holes in these plates need to engage a threaded insert that’s either one or two plates deep. Countersink these plates such that the screws are, at minimum, flush with the plate. Too deep is OK, as long as the screws don’t bottom-out past the threaded insert.

In more detail, there’s quite a bit of wiggle room on the depth of the countersink, and here’s why. Our plates come in increments of 3.175 mm. Our 6mm screw will engage the threads after passing through 1 plate. Our 8mm screw will need to pass through two plates before it engages the insert in the third plate. What this means is that the total distance of travel for the 6mm screw is two plates’ worth of thickness, or 6.35mm, and three-plates-worth of thickness, or 9.525mm for the 8mm screw. Hence, while the 6mm screw has about 0.35mm of wiggle room, and the 8mm screw has a whopping 1.5mm worth of wiggle room before either screw bottoms out.

4. Join Pulley Sections



  • qty 4:  assembled pulleys
  • qty 2: top_pulley_plate_insert_side
  • qty 2: top_pulley_plate_screw_side
  • qty 2: bottom_pulley_base_plate_insert_side
  • qty 2: bottom_pulley_base_plate_screw_side
  • qty 4: pulley spacer
  • qty 4: joint_spacer
  • qty 4: joint_connector_outer
  • qty 16: 6mm M2 socket cap flathead screws
  • qty 16: 8mm M2 socket cap flathead screws
  • qty 4: shoulder screw
  • qty 2: 8-32 nut
  • qty 4: 3D-printed cable_insert_bracket with inserted ferrules
  • qty 4: .5-in 4-40 female threaded standoffs
  • qty 12: .25-in 4-40 socket cap screws
  • qty 32: 3/16 4-40 button-head socket cap screws
  • qty 16: 612K-ND angle brackets


  • metric allen keys
  • imperial allen keys (I tried not to mix-and-match Jurassic and Metric…. but off-the-shelf components don’t come in every flavor, yo.)


Detail: Order of Operations

For each controller, I’d recommend building up the upper and lower halves separately and then joining them together afterwards. To secure both halves, we’ll be using those classy 612K-ND corner brackets that I mentioned in the previous installment.

Detail: Pulley Bore Diameter Tolerances

The shoulder screws should slide easily through the pulleys. If that’s not the case, feel free to drill them out with a 0.1875″ drill bit.

Detail: VSlot Extrusion Mating Points

Once assembled, these cable controllers can very easily be connected to two rails of Open Builds VSlot 20×20 extrusions. This features lets the user find a controller spacing that’s comfortable for their shoulders.

All right–we’re good to go for the controllers! Let’s move to the tentacle.

Tentacle Assembly

In this next section, we’ll walk through assembling the tentacle and hooking it up to a manual controller.

1. Prep Wheel Hubs


  • qty 18: wheel hubs + set screws
  • qty 18: Delrin vertebrae segments
  • qty 2 x 18: 4-40 x 3-16 in. button head screws


  • Drill press
  • 0.125″ or 4mm drill bit, depending on tentacle core diameter
  • vise

Each vertebrae segment consists of a wheel hub, a delrin plate, and two screws. (Yes, you can put in all four screws if you like, but the last two are unnecessary and just add extra weight.) Fashion yourself 18 of these nuggets.

Detail: Hub Diameter

Depending on what size core you’re using (4mm flexible shaft vs 3.175mm speedometer cable), you may need to widen the hub axle diameter to accommodate the core. By clamping these hubs in a vise, you can drill them out to the larger diameter of choice.

2. Cut Wire Rope to Lengths


  • qty ~25 feet (7.62 m): 1/32″ diameter wire rope
  • qty 4: Wire “Termination-Style” Crimp Ferrules


  • Wire Rope cutters These must be wire rope cutters. Don’t destroy your electronics snippers only to discover that they don’t work :(
  • Hefty Wire Cutters for spring guide only
  • Wire rope crimpers for small ferrules
  • Optional: mini blowtorch
  1. Cut down eight lengths of wire rope each at 3-ft (914 mm) lengths.
  2. Optional: On one end of each wire rope, blowtorch the tip until it becomes white-hot for about 8 seconds; then let it cool. This quick “heat treatment” will prevent that tip from fraying as easily.
  3. Gather up 4 of your 8 cables. On the un-torched ends (or either end if you didn’t blowtorch them), crimp on a “termination-style” ferrule.

3. Assemble Inflection Point Vertebrae


  • qty 4: Wire Loop Ferrules
  • qty 4: uncrimped remaining wire rope lengths


  • Wire crimpers
  1. Gather up the 4 remaining uncrimped wire rope lengths.
  2. On each end, loop the wire through the vertebrae at one four horizontal segments (See image above) and then back on itself.
  3. Slide the loop ferrule onto the rope and loop the short end of the rope back into the ferrule and crimp

4. Prep Upper Stage Cables


  • 8 vertebrae (plus-or-minus a few)30325771952_c503352a27_z
  • qty 4: wire ropes with end-stop style crimp
  • qty 1: speedometer cable or (better) flexible shaft cut to 24 inches (610 mm)
  • qty 4: continuous-length extension spring (aka: spring guide) at 24-inch (610) lengths


  • 1.5mm allen key

Ok, two TODOs in this department: wire and sleeve.

  1. Slide one vertebrae to the tip of your flexible core material.
    With the allen key, secure it firmly to the tip.
  2. Slide the remaining (7) vertebrae into the core 29810238603_3b11dd4862_zmaterial and space them evenly about an inch apart. With
    the allen key, secure then gently. (We’ll secure them down more permanently later.) The core material should fill up with vertebrae for about 1/3 of its total length at this point.
  3. For each of the four wire ropes, slide the uncrimped end from the holes in the top vertebrae down through the corresponding holes of each sequential vertebrae. Remove all the slack such that the ferrule connects with the top vertebrae.

5. Prep Lower Stage Cables with Inflection Point


  • 7 vertebrae (plus-or-minus a few)
  • Inflection point vertebrae with attached wire ropes
  1. Slide the inflection point vertebrae into the core material and secure it gently, evenly spaced just like the other vertebrae.
  2. Slide in 7 additional vertebrae and secure them gently like before. Slide the 4 wire ropes that start at the vertebrae through the corresponding holes in each of the lower vertebrae segments. The total vertebrae count at this point should span about 2/3 of the total flexible core material length.

6. Attach the Base Clamp30377120081_3338928fbc_z

The key to a good puppeteering act is to have the tentacle base rooted down firmly. Right now, I’ve got a temporary solution, an extra square clamp that’s rooted to the base. There’s no magic here, just an extra wheel hub and plate that are both closely butted up against the bottom segment.

7. Adjust vertebrae Spacing/Alignment

Ok, now’s the time to tighten down those vertebrae, but, first, we’ll give ourselves a chance to better align them. For each half of the tentacle, ensure that each segment is well-aligned with its fellow segments in that stage. Loosen and adjust as necessary. Then, tighten down each segment.


8. Sleeve Wire Ropes


  • qty 4: continuous-length extension spring (aka: spring guide) at 24-inch (610) lengths
  • qty 4: continuous-length extension spring at 18-inch (457 mm) lengths (You can cut these with a hefty wire cutter)


  • a hefty wire cutter

Almost there! Our extension spring selection above will become the cable conduit housing in this design. Four cable conduit housings will terminate at the bottom of the tentacle. The other four will terminate halfway up the tentacle at the inflection point, traveling through the lower section along the way.


  1. Slide the four longer cable conduit housings into each of the four longer wire lengths. Each of these housings will slide through the body of the lower tentacle through each of its four large gaps. Slide these cable conduit housings up to the inflection point where they can extend no farther.
  2. Slide the four shorter cable conduit housings into the four shorter wire lengths until they terminate at the base of the wires.

Nice–time to wire it into the controller!

 9. Attach to the Controllers

On our tentacle, each degree of freedom gets two complementary cables and each stage gets two degrees of freedom. On the controller-side, each pulley will join a pair of complementary cables to give that degree of freedom its full range of motion. (Confused? No worries! Check out Part I.)

Now that we have a mess of cables and housings on our hands, go through this mess and pick out each degree-of-freedom’s cable pairs. (Zippy tie them or tape them together temporarily to keep the mess in check.)

For each of these pairs, slide the cable and its complement into opposite 3D-printed conduit holders and string them under the first angle bracket in the pulley’s wire crimp. Take out all the slack on these cables. These need to be tight! That is, keep feeding the wire rope through the wire crimp until the cable conduit bumps into the 3D-printed conduit holder. Screw down the wire clamp for now without worrying too much about tension. Repeat this procedure for each cable pair.

cable_routing_pitch cable_routing_tilt Use this as a cheat sheet

10. Tension Cables

At this point, it might actually help to have the controller dissassembled into the two main components.

From here, with your two hands, apply some tension to the counteracting wire ropes and use one of your partner-in-crime’s two hands to screw down the wire clamp with an Allen key. Alas, this is the second time whilst hacking that I find myself pondering over when they’re finally going to release “third-hand” surgery. (The first case, of course, being soldering… Hand 1 holds the solder. Hand 2 holds the iron. Hand 3 holds the tweezers with the component. Truly, it’s a no-brainer for another arm here.)

29810265613_810607b9b9_zThis method of tensioning works well enough, but there’s a far better method if you’re willing to shell out a bit more cash for components. Instead, I propose constructing internal extension-spring tensioners from two vented screws and a standoff. Simply by unscrewing the vented screw, one can increase the tension along the cable. No third hand required!

For the vented screw jig pictured, I’m using McMaster-Carr’s 4-40 vented screw section, which has a vent diameter that’s just larger than 1/32″ diameter wire rope. This use case finally merits a legit reason to pick up a few of those “vented screws” on McMaster-Carr that I’ve been eyeballing for years every time I land on their catalog’s screw page.

11. Clamp down the Base

Don’t forget: getting that convincing, fluid tentacle movment comes from having the base rooted down firmly such that the entire spine resists twisting at the base. I’m using a small vise that clamps onto the remaining tentacle length to do the trick for now, but this section deserves a bit more design effort. While a vise will totally work, feel free to keep us all in the loop on more clever fixturing methods!


If you’ve made it this far with a sparkling new tentacle to boot–congrats! Now go make an army of 20, rig them up to a few dozen servos, and set them to the beat of some hip 70s disco. For the folks that have read this far, I hope you can take away a few new techniques-of-the-trade that you can bring to your next after-hours, robot design-a-thon. Finally, thanks for joining me in the last few weeks as we tour these strange beasts. Writing these last few posts has been a blast.

Filed under: Engineering

Two-Stage Tentacle Mechanisms Part II: the Cable Controller

A few weeks back, we got a taste for two-stage tentacle mechanisms. It’s a look at how to make a seemily complicated mechanism a lot less mysterious. This week, we’ll take a close look at one (of many) methods for puppeteering these beasts by hand. Best of all, it’s a method you can assemble at home!

Without a control scheme, our homebrew tentacle can only “squirm around” about as much as an overcooked noodle. It’s pretty useless without some sort of control mechanism to keep all the cables in check at proper tension. Since the tentacle’s motion is driven by nothing more than four cable pairs, it’s not too difficult to start imagining a few hobby servos and pulleys doing the job. To get us started, though, I’ve opted for hand controllers just like the puppeteers of the film industry.

Enter Manual Control

Hand controllers? Of all the possibilities offered by electronics, why select such an electronics-devoid caveman approach? Fear not. Hand controllers offer us a unique set of opportunities that aren’t easy to achieve with most alternatives.

First, these controllers offer a purely mechanical solution. What that means is that they’re relatively simple in terms of parts. There’s no power supply to worry about, no code bugs to scratch our head over. Once we fasten our cables in all the right spots (and unkink the snags), the controllers just work.

Second, unlike a hobby-servo alternative, these controllers are dead silent when driven by our arms. That “chirp” that’s so characteristic of those cheap hobby servos just isn’t there; and, unless you’ve got some crunch to your wrist and elbow movements, these hand controllers keep the sound of the tentacle motion down to a minimum. For aspiring filmmakers, a quiet prop might sound more appealing than a whiny electronic alternative — even if they can mix-or-delete that sound away in post-production.

Third, unless we have a nice haptics controller, hand control gives us one additional piece of information: force feedback. Can’t squirm any farther into the table or through an obstacle? An electronic solution without a force sensor wont know when to stop tugging. Since our hands clasp the controllers that clamp the cables that carry the tension force through the length of the tentacle, we’re in direct contact with the forces experienced by the tentacle. Because we can feel this force, we can feel the “hard-stop” when our tentacle hits a dead end in its range of motion.

Finally, professionals still use hand controllers as one of many options in their repertoire for puppet controllers. While we’re not machining our controllers from 6061 aluminum like the pros, our plastic alternative isn’t far from tested-and-tried schemes of the past.



I mentioned above that force-feedback comes from the controller’s “hard-wired” relationship to the cables in the actual tentacle. To make this point a bit clearer, one of the oddball consequences of this construction is backdrivability. What this means is that, with our hands, we can manipulate the tentacleand those movements will feed back up the cables to then drive the controller. This nifty feature is an unavoidable consequence of how the cable is wired. What’s more, it’s an important reminder that the forces that this tentacle “feels” will be carried up through the length of the cable back into the controllers. In other words, if we’re controlling our tentacle by hand and someone seizes it to prevent it from moving, we’ll feel that force carried into the controller to tell us to stop forcing more torque into the controllers.

Controller Inspiration

This controller is targeted for fab on a laser cutter. (Ok, Ok, there’s one 3D-printed part in the BOM too.) The design, though, is just an adaptation of controllers that I’ve seen from special-effects controllers online.

Image Credit: The Stan Winston School forums Image Credit: Animatronics Demo with Rick Lazzarini

Most controllers that I’ve seen so far tend to separate each degree of freedom into two separate axes, rather than integrate them both into a single multi-axis gimbal. I’m guessing that the reason behind this is ease of fabrication, but I also think that separating each degree of freedom into it’s own pivot point also makes the tentacle far easier to puppeteer with broad, deliberate, hand gestures that require distinct arm movements.

full_assembly_perspective 29962869216_abb3f699f0_z

I’ve modeled my controller to take after Landon’s from the Stan Winston Tutorial series. That said, since I was aiming for fabrication on a laser cutter, the finished controller took on an appearance that’s similar in character but separate in both look and feel.

I picked a laser cutter for part fabrication since most of us don’t have the luxury of easy access to a nearby CNV milling machine. Laser cutters, on the other hand, are a lot more likely to pop up in schools and hackerspaces — not to mention that Pololu and Ponoko will also kindly laser cut your parts and ship you back the results.

As for the actual design, my biggest change comes from swapping pulley orientations. Moving the pulley that controls the tentacle “pitch” down to the lower section forces the user to use their entire arm to control that “up-down” motion. In contrast, getting that same “up-down” motion from Landon’s controller relies far more strongly on just wrist movement. That orientation change on these controllers puts far less strain on my wrists, and I hope others can reap the benefit of that swap.

Controller Nuts and Bolts

Just like the tentacle, the controller is also a whirlwind of new parts, most of which we haven’t covered before until now. Here’s a quick breakdown of the key features and components that make this mechanism work.

Keystone Angle Brackets 612 and 621

612Few off-the-shelf hardware parts have been quite as enabling as these two angle brackets, formally known on Digikey as: 612K-ND and 621K-ND. I have so much affection for these parts because, to date, I can’t seem to find any other commodity angle bracket that’s quite as tiny as these two culprits. Furthermore, depending on the bracket type, one or both holes are tapped with a 4-40 thread feature, which makes them ideal for fastening into tight spots without having to worry about accommodating space for an additional screw.

Sure, nothing’s perfect, and these brackets are no exception. However these brackets are being fabricated, they seem to be popping off the assembly line and into my livingroom at an angle that’s not perpendicular enough to use them for any sort of precision alignment. That’s no dealbreaker, though. I use them here to fasten the two pulleys perpendicular to each other on the controller. In this case, the actual plates of Delrin do the work of holding the two pieces in the proper configuration relative to each other. The angle brackets just fasten them in place.

Laser-Cut Rivet Pulleys:

29914156481_613d8358a3_zIn a bold step to truly push Delrin as a functional material for rapid prototyping, behold my best example of a functional part so far: laser-cut pulleys! These pulleys are a four-plate concoction. When riveted together  (since Acetal doesn’t seem to care much for glue), they behave like a single unit.

To the untrained eye, it looks like an off-the-shelf part. However, two necessary features make this custom design easier to build up from the plates rather than adapt from any off-the-shelf counterpart. First, each pulley is doing the actual heavy lifting of simultaneously loosening and slackening the cable pair that creates the actual movement. To do so, those cables must be rigidly fixed to the pulley at a single point. For that job I’ve embedded two cable clamps into the top of the pulley. Next, this pulley needs to screw down into either a handle, if it’s used on top, or a second pulley, if it’s used on the bottom.

In both cases, those connection points are offset from the center, and most off-the-shelf pulleys simply don’t have any offset mounting holes or attachment points. With some light CAD work, I embedded mounting holes directly into the plate. The result is a pulley with mating features already located where they need to be once the parts are laser cut. What’s more, since the hole pattern that drives these mounting holes is the same for the handle and the joint connector, both top and bottom pulleys are identical — a nifty feature if I ever find myself mass-producing these controllers. (Unlikely, but good habits make scaling easier when it does count!) For the custom needs surrounding this pulley’s end-use, a custom revision just made sense, and they hold up just as nicely as any off-the-shelf solution.


29997648585_866d90d308_zThe pulleys might start off as four plates, but once I assemble them together, I can forget about ever needing to take it apart. My pulley will forevermore be a pulley, not the parts that constructed it. Since taking it apart doesn’t matter, I opted for rivets. Rivets give the pulley a polished look, not to mention that assembling these pulleys gives us the chance to enjoy a satisfying squish as we squash each rivet into place. On a more practical note, inserting each rivet is much faster than threading a hole and screwing in a screw for each hole.

DIY Cable Clamps:

cable_clampIn the homebrew rapid-prototyping world, we’re usually limited to soft or brittle materials since most of our parts are coming off of the 3D printer or laser cutter. What’s more, Delrin has yet another problem: it’s notoriously slippery, so our wire clamping feature can’t rely on pressing the wire against a Delrin plate. The wire will just slip! In these situations, we can redirect critical stress-bearing features to off-the-shelf hardware. Here, our cable clamps are made from two steel angle brackets. The wire rope simply slides through the cavity between these two brackets where it can be screwed down between a steel-on-steel connection.

Cable Conduit Termination with Ferrules and 3D Printing


Each of our cable conduits must terminate at a fixed point on the controller such that the wire rope can extend beyond the conduit and clamp into the pulley. That way, when the pulley tensions the wire, the conduit housing doesn’t move with it. Instead, tugging the controller merely changes the wire length from the pulley clamp to the end of the conduit.

For this part, I opted for a 3D-printed block with a ferrule pushed into it. These metal ferrules are pretty standard components from bicycle and motorbike shops, and it saves the 3D-printed part from wearing out over time. Just like the cable clamps made from angle brackets, these metal ferrules take the stress off our custom parts and redirect them to a sturdier part that we can find off-the shelf. Here, our cable conduit puts more stress on the ferrule than the pocket of the 3D printed part.

Extrusion Attachment Points


Since I can’t predict everyone’s shoulder widths, I added a few attachment points for Makerslide angle-brackets. The benefit here is that anyone can cut down an extrusion length and space out these controllers in a way that’s comfortable for them.

Get Ready for the Assembly Round:

For the curious, I’ve been doing my best to keep an up-to-date photo log and CAD model of this adventure. Tune in next week for a fully-blown BOM and dxf suite to recreate these controllers and the tentacle at home.

Filed under: Engineering, Featured