Really! Just busy with some real-life stuff, namely wedding related and home renovations. I haven’t forgotten about this pick & place stuff! Lately I’ve been spending most of my project time on getting Mosquino toward an official 1.0 release. The rev2 boards just came in, so once all the parts are in I should have one ready to test soon. Here they are!

As usual, click for fullsize. Clockwise from the bottom-left are a bistable display shield, microSD shield, low power boost board (as low as 0.6V to 3.3V), Peltier shield (thermal to electricity, ~20mV to 4.1V), vibration energy harvesting shield, a stackable LiPol / thinfilm battery power shield, and of course the Mosquino mainboard itself. You may have seen early versions of some of these on the Mosquino page already, but these implement bug fixes and the latest/finalized Mosquino pinout. Can’t wait to get playing with these!

(And no, purple is not the official / final color – The PCBs were made via Laen’s sweet batch PCB service; he likes to experiment with the colors from time to time. It’s not a ripoff of Lilypad…although the Peltier board can potentially harvest from typical bodyheat gradients (>=2degC), which is an interesting development for wearable computing projects to say the least!)

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Typical frog in a hot pot scenario; when I joined Comcast the modem lease was like $1.50 a month, and I didn’t even think about it. As of recently it’s now crept up to $7.00 a month, which kind of made me sit up in shock. How much do those things actually cost, anyway?

Answer: $16 on eBay!

Ditching the leased Comcast cable modem in favor of your own is a surprisingly simple process. In my experience, Comcast won’t even try to (intentionally) stonewall your request or tell you it can’t be done in order to keep the revenue. Unfortunately, their techs are not exactly the brightest lights in the harbor, so you might have to train them a little on how to do it. Here’s how…

Step 1: Buy the modem
Go to your favorite new or used equipment source and buy the modem. Make sure your purchase includes any necessary power cord (wall wart); if not, buy that too. Theoretically, any DOCSIS 2 or later modem will work with most cable Internet packages, but to be sure, check this list for modems tested and approved by Comcast for compatibility. Extremely fast or fancy internet packages might have special requirements. Personally, I just searched eBay for the exact model # of my existing leased modem, and bought that one. My total cost was about $21 for the modem and a 12V wall adapter.

Step 2: Plug in the modem
Before you go connecting anything, turn the new modem over and copy down the “HFC MAC” number printed on the bottom to someplace more convenient. Note, there may be several different numbers printed on the modem; the “HFC MAC” is what you want. Technically the “number” is in hexadecimal, so it can also include the letters A-F. Double- and triple-check that you copied it correctly!

Disconnect your leased modem and plug the new one in its place. Verify that the lights come on and blink just as with your old one. (It will still ‘see’ a modem signal when connected, even if it’s not activated yet.) Once it’s lighting and blinking, power-cycle your wireless router (or whatever attaches to the modem Ethernet cable) to make sure it picks up a fresh IP address from the new modem. Just to be safe, reboot your computer(s) after this to make sure the newly rebooted router gives them a fresh address too. Now your modem, wireless router and computer will be “connected” to one another as far as your home network is concerned, although they won’t be able to reach the Internet through the new modem yet.

Step 3: Activate the modem
The one and only piece of information you (and Comcast) will need for this is the “HFC MAC” number you wrote down earlier. Call the Customer Service # on your Comcast bill, and say to them:
“Hi, I’d like to use my own modem and return my leased modem.” When I did this, the main customer service gave me a separate phone # dedicated to handling this request. Call that # and repeat the request.

The Comcast person on the phone will ask for the number from your modem. Not all of them are smart or well-trained, so they may not know which number, nor tell you the correct number to provide. Whatever they say (or don’t), give the “HFC MAC” you copied earlier. Now, this is important! Have the Comcast person input the number and then recite the number back to you, to make SURE they input it correctly. This is important!

Before you hang up, start accessing Web sites and see if they start working. If the Comcast person input the # correctly, your Internet should start working again almost immediately. If not, login to your wireless router’s status page (consult its manual for how to do this) and make sure it obtained an IP address, gateway IP and DNS servers from the modem. This information may be listed under a section titled “DHCP” (a protocol for devices to request and assign IP addresses.) Try powercycling the router again while the modem is activated to make sure it gets an address.

Step 4: Return the old modem
Hopefully, everything is working now! The last thing to do is to pack up the old modem and its wall plug in a box and return it to Comcast. If it came in an official Comcast box (e.g. “self-install kit”) and you still have that box, use that box – but if not, my experience is they aren’t that picky (I used a shoe box). There is a brick-and-mortar Comcast service/payment center by my house, so I just returned it in person. If this is not an option, ask the Comcast person how to return it by mail. My experience at the Comcast payment center was very positive – just handed the modem over, they scanned a barcode on the bottom and it was automatically credited to my account. They handed back a receipt with my name/account # and the modem details on it and I was on my way. My next bill had a partial refund for the part of the month I was no longer leasing the modem. Done and done!

If all does not go well…

If your new modem isn’t delivering the Internet goods after activation, the Comcast person (billing department) will transfer you to a separate department (tech support), who have the power to ‘ping’ your modem and make sure it is visible on their end. ‘Your’ modem in this case is defined as the modem matching the HFC MAC # linked to your account, which is why it’s very important that the billing person has input the correct #, and input it correctly, BEFORE this point. Otherwise they can ‘ping’ all day and not get any result because their system is looking for the wrong damn modem! The Tech Support person has the power to ping but NOT the power to add or correct MAC #s on your account, so this sucks. Likewise, the billing department has the power to enter MAC #s, but NOT to ping the modem! If this magic number entry gets cocked up somehow, it will take a 3-way conference call between you, tech support and billing to sort it out, and not all Comcastic techs know how to pull this off with all those complicated phone buttons. I spent two hours bouncing between departments because the barely-English-speaking billing person miskeyed the # the first time.

For the insanely bored or curious…

“MAC” number stands for Medium Access Control number, which is a globally unique number (burned into the device by the manufacturer) that identifies YOUR device among the millions of others out there just like it. The “medium” referred to is the physical cable. Since your block’s local cable segment is a shared resource, this number is necessary to identify you as a paying customer and route the right bits to and from YOUR specific modem. The difference between the separate “HFC” and “CPE” MAC #s is that the HFC number (I’m told this stands for “Hybrid Fiber-Coax”, i.e. residential cable networks) is the one that’s visible on the coax (cable) side of the modem that your ISP sees, and the other (“Customer-Provided Equipment”) is the Ethernet-side number that’s visible to your equipment (e.g. wireless router). Don’t tell Comcast that number by mistake; they can’t see it on the cable end.

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Despite the impact of work, wedding planning and Super Metroid fan-hacks (not necessarily in that order ;-) on my freetime, my scheme to design a DIY-able open pick & place system is starting to come along. So far, there is a proper vacuum placement head, a rough idea of what the software architecture might look like, and this. For those who saw the last post, you probably guessed what it was leading up to.

This is a simple proof-of-concept of a SMT tape-and-reel part feeder design. The main parts are a stepper motor and feed sprocket to advance the tape, two walls with guide slots, and a simple slider mechanism to allow the feeder to accept tapes of varying width. Please note that it does not (yet) include any mechanism for peeling and disposing of the tape covering. Suggestions and innovations in this area (as well as all others) are welcome!

All the parts were cut on a CNC mill – design files and G-code are available here. The .cb files included can be opened with the free version of CamBam. More photos / video and design details are available below.

The Tape Standard
The geometry of the standardized tape that holds SMT parts is documented in EIA-481-2-A, which until very recently was only available at a price too high for mortals (or from your favorite ‘alternative’ source, wink nudge). It appears that EIA disbanded at the end of 2010 and the documents are now public. Regardless, here are the parts of interest to us building a DIY tape-and-reel feeder:

Pitch (distance between sprocket holes): 4mm
Sprocket hole diameter: 1.5mm
Center of sprocket hole to edge of tape: 1.75mm
Center of sprocket hole to edge of component wells: min. 0.75mm??? (seemingly not specified; varies between manufacturers)
On opposite side of tape – ending edge of component wells to edge of tape: 0.6mm min.
Tape thickness: 0.2 ~ 0.4mm, not including covering.

The standard tape widths are 8/12/16/24/32/44/56 mm. For tapes 32mm and wider, a row of slightly elongated (same pitch) sprocket holes is added to the other side. According to various sources, the standard also says the pitch between part wells should be a multiple of 4mm and “Pin 1″ (if any) should generally be on the sprocket side and facing forward. A longer explanation of the part orientation rules is that the part should be a) widthwise (its longer dimension, if any, across the tape); b) Pin 1 toward the round sprocket holes (unless this conflicts with the first rule); c) Pin 1 facing in the direction of travel (unless this conflicts with the first 2 rules). How religiously any given vendor adheres to these rules is anybody’s guess. There is also no rule saying the ‘well’ or pocket holding each part has to remotely match the size of the part (except to prevent it being able to flip over or rotate 90 degrees during shipping), so visual positioning correction is occasionally needed for parts from particularly lazy vendors.

Feeder Design Points
With these things in mind, the shown test-design uses the following dimensions, which seem to work well with varying size tape samples I fed through it:

Sprocket thickness of 0.7874mm (.031″) – this is a ‘standard’ stock thickness in the US, so it was an easy first test. I sunk the sprocket so that it lies flush with the inside wall. With these values, the depth of the tape track is cut to 2.14376mm (0.0844 inches) to put the edge of the tape flush with the track when on the sprocket, forcing it to stay straight despite all the feed force being delivered on one side. For the ‘outside’ (non-driven side) wall, the track is cut to a depth of 1mm (0.039 inches). The width of the slot is 0.79375mm (0.03125″), as this is the closest (commonly available in the US) milling bit width that will accommodate both plastic and the slightly thicker paper tapes. To assist loading tape, a wider ‘mouth’ is cut on the input side of both sides’ slot, tapering to the slot width to guide the tape in. In reality, the mouth you see in the photos is not really large enough to be useful (it looked a lot bigger on my monitor!…). Also, the mouth on the non-drive side in the photos is on the wrong side since I completely forgot to account for this half being flipped over :p These are corrected in the downloadable files.

With the sprocket as designed, the tape track radius is 13.6mm (0.536″), and the track makes a 180 degree pass around the sprocket to eject the spent tape at the bottom of the same end it comes in on. In hand-testing some tape around the sprocket, I found it does not always sit flush against the sprocket throughout the entire 180 degrees, so the tape track is widened a bit around the sprocket to accommodate. The ~31mm sprocket diameter / number of teeth (22) was chosen purely for convenience on my part, as this is the tallest that would comfortably fit on the homebrew CNC mill I’m using for testing. In practice, a larger diameter is advisable so as not to limit the size of parts (deepness or length of the ‘wells’ vs. sprocket diameter and bend radius) that can be fed. Also, the reels themselves will be much taller than this anyway. Just keep in mind that as sprocket diameter goes up, so will the required motor torque to advance the sprocket one step, and the linear distance per step. At some point some form of gear reduction will be necessary vs. simply tacking the sprocket directly to the motor shaft.

To handle a wide (pun intended) variety of tape widths, a trio of smooth nylon PCB standoffs (0.250″ dia) are sunk and bolted into the drive side to act as sliding rails for the halves to be pulled apart to the desired width. A rubber band around both halves keeps them tensioned and in contact with the tape edges when loaded. This could definitely stand improvement, but it works for now.

Despite being a quick ‘n dirty test piece, the action of this feeder (by hand) is surprisingly smooth. The nylon spacers are pretty slippery, and the Delrin also provides a smooth, low-friction surface when machined. With the motor is a different story; these tin-can motors are 7.5deg/step and the driver board I’m using right now doesn’t really support microstepping low-current motors.

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My page that tells you your IP address is up and running again, after a PHP configuration change by my web host knocked it out. Anyway, enjoy the glory of finding out your external IP address without getting socked by porn popups!

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This is a quick follow up to the pick & place head article, in which I actually build the darn thing :-) As in, not just fit-test the parts together and take a picture, but actually pick and place some stuff with it. I’ve been busy/lazy, so not too much to show in terms of software yet (the video you see below is running a ‘dumb’ g-code placement script). The parts list has been updated will be updated in the next couple days, along with new CamBam/DXF files.

Live test of the head as currently designed. This is bolted to my ghetto homebrew CNC mill, which is kinda slow. On a more built-for-purpose (or less ghetto) machine, performance should be much better.

The webcam’s weird eyeball-shaped case has been removed, revealing a rectangular board with sanely-spaced mounting holes in its corners. Also, a proper solenoid valve has been bolted to the head and hooked up to a reversed aquarium pump for suction. The rubber nozzles are from a sacrificial el-cheapo SMD vacuum pen ($3USD ,eBay), which comes with three sizes that fit on a standard 16-gauge needle.

Otherwise, it’s pretty much as described in the previous post.

A little bit of guts. This board holds a transistor to drive the 12VDC solenoid valve from a parallel port pin, Pololu microstepping motor driver (Allegro A4983) and 5V regulator. At the top you can make out a simple pressure sensor conditioning circuit that isn’t hooked up yet.

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Quick ‘n dirty (but working!) image segmenter for randomly-strewn part identification. About 1 page worth of scripting takes an image of objects on background, determines which part is the background, determines the outside contour of each object and numbers each as a separate object. Now that it’s known where to look for one specific object, the task of identifying that object (or just matching it to another just like it) becomes a whole lot simpler. Combined with the auto-aligner, this reduces a “naive” (bruteforce cross-correlation between needle and haystack images) image matcher to only having to scan against 4 orientations (90-degree rotations) to find which has Pin 1 in the right place (and whether it’s the same part, etc.) Hopefully as I dig deeper into opencv, there is a less-naive algorithm builtin for this that does not rely on contrast/color historgrams: most electronic parts basically consist of a flat black body and shiny reflective metal leads (i.e. appearing the same color as your light source and/or the background, and/or whatever happens to be nearby at the moment). Edge-based stuff still seems like a better approach, though I would welcome being proven wrong if it means not having to write the identifier from scratch myself :-)

Steps in brief:
The first image was taken using the actual webcam that will be attached to the pick n place head, looking at a handful of representative parts on a piece of white paper. This image was dumbly processed using a Sobel edge-detector (it’s builtin to Gimp and I was feeling lazy), Gaussian blur to expand the soon-to-be-resulting mask around the part a little and close any gaps in the edge-detection result, and finally threshold the result to produce the second image. The goal in these steps is to produce a closed-form contour blob for each part that’s at least as wide as the part, while minimizing stray blobs from random noise / dirt specs / etc. (internal, fully-enclosed blobs/noise due to part features/markings is OK). Finally, opencv’s FindContours function is run (mode=CV_RETR_EXTERNAL) on the resulting image, returning a vector that contains a polygonal approximation of each external contour found. Each discrete (non-touching) contour blob is returned separately, that is, every part in the frame is now effectively tagged and numbered!

There are a couple noise points identified in the image above. Better-chosen constants for the initial image operations (threshold, blur radius, …) may help, but I’ll probably end up having it measure the area of the blobs and throw away any that’s too small to possibly contain a valid part. Switching to a more advanced edge-detector, e.g. Canny, may help too. In any case, the full image matcher should figure it out eventually :-)

Code Demo – basically ripped straight from the pyopencv examples
Segmentation example – requires Python (2.6) and opencv 2.1.0 / pyopencv.

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This weekend I got some parts in and put together a preliminary placement head for my open-source pick ‘n place project. My requirements are that it be buildable with off-the-shelf parts (ideally same-source, to save on shipping) and no special equipment, allow +/-180 degree rotation while maintaining an undisturbed vacuum, and support interchanging of the “tools” (vacuum needles). All that’s really needed to build this are the discrete parts shown, a bit of drillable plastic (e.g. Delrin) for the base material, and a drill. A drill press would be handy (a CNC mill *really* handy, and not such an out-there thing to have considering you are probably retrofitting this onto one).

This head consists of a hollow rotary shaft with a Luer lock fitting on one end, right-angle flexible tubing barb on the other end, and a large toothbelt (notched belt, timing belt) gear in between. The shaft is held in place but allowed to rotate by a pair of bearings, and the rotation is provided by a small stepper motor at the other end of the toothbelt. The gear ratio is approximately 5.2:1, providing a rotational resolution of about 0.35 degrees/step with a common 200 step/rev stepper motor (if no microstepping is used). Finally, just to the left of it is a 1024×768 Webcam with manually adjustable focus and a ring of built-in LEDs for lighting. The webcam mounting is definitely not ideal, given the camera’s weird eyeball-like shape. Tentative plan is to lash it down with some string, align it nicely with respect to the CNC table, then backfill the opening the camera’s butt sits in with epoxy.

The hardest part was finding a combination of parts that would all fit together nicely. Currently, the fits are mostly exact to “pretty damn good”, but a bit of adhesive is needed to join them permanently.

Parts List
Unless otherwise noted, all of these parts were sourced from Small Parts Inc. in the US due to the large selection and an actually competent parametric search engine, which was a great help in finding combinations of mutually-fittable parts. Accordingly, measures are in Imperial unless noted otherwise (that’s just how they come here).

Misc. Parts
2x 2″ x 4.5″, 1/4″ thick pieces of Delrin or similar
4x 1/2″, #4-40 bolts and nuts (assuming 2 bolts for stepper motor)
4x 1/2″, #8-32 bolts for standoffs
1x Webcam, manual focus, hi-res and builtin lighting strongly recommended
1x 3mm shaft stepper motor*
1x Method of attaching to your mill – a bit of aluminum angle bracket, or a dovetail, etc., depending on your mill.
1x 3-way air solenoid valve
1x Vacuum source (see here for a cheap one)
Air tubing and appropriate couplings to your solenoid valve. The head’s air path terminates in a 3/32″ hose barb, so you’ll want a 3/32″ to (whatever) barb adapter, or a 3/32 that screws directly into your solenoid. Those using metric are on your own :-) but will probably have an easier time of it anyway.

* The timing pulleys and stepper motors only come in a handful of diameters (imperial for the pulleys and usually metric for the small motors), so a 3mm (.118″) motor onto a .125″ ID pulley was the closest I could come up with in a reasonable amount of effort. Any small, el-cheapo permanent magnet (“tin can”) stepper motor should work here, but sourcing it may be annoying. Off-the-shelf 3mm-shaft motors I found are Jameco’s ValuePro 42BY48H08, Anaheim Automation’s TSM42 series, and Portescap’s 42/44 series e.g. 42×048 and 42S100. This surplus stepper is also worth a look, but you’ll have to remove a pre-attached plastic(?) gearhead. Beware, many of these smaller motors are 7.5deg/step, so even with the gear reduction, you will probably want to look at microstepping them to ensure adequate rotational resolution. Also, most of the companies selling them have no online click-and-buy ordering; you’ll have to phone up a salesdouche at the least, hope that you are worth their time to buy One Lousy Motor, and possibly haggle (“Request a Quote”). How companies that don’t know what their product costs stay in business is beyond me, but that’s a rant for another day.

If you want to skip that hassle, I’ve taken an alternative approach and simply bodged a surplus 2mm-shaft motor up to a 3mm shaft by gluing a short piece of thicker steel tubing onto the existing shaft (see partlist).

Design Files
CamBam drawings with machining operations for the top and bottom plates. The machining ops assume 1/4″ thick plastic, 1/8″ endmill for most cuts, and .166″ (#19) drill for the #8-32 bolt holes into the standoffs. It’s designed for the Cubeternet webcam (or equivalent eyeball-cam) and a stepper motor with 42mm center-to-center mounting holes. You can get the free CamBam at http://www.cambam.co.uk/.

Note, I made some small improvements to these files after the above prototype was carved, so what you see in the file will not match it exactly. In particular, the standoffs were moved to more optimal places and a feature has been added allowing the motor to be slid to remove any slack in the belt.

Assembly
The assembly should be pretty self-explanatory. One bearing on each of the Delrin plates (inset the ball bearing if you can; otherwise gluing it down should be fine). The hollow shaft goes thru the bearings, Luer adapter and hose barb go on either end (use adhesive, just don’t clog the air path with it). The motor shaft center should sit just a hair (50-100 mils?) over 1.75″ from the hollow shaft. On mine, an online calculator produced the 1.75 figure, but the belt turned out to be a bit loose once built this way. If possible, make an elongated hole for one of the motor screws so the motor position can be adjusted to tension the belt. You could probably also insert a peg somewhere in the belt path to push it inward and take up the slack. With the camera focus set such that the largest part you will ever populate can fit in-frame, find the resulting camera height (distance from part) and set the depth of the shaft so that the camera is “in focus” maybe an inch or two above the placement position (i.e. with the needle touching the board). This will allow the head to focus on parts without touching the needle down.

For my build, I used instant glue to attach the Luer adapter to the needle shaft, and hot-melt glue to tack down the large pulley and hose barb. None of these parts should be seeing significant force; if they are, you’re Doing It Wrong and the hot glue should hopefully break loose before something more important does. Using a non-permanent adhesive for the hose barb and pulley also allows this assembly to be disassembled later if needed. The shaft itself is free-floating and the large pulley rests against the ball bearing due to gravity. This will prevent damage due to crashing the needle into the table or too-tall part, but if you experience problems with the shaft riding up on its own, try adding a bit of extra weight or put a dab of adhesive where the shaft passes through the lower bearing.

Suggested “v2″ improvements
–Move air valve (if/when one is specified) onto head to minimize air volume between valve and head. Needed? (may be beneficial for reversed aquarium pumps or other weak vacuum sources)
–Bump detect: rather than firmly adhere the shaft into the bearing, allow it to float up and down, normally resting by gravity with the large pulley against the ball bearing. Place a contact switch just above the pulley: if the head/part contacts the surface with more than minimal force (enough to lift the shaft), contact switch is triggered. This could be used to halt the machine if a bump was not expected. If the switch’s trigger position is reliable enough, it could be used intentionally to automatically determine component heights.
–Probe function: There is a conductive metal path from the needlepoint all the way up to and including the bearing outer race, so it would be easy to touch a contact here and use the needle to probe for any conductive objects (e.g. find the tabletop if it is metal, or some capacitive shenanigans for PCBs/etc.). Useful?

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So, there’s some really cool, empowering stuff going down these days with regard to manufacturing. Cartesian machines (i.e. CNC mills) are relatively simple to build from off-the-shelf parts; there are a bajillion people doing this and plenty of ready-made open-source designs available. More recently, hobbyists have gotten in on designing open-source rapid prototypers (3D printers); as a result, designs have now crossed the sub-$1000 threshold off-the-shelf, and you can even build a GPL’ed 3D printer that can almost replicate itself!

One thing that I haven’t seen cross the blood-brain barrier of proprietary commercial systems is pick-and-place machines that can assemble electronics. These things are badass; full of automated win and articulating robotic arms, but they’re also damned expensive: the crap ones start at >$10k and use literally a fishing-lure-and-weight type arrangement to peel back the tape covering tape-and-reel parts, so you have to keep resetting the weights. Those with more advanced / less manual feeders scale skyward from there. And of course, the software end of these things, especially machine vision algorithms to place parts more accurately, is some serious $ecret $auce. So… let’s change this!

Most of the “big stuff” is straightforward: The PCB layout software generates a list of coordinates for each part. A small vacuum needle mounted on a Cartesian head picks up each part from a known location, rotates it 90/180/etc. degrees as needed, and sets it down at its coordinates. It does not even need to be 100% accurate: surface tension of the solder during reflow will pull most minorly misaligned parts back into place.

The big barriers are:

1) Low cost / self-manufacturable feed mechanisms:
Electronic parts are packaged in several different ways, most commonly tape-and-reel, plastic tubes, or in trays. Each has a different, maybe cumbersome, way of knowing the location of the next part in the package and freeing the part from the package. Picking up stuff and putting it down is easy compared to dealing with the wide variety of tape and tube sizes reliably. Oh, and if your board uses 50 unique parts, you need 50 feeders. Hence the emphasis on making them cheap and mass-self-produceable, e.g. by CNC or casting or 3D printing.

and/or…

2) Machine Vision
For larger parts, once the first part is successfully picked (e.g. by human intervention), it is enough to know how many parts per inch of tape, advance the tape a known amount per pick, then just grab blindly for the part and plant it at its destination coordinates. But for smaller and finer parts, this is not accurate enough: the parts can be slightly off-center or crooked in their tape wells, and this becomes significant as the part size decreases. Professional machines use a set of cameras and image processing algorithms to recognize the part, find its dead center and correct any rotational error. In theory, a suitably good vision system would allow you to peel back the tape and just sprinkle the parts on the table, forgoing feed mechanisms entirely at the expense of some small manual labor. Actually programming this algorithm on the other hand…

Another nice thing to have would be:

3) Automatic needle swapping. Many more advanced CNC mills are able to spit out their current tool, e.g. a specific size drill bit (in a known location in a tool rack) and pick up a different tool. It would be nice for the pick and place machine to be able to change to smaller and larger needles/suction cups to handle large and small parts seamlessly. If not, placements can be sorted, e.g. smallest to largest, so that the needle only has to be manually changed a couple times.

I’ve made some very initial feasibility-study stabs at building such a machine, and begun building a bit of hardware. I created a separate page for this project with more detailed specs/documentation and progress so far:
Pick and Place Project

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