Back in the States

Time flies when you're having fun and don't have a laptop. Last week was both busy and slim on laptops, but now that I've returned to the States, it seems my Lenovo is back from the dead somehow.

Monday we spent at the hotel, as much of Ghana observes the end of Ramadan.  On Tuesday, myself, Aimee, Benjamin, and Edward Antwi journeyed to Suamee magazine with a hastily assembled machine #2 and extra coin mechanism. Our mission was to find, interview, and contract with local businessmen to produce the design in quantity. Benjamin's acquaintance with a local fabrication shop yielded us metalworkers, who were happy to assemble the sheet metal components. After some back of the blueprints math and amortization considerations, Edward arranged for the construction of up to six cases. We then traveled to another shop, this one a machinist, hoping to find someone capable of duplicating the Beaver coin mechanism. He was intrigued by the device, but agreed that any replication would be difficult if not impossible with subtraction techniques. While he offered sand casting as a possibility, we shared a concern that the accuracy afforded by sand casting simply would not suffice. This was confirmed later in the evening by phone after our machinist consulted other specialized sand casters.

Thursday, we returned to the shop for our final day of assembly. As we would be leaving the remaining components for seven additional machines with Edward and the universities, it was essential that we complete machines #2 and #3 to a state where they could be used as prototypes for a new generation of devices. To this end, we assembled and tested the two over the mid-week, discovering a new issue or two along the way -- Particularly, both machines had to be disassembled multiple times for issues with the coin mechanism, as well as issues with the axle mounting locations.

Beaver Coin Corporation holds a special place in my heart. While the ratcheting sound of the one-way gear is soothing and has grown melodic to my ears over the past year, I have a particular hatred for whoever designed the hole pattern which holds the device together. In short, two cast halves are mated about a rotating assembly, with four screws about the perimeter. If any of the screws are loose, the thing sits funky and eats coins or itself. Confused? here.

 Let me take a moment to talk about the feature labelled "Evil Bolt of Doom." This particular bolt is just like its friends, a short little machine screw. With a Robertson head and a steel alloy, though, he doesn't have much to worry about. His partner, however, wouldn't turn out quite the same.

See, all four bolts thread into tapped threads in cast "sleeves," threading about 6 or 7 threads of contact. All except the Evil Bolt of Doom, which threads into a sleeve calmly only threaded at the bottom half. This leads to anywhere from 0 to about 4 threads of engagement, which meant that if the spacers were slightly too thick (which they were) or if the case was slightly bent (which also happens) this screw wouldn't catch, and often would happily a few miserable threads out of its sleeve and promptly strip the hole entirely. I quickly learned to install all the other screws first to appropriate torque, and then install the Evil Bolt of Doom to a much lower and cautious torque.

Somebody should really fix that, it's annoying and wasted hours of assembly.

We also encountered problems with vending in these two machines, which we addressed but didn't meet our standards set with the first machine. Most of the issues stemmed from a loose and inaccurate drilling of the mounting holes for the axle. With these holes off-location, the axle would sit at a noticeable angle to the inventory chutes, leading to starkly different results from each. To rectify this, we drilled the holes oversized but centered, and then created a "shim" of Gorilla Tape, which we added in a one-layer-thick wrap to the axle, to match the oversized diameter.

Our unresolved consistency concerns with machines #2 and #3 stem from their lack of consistent quantity of condoms vended. Neither machine jams, nor steals your money, but neither consistently vended a steady number from both chutes. We left the "proof to the readers," so to speak -- in hopes that rising to solve the problem will lead Edward's team to engineer better designs for these problem areas.

Friday's flight back was largely uneventful, though the tedium of airport security was a bit more than I'm used to -- the Accra airport leads one through three security checkpoints and at least as many passport inspections, finally dumping you in a securities--off glass boarding gate, where you sit quite helpless wondering what's on the departure signs behind you, and where exactly is this aircraft anyway, weren't we supposed to board a few minutes ago? Once in the air, however, we made excellent time and caught New York sleepy and unaware -- like a grumpy bear not quite awake -- and made our way quickly through the American side of the security show. By mid-morning, we were all safely headed back to Albany.

Friday, and Thursday, and Wednesday, and stuff

The midweek was productive, but a bit slow. We've gotten quite a bit done on the other two demonstration models, and brainstormed more solutions for Helena's unit. Scheduling conflicts prevented her from meeting yesterday as planned, so Aimee and I went back out this afternoon. The end results are stunning -- apart from major usability improvements for the vendor, the external design looks a thousand times better with Kente cloth. Gabriel, of solar project (Atonso) fame, prepared the cloths yesterday, and the end result is nothing short of fantastic.

Vending machine!

Flattering photograph of Aimee

The internet is too slow here to upload much more, it took twenty minutes to get those two up. More to come next week!

Tuesday the Second, Machine installation

Today we put some finishing touches on our first machine, and travelled back to the Suntreso hospital to install the machine at Helena's HIV clinic. Installation went without a hitch, and Helena identified a few minor tweaks she'd like us to make over the next few days --

*Adding more color to the machine, perhaps in the form of images or paint.
*Improving the side instructions and matching them to the vend slot design
*Improving the condom vend slot, smoothing the edges and increasing the size slightly to ease access
*Improving the inventory chute, to ease filling the machine
*Incorporating the Red Ribbon symbol in the exterior design of the machine in some manner

To address these, Aimee and I have decided to

*Increase the size and modify the design of the front image, adding a large colored Red Ribbon symbol
*Modify the side instruction dialog to match the vending slot, and add information for if the machine will not take the coin (i.e. is empty and interlock is engaged)
*Filing and duct taping the edges of the vend slot, as well as bending back a tab at the top surface (simultaneously heightening the slot and removing the sharp edge)
*Modifying the inventory chute faceplate design to allow removal of inventory followers, and ease filling from the top section of the inventory -- more on that later

Overall, Helena was very happy with the device, and looks forward to installations at more clinics soon.

Monday again!

Well, we finished up the final touches on the first machine -- designing and folding a coin tray, while Phillip welded inventory followers. With the machine all set to go, we went to lunch, looking forward to visiting Helena at the HIV clinic to show off our product.

After lunch, Aimee and I realized that we'd (of course) left the machine at the shop, which was now locked.

Unfortunately, there's no way to type a facepalm.

Nevertheless, we had an extremely productive visit with Helena. We were able to explain the rough dimensions and specifications of the new machine, and discussed the future possibilities for installation sites -- Helena is an extremely bright and quick mind, and she's very optimistic about our new model. She sees opportunities at every HIV/ART clinic in the Kumasi area -- but more importantly, she views these sites as proving and improving grounds for our design, which she believes the Ghanaian government itself may well be interested in for application across the country. I asked Helena how many clinics she was proposing, and she named nine in the Kumasi municipal area, with dozens more in the outskirts -- and close to 150 across the country. I'm hopeful the project will continue humming along, particularly with Jorge Appiah's aid after our departure. It seems that the sky's the limit, so to speak.

We also picked up 1,440 condoms (!), which Helena, it seems, can sell to anyone from her clinics for 5 Cedis/144 -- a massive profit margin for the vendor if vended at 50peswa/ea, and a ready and available source of condoms at HIV clinics across the area. Tomorrow morning, we'll use a package to evaluate and test the first machine. Assuming any issues are correctable in the morning, and we can achieve a >98% vend rate, we'll return to the clinic tomorrow and install the first machine!

Thursday & Friday, First machine completed

Thursday was a fairly uneventful day. We arrived in the morning and discovered the planer tech was on vacation out of the district, and wouldn't be available. However, Ato, the shop foreman, suggested we take our blueprints and raw stock to the campus carpentry shop -- which normally concerns themselves with the day-to-day carpentry needs of the school, such as cabinets, bed-frames, and the like. While communication was a challenge, we were able to meet it, and the craftsmen there were willing to take a few minutes to help the confused white folk. Not wishing to ask too much, we had them mill one set of components, enough to complete one machine. By the time we'd finished all this, Aimee's infallible Lunch Break Tummy Clock indicated that it was indeed closing time at the shop, and we wrapped things up for the day.

This morning, emboldened by what passes for a Spanish Omelette here at the Guest House, we returned to the machine shop to assemble a machine. While I was too busy worrying and working to take many photographs, Aimee carefully documented the entire assembly process, and is in the midst of doing important things with those pictures. Apart from a few minor snags, the machine went together without a hitch. Jorge Appiah, whose name I've been misspelling for a few days now, stopped by around noon to critique our design -- as management must always descend upon engineers during the critical stage of any project.

Fortunately, by closing/lunch time, Aimee, Phillip, an Oxford Comma, and I had finished the first machine, and addressed many of Jorge's concerns -- most of which had to do with security and the risks of Ghana, which he does understand far better than we do. Some of his notes we've incorporated into our future revisions list, and others we enacted directly on this first model, which we understand will be mounted in a safe and secure location inside Helena Afriyie-Siaw's HIV clinic here in Kumasi.

The reaction from Jorge and our Ghanaian cohorts to the completed system was nothing short of jubilation, everyone is quite pleased -- dare I say astounded -- by the device. Phillip is keenly interested in continuing development of the system after our departure, and I gave him a set of blueprints today that I think will go to great use. Jorge believes that local technicians can reverse-engineer, simplify, and replicate the Beaver Coin Mechanism we're currently using, and intends to take a coin mechanism to show a few acquaintances on Monday. We've contacted Helena to arrange purchase of condoms in bulk (144 for 5 Cedis, at an exchange rate of $0.29 to the Cedi -- it's a rough economy here). Our current plan is to pick up 1,440 condoms on Monday, and test this machine extensively then. Assuming all doesn't go well and we can fix it within a day or so, we'll have this machine installed in the Clinic early next week, and the remaining two machines completed around the same time. I'm very much  looking forward to demonstrating this, ahem, fully operational battle station to everyone; albeit a bit less so to explaining the inevitable malfunction upon demonstration.

Here's to the first Ghanaian coin-operated vending machine!

Wednesday

Today wasn't quite as great as one would hope, but everything can't be roses. It's the rainy season here, and today is the first of a predicted four or five days of rain, which put a dreary tone to the morning. However, we got a few little things done, installing the coin mechanisms in the three cases we've completed, and riveting hinges to the lids. After measuring the wood that was available at the shop, it turned out to be both too thick and too narrow -- and while there's a planer here, there isn't a board stretcher. (that's a joke). The wood was also second-use, and had been exposed to weather for quite some time, leading to warping and saturation. I opted to head to 'Wood Village' with Felix, our driver for the duration of our stay, as well as Aimee, Papa, Michael, and Phillip. We were able to purchase twenty board feet of 1x12 roughcut (pine?) there, for only 50 Cedis -- or about 15USD. Try getting that price in the states. The proprietors of the massive wood yard, which was essentially the back side of an even more massive sawmill, offered to plane the boards to thickness for a few extra Cedis -- great! less work for us -- but alas, the entire district's power had been knocked out by the storm. We'd forgotten about that, as KNUST has auxiliary generators to power the machine shop -- this is a pretty common occurrence here.

Phillip mentioned that there's a planer here at KNUST, but the technician who's trained to operate it was on leave for the summer. Pish posh, I'll do it myself, how hard can a planer be?

Apparently quite hard when it's fifty years old, and while I think I could use the machine if it came down to it, I'll feel much more comfortable with someone familiar with this particular model using it. The shop foreman was able to contact the technician, who offered to come in tomorrow morning and assist for a few Cedis. Hopefully we'll be able to plane and cut the boards then, and assemble all three machines by the weekend.

This afternoon, Aimee and I dismantled a printer which Ron had acquired and hoped to use as a case. I was initially optimistic, as the external layout looks fairly conducive to the geometry of the devices. Upon opening it up, however, it became clear that the internal mechanisms are far too structural, as we'd feared. Desktop computer cases may be more applicable, as they're designed to be self-contained -- we also thought of muffler cans or auxiliary fluid tanks from trucks, which could be about the right size and shape. Time will tell if the Ghanaians can recycle these into cases -- there's a limit to how crude and simple a device can be made while maintaining functionality, and we're quickly approaching it with ideas like this.

A number of new faces joined us at lunch today, including two students of George's (Ron's entrepenauer and mechanical engineering professor friend). Apparently word's spread about this vending machine idea, and these students are very interested in getting on board. I find that I spend the most time explaining the coin mechanism itself: It seems that Ghana really doesn't have such devices, indeed George himself was confused initially that the device would only vend if a coin was inserted. As such, I think this is a definite area of development for next year -- designing and implementing a truly open source coin mechanism would remove the sole proprietary part from the design, and make the entire system truly Ghana-capable from the ground up.

Tuesdays...

Now that yesterday's published.

We arrived at the machine shop at eight this morning, with sheet metal haphazardly strapped to the roof of our ancient shuttlebus. Papa and Michael again met us there, and brought with them a few more students from KNUST -- Phillip, a welder and son of a welder, and a few of his friends whose names I'll remember as soon as this publishes. Aimee and I were able to jigsaw-puzzle three units onto our single half-sheet of stainless, which cut incredibly easily with the aviation shears I brought. Papa and I set to cutting parts, which Aimee then hauled over to the drill press.



Phillip and I were able to set up a jigsaw station and he took over cutting the interior cuts -- such as the vending area in the lid, and the coin mechanism location in the case. Before I realized it, we had an entire machine shop humming out vending machine cases.

Phillip hard at work.

All these hands made light work, and I found myself wandering aimlessly a few times -- So I took pictures of big shiny machinery. Some of the equipment in the KNUST shop is truly impressive, obviously the biggest ones are the coolest.

Massive German drill press --  Aimee for scale. The main column is 12" diameter solid steel.

Partially uncovered 12 foot bed lathe. For scale, the 4-jaw chuck mounted is 18" diameter. The workpiece is near eye level for me at 6 foot.

A truly massive vertical mill -- both tables are 2'x4'. I estimated the capacity around 5 foot cubic. The top of the head towers around 12 feet off the ground.

By mid morning, we'd cut and drilled all three sets of components, and were faced with our largest challenge yet -- how to fold the cases without a sheet metal brake. As I pantomined the device I wished we had here in Ghana, Phillip realized that there was a fifty year old brake in the shop next door.

First case cut in Ghana -- this was a good moment.

Fruits of our labors -- a bunch of finished parts

Sheet Brake!

Whoa, those actually look like cases.

With the sheet brake and the number of hands on the project, we went from sheet of steel to three cases in about four hours. I assembled a coin mechanism in the case to demonstrate, and asked Phillip to run a 50 Peswa through. I think this was the moment that the KNUST students suddenly realized how this all works, and they ate it up -- they were incredibly excited to work the mechanism, the ratcheting click of a coin going through is quite satisfying.

Somewhere during the morning, an unidentified entrepreneur contact of Ron's who I know only as "George" stopped by the shop. He was equally, if not even more excited as Ron described the purpose of the project. He's very interested in continuing the experiment after we leave, and I'm sure Ron knows more about that, as will I in the future.

After how well everything has gone, I'm convinced there's a nightmare somewhere up ahead -- Murphy works on this side of the Atlantic as well. Tomorrow we'll be hunting for and cutting wooden components, so there'll be plenty of opportunities to knock on wood, as the saying goes.

Mondays...

This post coming to you live from Kumasi, on the evening of Monday -- oh wait, no it's not, because my T430 decided to fry in the middle of writing it. The flashing light pattern indicates a fried systems board, of course, when i'm 5500 miles from Lenovo support. Fortunately we brought extra netbooks for another project, and I've been able to borrow one of those.

As I was saying yesterday...

We got an early start today in the KNUST machine shop, crossdrilling axles and cutting out sheet metal components. Upon arriving, we were met by two Ghanaian students, Papa and Michael, who immediately took over the drill press in a merry fashion. This got a nice assembly line going, and we were able to finish all ten axle assemblies, as well as cut and drill all ten interface plates by lunchtime.

Aimee hitting metal things with another piece of metal

Engineery looking things

Papa and Michael hard at work. It's wonderful to converse in the universal language of machine shop.

Lots of holes.

In the afternoon, we piled into a KNUST van and careened through Ghanaian traffic to track down sheet metal and additional components for various projects. Our destination was a district known as "the magazine," where we found essentially a square mile chop shop. Roads were packed with small shops and customers alike, with each area taking on a distinctive flavor -- at one end, we found dozens of tractor-trailers and heavy equipment in various states of disassembly. On another street, the road was covered in 1" steel cable being sorted by dozens of Ghanaians. Yet another corner sold massive AC/DC motors, some the size of a keg -- you can see them in the corner of the photographs below.

Looking down one street in the maze of shops

Unsuspecting engineers in their natural environment, also giant motors.

Also a street

Might be a street. Not sure.

At one of the new-product shops, we purchased about 20 square feet of 1mm Steel, which we'll use tomorrow for the cases and lids. I'm optimistic that we can finish a few units by the end of this week, and then produce the remainder quickly, as most parts will already be prepared in quantity. Tomorrow, we'll head back to the machine shop bright and early, and begin cutting the first two cases.

Arrival

After two days of traveling by bus, plane, and train, we've arrived safely at KNUST in Kumasi. We spent last night in Accra at a beachfront resort, the Afia Beach Hotel, where I discovered that my stomach doesn't agree with Ghanaian food -- or perhaps it's just food poisoning from Delta. One way or another, hopefully the queasiness will go away by tomorrow.

We're all very eager to get to work, and I believe we'll visit the machine shop Monday. In the meanwhile, I've unpacked and settled in. We strolled the open-air markets this afternoon, attempting to source e-waste type materials for further development on the project, and have a few leads to follow up next week.

Pre-Departure

We've been cleared to leave for Kumasi, Ghana tomorrow, following a regrettable but necessary delay beyond the field expedition's control. As such, we'll only be on the ground for about 18 days, instead of the anticipated ~28. While this will make the project quite challenging, I'm looking forward to the opportunity. I've used the last week to continue stateside production of components, and work out a few small details like mounting locations and hardware.

The project's online presence has spread -- while I'm still using the Google Drive repository for my personal development files, David has installed and hosted a wikipedia site for the project, as well as updating his personal page to reflect the project's current direction.

I'm slightly conflicted about the amount of manufacturing done here in the states. I'm keenly aware that, while the methods and tools I've used are comparable to those available overseas, there's no replacement for on-site development. I'm certain, however, that without prior manufacture, I'd be unable to deploy the devices during my brief time in Ghana.

From an engineering side, development has been frozen with Version 0.33. The manufacturing prototype exhibited excellent vending characteristics, with <2% jam rate and <4% double-vend rate. I'm attributing this primarily to improvements to the inventory chute, which also greatly simplified manufacture of the (previously "W" shaped) faceplate. Pictures of the updated design can be found on the wikipedia as linked.

Further updates from Kumasi as soon as I'm on the ground!

Assembly of 0.32, testing

I spent last evening assembling the latest revision of 0.32, the current production prototype. Below are some images from throughout the assembly process:

Cutting new interface plates from a sheet of steel

Cutting the first version of the new interface plate.

One of the major changes was the move of the interface plate from the inventory chute, to the axle/bracket assembly. Along with the front plate, which has been modified to a curved profile, these components help make the axle assembly far sturdier.

Completed "Magic Box," note the 2nd revision of the interface plate, using countersunk screws

 

 

Countersinks.

This technique requires using a thick (~2mm) steel (preferably) or aluminum sheet for the interface plate -- something rigid enough to hold up under the weight of the inventory, as well as smooth and flat enough to vend smoothly. Below, you can see the thickness difference between the thin casing sheet, and the interface plate's sheet steel.

Note the radius of PN008, the front plate. The interface plate, PN003, is resting edge-on in the vending tray lip.

I've also chamfered the corners of PN008, hoping to reduce the occurrences of condoms catching on the plate during vend. This hasn't been too helpful, as testing has shown. I'm optimistic that improvements could be found by tucking the plate under the interface plate -- a kind of tabbed arrangement, that would eliminate any and all edges from the process. I'd hoped at one point to convert PN003&PN008 to a single part, reducing the number of cuts to two cutouts for cam clearance, but requiring a sharp and accurate bend at the leading edge (where the two parts currently meet). Using the thick steel for the interface plate, however, prevents this -- so I've got to find a way to eliminate the corners between the parts which are causing the problem.

This revision also includes the new cam design, which I'm quite pleased with. I'm going to attempt to produce more of the cams over the next few days, and make sure this design will work for production in Ghana.

Upon assembly, I've collected about 100 data points of vending, 50 per chute. Below are the results:


I've also eliminated the gap designed into the inventory chute: by moving the interface plate to the "magic box" and doing this, the inventory chute is now symmetric -- with the exception of the interface bar, the bottom of the "W" shaped section on the face:

Inventory chute, old design. New CAD model to come soon. Note the W, however.

 I've experimented with flipping the inventory chute over, to determine if the interface bar is necessary for reliability. Below you can see the results.

Compare this with the results after reorienting the inventory chute to utilize the interface bar:

There's an appreciable number of double vends and a few non-vends. Those were all caused by a condom becoming trapped under PN008 during vend, which then necessitated a manual clearing of the jam after another failed vend -- thus a single jam shows as two error points. I'm optimistic that improving the PN008 design can eliminate this issue.

Hinge & Latch Design, Ver. 0.32

I've reconsidered the hinge mechanism, as well as some mechanical improvements to the interface plate and mounting system down there. Also set up P/Ns and hole patterns for security fasteners where necessary, and redesigned the axle mount blocks again. I'm too tired to describe in depth, but most modifications are clearly evolutionary and self-explanatory.

Full Version 0.32

Case hidden

Case assembly, fastener details seen below

These are standard tamper-proof screws, there's a variety of head designs available

The interface plate has been removed from the inventory chutes...

...and now forms the top surface of the newly-christened Magic Box.

As is the current custom, I've uploaded 0.32 to the public Google Drive Folder. This version is pretty much ready for production, barring the cam alignment and functionality issues that I'll fight with for the next month.

Cams

I spent a trying three hours in the Student Machine Shop today, attempting to cut out cams from a section of 3/16" pegboard. This turned out more difficult than I'd have expected, as I'd foolishly selected such a dense material that the laser-cutter was incapable of cutting at speed. I was able to cut about half of the laminate sections for one machine, which was enough to convince me that this wasn't saving any effort.

But hey, at least it looks cool, right?

I've got more than enough cams now, however, to experiment with different profiles over the weekend in a controlled fashion. Tuesday is the next opportunity to use the campus lasercutter, but I'll likely cut new cams tonight using traditional methods. The incorporation of the alignment peg has allowed me to improve the cam mounting system as well -- before and after models seen below.

Old cam mounting method, note the professional screw and cotter pin

New cam mounting method, cutaway view

Both cam halves visible here.

 This new design constrains cam motion better, allows installation and removal of cams without tools or permanent modifications, and reduces each cam location dimension to a single cotter pin mounting point -- it looks more complex, but simplifies the installation and construction of the cams greatly. I'm also very optimistic about a split cam, as opposed to a solid cross-section. I believe that this will increase pressure at contact points, increasing the likelihood of non-slip frictional contact there.

0.32, Oh god it's June 5th already

Weeks stretch into months, as usual. With finals week(s) and a vacation afterwards to return to human, I've finally gotten back to work on the project in earnest this week. I've worked out a number of small issues which Dr. Eglash, David, and I identified last semester -- most on paper and a few still in my head. The last outstanding issue, as always, is these cams. I've realized that the leading edge, the highest point on the cam, is extremely critical, as it has to catch -- not slip-- in order to vend.

Guaranteed not to scale

I think I've been shooting myself in the foot with designs incorporating a fillet on that notch. I've redesigned the cam, scaling it up by 7%, reducing the fillet to 1mm, and incorporating an alignment peg system to allow lamination of variable cam width from on-hand material -- I see no reason this wouldn't work as well with lasercut scraps of underutilized, burning plastic from the Accra scrapyards, but that's another project.

 I'll be testing this new design tomorrow, hopefully all will work out well. Apart from a few little things, like moving the hinge to the side and incorporating riveted box design, the system will be essentially set to manufacture -- the next unit made will be a production model from here.

Version 0.31 update

I've been working on preparing the design for production this summer, as we've now hit 10 weeks until I leave for Ghana. I've re-packaged the CAD model (Dragon 0.31) and uploaded it, but more importantly, the Google Drive Repository now includes PDF blueprints. This effectively marks the release of the design for public development, and I hope to implement more detailed assembly instructions and imagery as the design continues to evolve.

I've been working on assembling a copy of 0.31, using "basement power tools" level equipment. I'm not entirely satisfied with the system, particularly with the supports for the cam assembly. I'll be redesigning those and releasing a new update (0.32 probably) within the next week or two. However, I have assembled a case and functional front access cover, which exceeded my expectations. By using a sheet steel and end cap design, I've been able to reduce the thickness of sheet steel to 28ga  -- about 0.3mm. This has brought cost down by an order of magnitude, and makes cutting and bending components far easier.

While the incorporation of plywood has eased assembly and reduced the complexity of the model, I feel that there's still improvements to be made. I'm interested in replacing the endcaps with sheet metal angle brackets, perhaps riveted. I'm slightly concerned about accessible screws on the outside of the device, and using rivets would also solve that -- while I've designed the case to be impossible to access without access to the rear or the padlock, I'm concerned about encouraging petty vandalism with exposed Phillips Heads. Rivet guns are cheap and readily available in Accra, I'll want to make sure both options are possible. There's also currently unused scraps created from cutting out the case, I'm interested in reducing material requirements by using those.


I've done some initial hunting for sheet steel and other suppliers in Accra, and the results are promising. While I won't know for sure until I get there, it looks like many materials should be easier to find than I've feared.

Here's some pictures of things and such:

Face of inventory chute (PN001), cut from 23/32 plywood

Inventory chute (PN002), also from 23/32 plywood this time

Drilling the mounting holes in the case. Note shameless product placement.

The case was cut by printing the pdf blueprint at 1:1 scale, rubber cementing it over 28ga sheet steel, and using tin snips to cut along the lines. Pretty painless. All blueprints are also fully dimensioned, allowing traditional layout methods as well, if a printer isn't readily accessible.

Here's the case and inventory chute inside. Note the lock mount, and two hinges. These aren't in 0.31's CAD models or blueprints, but I'll incorporate them in 0.32.

Mostly closed. The 40x150mm slot for the customer to recieve the product hasn't been cut yet, since I'm still adjusting the design of the cam mechanism and the location may change slightly.

Case, in open position, and removed inventory chute. The blueprints are still on the outside of the case, since they look cool and I'm too lazy to remove them. It's also much easier to mark on paper than the steel underneath, and protects the steel from scratching during assembly.

Spring Break Report

I've noticed the double vend issue is persistent occasionally, particularly with very thin packaged condoms and even more so when a section of the inventory is all thin condoms. I think that further reducing the height of the aforementioned face slot by another increment will clean this up more. I've redesigned the inventory chute with thicker plywood and the inventory height adjustment, and a few other minor details.

I've also redesigned the case to reflect a coin mechanism location, and reduced overall dimensions -- (190mm W, 475mm H, 155mm D)  compared to (275mm W, 500mm H, 120mm D) for the current model -- 50.8% volumetric.

This also has reduced the amount of sheet metal required from 8 sqft. to just over 3.5 sqft. This of course isn't free, the new model incorporates 3 sqft of plywood which was not included in the previous design. However, this version 0.3 is also weld- and machine-screw free, incredibly. This eliminates welding equipment from the assembly requirements, as well as specialized hardware. These joints have been replaced or redesigned to incorporate tapered thread screws -- think wood screws, or drywall screws -- that's the thing, they're very interchangeable and far more common.

I've uploaded a copy of my working folder for this project, in the spirit of open source. The folder will be maintained at Google Drive, accessed (read- and download- only) at the following link. The data is provided under GNU FDL.

Current CAD models are in proprietary Solidworks format. I'm looking into options for exporting the data to a more friendly format, such as STL or another polygonal format. This does, however, preclude the end-user from practically modifying the design. There are open-source CAD formats available, I'll have to look further into those possibilities.

Perspective view, note new shield design, coin tray, braces, removable inventory chute (slides out front), secure vend slot.

Partial cutaway view of mechanism

Side view, cutaway

Side view, gear orientation