At work, virtually all my coworker have product development in their “DNA”. We are all creative types, who takes lots of pride in bringing a product from an idea to life. And so consequently, whenever we read about some new widget or tool, we’ve always tried to convince our boss that it would benefit the company tremendously, if only if we have the latest and greatest Super Machine 2000.
Our boss, who’s rarely wrong, always tell us that as design engineers, our time is the most valuable spent designing. “Whenever we need something, and need something quick, we just toss money at someone and have them bang it out and put it in a Fedex overnight box”.
My buddy Dave’s grandparents owns a laser engraver. They own a trophy engraving shop and laundromat down in Renton. It’s really wierd to think of a sweet old lady at the controls of an Epilog 20W CO2 laser system… but she doesreally good work. So the next time you need something engraved, check out the Puhich Dry Cleaners in Renton on 319 Main Ave. South.
I know what a 20W CO2 laser can do; it can do a lot more than mark plastic and burn through anodize layer on aluminum. There was a discussion thread on making lens cap holders, so I drew one up in Soldiworks real quick:
Here’s the test run in paper. So far so good, right?
Unfortunately, the laser engraver is running on Windows 98. It requires a firmware update before it can talk to anything past Win98, and there is always a risk of bricking a machine doing a firmware update. So we are stuck with a computer that works – abet a very slow one, with a parallel port printer connection. (I bet some of the folks I know had never seen one… they went the way of the dodo after USB became popular).
Complicating the problem is that the printer driver runs as a Corel Draw plugin. Corel Draw 8, to be exact. And even the earliest DXF that Solidworks can save the file in, the simple fillets on the drawings don’t quite come through – let alone the more complicated splines and polylines.
The example above worked okay, because the laser cut it out as a *Raster* art, instead of a vector art. But cutting in raster mode drastically drops the laser’s power output. And it’s not like you can run multiple passes over the same piece of PTFE either – the slow heat transfer of doing so just warps the plastic – and the results looked like someone tried cutting the material with a dull butter knife.
Obviously something like this, out of 3mm PMMA, will be a bit out of the question:
So my options are:
1) Try to mitigate the risk of the current laser cutter’s firmware upgrade (maybe see if I can do a hardware replacement of the logic board, upgrade the computer to something snazzy, then retry the Solidworks -> laser cutter workflow.
2) Pay someone like Pololu online to do the laser cutting for me. Essentially, someone else will be eating part of my lunch if these products go on sale. Might be okay if there’s only a few parts, but I’ll have to rethink the design a little bit.
Turns out, RedWolf airsoft out of Hong Kong will happily sell me a 30mm silencer for about $US10.00. Aluminum barrel, both ends with a machined aluminum plug. They even put a 14mm CW thread on one end and 14mm CCW threads on the other, so out of the box, the dang thing will fit on just about every single airsoft gun out there.
In Hong Kong, we have a saying that “the flour costs more than the bread”. The term originated from the housing bubble days where the value of the land gets bid up so quickly that older apartment buildings prices are being outstripped by the land value of neighbouring lots, but it also applies to engineering and business where by some form of competitive advantage (and economies of scale), someone can build a product cheaper than you can even start sourcing raw materials.
Got a cool little bookmark for all my troubles with the laser cutter though…
As we sail pass the 200% funded mark tonight, I’d like to turn our attention back to the engineering side and share some cool news with you all:
What you are looking at is the CAD screenshot for the injection mold for OpenBeam. The yellow and green parts represents the steel core and cavity that will be used to form the plastic parts; the red pins are the “ejection pins” that pushes the parts out of the mold when the mold opens; and the area in the top is the nozzle where plastic is injected. The forces involved in the process is measured in tens of tonnes, so as you can imagine, the mold has to be built out of very, very strong materials.
Two nights ago I signed off on the mold designs; our friends at the injection molder had done a fantastic job with the tooling design and finished this phase of the project 5 days ahead of schedule. If you look at the Gantt chart on the previous update, this means we can start the injection mold fabrication five days earlier. At this rate, we should be able to have injection molded first samples at Seattle Maker Faire.
Eagle-eyed readers might notice that there are extra parts in the mold:
Thanks to all of your support, I was able to add two more parts into the OpenBeam system at launch time. Can you see them in the mold cavity drawings above?
The new parts are:
A feet / end cap
And a 608 bearing to NEMA 17 adapter
The feet end caps are pretty straight forward. You can attach them to either the end of an extrusion or to the side of an extrusion, like so. The screw sit in a counterbore in the part, and you have the option of sticking a 3M Bumpon into the big circular recess to make the part non-skid:
The 608 Bearing to NEMA 17 mount adapter is designed with robotics and machine builders in mind. It allows you to put a 608 bearing (aka rollerblade bearing, one of the most common and least expensive ball bearings on the market) concentric to a NEMA17 motor shaft using the same mounting brackets easily. This allows pulleys, support bearings, idler wheels, etc to be added without much trouble.
The shaft clamp got a slight make-over too, based on usability studies on the 3D printed models:
Now, a single size shaft clamp will clamp on a shaft all the way from 7 to 15mm. Also, a separate screw clamps the shaft clamp to the beam; the inner screws are strictly for clamping onto the shaft. This will make it much easier to work with the shaft clamp and for repositioning things.
The “L plate” got a face lift as well:
The additional hole now allows the plate to be in a 45 degree gusset brace:
I couldn’t have made the improvements without your support, so it’s only fair that these changes are reflected in your reward packages. Every reward package will receive a number of the feet pieces; if your reward package came with NEMA 17 motor mount plates, you’ll be receiving the 608 bearing adapters as well.
In other engineering news; some of you have been asking for structural analysis data on OpenBeam. My engineering buddy Jared will be helping me run some simulations – since I lack the necessary FEA package in my version of Solidworks to do so, and I’ve been pretty swamped with business startup tasks. If you’re into racing cars, you should check out Jared’s website here. He does some amazing work, and we should get some nice engineering data from Jared in a week or so.
Other business startup tasks:
You may have noticed the URL in the screenshots that’s molded into each of the plastic parts. As I mentioned in the Kickstarter video – it doesn’t do anyone any good if you cannot buy the components on an individual, a-la-carte basis after the project is over.
OpenBeamUSA.com is currently under development to be the webstore and knowledge base for this product. There, you will find project blogs, application notes, how-to videos, and eventually, the design files for OpenBeam. (Please no-one laugh at the URL, it’s very, very much under development at this point. And please don’t try placing orders. It *will* break. In fact, I will be switching ecommerce host in the next few days).
I am also happy to announce that we have signed up our first retail storefront partnership. Metrix: Create Space will be a stocking distributor here in Seattle; seven days a week, noon till midnight, you will be able to walk in and buy OpenBeam components and extrusions from them. We look forward to announcing more retail partnerships soon. Online dealerships and international sales channels are also in the works.
It’s been a pretty incredible journey so far; every day brings new challenges, new problems to solve – but that’s a subject for the next update. My focus remains the same – to get these parts into your hands as soon as possible, and to show this at as many Maker Fares as I can, and spread the word far and wide. I really look forward to seeing what each of you will be building with this product!
Thank you for your support on OpenBeam,
(+ somewhat annoyed & neglected girlfriend, and her furry monster puppy)
This XKCD cartoon sums it up about marketing oneself:
Quick status update on the bullet flight sensor. This is heading into systems integration testing next, where I’ll be firing up each section of the circuit and making sure it all works. Missing is the break beam sensor that I put a air rifle round through by accident :-)
Note the “unusual” arrangement with the pocket wizard. The “hot shoe adapter” is actually plugged into the sensor to simulate a camera’s hotshoe firing the pocket wizard.
Successful night at Tam Labs tonight! :-)
Tonight, the goal was to test the breadboarded prototype of the bullet flight sensor’s electronics. Remember – I am a mechanical engineer; this is a completely new foray into the world of electronics for me, aside from some simple “hook a solid state relay to a microprocessor and bit bang some code to turn on the rice cooker” projects. So even though this may seem like kindergarden EE stuff, it’s a fairly big leap for me, design wise; I’m no longer relying on the ability to clobber code and instead using discrete logic ICs and doing actual calculations and setting RC time constants, etc.
We begin with the breadboarded model:
And our setup in the lab:
On the bench is a trusty oscilloscope to look at the signals at different lines, a DC power supply set to 5V, 100mA current limit, and a signal generator. The signal generator won’t be used for this project here.
First, I verified that the *new* sensor is working – the last one had a round put through it by accident:
Next, I verified that the 555IC is getting the power that it needs. Turns out that the power rails aren’t fully connected all the way. A bit of poking with an ohm-meter fixed that. Now I am ready to insert my test points:
And trip the break-beam sensor, with my gimpy fingers:
Orange line, or Ch1, is my sensor’s output. It goes from High to Low when the beam is broken. The turquoise line, or Ch2, is my 555′s trigger output. It goes from low to high when the input pulse is received. That’s a VERY promising sign.
My fat butter fingers can only move so fast through a 10mm opening, so the event scrolls off the oscilloscope’s screen. I tried dropping a small machine screw through the opening, but that actually prove to be much harder than expected (don’t laugh!). Frustrated, I finally came up with the following idea:
By flexing the rubber ducky antenna on one of my pocket wizards and getting it to spring through the break-beam sensor gap, I can generate a quick enough blip from the sensor:
Each major division is 5 milli-second on this setting, so the rubber ducky antenna is only in the beam’s path for about 10mS. My fingers can’t move *that* fast, for sure :-)
Repeating the test again a few times, got me the same result:
Note that irregardless of the pulse length from the sensor, the 555′s output always sits at about 35ms. This is a litte bit off from the design goal of 40ms (1/250 second shutter speed, or sync speed on a 1.6x crop camera), but close enough for government work. I attribute the difference in component value tolerances on setting the RC constant.
Now the final test – does the output from the 555 trip the SCR to fire the strobe and pocket wizard?
(I selected an SCR instead of a cheaper / more common transistor. The SCR is rated to 400V, so even an older, high voltage “digital camera killer” flash will work on this sensor. )
*drum roll please*
Turns out the same bug that bit me on the 555 timer bit me again. The top and bottom half of the power bus on this breadboard is not connected, and the SCR wasn’t grounded properly because of that. Now, plugging in a pocket wizard, this is what I get (with Ch2 now monitoring the anode of the SCR):
Interesting, it seems to add a bit of noise to the sensor output line. But the characteristic beep of the PW firing can be heard as the beam is broken. (Note that the sync voltage of the pocket wizard is only 3V or so).
Plugging in the 580EXii:
Again, some electronic noise on the sensor line, but we got what we need out of it – the clean voltage drop that triggers the monostable multivibrator.
And here’s the happy camera dork with his new toy (click link for video:)
Now that the circuit is verified working, I am okay with releasing the resources to order the acrylic for laser cutting to form the chassis, as well as starting PCB layout. Stay tuned… :-)
I’ve really been lagging on my blogging. Here’s a quick update.
I’ve recently found myself working out of the Beaverton office again, so late one night after finishing up I hopped onto the company’s aging, crusty lathe:
These are custom captive screws for the Benro quick-release plates I picked up in Hong Kong. I’m mounting the Benro plates to a piece of 8020 1010 extrusion, and the T-slots are a little bit deeper than an ISO standard camera mount. So, for my application, a custom screw would be needed.
I’m actually pretty happy with how this turned out; the machine is old and the hand-ground parting tool isn’t the best for cutting stainless steel.
To chuck the screw into the chuck without damaging it, I took a page from an old machinist trick of slotting a nut with a hacksaw and clamping it in a 3-Jaw chuck. I started with a 1/4-20 x 0.5″ SAE button head socket cap screw.
(Note: Yes, I am aware that the standard tripod thread is a 1/4-20 British Standard Whitworth – cut with a 55 deg angle instead of a 60 deg angle. I challenge the reader to find one here in a hardware store in the good ol’ USA. A 60 deg SAE thread is “close enough” for this application with some very minor interference)
The resultant screw is a bit too long, so I trimmed it down a little bit with my motor tool.
The tool is a Taiwanese made version of the Foredom – a 600W motor on a flex shaft and a foot pedal for actuation. It takes all the standard Dremel accessories and it’ll slice through stainless pretty easily. I lined the jaws of my Wilton vice with some engineering paper scrap, and used my pano clamp as a clamping base for the tripod plate. Then, using another machinist’s trick, I put a nut on each of the screws to be cut. When removing the nut, the nut acts as a tap and cleans out any debris on the screw threads and restores the proper thread form. :-)
And BTW – at 20,000+ RPM and with 600W of power behind the disc – any slip up is … painful. Warning: somewhat graphic picture ahead:
The wound looks A LOT worse than it actually is. I think the heat from the abrasive blade cauterized the wound – it didn’t bleed much. Digging all the abrasive grit out under running water was a different story – good reminder to be more careful the next time.
And here’s the finished rig! Now, I need to order some 3D glasses…