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I previously worked on Virtual Reality and other hardware at Valve.  I currently work at Google[x].

Prior to starting at Valve, I built computer peripherals such as keyboards, mice, and joysticks that were designed to be used inside MRI machines.  My company, Mag Design and Engineering, sold these devices directly to researchers at academic institutions who used them to publish scientific papers in peer-reviewed journals.

After work, I spend time on many different types of projects that usually involve circuit design, machining, material selection, and general fabrication/hacking.  My favorite place to be is my home workshop.

ben dot krasnow at gmail

http://www.youtube.com/user/bkraz333

http://www.linkedin.com/pub/ben-krasnow/4/6a9/679

http://www.twitter.com/BenKrasnow

Tuesday, September 29, 2009

Google Checkout is making PayPal look good

This post is definitely off-topic for my blog, but I am extremely disappointed with Google Checkout's Merchant services, and I want to publicize the difficulty.

I have a customer that placed an order on my website and paid with Google Checkout. Her credit card was listed as "declined", so she called her credit card company to find out why. The credit card company responded that they had no record of the Google Checkout transaction at all, and there were no declined transactions on the account.

Of course, Google Checkout has no support phone number. Apparently they recently removed their support email address and online support contact form.

UPDATE: I found the "contact us" link at the bottom of the page, which allows merchants to enter an order number and request assistance, but there is no text entry box to actually describe the exact problem.



So now I am stuck with a very frustrated customer and perhaps a lost order. Worse, I have no way of fixing the situation because Google Checkout has no way of being contacted with details about the problem. Thanks, Google.


Here's some links to others who have had problems all stemming from the complete lack of merchant support.

http://www.shaftek.org/blog/2009/03/04/contact-phone-number-for-google-checkout/

http://www.google.com/support/forum/p/checkout-merchants/thread?tid=1c4ddc2e27f4ec72&hl=en

http://news.zdnet.com/2100-9595_22-341375.html

http://www.google.com/support/forum/p/checkout-merchants/thread?tid=67e6e5c02c6f3233&hl=en

Thursday, September 24, 2009

Telescope magnification

A friend recently asked me about telescopes, and it made me think about the pictures that I took with my telescope which I haven't looked at in years. This series of photos was a test of the range of magnifications possible with a couple camera lenses and the telescope.

These photos were shot with a Nikon FE2, with some run-of-the-mill 400ASA color film. The photos were developed and printed 4x6 at a 1-hour photo place. I scanned the photos with a flatbed scanner.

50mm Nikon lens. This is essentially the field of view that normal human vision has.

135mm Vivitar lens.

2032mm Celestron Nextar 8" SCT telescope. Prime focus. The ceramic insulator is just visible in the lower right corner.

The same telescope using eyepiece projection -- I forget the focal length of the eyepiece. The white halo in the center of the image is an artifact of my shoddily-mounted eyepiece setup.

A shorter focal length eyepiece increases the magnification even more. This is probably a 6mm eyepiece, giving 2032/6 = 338x magnification. The photo is blurry, but this is mainly due to tiny vibrations in the 'scope and camera. When viewing this directly through the eyepiece, the image is pretty sharp since human eyes and brains have better image processing than cameras.

Tuesday, September 22, 2009

Stainless steel conical beer fermenter Pt.3

I just finished welding together the stainles racking cane for the beer fermenter project.

Even though this may not look like much, I am quite proud. It is a 5/8" dia stainless tube, but the wall thickness is only .020". I sliced it on my new metal band saw, reoriented the pieces to make an elbow, then tacked it in two places, and welded all the way around. It's air-tight. The trick is to get the tacks done really quickly. I only used filler (.035") to make the tacks, then just fusion welded it in very short sections (a few seconds at a time). I blew through it once, and had to repair it with filler.

Here's the tube welded to a tri-clamp plate, which is welded to one side of a three-piece ball valve.

Here's the other side of the ball valve welded to a hose barb.

The complete assembly is attached to the tri-clamp port on the side of the tank. The purpose of all this hardware is to be able to rotate the racking cane while draining beer from the tank. Thus, the height at which the beer is drawn can be adjusted. This allows the maximum amount of clear beer to be drawn from the tank without getting any cloudy beer that has settled to the bottom.

Inside the tank.

Stainless steel conical beer fermenter Pt.2

The next step in the beer fermenter project is to mount some copper blocks to the outside of the stainless tank. The purpose of these blocks will be to thermally couple two peltier devices to the surface of the tank. The tank is cylindrical (near the top) and the peltiers are flat, so the copper blocks must be curved on one face, and flat on the other. I started by cutting off some chunks of copper and milling the edges square.



Next, I used a long end mill to profile the sides with a radius that matches the outside of the stainless tank. My plan was to silver solder the copper blocks to the stainless tank exterior. This turned out to be a very bad idea. I started by fluxing the copper and stainless, then separately covering them with a thin layer of silver solder. No problem yet. I put the semi-cooled block onto the tank, and planned to heat the tank and block and let the two solder-covered surfaces melt together. This started working, but then the stainless expanded dramatically under the block. The copper was lifted a clear 1/4" off the surface near the edges, while the center was making contact. I removed the heat, and looked inside the tank to find this new disaster:

A monster crack had developed in the wall of the tank! I am still not sure why this happened. It obviously has something to do with the metals' differing rates of expansion, but I had no idea the consequences could be so damaging. Perhaps this has something to do with the stresses in the metal from the spinning (cone-forming) operation?

Luckily it wasn't too difficult to repair the crack. Since the crack went clear through the tank wall, I had to fight the silver solder which was molten and trying to flow into the weld puddle. The copper blocks must be making good thermal contact, since I maxed my TIG machine out at 200A, and it was just enough to comfortably weld.

There are two copper blocks (each made of two pieces of bar). In order to avoid the silver-soldering nightmare again, I used silver epoxy to join the copper to the tank. After both blocks were attached, I mounted the assembly in the milling machine, and flattened the faces.

If I were going to do this again, I would profile the copper backside, flatten the face, then use silver epoxy to attach it to the tank.

UPDATE: This method did NOT work. I was not able to hold the glass without rocking it very slightly. This created a very smooth, but curved surface on the copper. It was unsuitable to mount the peltier.

Here, I am removing the milling marks with sandpaper mounted on a 1/4" thick glass plate. This took a very long time. In fact, I am still "going up through the grits" right now. The next step will be to weld a small threaded boss on either side of the copper blocks. This will serve as an attachment point for the peltier heatsink. The peltier itself will be pinched between the copper and the heatsink.

Thursday, September 17, 2009

Three-way flow regulator for argon shielding gas

The serious TIG welders have two flow regulators on their argon supply -- one for the torch, and the other for the purge argon on the backside of the weld. I found some cheap flow regulators on eBay, and I made a manifold for the two I bought plus the original regulator. I've imagined situations where three regulators might be helpful like welding a gusset on the outside of a tank. The gusset would need backing gas in addition to the torch side, and the inside of the tank would need to be purged as well. Who knows.
I made the manifold itself out of a block of white Delrin with four 1/4-18 pipe threads cut into it. The original regulator (on the left) has 1/4-18 straight threads. I just ran my tap really deep into the Delrin so that the regulator would fit in. It's very easy to make metal fittings seal with Delrin and no Telfon tape is necessary. The Chinese argon pressure regulator also had a 1/4-18 female straight thread which was intended to seal on the end of the pipe. A regular 1/4" brass pipe thread nipple worked just fine and presumably bottomed out and sealed on its end.

Wednesday, September 16, 2009

DIY stainless steel conical beer fermenter Pt.1

Please search my blog for "fermenter" to find all of the posts regarding this project.

I am building a stainless steel tank that will eventually become a very unique beer-brewing vessel. My idea is to make a tank such that the entire process can take place without ever having to transfer the beer from one tank to another. This vessel will boil the wort, chill the wort, provide a temperature-controlled fermentation period, allow the trub to be removed, and provide a secondary fermentation. This tank was designed with my experience in brewing about 30 5-gallon batches of beer using the extract process. I don't have much inspiration to do all-grain brewing yet.

Having said all of that, I am also learning to TIG weld, and this project will provide many different welding setups -- all in stainless steel.


I bought a stainless steel conical hopper, model TMS14514 from
http://www.toledometalspinning.com/products/hoppers/priceList.asp

Toledo Metal Spinning sent the item very quickly, and I am impressed with the quality. The edges are extremely flat, and the overall finish and dimensional tolerances are great.

It holds 6.4 gallons total, so a 5 gallon batch of beer should fit pretty well. The hopper is a continuous piece with no hole in the bottom. I will be mounting a butterfly valve at the apex, so I need to cut the tip off to match the diameter of the valve housing. I knew before I ordered the hopper that I would only need to slice off about 1/8" off the end.

I used a slitting saw in my milling machine to do the job. This left me with a super flat clean edge. 70 RPM, 0.5 inches per minute, however the feed rate is measured at center of the saw, and I programmed a G2 circular path. This means the feed at the cutting point is probably lower. I had problems with chatter, thus necessitating this low feed rate.

This is one half of the butterfly valve housing after I welded it to the cone. The blue hose is silicone, and is carrying argon to the backside of the weld. In addition to the foil on top, I have made a dam with aluminum foil and tape inside the neck of the cone to trap the argon in the space around the weld.

Since the first weld went so well, I decided to weld on the inside of the fitting as well. Ultimately, this was not a great idea, but the weld itself went well. I used a copper tube with a line of tiny holes drilled in it to disperse backing argon to the outside of the cone. I had a fair bit of room inside the valve fitting for the TIG torch and filler rod.

I used a die grinder to smooth out the interior weld. After putting it together, it leaked! I had used the die grinder too much, and made the metal thin enough where a tiny pinhole in the weld made it all the way through the metal. I re-welded the outside bead, and then realized that I should have just made a couple of passes on the exterior to build up material. Then I could die-grind away the inside until I ground into the weld bead. No need to weld the interior. This would provide a nice smooth surface inside the tank and ensure there was enough material to keep it structurally sound.


It looks good now.


I originally started to cut this hole with a high-quality hole-saw in a corded drill. After a few seconds, I realized it was probably not going to work. Stainless is just such a tough metal, cutting tools just bounce off it. I used a free-hand plasma cutter to make the hole.

I made another aluminum foil/tape dam around the wall on the interior.


The weld went pretty well.



This time, I learned how to do it. Instead of welding on the inside, I just built up a nice bead, then used the die-grinder on the interior until I ground into the bead. It's nice and smooth on the inside.

Sunday, September 13, 2009

Repairing a stainless butterfly valve

I am preparing to build a stainless steel beer-brewing tank. In preparation, I've been buying various stainless valves and tubes from eBay. The bottom of the brew-tank needs a large valve -- preferably a butterfly valve. I found one on eBay for less than $20 shipped. The seller said it was a "great valve". As it turned out, the only thing great about it was the price.
This thing has had a very hard life. Luckily, there is nothing missing, and all of the pieces are in fair shape except for the rubber seal.


Not only does the seal look bad, but it smells bad too. It has a strange sweet smell like antifreeze. I don't want my beer touching this thing even if it didn't leak. I decided to make a replacement since there is no manufacturer listed on the valve and buying a replacement seemed like a long-shot. First, I sandblasted the metal parts.


It's mostly OK, but there is some pitting. It may not cause any leaks.

I have some Dow MDX4-4210 "biomedical" elastomer left over from a work project. This stuff is basically liquid silicone that, when mixed with a catalyst, cures into a solid piece. The cure time is almost a day at room temperature, but only a couple hours at 130*F.
I machined a two-part mold out of 1" thick aluminum.

After mixing the silicone and catalyst, there are thousands of trapped air bubbles in the mixture. This will create a part that is more like a sponge than a solid piece of rubber. The product information sheet suggested de-gassing the mixed silicone in a vacuum chamber for 30 minutes, which is what I did. It works great, and the cure time is so long at room temperature, there is no danger of running out of "pot life".

I used a custom-made punch to cut the shaft holes after the piece was cured and removed from the mold. The replacement seal is a lot softer than the original. I don't know if/how that would affect the valve's operation. I'll probably test this valve before I weld it onto the brew tank.

Rust in the aquarium / Passivating stainless steel

OK, so I owe the titanium fanboys an apology. In my original post about aquarium chillers, I asserted that a stainless steel chiller coil would not rust in a saltwater aquarium. The coil in my tank rusted after about 6 months. Take a look:

I decided to sandblast the part so that I could see how extensive the damage was.

Yeow! The metal must have been exceptionally thin, and the sandblasting blew right through it!

I used 316 SS filler rod, and TIG welded the hole shut. The blue tube is an argon hose to protect the inside of the stainless tube from oxidation while welding.


Now it's all patched up. The heavy corrosion was localized around the area where the stainless coil entered the plastic filter box (see top picture) . My guess is that vibration from the pump caused the rough surface of the plastic to abrade the passivated layer on the stainless, thus causing a localized spot where the metal was unprotected. I've heard that passivated the stainless in an acid bath can create a stronger, more uniform passive layer. There are two common acids used to passivate stainless: nitric and citric. Nitric acid is nasty stuff, and it's possible to damage the stainless parts if the procedure is done incorrectly. Citric acid seems to be just as effective as nitric, and it's non-toxic. Here is the best reference on citric acid passivation:

http://www.astropak.com/downloads/technical_papers/boeing_passivation.pdf

I mixed a %15-by-weight solution of citric acid in water. I got 2lbs of citric acid on eBay for under $10 shipped. I submerged the stainless coil in the solution for 2 hours at room temperature. I could see the surface changed a bit -- the shade of gray was a little different. Hopefully this means it built up a nice strong oxide layer.

I've put the coil back into the aquarium, and added some silicone pads to the filter box so that the plastic would not scrape away at the stainless coil. I'll keep you updated to see how effective it is.

Saturday, September 12, 2009

Cutting a corner radius on the lathe

I use a round-over router bit in my lathe toolpost to leave an attractive, uniform edge on the part. I mostly work with plastic, so the tooling angles are not as critical as for metal.



Here are two 1" long 1" dia sections of white Delrin. The upper piece has its right edge rounded over by the 1/8" radius router bit.

Saturday, September 5, 2009

Peltier power supply and integrated PID controller

I am preparing to build a beer-brewing tank that will be temperature controlled. The goal is to keep the vessel at a very steady 72*F. Depending on the time of year, this might require heating and/or cooling 24 hours per day, or heating during the night and cooling during the day. Since the only heat load on the vessel is the heat leakage through its insulation, the total amount of heat that needs to be pumped is fairly low. This might be a good application for a Peltier heat pump since the heat load is low and the heat pump direction might need to be changed often.

As I mentioned in my aquarium chiller post, the Peltier module must not be controlled by PWM (pulse width modulation) or on/off thermostatic control. During the 'off' part of the cycle, heat will flow backward through the Peltier device and decrease efficiency almost to zero. Ideally, the PWM output should be smoothed with an L-C (inductor-capacitor) circuit to provide clean DC power to the device.

I happened to disassemble a thermoelectric refrigerator (and replaced its guts with a refrigerant-based system in a previous post) and had a 115VAC Peltier power supply and Peltier module. The power supply uses a TL494 IC to control a 115V->12V high-frequency transformer. The output of the transformer is smoothed with an L-C circuit. The TL494 is controlled by the output of a thermistor and digital thermostat, thus sending more power into the transformer when the fridge's temperature exceeds the thermostat set-point, and reducing power when the temperature falls below the set-point. I couldn't figure out the analog side of the circuit which had a few op-amps. Instead, I discovered that I could throttle the power supply by putting voltage on the TL494's DTC (dead-time control) pin, which wasn't used in the original circuit. Cool. So now I have an efficient power supply that I can throttle from 0V to 12.5V (full power) to the Peltier.

Next, I need a thermostat to control the power supply and also reverse the polarity of the Peltier device (to switch from heating to cooling). I thought about using an Arduino to do the whole thing: sense the temperature, provide a UI with LCD and buttons, process the PID loop, and send output to the power supply. My biggest worry was the UI. There are actually a lot of parameters in a PID loop, and I didn't feel like writing code to make all of them user-selectable. I also had another Eurotherm 2132 PID controller (same as the aquarium project) which I really like. I decided to use the Eurotherm and build a circuit to convert its output into a control signal for the power supply.

The Eurotherm has two outputs, a relay and a driver output for an external solid-state relay. I removed its internal relay and directed the relay's coil wire connections to the Eurotherm's rear terminals. I then used an optoisolator to interface the Eurotherm's floating outputs to the rest of my signal-converter circuit. The Eurotherm can be configured so that its output 'cycle' for each output is 1 second. Thus, it essentially outputs a PWM signal at 1Hz for cooling, and another 1Hz PWM signal for heating. I wrote a little code for an Atmel AVR ATMega8 that reads the two control signals from the Eurotherm and outputs a voltage that controls the Peltier power supply. It does this by generating high-frequency PWM and smoothing it with a simple R-C low-pass filter. The current draw is very low. The AVR also controls an NPN transistor that drives a DPDT relay. The relay will reverse the polarity of the Peltier device.


All of the above-mentioned circuitry is crammed into an acrylic box that I made for this project (left). The Peltier module has a small heatsink and a large heatsink with two fans (right).





I modified the power supply (by removing a fuse, and adding a fan), and tested it with two Peltier devices hooked in parallel. It seemed fine at 12.5V and 7A.

The next step is to mount the Peltier devices onto the brew tank and test it out.

The tank will hold 5 gallons. For thermodynamic analysis, I will assume it's water. So, that's about 20 liters, and water has a specific heat of 4.2J/g*C, so the tank will require 4.2(20)(1000)=84KJ to change 1*C. If the Peltiers are consuming 12.5(7)=88W, and are 50% efficient, they will be pumping about 44W (in cooling mode), which is 44J/s.

In order to change the tank's temperature by 1*C, the system will need 84000/44 = 1900 seconds, or 30 minutes. This is good and bad. The good news is that the tank will remain very stable, as it is not in danger of being quickly influenced by the Peltier. The bad news is that the tank must start out fairly close to the target temperature, or else it will take a long time to be regulated by the system.

Tuesday, September 1, 2009

Stainless TIG welding update

OK, I have learned a few more things about welding stainless steels with TIG. I am far from an authoritative source on the subject, but I hope to share what I do know:

* Keep the weld bead width as thin as possible. This is really key to everything else, and making a thin weld bead will force the welder to do everything else correctly (ie keep the current to a minimum, keep the electrode close to the surface, etc).

* Minimize the heat input to the work by any means necessary: Lower the amperage, bring the electrode closer to the surface, use copper chill blocks, stitch-weld 1" sections and allow the work to cool between welds.

*Keep the tungsten electrode sharpened to a needle-point. The length of the taper should cover about 2.5 times the electrode diameter, and I normally leave the tip fully sharp for low-amperage welding. I've never had a problem with the tip breaking, and it helps direct the arc.

* The part fit-up must be superb. I always try to tell myself "sure, I can fill that gap", but no. With stainless, filling the gap means dripping lots of filler rod, which will be very hot and leave the weld in very bad condition. The excessive heat will "burn" the chromium out of the alloy.

* The electrode should be as close to the surface as possible. This is not an exaggeration. I mean really get the electrode as close as you can without touching the puddle. A small, hot arc is much more effective than a large cool arc.

* Use thin filler rod. If you're welding 1/16" thick stainless, I'd say the weld bead should be 1/8" wide or less. This will be a problem to weld with 1/16" rod, because it is difficult to dispense a small enough amount of rod to keep the bead thin enough. Additionally, since the electrode is being held very close to the surface, there isn't much room to stick the rod into the puddle. Using .045" and .035" rod is a HUGE help.


* Don't let the arc melt the rod! When adding rod, move the torch backward a tiny bit so that you can dip the rod into the puddle, then pull the rod out of the puddle, and advance both of your hands forward in the weld direction. I can tell that I've messed up when I see the rod form a ball on the end, and the arc changes color. If the weld is important, I would cut the end off the rod and start again.

* When the weld is all done, check the colors to see how corrosion-resistant the weld will likely be:

Gray, pinkish-gray, black = Not good. The stainless has been chemically changed at the surface
Dark blue, purple, turquoise = Borderline OK. Acceptable for some situations.
Gold, silver = Perfect.



* The most common fill rod for welding stainless is 308. As near as I can tell, 308 can be used on anything, but it would be unwise to use it on higher grades of stainless like 316. I tried both 308 and 316 fill rods on 304 base metal. They behave pretty similarly, but 308 seems to melt a little more easily.

* Most rods and base metals can be obtained with an "L" designation, like 304L or 308L. These are low-carbon alloys and are preferable over the non-L alloys because welding can cause carbon to precipitate in the metal. The upshot is that welding 304 will have a more deleterious effect on its corrosion resistance than welding 304L. How important is this effect? I don't know. All of the information that I found on the net was purely anecdotal and poorly documented.



This was attempted with 1/16" filler. Very inconsistent bead width.


This was done with .045" filler. It's not perfect, but much better. Both welds were stitch-welded in 1" sections.