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Posted by Jack Crossfire | Nov 07, 2014 @ 10:21 PM | 3,316 Views

It was finally time for a 3rd stab at a contact lens agitator. After years of levitation & home made linear motors, this one would be a tried & true laboratory shaker, using a stepper motor. The linear motor couldn't make enough thrust, was too noisy, & shed metal filings. The levitator had proven completely ineffective but looked neat.

There was hope a computer fan could do the job. Those turned out to use a dead simple half bridge. 1 pin is always 12V. The other 2 pins alternate going to ground. They spin in only 1 direction, no matter the polarity.

The next step was a traditional brushless gimbal motor. A 3 phase motor controller would have been ideal, but completely unaffordable. A pair of BJT's from a burned out lightbulb would do the job. They didn't need spudger diodes like MOSFETs. The same half bridge arrangement of a computer fan actually provided enough of a shaking motion when applied to a brushless gimbal motor.

After much effort, a C program for driving it with PWM wouldn't compile properly. The compiler choked on a counter equality comparison. After redoing it in assembly, PWM was once again a noisy failure. Even at 22khz, it was too noisy because the PIC at 8Mhz couldn't get the timing close enough. A linear regulator would lower the 20V input to control speed, the heat from which would heat the payload.

How to mount a regulator on a CPU heatsink to heat the payload....Continue Reading
Posted by Jack Crossfire | Nov 01, 2014 @ 04:20 AM | 3,781 Views

That was disappointing. They lost 3 in 2007, when an oxidizer tank exploded. Like last time, they'll never release the cause of the accident. This was probably another oxidizer tank failure. The pilots would have been ejected by the blast. The guy in the left seat would have been the unlucky one, knocked by just the right piece of carbon fiber to knock him out.

There comes a point in a space program when enough people have been lost by the same cause that there is a definite safety issue in the management or the system. Hybrid rocket engines just may not be safe enough because they require too much gas under too much pressure for current materials. People have struggled with carbon fiber tanks for decades. They haven't been consistently able to contain a rated pressure.

It's hard to believe they'll be able to make another vehicle without any money coming in from customers. The plan was always to mass produce them, but only after the money was coming in from the 1st one. Dick Branson had slowed funding to a crawl. It's hard to slow it any further without stopping it.

It's yet another story of another guy giving his life in the quest to reach space. As long as space is just 62 miles away, they'll keep reaching for it & some won't come back. Maybe we'll lose 1 per decade. No-one died in the 1990's, when the number of people going up was at its peak. There hasn't been enough money since then. The 2010's are still benign compared to the 2000's.

Virgin Galactic/Scaled was the last to continue the legend of people coming to the high desert of Calif* to ride a vehicle into space, test pilots whose names no-one knew, who rode horses & drank at a run down bar. The legend is really over. Kazakstan ended up being the place for going into space. The new space cowboys drink Vodka & drive trucks with dashcams on the wrong side of the road.
Posted by Jack Crossfire | Oct 28, 2014 @ 10:42 PM | 3,401 Views
Working for the Modern San Francisco Startup is a new experience. The commute is 90 minutes. Everyone was born after you went to your last baseball game. All the jobs are now in the city, where 15 years ago they were all in the valley. The current cycle back to the city began in 2007 when real estate plummeted. Now the city is ferociously expensive while the valley is the wasteland.

All the assets are stored on web application cloud servers: asana for project management, bitbucket for code repository, gmail for email, & for documents. Even all the lunches are ordered on obscure cloud services like It's surprising how much cloud still isn't Google, if you look hard enough.

There's no more full time IT guy & server room. It's all web services. There are but 2 areas this cloud web generation will absolutely not use touch cloud services for, however: DATING. They all met their partners in BARS & NIGHTCLUBS. NO ONLINE DATING! NEVER!

The other thing is working from home. For all the webification, there is no working from home. The topic of physically being in an office is still as sacred as where the romantic relationship starts.

It's surprisingly easy for them to find the best people for the job. Programming is no longer a black box known only by a few savants, but manestream material, nowadays. It's a significant change from 2001, when it was very hard to find someone who knew what they were doing.

Of course,...Continue Reading
Posted by Jack Crossfire | Oct 21, 2014 @ 10:22 PM | 4,213 Views
Inspired by the continued existence of a AA consuming toy fan from the 1980's, it was time to build something more efficient with RC parts.

Dumb Blond hottie

You wouldn't believe how hard it is to make a fan. The mane problem was noise, which RC parts aren't designed to avoid, but which is a critical design feature for appliances. The other problem was safety. A prop saver did absolutely nothing. The prop still shattered in an obstruction test. This is 1 area where 3D printing a shroud would be useful. For now, a wire provides some minimal protection from accidentally coming in from the side.

...Continue Reading
Posted by Jack Crossfire | Oct 19, 2014 @ 01:49 AM | 3,530 Views

Anothor 9.0V rover run at rock bottom 9min/mile. Hit 8m16s in the fastest mile. A 90 minute commute doesn't leave any time for hacking, so the balky steering lives on.

The very last rover run was after canned soup, frozen chicken, & a long session of diahrea. At 9.2V, with reduced D gain, the steering was still impossible. The fastest mile was 8m4s. The entire flat section was at 8m49s/mile.

More of the .25 mile graph poked above the 8m mark. The uphill part went faster than the downhill part, so trail condition affected speed more than voltage. It was definitely harder, partly because of lack of exercise & because it was 2 days after the last rover run. The brushless rover never did match the G-buggy in consistency or steering, as bad as the g-buggy was.

It was the last of the intense speed runs. The commute has put an end to the illustrious 4 year running career & the salads. Speed never equaled its peak in Feb. It's interesting to look at the training log & ponder what worked.

For the 1st time in 4 years, was much less hungry in the last week. Felt much less appetite from lack of exercise. 15 hours a week of sitting in a train is pure hell on a body. Looks like the fitness of the last 4 years has come to an end, but these are the sacrifices required to make 1/2 what you did 10 years ago, in the new economy.
Posted by Jack Crossfire | Oct 11, 2014 @ 06:24 AM | 3,699 Views
No-one refers to Apple by the CEO name or "Steve & Co" anymore. Now, it's consistently referred to as Apple.

Using the common dial of a watch as the user input of a smart watch was the most obvious solution to the most obvious problem no-one ever thought of.

The watch allows you to feel someone else's tapping or heartbeat in realtime, by vibrating. It's another thing you wonder why it wasn't done 10 years ago.

Conspicuously absent from Apple news is a drone product, 3D printing product, or glasses product.
Posted by Jack Crossfire | Oct 09, 2014 @ 12:21 PM | 3,350 Views

It was the 1st clear sky in 7 years, but decided not to make a movie for fear the whole thing wasn't going to be in the dark.
Posted by Jack Crossfire | Oct 08, 2014 @ 07:18 PM | 3,834 Views

Always amusing to see photos that were impossible just 3 years ago. It's taken for granted now, but only a tick of the clock ago, camera sensors weren't fast enough to get razor sharp, handheld images from an airplane in near total darkness.

We all had the experience of trying to get night shots from airliners. It was completely hopeless for a camera made in 2008.

That took working the proverbial ass off.

Forget about live video of auroras. The only way to see what an aurora looked like in real time before 2012 was to drive 3000 miles. Most of the world could only imagine from timelapses & artist renditions. Now everyone has seen an aurora in real time.
Posted by Jack Crossfire | Oct 05, 2014 @ 11:33 PM | 4,260 Views

Never build 1 when you can build 2 for twice the price. Everyone knows about Stennis space center, the A-1 test stand where the SSME & F-1 were tested. Lesser known is the even bigger B-1/B-2 test stand where the complete S-IC & shuttle core were test fired.

Little did you know an identical set of test stands was built in Huntsville, in an age long before Stennis. The mighty S1C test stand was built from 1960 - 1964 for $30 million & would test the 1st 4 S-IC stages. You can't even buy a house for $30 million, anymore.

...Continue Reading
Posted by Jack Crossfire | Oct 04, 2014 @ 02:16 AM | 4,069 Views
Had granola cerial with no pepto bismol, since it might interfere with nutrient absorption. At 9V, it did the actual 13.1 segment in 1h58m2s including red lights. Red lights took 30s. The fastest mile was 8m7s on the uphill. Speed was highly erratic, with some quarter mile segments going extremely fast. Any benefit from PWM regulation was lost to flips & spinouts. Steering was non functional. Ate a caffeine free powergel at 11.5mi, which went everywhere. Couldn't drive while eating. The 1Ah battery had no problem. Got a bowel movement at 13.72mi.
Posted by Jack Crossfire | Sep 30, 2014 @ 09:14 PM | 3,667 Views

The answer is still no. You can't make your own private router with 2 mile range out of a pair of LTE phones. As far as what can be deciphered from the hindi accents, it's not a point to point version of LTE but a way for devices to discover nearby devices. They broadcast a very brief 128 bit ID on the LTE physical layer which is directly received by devices within 500m, to allow device discovery, but the data communication is still over a paid, bandwidth capped, tower based LTE plan.

Of course, the hype is just as insane as the Intel Edison 2 weeks ago & the Google Tango before that. Does anyone remember what Google Tango was?
Posted by Jack Crossfire | Sep 29, 2014 @ 08:39 PM | 3,554 Views
Make It Wearable Finalists | Meet Team Nixie (1 min 52 sec)

Couldn't believe how many people actually thought it was real. It's another example of how millennials believe absolutely everything they're told, while we would always ask questions, 20 years ago. They're just as believing on the economy & politicians. Not sure why this is. Maybe they know a lot less about physics than us.

Besides the industrial design which obviously won't work & has nothing to do with the stated purpose of making it small, if it was something which actually flew, wind resistance still wouldn't be there. It still requires a pink marker or an image processing ASIC. It's actually smaller than the Edison board he's trying to base it on.

The problem with prototyping an optically guided follow cam, using a laptop for image processing, was the antenna on the transmitter always falling off. Those Chinese never gave any thought to how fragile a postage stamp was for soldering an antenna to. Once it breaks off, the trace is gone.

It really needs a breakout board with the voltage regulators & a surface mount antenna, which is not the optimum weight.
Posted by Jack Crossfire | Sep 27, 2014 @ 07:51 PM | 3,835 Views

Interesting nuggets from a long past coworker who went to Google 12 years ago & never looked back. After the winning the 2 largest IPO's of their time, he now works 20 hours/week, buys supercars, flies a Cessna for fun, has enough wealth to own a house. For all the bad parts of big corporations & the stories of Google eternally hanging its employees 1 foot out the door, a long term stint in that place creates possibilities you can't believe.

To be sure, his job seems dry. It's the same task people did 20 years ago: installing Linux distributions on servers. He made a go at physical computing in 2011, like everyone else, but it never became a replacement for the old job. For all the talk about robotics, Andy Rubin, & Sebastian Thrun, Google is still foremost a web application company & you will never encounter a robotics expert in your daily routine.

There's some novelty in photos taken by the generation which took the 1st digital camera photos. Because they're still a technological wonder to the guy taking them, they seem more significant.

It's another look at a parallel world where just installing Linux, going to Linux conferences, & taking digital photos are still big deals. If you can stay enthusiastic about 1 thing for 20 years, the rewards are huge, but it may be our generation is becoming the new generation of grandpas stuck in its own point in time, always seeing newness in what youngins see as obsolete.
Posted by Jack Crossfire | Sep 26, 2014 @ 11:20 PM | 3,061 Views

The 1st rover test was crazy fast. Visor was dripping sweat for the 1st time. Used new rover firmware which uses a linear PWM scale based on battery voltage. Set it to 9.5V. It was in the 7m50s range going downhill for 2 miles & the 8m range going uphill for 2 miles. The target pace is 8m20s going downhill, 8m40s going uphill. Might have to lowball the downhill speed to make the uphill speed accessible. The scaled PWM definitely pulled in the gap between starting & ending speed even though it's not the most accurate power regulation.

The fastest mile was 7m46s going downhill, which was way beyond any previous mile. GPS reported a 7m44s mile going uphill, but it must have been a glitch. Had a diarrhea break after 3 miles. After that, the phone measured a heart rate of 143 which quickly dropped to 115. There were many stops for flips & traffic, steeper hills where it dropped to 10m/mile.
Posted by Jack Crossfire | Sep 25, 2014 @ 08:02 PM | 3,315 Views

Did anyone know Gopro had its IPO last year? The story of the day during their IPO was world cup. Did anyone care about the world cup?

Interviewed there, years before the IPO. The manager was a jerk, had thousands of applicants, wanted a known quantity. Experience was no longer enough.

Their product is the best in a bad neighborhood, but still a POS. SD card failures need to be built into the recording pipeline. Rather than shutting down, it needs to try opening a new file. It also needs downloading recordings over Wifi.

Helas, stock traders have redirected the company's focus from improving the camera to creating a social network which is to be sold to Google. Gopro tube is the next Twitch. The buyout is going to be well over $10 billion, many times more than Twitch or the 'tube. Another batch of people aren't going to have to work anymore.
Posted by Jack Crossfire | Sep 25, 2014 @ 06:21 AM | 3,402 Views

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It's not about common sense. It's about knowing the secret handshake.
Posted by Jack Crossfire | Sep 24, 2014 @ 02:23 AM | 3,610 Views

Though SpaceX never revealed any detailed diagrams of Falcon 9, they did reveal 1 low resolution diagram which was captured in a blog in 2008.

So the video was the LOX tank. The spheres in frame were carbon fiber helium tanks used to pressurize the LOX tank. The temperature in there was −297.33F. Helium liquifies at -452F, so the spheres would still work when submerged. The fuel is presumably pressurized with exhaust.

All of the stages use common bulkheads between fuel & oxidizer. There's nothing on the 1st stage, no public displays where you can see the plumbing up close, no diagrams.
Posted by Jack Crossfire | Sep 21, 2014 @ 09:33 PM | 3,064 Views
It seems like it shouldn't be a big deal to design a constant power supply for a rover. It just needs the same standard current sensor that every RC plane has. 3D Robotics actually donated a current sensor with integrated 5V regulator. The problem is the rover is too small to fit it anywhere.

Sadly, regulating power by making PWM proportional to voltage didn't work. The idea was higher voltage at lower duty cycle would be equal to lower voltage at higher duty cycle, but power still increased with increasing voltage. The motors aren't constant resistance for all voltage & there's an unknown power usage from automated steering. It wasn't as effective as a linear regulator, which was still not true power regulation.

3DR uses an INA169 current sensor, which is an op-amp calibrated to convert the voltage difference across a 0.0005R resistor into a known voltage range. Their current range is 90A, while the rover needs 2A.

That leaves building something out of a 1R resistor with an op-amp. The maximum voltage drop should be 2V with a maximum current at 2A, but it's actually PWM with the maximum current an unknown higher amount for a shorter duty cycle. Then the PWM result needs to be smoothed.

They limit the bandwidth with a .1uF & 110k described in the datasheet. Using 1/(2piRC) gives 14Hz. Your best bet is to probe the resistor output & smooth it as much as possible with a big cap.

Constant power remanes a bridge too far for something which also needs a suspension system. Some waveforms showed nothing abnormal.

Deriving PWM purely from voltage, no load, at 12.5V we have .19A 2.38W

At 10V, we have .20A 2W

At 9V, we have .24A 2.16W

As usual, the frequency response of the probe makes suspect voltage ranges.

With constant PWM for all voltage, we have

12.5V .43A 5.3W
10V .37A 3.7W
9V .33A 2.97W

So voltage derived PWM is better than nothing, in the normal voltage range.
Posted by Jack Crossfire | Sep 21, 2014 @ 02:25 AM | 3,152 Views
There were some intriguing views inside the Falcon 9 2nd stage fuel tank, during the CRS-4 launch. They showed brief segments as the depletion rate got faster & faster. Right before exhaustion, the blob stopped dropping & floated up in weightlessness, like a goo. There's no reserve in those launches. Kind of scary to see a giant webbed blob of fluid slowly floating towards you through the air, as if commanded by a mind of its own to drown you.

Falcon 9 fuel tank cam (0 min 46 sec)

Fuel tank cams are useful for showing the amount of actual reserve compared to the predicted reserve, how well it's settled on the bottom for an engine restart, how much it sloshes. Bonus footage: a timelapse of another launch

Falcon 9 OG2 timelapse (0 min 41 sec)
...Continue Reading