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Jack Crossfire's blog
Posted by Jack Crossfire | Jul 13, 2014 @ 08:50 PM | 2,282 Views
A better metric never discussed on the internets is how much a rocket can launch in a given timespan, rather than the amount it can launch in a single flight or the cost per mass in a single flight. The ground crew has to be paid constantly, no matter how many launches they send off.

Today's launch rates are glacially slow, compared to just 5 years ago. For all the difficulty in getting Falcon 9 to launch 3 times per year or Antares to launch once per year, it's hard to believe they were able to launch the monstrous shuttle 5 times in 2009.

The amount of mass launched in a fixed timespan is much lower today than it was 30 years ago. 30 years ago, they were putting 240,000 lbs of payload in low Earth orbit per year. It wasn't very good for the crew, but it was the highest capacity ever achieved. At $4 billion/year, it was $17,000/lb.

Today, Falcon 9 can put around 22,000 lbs per year in low Earth orbit. Antares can deliver 4400lbs per year. There aren't any figures for how much it's costing. If it was equivalent to the shuttle, Falcon 9 would be burning roughly $374 million/year. Antares would be burning roughly $74 million/year.

It actually doesn't sound far off what the rumors have been. There isn't any of the disclosure under the commercial programs that there was under the shuttle program. $57 million per flight could be a significant loss.
Posted by Jack Crossfire | Jul 12, 2014 @ 01:22 AM | 2,123 Views

The 1st run with the brushless direct drive rover went way beyond predicted range, yet again. Range on 2S 900mAh was over 8 miles. Maximum downhill speed was 8 min/mile. Uphill speed sagged to 8m50s/mile. It was hopeless on rough terrain. It needed D feedback & shorter battery cables.

It was finally documented with the latest improvements.

Brushless direct drive rover (4 min 57 sec)

The camera made it top heavy enough to flip over from the smallest obstacle.
Posted by Jack Crossfire | Jul 10, 2014 @ 11:42 PM | 2,225 Views
The most expensive apartment in town is equivalent to the current situation, but 10 years behind in price. It has only 1 wall with windows, has open space, has a really solid front door. The most reasonable cheap place is another $300 cheaper, has 2 sides with windows, no open space. It's in a dump, has bars on the door with a separate lock, no bars on the windows, & has a really dumpy pool visible from the street. The difference is $3660/year. Between those 2 are other places which are extremely dumpy or not reasonable.

There's definitely a correlation between price & standard of living. It's not easy to endure a drop in standard of living & it seems worth spending zillions of dollars on happiness, which brings up the blond hottie paradox. Do unattainable middle age blond hotties spend zillions of dollars on expensive stuff because they can or because they're miserable? The other factor is if the price was sigificant, wouldn't you already have downgraded? Another choice of standard of living over price happened in 1998. It still seems impossible to say it wasn't worth it.

The mortgage & student loan booms have turned the west half of Bakersfield into an extension of LA, while the east half descends into the abyss. New construction, valley girls, & shiny black Audis straight off the 405 abound. The boom is far from the freeways, so it's not obvious to the Las Vegas trade show travelers, but a new superhighway seems destined to connect the new area to the 5.

The weather is difficult, but everywhere is difficult compared to the bay area. Eliminating sources of stress seems to be a noble priority.
Posted by Jack Crossfire | Jul 09, 2014 @ 03:20 PM | 2,013 Views

The 1st road test with motor sensors worked perfectly. It definitely needed breaks & slightly faster startup. The stalls were gone. 7.4V got it to the 7.5mph range, without getting hot. Based on the rolling distance, it probably was near the no load current of 0.3A. It was virtually silent. Radio range was only 10ft.

It easily rolled over rough terrain. The rolling distance without breaks was surprisingly long. Even with no power, it rolled into curbs hard enough to flip over, but didn't flip over on rough road. The sensors seemed to withstand it. The castor wheel assemblies crumpled, reducing the impact.

Startup was a hard coded stepper acceleration, transitioning to commutating mode, to keep the wheels from slipping. That failed miserably. It slipped when rotating to the 1st step. The sensors couldn't make it transition into commutating mode seamlessly. Tried ramping PWM without a stepper state & it still lost steering. Carefully setting it to wait for the right stepper phase would probably solve the transition problem, but not the 1st step.

The only practical way to get straight driving was to go straight into full power. It didn't slip as much as feared. It used less current. Stepper acceleration is a dead topic. It consumes a lot of current for purely visual appeal.

After implementing heading hold steering & all the manual controls, it worked perfectly. All the issues with bang bang steering were gone....Continue Reading
Posted by Jack Crossfire | Jul 08, 2014 @ 05:50 PM | 2,322 Views

Operations & checkout building then & now.

Spaceships then & now.
Posted by Jack Crossfire | Jul 07, 2014 @ 05:02 PM | 2,264 Views

Soaked in thin CA glue to make it more solid.

This alignment was too widely spaced. The alignment had to be spot on to get reliable commutation. They had to be right on the edge of the magnets. The misaligned sensors gave 111, 000, or just 2 patterns with very small ranges for the other patterns. The aligned sensors gave all 6 patterns.

...Continue Reading
Posted by Jack Crossfire | Jul 06, 2014 @ 03:45 AM | 2,282 Views

An experiment with derating the commutation time revealed very little derating could be done before the commutation time was too long to get useful back EMF. The working speed of the motor is just too low to use back EMF of any kind, even though it's fast enough to start it. It only starts because the commutation time is lowpass filtered & speeds up fast enough to get it into the sustainable range. The only solution is a sensor.

The loss of steering during startup was caused by the motors not changing state at the same time. Having the phase & state changes synchronized solved that problem until they stalled. At 15V, they still occasionally stalled when hitting rough pavement. A sensor would solve that & decrease the current.

There are no teardowns of a sensored motor, but blurry, shaky videos appear to show home made attempts with 3 hall effect sensors outside the motor casing. 1 guy used them in a modified e-bike. E-bikes are as common in the bay area today as Priuses were, 10 years ago. Of course, no-one has a clue how they work. That requires going to Hong Kong.

There are no examples of 2 sensored motors being used. It's a very complicated ordeal that makes people give up after converting 1.

A single A1321 sensor is applied to the outside & powered by 3.3V.

Waveform when turned manually.

...Continue Reading
Posted by Jack Crossfire | Jul 05, 2014 @ 06:23 PM | 2,153 Views

July 4 2014 fireworks timelapse (2 min 16 sec)

Decided to timelapse everything until the grand finale. Ran down with the guerilla pod, which was useless for video. At least the traffic was better than driving down with the video tripod. Being many years since the last manually exposed fireworks video, forgot everything.

1/30 F/2.8 ISO 1600 was a decent exposure. Stopping down would have sharpened the dots, but added noise. Desperately needed a video of a past show to know where to point the camera, but Sprint was completely down. Had to reposition during the show. 15mm with 1.6x cropping was just wide enough to get everything.

Audio was at the lowest setting. Clapping produced a decent approximation of the maximum loudness. Should have used a simple pair of outboard electret condensers, at minimum. Anything would have had better stereo separation than the Canon's microphone. Amazingly, it still managed to differentiate the guy on the right.

...Continue Reading
Posted by Jack Crossfire | Jul 04, 2014 @ 04:48 PM | 1,676 Views
The follow me concept using GPS is nothing new. It was demonstrated in 2008 at long range, with the normal lens cameras of the time.
MikroKopter - FollowMe on the Wakeboard (5 min 43 sec)

Now, they're doing it at slightly closer ranges, with modern wide angle, stabilized cameras. It has always depended on a very accurate attitude estimation with GPS coordinate triangulation.

The athlete still looks like a tiny dot. The newest videos are a lot more edited for when the athlete goes out of frame. It has the feel of trying to get a lot more mileage out of the same old capability.

Getting a closeup is really hard. The easiest way is to have a very long lens camera with many levels of stabilization & chroma key detection of the athlete. The last of the Sony Handycams had excellent stabilization. So far, they're all marketing gopro cameras, so this method is not being demonstrated any time soon.

The HDR-PJ540 is the current optically stabilized one. It's quite large & expensive. Stabilization on that level is now a novelty feature, since no-one cares. It's a huge investment, just for the follow me mode.

Another way is to fly up close. The advantage is a much easier time initializing it, much smaller vehicle, getting the athlete started in frame, & ability to fly in confined spaces.

GPS is no good. The athlete has to be the navigation reference. Time of flight cameras & structured light cameras don't work in daylight. The movie camera alone can resolve position, within strict limits. It would take having the athlete wear multiple chroma key markers & having 2 markers in frame at all time. The markers either have to be a constant distance apart or they need a way to tell how far apart they are, maybe by some electromagnetic sensor which has been demonstrated. Single camera autopilots have been done before.

It still would need GPS at long range. Any method using chroma keying without a GPS aid is going to be prone to false positives & flying away.
Posted by Jack Crossfire | Jul 02, 2014 @ 11:11 PM | 2,027 Views

The most amusing part is that biology majors still make the least, even when they work in engineering. Coworkers who studied physics did indeed have a much easier time getting jobs. The study probably only looked at people working in engineering.

After taxes, the highest bracket only makes $1.5 million in his lifetime. The average house in a dot com area is $2 million.

The author made a big deal about eliminating selection bias, basically people getting engineering degrees because they're smarter in the 1st place. Wish studies that showed married women live longer than single women would correct for selection bias. Men pick women in better health. Marriage has the opposite effect on men's health.

So the blog is moving to Bakersfield because Tampa is completely unaffordable. The out of state tuition alone is bleak. The rent is equivalent to Silicon Valley, 10 years ago. Bakersfield has the same temperature as Death Valley, but the heat index is the same as Tampa. Who knew all those tourist attractions in Fl*rida had the same heat index as death valley.
Posted by Jack Crossfire | Jul 02, 2014 @ 04:55 AM | 2,247 Views

Decided to kick it up to 15V with fixed commutation mode & it actually exceeded the required speed at 8.5mph. It sucked 2.8A to start & 1.9A to run. Keeping it going straight during the start was a problem. After commutation begins, it's quite stable. The commutation was much slower than the optimum speed, but required to get enough torque. The coils got too hot.

Some more debugging & speed regulation could slightly reduce the current. The idea is to use back EMF, but add a certain delay so the voltage is regulating speed, yet it's less sensitive to stalling. This has been tried before, without success. Its range on 4S 900mAh would probably be 20 min or equivalent to the brushless Losi micro T on 2S 200mAh.

Another idea would be to measure the back EMF time. If it was too far ahead of commutation, reduce the voltage in the next phase according to a PID controller. If it was too far behind, increase the voltage in the next phase. That would give better torque, but not slow down on hills. Normal rovers use flywheels or slip clutches to avoid stalling.

The time for this has probably run out. There probably is a future in direct drive brushless rovers. They offer a way to get a wide range of speeds or more biomorphic movement. A direct drive robot can slowly rotate to scan a scene, then dart forward. A conventional robot is geared to go either extremely slowly or extremely fast.
Posted by Jack Crossfire | Jul 01, 2014 @ 01:45 AM | 2,735 Views

So the VIIRS was built in LA. There's no data on how it works, whether it's based on a large aperture or an extremely radiation hardened DSLR sensor. It's sensitive enough to detect a flashlight in the ocean. Connoisseurs of its data have noticed a large patch of lights in N Dakota which didn't exist 15 years ago.

...Continue Reading
Posted by Jack Crossfire | Jun 29, 2014 @ 06:34 PM | 1,865 Views
It was worth documenting the last bit of data from the back EMF motor control fiasco. It begins with the full power applied.

Oscilloscope plots of the full power voltage are never shown, but they have the clearest view of the 2 powered phases with the back EMF clearly visible in the floating phase. There's a glitch where it goes from 9V to floating. Software detects the halfway point to determine the commutation time.

The normal oscilloscope plot shows PWM modulated voltages. The back EMF phase is less visible. The writers for EETimes tend to be more interested in showing they fully understand the concept personally, with the most obtuse diagrams, rather than conveying it to someone else.

...Continue Reading
Posted by Jack Crossfire | Jun 29, 2014 @ 01:43 AM | 1,980 Views

A tool that everyone alive & especially aerial shooters could use is a way to plan shots based on focal length & satellite photos. There are probably many tools around, somewhere. A quick review of the Goog store didn't reveal any, so threw together some more Javascript.

While it's nowhere close to a comprehensive solution, it does the absolute minimum of superimposing field of view for a given focal length on a satellite photo. No more packing anything but the exact lens you need.

It's hard coded for a 35mm DSLR of a certain crop factor, horizontally mounted. The next step would be either a vertical mount option or direct entry of the sensor width. Height of the field of view can't be easily conveyed. The oblique satellite photo gives a rough estimation of the height of an object, relative to the field of view. A street view overlay could be more useful, but their imagery is limited to just public roads.

Field of view gets less accurate as the lens gets wider. It probably doesn't represent a fisheye lens at all.
Posted by Jack Crossfire | Jun 27, 2014 @ 10:58 PM | 1,907 Views
A good read is the complete archives of Compute magazine, from 1981-1990:

Where were the breakthrough solutions in 1985?

The Computerized Home - Switchbox

Undoubtedly Switchbox was a lot cheaper than the $3 billion Google paid for Nest.

The Digital Diet Staying In Shape With Your Computer

Not to be confused with the billions pouring into wearable fitness tracker startups.

Then there's everyone's favorite

Travelshopper lets you scan flight availabilities (on virtually any airline worldwide), find airfare bargains...

Except for the names, it's the same story.

To be sure, we live manely the same way we did 30 years ago. It can be depressing to see the same problems being solved then that you're solving today, but that applies to everyone. Every profession still does manely the same thing it did 30 years ago, whether in technology or anything else.

The 1 thing that sort of feels new is the drone. It absolutely didn't exist in anyone's mind until 2007, but energy storage continues to keep it out of the realm of practical problems like the Digital Diet. Aerospace is intriguing in that space missions are much cheaper, yet there are far less of them.

Doctors, lawyers, & teachers solve exactly the same problems they did 100 years ago, despite minor changes to their tools. These are not professions for you if reading about your same task being done 30 years ago is depressing. Most people aren't this way about the past, but some do need to solve new problems.
Posted by Jack Crossfire | Jun 26, 2014 @ 11:16 PM | 2,695 Views

A motor is tested for a winding error by using the right hand rule, a fixed current source, & permanent magnet. 10 & 3 were swapped.

The balancer was officially recycled after an attempt to make it balance. There was a lot more involved than expected. Mass distribution made a difference. Less mass was better. It couldn't balance with a battery anywhere on it. An outer loop needed to calculate a target angle based on the number of motor steps. An inner loop needed to hit the target angle by giving motor steps. It didn't seem to have enough traction on the carpet. There seemed to be a maximum limit on the feedback rate.

...Continue Reading
Posted by Jack Crossfire | Jun 25, 2014 @ 04:53 PM | 3,762 Views
So Virgin sent out a hidden update which disabled the wifi tethering again. It also disabled bluetooth networking. Merely changing phone numbers caused it to download the update. The update didn't affect the Android core.

For many years, people networked using bluetooth + ppp. They opened a serial console over bluetooth which required some AT commands to get the console to go into PPP mode. Then Android introduced PPP over ADB. Then a new standard for networking over bluetooth appeared called PAN.

Now some random notes for PAN.

# enable bluetooth dongle on the laptop
hciconfig hci0 up
# A menu option is required to allow the phone to be discovered by the laptop
hcitool scan
# Connect the phone to a /dev/rfcomm node
rfcomm bind 0 BC:F5:AC:2B:34:96
rfcomm show 0
# test connection
l2ping BC:F5:AC:2B:34:96
# Allow the PC to be discovered by the phone
hciconfig hci0 piscan
# Show status of PC
# allow phone to pair
bluetooth-agent 1234

# change class to networking device
Class = 0x020100
# restart bluetoothd
killall bluetoothd

# bluetooth networking module
modprobe bnep
pand --connect BC:F5:AC:2B:34:96
ifconfig bnep0
route add default gw

# on the phone
iptables -t nat -A POSTROUTING -j MASQUERADE
echo "1" > /proc/sys/net/ipv4/ip_forward

PAN was the closest to working. It forwarded ICMP & UDP, but upon the 1st TCP connection, disabled the bnep0 device.

Another idea was to use the PC...Continue Reading
Posted by Jack Crossfire | Jun 24, 2014 @ 02:10 AM | 2,056 Views
Due to its extremely remote location, the Goog couldn't find any decent photos of the teardown. It's 3.5 miles from the nearest parking lot. Decided to try to bring it to the viewers at home, like they never saw it before.

The infamous pier was reinforced before separating the mane span. In the old days, it took a complicated shock absorber like this to absorb the pushing of an earthquake. The road would collapse. If someone died, so be it. The shock absorber would rip apart if the pushing force from the mane span was replaced by a pulling force.

...Continue Reading
Posted by Jack Crossfire | Jun 21, 2014 @ 05:28 PM | 1,985 Views

Self balancing motorcycles have been promised forever. Self balancing is the key to any robotic motorcycle. Some tried reaction wheels. Some tried legs to push themselves back up after falling over. has been working on one since 2012 & recently bought a lot of advertizing.

There's 1 drawing of 2 control moment gyros. They claim thousands of ft-lbs of torque. The videos are carefully designed to have forces pushing at very low points, for short periods of time, to minimize the angular momentum & not saturate the gyros. No turns are shown. It needs a fancy turning algorithm to desaturate the gyros.

It needs to deploy its automatic kick stands or ask the driver to stick a foot out, if it's stationary for too long. It hardly seems worth the complexity & mass, just so the driver can be protected from the weather.

...Continue Reading
Posted by Jack Crossfire | Jun 20, 2014 @ 03:33 PM | 1,902 Views
It was time to recycle the G-buggy. After 109 miles, with no replacement parts, nothing on it was considered useful.

It left behind a decent drive system with high torque & very little gear reduction. The torque was much higher than any replacement, making the replacements seem unlikely to work.

Very beefy motor with lots of power factor correction. They still have to invest in efficiency, even on the cheapest toys. Someone must have sat down with a voltmeter & current meter, connected various capacitors & inductors until the phases lined up.

...Continue Reading