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Archive for June, 2014
Posted by Jack Crossfire | Jun 29, 2014 @ 05:34 PM | 5,300 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 @ 12:43 AM | 5,229 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 @ 09:58 PM | 5,067 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 @ 10:16 PM | 6,290 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 @ 03:53 PM | 6,952 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 @ 01:10 AM | 5,208 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 @ 04:28 PM | 5,063 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. http://litmotors.com/c1/ 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 @ 02:33 PM | 5,098 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
Posted by Jack Crossfire | Jun 18, 2014 @ 08:29 PM | 5,253 Views
A new plan was the simplest possible brushed motor wheeled thing. It would passively balance when stationary, allowing it to turn. It would rest on a 3rd wheel when moving, limiting it to very slow turns. A 4th wheel or springy thing would be provided, to keep it from flipping over.

After some time, discovered the spare EM812's are not real MOSFET motor drivers, but the cheapest won hung low BJT bridges. The G-buggy's controller was still impossible to beat, as a simple motor driver.

Some geared brushed motors didn't have nearly as much starting torque as the direct drive brushless motors. Brushed motors were the simplest, lowest voltage solution.

There's real appeal in a passively stable, brushless direct drive solution, from the standpoint of efficiency, but it requires a lot of software magic to get enough starting torque, then transition to back EMF mode for optimum efficiency. The startup is still terribly inefficient. Sensored motors are apparently the recommended solution for a wheeled vehicle.

The passively stable brushless direct drive solution would use up all the parts that could make a balancing robot. A balancing robot that balanced when stationary, then used a 3rd wheel for speed is still tantalizing. There's another idea of a balancing robot that used a control moment gyro for stability at high speed. It needs just enough inertia to dampen the forward flip, but can stabilize itself with its 2 wheels, unlike the reaction wheel unicycles. That...Continue Reading
Posted by Jack Crossfire | Jun 16, 2014 @ 04:49 PM | 5,759 Views

Time to recycle it. It was an extremely overpriced, bare minimum toy Wowwee rushed to Toys R Us stores, as a last minute XMas gift someone in a hurry could buy locally.

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Posted by Jack Crossfire | Jun 15, 2014 @ 10:51 PM | 5,483 Views
The old G-buggy officially died after 109 miles. A wheel axle bent when it was stepped on. More predictable steering might have prevented the human collision.

Another part of its frame had long been cracked. It's hard to think of another pacing mechanism besides the treadmill. The recent focus of investors has been heartrate monitors, but these are not realtime.
Posted by Jack Crossfire | Jun 15, 2014 @ 12:21 AM | 5,242 Views
The decision was made to go for full functionality without ESC mode, using a table of power vs speed, if at all. It doesn't look like a balancer is going to hit the required speed, even with a modern 1khz IMU & direct drive motors. With 900Mah batteries in stepper mode, the range would be 4 miles.

Getting over curbs would be an ordeal. The problem is a stopping force on the wheels causes it to flip forward. It needs a sudden boost in power to get the wheels in front of its center of gravity again. Most balancers use gear motors with a low maximum speed, to get good stationary power, but the steppers would still be near their maximum speed at 7.5mph.

The segway can go 12mph, for $2000. Nbot was still the most fully documented, seemed the fastest, but was far too slow. It demonstrated the front flipping problem nicely. There was a video of a really slow one in a balancing robot race.

Jesus Dominguez in RoboGames (1 min 6 sec)

Recently, a passively stable 2 wheeler called Outrunner appeared. It was 1 of many unsuccessful projects in the kickstarter underworld.

OutRunner OffRoad (1 min 21 sec)
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Posted by Jack Crossfire | Jun 13, 2014 @ 04:14 PM | 4,638 Views
So the last interview was the standard bit packing problem from many interviews before & that was the entirety of their dialog. They want you to pack a certain number of bits from each byte of an array into another array.

The traditional way of implementing it as fast as possible for an interview was to create a temp array of 1 byte per bit, write the packed data to the temp array, convert the temp array from bytes to bits. The way real compressors do it is to spend the time to make a write_bit function that writes a single bit at a time to the output array, maintaining the required state variables for the destination bit between calls, & padding the final byte with 0's. Suspect they want the latter.

Rather than spend the time verifying it alone, figured he had a test data set which would quickly show if it worked. That revealed a function argument was implemented for the number of bits to keep, but he wanted it for the number of bits to remove. Reversed the variable & it worked, but this ended the interview.

Out of a pool of many thousands of applicants, some would have had recent memory of data compressors with the write_bit method, some would have nailed it on the 1st try, some would have verified it on their own, appearing to nail it on the 1st try, some would have copied the solution from past interviews, some would have had snazzier solutions. The winner is purely random, but good enough. It may be they already had someone else picked, but had to follow through on the interview process for immigration laws.

Peers say they're "just hanging on" & the democrat controlled news media isn't covering reality. Reviewing what some of them did over the last 15 years made the MS seem a lot more important.
Posted by Jack Crossfire | Jun 13, 2014 @ 05:16 AM | 4,955 Views
A quick test revealed the 50 turn motors could reach the required 8mph with the required torque, at 15V 0.6A. They probably need active cooling & stall detection. It comes to 15V 1.2A for the motors, 6V 0.25A for the cooling fans, 3.3V 0.06A for the CPU. It would take 2Ah, 15V which is too heavy with modern batteries.

It's more efficient to reach that speed in ESC mode than stepper mode, but transitioning from stepper mode to ESC mode would require a super algorithm. It needs to power all 3 phases & adjust phase for stationary balancing, then when RPM reaches a certain point, powers just 2 phases & adjusts voltage for balancing.

The balancing robot needs an outer loop further regulating speed by tilt angle. If the inner loop voltage is too high, it tilts less. If it's too low, it tilts more. If it's stationary, it needs to tilt based on the amount of phase change.

Such an algorithm would have earned a master's degree, 15 years ago. Amusingly, a commenter on a goo tube video about the nbot balancing robot wrote "When you get that awkward [interview] question 'so what skills do you have for us', slap that robot on the table and you can name you salery. After all, how many people do you know who can make one of these from scatch?" 5 years ago. Times have changed so much, jobs have become so much more specialized, & robots have become so much more commoditized, such a thing won't get any more than a teary eyed "My kid got 5 for XMas. Moving on..."
Posted by Jack Crossfire | Jun 11, 2014 @ 10:25 PM | 5,962 Views
The old Yamaha HTR-5230 had problems ever since year 3. Its volume control finally broke, after 14 years. It has too many complex mechanical solutions for simple problems.

A modern replacement would be $200 with no speakers, all to replace a single pot. A search for a single pot connected to an ADC revealed this instead:

The pinout on the board:

+10 - +12 MOTOR
-12 - -12
+12A - +12 OP-AMP

Another 12 pins are where the 6 audio channels are routed through.

...Continue Reading
Posted by Jack Crossfire | Jun 10, 2014 @ 11:16 PM | 5,349 Views

Reading about refinery fires makes workers seem a lot less important than they were 15 years ago. The absolute worst disaster killed 4 & crippled 1 who jumped from a rusted 100ft tower that you drive by every day. The modern luxury SUV is built on blood, a nest of rusted 100 year old pipes with lots of gremlins, future leaks in development, tales of men burned alive, bosses ordering pipes cut before being fully drained, maintenance deferred to squeeze out maximum production.

Most of US's refineries are ancient, deteriorating structures, built around 1905. This ancient, deteriorating infrastructure won WWI, WWII, but lost everything since. In WWII, it received an upgrade in the form of fluid catalytic cracking. This provided the efficiency edge required to win WWII. Otherwise, there were incremental improvements to comply with environmental regulations. Some environmental regulations push the limit of chemical engineering & cost lives to produce.

There are still many pieces from 1905, operating on the ragged edge of failure, carrying extremely flammable materials in exotic states never encountered in normal life, at temperatures hotter than Venus. The heart of the operation is the distiller/regenerator unit, an extremely complicated, ragged nest of rusted pipe, all designed by someone, with every elbow of every pipe stored in either in a CAD file somewhere or someone's head. An army of workers constantly replaces aging pipes & builds new plants that some chemical engineer dreamed up.

The pictured section was built in 1971, burned down in 2012 when an ancient pipe rusted through & was rebuilt in 2013.

The tower of death, on which a naptha leak burned 4 workers to death & a 5th lept in 1999.

Where a worker was burned to death in an explosion in 1997, after many years of the 30 year old system beginning to show issues.


Posted by Jack Crossfire | Jun 08, 2014 @ 05:14 PM | 4,846 Views

The compressor proved essential over the last 15 years, but with a proper Lipo, it's so much more convenient. No more draining the car battery, opening different car doors, shuffling the cable, leaving the key in the ignition to power it. Very old cars require keys to be in a slot & don't automatically inflate their tires, but they don't have the mandated GPS tracking, remote engine cutoff, & tax premiums the government now requires.
Posted by Jack Crossfire | Jun 07, 2014 @ 04:23 PM | 5,653 Views

Despite all fears of shoemageddon, the 1st RC car run with the new shoes happened with no issues. It was a bit easier, thanks to 2 easy days. Didn't feel any hunger, thanks to a large salad with nothing else. The shoes just felt heavy. Fully intact soles put them at 11.6oz. After wearing down, they were 10oz.

At 7.4V, GPS reported the fastest segment was 8m8s per mile for 1.8 miles. The same segment uphill was 8m31s per mile. After GPS reported 10.25 miles, the battery started fading fast. Automatic steering died completely. It now has 109 miles on it. Used gyro * 4 for the automated steering, to no avail.

Still expect the tires to go before the motor. It's going to suck to spend $44 on another piece of junk instead of an ideal solution.
Posted by Jack Crossfire | Jun 06, 2014 @ 04:30 PM | 5,184 Views
SpaceX Landing Restoration 2014/06/04 20:52:32 GMT (0 min 21 sec)



Reading about how the restoration of that video was done, it's amazing how many people are able to hand restore a corrupted H.264 video stream, fixing the corrupted headers in a hex editor, writing a custom macroblock editor to fix the macroblock encodings in every single frame.

Years ago, it was a small miracle just for someone to know what a GOP was, let alone fix the macroblock encodings. Overnight, that skill became normal. From their piano competitions, to their self driving cars, to their H.264 video repairs, the millenials are a new league of talent, far more than generation Y & a different universe than generation X. It explains why job interviews are so much harder than 5 years ago & feel a lot more like standing on your head.

Fixing the SpaceX video was an exceptional case that required experts in H.264 macro block encoding editor writing. Attacking exceptional cases that require standing on your head is almost entirely what feeds the new economy.

It was the 1st time a 1st stage ever landed itself. It was an idea proposed only in drawings, for almost a century. They only launch 3 times per year, with 1 launch capable of having enough margin to attempt a recovery. The powered descent is too expensive to make more than 33% of their launchers recoverable. To be 100% recoverable, they would have to move the remaneing 2 launches per year to Falcon 9 heavy, which would be completely unaffordable.
Posted by Jack Crossfire | Jun 05, 2014 @ 09:27 PM | 5,309 Views

Now some interesting nuggets about the reprinted satellite photos which 1st appeared on May 25, 2011 from http://www.benedictredgrove.com/aeronautical/01.

...Continue Reading