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Jack Crossfire's blog
Posted by Jack Crossfire | Dec 25, 2014 @ 10:19 PM | 2,774 Views

The 1st tachometer sensed 1 wheel revolution. It barely had enough deflection to flip a logic level & took a very long time to get a reading.

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Posted by Jack Crossfire | Dec 24, 2014 @ 10:27 PM | 3,040 Views

Whacked on the ages old 5V BEC to try to maximize the range, then tried constant RPM set to 500 or 9m18s/mile.

The result was higher speed going uphill than downhill, with the total speed in the 10minute/mile range. It must have been the lousy tracking of rpm.

Then of course, the range was reduced to 4.5 miles. The BEC was actually less efficient than straight PWM. As for measuring power independent of voltage, only the current feeding the BEC was measured, so the power would vary as the ESC efficiency changed at different voltages. The rough figures showed 15W on the downhill & 17W on the uphill.

Then, there were the usual software problems. Throttle always reset during fast turns & sometimes reset during slow turns. Acceleration was too slow. A faster tachometer is needed.

Ran all 9 miles looking at data on the phone. Probably need to capture the bluetooth data. During these long runs, a wish list topped by automatic path following always forms. Automatic path following can be reduced to a simple problem: determining what's 1 material & what's another material in an image. 1 material is usually asphalt. The other material is grass, gravel, or dirt.

The computer always knows asphalt is on the left & other stuff is on the right. It can get the color on the leftmost & rightmost parts of the image. Then it can work inwards until the colors change.
Posted by Jack Crossfire | Dec 21, 2014 @ 05:10 PM | 2,918 Views
So what happens when power is constant & voltage is changed?

Was hoping there would be an identical percentage decrease in RPM for all power. Instead, the RPM for 25W decreased 9% while the RPM for 10W decreased 4% as the voltage increased.

RPM decrease at 12V vs 9V:
25W 9%
22W 8%
15W 6%
10W 4%

It was a table just as complex as scaling PWM based on voltage. The rainy season was over & there was enough time before the next commute to try out constant power at a roughly constant voltage anyways.

The speed variation on hills was wider than any other method. It became clear that humans need a lot less power going uphill & a lot more power going downhill than a motor to achieve the same speed. It's the same as how humans don't hear all frequencies equally.

The next step would be a hall effect sensor tachometer. It's all purely speculation about what a human can keep up with, faking a speed that feels like constant effort instead of trying to predict constant effort from power. The tachometer could be combined with an accelerometer to give it some variability based on incline. The current sensor is useless.
Posted by Jack Crossfire | Dec 20, 2014 @ 03:58 AM | 2,107 Views
After much playing with LTspice, it became clear that it was erratic with small voltages. Sometimes it would actually work. Usually, it would go to full maximum. With large voltages, it always correctly simulated the difference amplifier.

It was time to build up a circuit with an LM324. Amazingly, it worked. It measured 1-5A nearly linearly, using a length of wire & some spare trim pots.

Using a high rail voltage with voltage divider cut the op-amp dropout voltage by half, making the LM324 reasonable. The bog standard difference amplifier did exactly what a proper INA169 sensor did.

With all the effort in the dynamo & the current sensor, you might as well try making the constant power throttle regulator you always dreamed of. Even with a power factor correcting cap, the current was still oscillating wildly from the PWM. Averaging the current & voltage down to 10Hz made a very stable power reading. It was an actual power reading from a bunch of spare parts.

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Posted by Jack Crossfire | Dec 14, 2014 @ 07:25 PM | 3,232 Views

Building a dynamo was long dreaded, but necessary to have any hope of regulating the speed.

Out of sheer luck, the Tamiya came with a tool which perfectly coupled 1 shaft end with a spare motor. A simple jig could hold everything together. The bench supply couldn't provide stable voltage because the current & voltage were out of phase. The old LM317 system with giant capacitor could provide stable voltage.

The load could be adjusted by shorting out different motor leads with different lengths of wire. An op-amp measured the current between 2 motor leads to give RPM. It was surprising that the op-amp was so sensitive, it could detect the current in a short piece of wire.

An input had to be grounded for this to work. Letting the motor leads float above ground only showed 0V. There was a lot of ringing when the motor leads weren't shorted, too.

Relying on the phone app to show voltage & the oscilloscope to show RPM. It had 1 more problem: the speed fluctuated. If it started slow & ramped up, the speed would be higher than if it started fast. Slight variations in wheel pressure also affected speed.

A software program would have to step though the entire PWM range for each voltage to build a table of RPMs. Then, given a target PWM value & target voltage, it could look up a modified PWM value for the real voltage that would give the same power. There are still dreams of measuring the current accurately enough to make constant power feedback.
Posted by Jack Crossfire | Dec 13, 2014 @ 09:33 PM | 3,854 Views

Some video of the 7.4V drive:

8 mile lunchbox drive (3 min 49 sec)

Tamiya Lunchbox run highlights (3 min 58 sec)
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Posted by Jack Crossfire | Dec 13, 2014 @ 01:48 AM | 3,479 Views
So oil prices started plummeting at the same time quantitative easing ended. The media promoted it as a victory for Obama's energy policies & supply catching up to demand, but if that was true, prices would have fallen back in 2008.

More likely, the decline in housing prices that was averted in 2008 by printing money has resumed in a new form. Too few people are making too little money to sustain $100 oil. The government guarantees all mortgages against all losses, so $100 million bungalows can thrive even in a world with no jobs, but it doesn't guarantee oil. Even in Calif*, gas fell below $3 for the 1st time in 10 years despite a doubling in taxes.

So assuming it is the lack of money & not the reincarnation of Einstein you elected, & the government isn't going to subsidize oil prices with another $5 trillion, lots of people in N Dakota, Canadia, & Alaska, are going to lose their jobs. What's going to happen to Tesla when the allure of avoiding those scorching $3 gallons of gas is gone or are people buying Teslas because of something besides the fact that they're electric?

The promise of gas disappearing caused huge investments in lithium production for electric cars & a plummeting in lipo prices. To be clear, Teslas never used lipos. They used traditional, higher capacity ion batteries in metal cans. Still, they did create a lot of speculation in lithium production that benefited everyone. The world reinvented itself for a future without gas, heavily dependent on electricity storage.

The millions of people extracting oil & producing electric cars in a world with plummeting gas prices now look a lot like the millions of people working at webvan in a world with plummeting demand for mail order groceries, 15 years ago, but there wasn't socialism back then. Socialism is a new beast. The government could subsidize Tesla & the gigafactory with $4 or $5 billion. Google could easily buy them out for $50 billion. Technically, $100,000 electric cars can thrive in a world with no jobs & no demand for electric cars.
Posted by Jack Crossfire | Dec 07, 2014 @ 10:56 PM | 2,275 Views

The lunch box finally started moving, after 2 weeks of baby steps between commutes. An extra 2 days were burned in a last ditch effort to get it going on a dspic33. The pickit ended up completely bricked when it tried to update its firmware in a virtual machine. Virtualbox can't emulate USB ports accurately, which probably causes any USB firmware update to fail. Fortunately, the ARM solution took a lot less time to implement.

The servo steering was bang on, with no D term required. Didn't have any stripped gears, despite using the cheapest plastic Tower Hobbies servo. Making it talk to a phone app took an immense amount of code, but proved vital.

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Posted by Jack Crossfire | Dec 04, 2014 @ 10:46 PM | 2,339 Views
Gantry rolled back from Orion (5 min 26 sec)

It's a really important launch, because it's the 1st time a prototype of a vehicle which could someday carry humans is being launched since 2011.

The prototype can't carry humans, has no seats, no instrument panel, & has never been photographed on the inside, but we're told it simulates the requirements of a crewed vehicle, if it's ever funded.

It took 10 years to build this one. There isn't enough money to launch another one for 4 more years. Humans are going to ride Dragon long before Orion ever takes them anywhere.

It's being launched on your favorite rocket, the one you saw in person twice, carrying She Jehovah's payloads. The fact that it takes the largest rocket in the world to launch a tiny capsule shows how much more energy it takes to put a spaceship around the moon than the nominal mission to low Earth orbit. It's been 40 years since such a large rocket for such a small capsule was part of the human experience.

The manned version will be partly made in Europe, by trading investments in the space station from the 1980's for services today for which there was no money. The space station has proven an invaluable bank account for services NASA couldn't possibly afford today.

The rounded cover looked like something from the old west, when it was 1st unveiled 10 years ago. It turned out to not be a stylized artist rendition, but the actual shape.
Posted by Jack Crossfire | Nov 28, 2014 @ 01:54 AM | 2,815 Views
After many years, it finally consumed all the batteries in the apartment, so it was time to fix it.

The label of screw threads was removed forever. It only looked neat, but was never used.

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Posted by Jack Crossfire | Nov 27, 2014 @ 06:47 PM | 3,143 Views
The 3DR current sensor outputs 0.3V for 5A, 0.1V for 2A, 0.05V for 1A. It was designed for much higher current. It's nonlinear, under 5A. After tearing it down while thinking it over, the decision was made to try a home made shunt resistor.

Based on the internet, the target current is 0-5A. A simple power supply exercise reveals a small piece of wire drops 0.027V at 5A. It would need 122x gain to reach full range. Bench power supplies are quite useful for measuring extremely low resistances.

Then, it was decided a full power regulated system would need to sense current, voltage, gyro, & a voltage representing target power. Then it would need a fixed point multiply. None of the G-buggy circuit could be reused. It would need a higher end microcontroller with the full MP lab build system, finally using the pickit that arrived years ago. The era of the home made programmer with gpasm was over.

Then it was decided making it through hole wasn't worth it. A tried & true surface mount ARM would support bluetooth for phone configuration, 400Mhz for the hand controller, & have real floating point power calculations.

The ancient dspic33fj128mc802 may never be used. It's not worth building a through hole board & bringing up yet another build environment.
Posted by Jack Crossfire | Nov 24, 2014 @ 11:49 PM | 2,841 Views
It was decided the trail was too rutted to get any training effect with the home made rover. After months of passively researching the problem, finally did a sort by price on Horizon, yielding the Tamiya Lunch Box, a 30 year old design. It was the largest thing for its price, big enough to navigate the rutted trail.

Tamiya Lunch Box $105
- working motor included
- plenty of room for gear
- endurance over 1 hour with 5Ah 12V battery
- obsolete 1987 design
- needs bearings

The cheapest hobbyking option was the Quanum Vandal.

Quanum Vandal $64
- modern design
- no motor included There is a 3700kV & 2200kV brushless motor in the apartment.
- probably too low to get up curbs
- unknown endurance
- 142x46x24mm battery

$64 for proportional steering was a lot better than 6 months ago, but the deciding factor was of course

Horizon - free shipping + $10 tax
Hobbyking - $52 shipping, cash only + no tax

The cheapest for the largest size was the lunch box, for all its horror stories. The mane horror stories are the inferior plastic bushings & the chassis bending. There wasn't enough money for any more than the very cheapest thing big enough to get over the curbs.

The funny thing about day jobs is when they're gone, you think you'll spend like no tomorrow when they come back. When they come back, you realize why you never spent like no tomorrow before they were gone. Inherit it, steal it, get lucky on kickstarter, or qualify for bigger loans, but no-one makes money from working.

Step 1 is to determine the current draw of the box & PWM range of the stock ESC.

Step 2 is convert the G-Buggy electronics to a power sensing throttle, outputting real PWM signals for the throttle & steering. The voltage regulator needs to be replaced with a shunt resistor calibrated for the current draw.

With the full headlights, it should be a rolling city on the trail.
Posted by Jack Crossfire | Nov 23, 2014 @ 01:43 AM | 3,242 Views
Capturing HDMI video from an iPad 2 is like going back to the world of 1997. The capture cards are hundreds of dollars. They use PCI. When was the last time something used PCI? They use ancient custom FPGA compression chips to output ancient, horrible quality MPEG-2 compression. The cables are a fortune. The 30 pin connector is 2 generations old. There is no Linux support. There are cheaper grey market items on ebay, but the grey market has never actually shipped anything.

The thing is $50 camcorders have been compressing HD video from image sensors for years. They all use the same $1 Ambarella chip to generate high quality x264 compression. It takes parallel data in the same format from an image sensor as an HDMI decoder would generate. You could hack something out of an FPGA to forward data from an HDMI cable to a stock camcorder. The trick would be the soldering.

The leaders of the cheap market are the Timeleak HD72A & Roxio Game Capture HD. Only the Timeleak can capture HDCP protected content but it has no compression. An intriguing device is the Grabbee HD, which compresses to USB. If the grey market item actually arrived, it would have to be used in Windows. Video capture in Linux is something which has risen & fallen, but it's something that would be rarely used. It would only capture 1 game on the iPad.
Posted by Jack Crossfire | Nov 19, 2014 @ 12:37 AM | 3,089 Views
Posted by Jack Crossfire | Nov 16, 2014 @ 03:44 PM | 2,976 Views
Ultramap finally compiled, after a week. The phone no longer showed a static menu button, so it required a layout change, which required recompiling the program. Adb no longer worked with the new phone & required an upgrade, but Eclipse wouldn't upgrade, so a new version of eclipse was required.

Eclipse wasn't catching all the errors in the version change & running it with constant missing class errors. The xmlns:android="" line wasn't compiling anymore but wasn't necessary. The phone version was API 19 but Eclipse was compiling 20. Eclipse needed to install API 19 from Window->Android SDK manager. The API number isn't the same as the 4.4 number & there's no easy way to find out what API correlates to the 4.4 number.

All the files needed to be hand tweeked to say android-19. The AndroidManifest.xml files then needed to say android:targetSdkVersion="19"

Installing Google maps API is a multi step process. You have to download an Eclipse project called Google play services in Window->Android SDK manager, import it as an existing project from the android-sdks/extras directory, & compile it as a library. It has to be linked into your app project, but there are multiple properties dialogs with multiple fields for libraries.

Adding the jar file to Package explorer->Ultramap->properties->project references doesn't work. The entire google play services...Continue Reading
Posted by Jack Crossfire | Nov 15, 2014 @ 04:44 PM | 2,778 Views
The decision was made to convert contact lens agitator #2 to a traditional levitator, since so much work went into it. Would find a cheap thing to hang from it. Instead of reusing the existing electronics, would make a simpler circuit using knowledge gained over 9 years to do a better job. The original circuit had a full H bridge. The new circuit would just pull.

Opening it after 9 years revealed a few critters. It was indeed a steaming pile of dog turd. It was a miracle the original circuit ever worked at all, since it didn't use star grounding, relied on a dog slow LM324, had a lot of unnecessary parts for what seemed to be lowpass filtering. It relied on extreme capacitance to work around the grounding. It was the product of many experiments without an oscilloscope.

The 1st attempt used a MOSFET with full belt & braces snubber diodes. It quickly overheated & destroyed itself. It went back to a tried & true BJT with no snubber diodes.

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Posted by Jack Crossfire | Nov 07, 2014 @ 10:21 PM | 2,976 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 | 3,479 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 | 3,096 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 | 3,913 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.

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