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Posted by Jack Crossfire | Jan 09, 2015 @ 10:58 PM | 3,802 Views

As bad as the quality is, compared to what you can download from Australia, there's nothing like seeing it as it appeared over your home.
Posted by Jack Crossfire | Jan 07, 2015 @ 09:53 PM | 3,686 Views
Last year, a car which followed the athlete instead of the path began to emerge as the best solution, but a car in front doesn't know where you're heading, only which way to turn to keep you in frame. This causes it to drive in circles.

Setting the car to follow a desired magnetic heading won't work on its own, because the magnetic heading isn't precise enough. The latest theory is if the car senses both a desired magnetic heading & the direction towards the human, it can stay on the path. This works only if the human is directly behind the car, with decreasing accuracy as the human moves alongside the car.

The car maneuvers so the angle from the human to the car to the desired magnetic heading is 180. The desired magnetic heading is changed from the stick controller to steer the car.

If the desired magnetic heading is off, following it leads the car off the path, but the human stays on the path. As the car heads off the path, the human-car-magnetic heading shrinks & the car turns back towards the path to make it approach 180 again. Wherever the human goes on the path, the car maneuvers to stay in front.

The 2nd case is the human alongside the car. This requires a different algorithm that maintains a fixed distance to the human. If the human gets farther away, the car steers to reduce the distance. This would be much less accurate than following behind the car.

The 3rd case is the human in front of the car. It just needs the...Continue Reading
Posted by Jack Crossfire | Jan 04, 2015 @ 06:43 PM | 3,228 Views

Drove another 8.5 miles with the forward looking webcam. This would be the actual video technology in a path following solution. Had both batteries onboard. The old battery only went 3 miles & the new battery had more than 5.5 miles. Time to send Hobbyking another cash infusion. Also suspect 10min/mile is much less efficient for the current gearing.

Tried driving off a curb, but flipped, snapped off the wide angle lens, & this made the pi crash. Fortunately, it got 8 miles of footage. Forward looking video had much higher compression.

Edge detection showed promise, with gopro footage. Helas, JPEG compression erased too much detail & created too many macroblock lines. Would need to try again with the webcam in uncompressed mode. The wide angle lens was a waste of time for forward vision & created too many reflections.

Original image

...Continue Reading
Posted by Jack Crossfire | Jan 04, 2015 @ 12:17 AM | 3,953 Views

It was time to gather some test footage for a vision based path following algorithm. The only way was a complete setup with the actual camera in the actual position.

Glued a wide angle lens on it & mounted it to get the widest possible field of view.

...Continue Reading
Posted by Jack Crossfire | Dec 29, 2014 @ 09:49 PM | 3,323 Views
It takes about a day to process & upload a video to the goog, so many miles of driving video have now accumulated, all on the same test trail. It's accumulated over 50 miles, since its arrival 1 month ago. To drive an RC car 50 miles, you have to run 50 miles.

9 mile Tamiya drive (4 min 2 sec)

9 mile Tamiya drive. Side looking cam (4 min 39 sec)
...Continue Reading
Posted by Jack Crossfire | Dec 28, 2014 @ 09:36 PM | 3,274 Views

A straight test of RPM vs PWM showed the dreaded stair stepping.

A test of minutes/mile using the most precise, slowest RPM feedback still showed stair stepping above RPM's where it oscillated. So either the Tamiya ESC wasn't precise enough or the mechanics had some voodoo. It's probably a limitation of all ESCs whether brushed or brushless. The next solution was to install the H-bridge from the G-buggy.

...Continue Reading
Posted by Jack Crossfire | Dec 27, 2014 @ 03:19 AM | 3,408 Views
Posted by Jack Crossfire | Dec 25, 2014 @ 10:19 PM | 3,293 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.

...Continue Reading
Posted by Jack Crossfire | Dec 24, 2014 @ 10:27 PM | 3,519 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 | 3,391 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 | 2,606 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.

...Continue Reading
Posted by Jack Crossfire | Dec 14, 2014 @ 07:25 PM | 3,687 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 | 4,503 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 | 3,902 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 | 2,645 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.

...Continue Reading
Posted by Jack Crossfire | Dec 04, 2014 @ 10:46 PM | 2,713 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 | 3,266 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.

...Continue Reading
Posted by Jack Crossfire | Nov 27, 2014 @ 06:47 PM | 3,596 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 | 3,306 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 | 3,732 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.