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Archive for June, 2016
Posted by Jack Crossfire | Jun 29, 2016 @ 12:01 AM | 6,177 Views
Finally decided to reduce the Feiyu to the simplest possible circuit: a single P MOSFET feeding an N MOSFET through a single motor winding. This gave the same knee graph, current getting less negative as the N MOSFET duty cycle approached the P MOSFET duty cycle, then stalling at around 870. The stall region occupied more of the curve as the deadband increased.

The only way to see all the voltages involved was compositing multiple 2 channel scope views to make 4 channels. On the unknown Feiyu part, the MOSFETs are inverted so they're off if the gate is 0.

Strange physics (0 min 56 sec)

The time of N turning on is ramped from before P turning on to after P turning off. Reverse current happens when both MOSFETs are off, then breaks down when the N off time hits a certain point after P turning on. For later N on times, the behavior is expected. The length of both N & P at 6V increases because there's no place for the charge to go when both MOSFETS are off. The reverse current didn't happen with a purely resistive load.

Basically, the reverse current is a function of the duration of the current flowing from P to N & breaks down accordingly when the P to N is reduced. When N is on with P off, flux in the motor core is trying to send current from N to P, which only flows when N turns off. This is reluctance cogging.
Posted by Jack Crossfire | Jun 26, 2016 @ 07:55 PM | 5,857 Views
The last experiments with The Feiyu involved feeling the amount of torque as the phase changed. This revealed the torque dropping to 0 & the motor stalling exactly where there was a glitch in the current sensed by the resistors. That was where the current of a phase reversed direction or where the PWM on any of the phases crossed halfway.

The next step was holding 1 phase at a constant PWM while ramping a 2nd phase from 0 to the 1st phase. The 3rd phase was disconnected. This started with strongly negative current through the current sense resistor. The current approached 0 as the 2 phases got closer.

This revealed the same glitch when the variable PWM started approaching the fixed PWM & 0 current. It was more clear that the current approached 0 faster than it should have as the PWM increased, then leveled off until it hit 0.

Tried the 2 phase test with different values of the constant PWM. That varied the point of inflection in the variable current to match where the stationary PWM was.
Posted by Jack Crossfire | Jun 23, 2016 @ 10:17 PM | 5,792 Views
Another bit of video surfaced from USlaunchreport. To someone who works in industrial plants, this kind of piping looks normal, but it's quite outside the normal human experience.

Of mane interest is how they routed propellant to 9 engines in the most efficient way, how they prevented cavitation, & the enormous number of wires heading to where the intake pipe is. That would be where the ground service arm attaches. 1st stage tanks would be filled from the base. 2nd stage tanks would be filled by pipes higher up. All pipes are as short & narrow as possible, yet it still takes a very big pipe of LOX running down the middle of the fuel tank. The pipe would be completely full at liftoff, forming a significant part of the total capacity.

The manufacturing of the manifold would be quite a sight, from above. More likely the top side can only be seen after an explosion, since parts would be added from the fuel tank down.
Posted by Jack Crossfire | Jun 22, 2016 @ 12:02 AM | 6,172 Views

The rumors of Paul Allen's death were greatly exaggerated. Stratolaunch is still around, though over the years they've lost all the partners who could have provided the rocket & slowed construction way down. Now, it's just a platform for carrying a large payload to 30,000ft. It can't fly higher, probably because of pressurization limits. It's shorter than a passenger jet but slightly wider. It's mane difference is being much lighter for its size.

If SpaceX bailed out years ago because of differing opinions, they've definitely bailed out of air launched rockets now. The Falcon 9 can reuse everything up to 5000mph & 224000ft. The stratolaunch can reuse everything up to 500mph & 30,000ft. The laws of physics have made vertically launched rockets cheaper than horizontally launched air breathers. Perhaps atmospheric drag costs more than the benefits of the Bernoulli effect. Orbit requires a lot more speed than lift, so it's more important to get above the atmosphere as fast as possible than get as high as possible with the least power.

Their other problem is no existing launch system can be bolted on the stratolauncher. There isn't enough money to invent a new rocket just for that, even with Janet Yellen hurling free money.

Interestingly, a review of all of the SpaceX stage separations showed higher speed with higher orbit, but lower altitude with higher orbit:

Orbcommmm LEO SUCCESS: 6012km/h 74km
JASON-3 POLAR FAIL: 6147km/h 66.5km
SES-9 GTO FAIL: 8325km/h 64.6km
CRS-8 LEO SUCCESS: 6608km/h 71km
JCSAT-14 GTO SUCCESS: 8355km/h 66.6km
THAICOM 8 GTO SUCCESS: 8343km/h 65.6km
Eutelsat/ABS GTO FAIL: 8361km/h 65.7km
Posted by Jack Crossfire | Jun 19, 2016 @ 06:50 PM | 5,687 Views
He does indeed crash them, even though it's rarely shown in the videos. Instead of attempting repairs, he just buys new ones, brushless gimbal, remote control, electronics, & all. So the navigation is a whole lot better than 10 years ago, with more GPS satellites, accelerometer fusion, fusion of sonar & optical flow, but crashes are still a fact of life. The rumors of bulletproof obstacle detection & weather avoidance are greatly exaggerated.

He never says how often he crashes into people, but he probably has the fine lettering of the law arranged to place liability on his company instead of himself. Everything he buys himself is written off as a business expense, because it all goes to making videos which promote his business.


Posted by Jack Crossfire | Jun 18, 2016 @ 10:20 PM | 5,863 Views
Graphed the 2 current resistors for all phase & got the same nonsensical wave. They should have been sine waves, but looked more like sine waves with humps. From these 2 resistors, it should be possible to derive the current in the 3rd winding, revealing the total current of the motor. The total current should be constant, but the waveforms said otherwise.

Graphed the resistors with no current, but instead of 0, got values near the top of the waveforms. These were virtual grounds, revealing the waveforms were the bottom half of sine waves. They got a little above virtual ground, but quickly broke down.

The mowtimeter showed the MOSFETs providing current in both directions, but the resistors didn't. The resistors only measured current going into ground. Why did they bother with a virtual ground if they only showed the bottom half?
Posted by Jack Crossfire | Jun 17, 2016 @ 11:32 PM | 5,911 Views
Finally found the hackaday nugget about anti cogging algorithms.


Not sure why it was written in the form of a research paper with grants, long after Chinese perfected anticogging in their gimbals. At least, it is very math intensive & if it wasn't published, it would have remaned a Chinese secret forever.

A simple algorithm tabulating phase offsets for each angle did indeed make the motor slightly smoother but not perfect. The hall effect sensor was key to developing the anticogging table. It became clear that anticogging was still a science project, not useful in commercial products. Another key was the motor doesn't have any cogging with no current.

Also, any anti cogging based on the current sensors isn't useful because any closed loop is too slow. The needle pointed back to the electronics rather than the motor being the problem.

At least, it made a graph of phase offset vs angle.
Posted by Jack Crossfire | Jun 15, 2016 @ 03:09 PM | 6,022 Views
It's been 20 years now of watching college students gloat about how they were going to rekindle the interest of young people & women in the space program. 1st, generation Y was going to restart it with myspace. Then Elon Musk had a strict policy of not hiring anyone over 30 & male. Indeed, the people working in aerospace startups these days are all under 30 & a small number are women, examples of rekindled interest at least among people employed in the industry.

The trick is, the people who aren't employed in the industry but read about it are all old & male. There is absolutely no interest among female millenials & male millenials can barely register any knowledge of the space program.

The space program is like classical music, where all the musicians are under 30 but all the audiences are old & dying off. The paying public is once again old timers trying to relive their childhood memories of the Apollo program, but few from a later time have replaced the growing number of empty seats in the audience. All the aerospace conventions are filled with old timers attending & young timers exhibiting.

The young timers would rather go to comic cons, game cons, or mobile app cons, but not real aerospace cons unless they're employees. Some millenials know the existence of a Falcon 9, but they don't know the Falcon 9 has never carried humans, that it routinely launches 2 satellites at a time, or that it's not fully reusable.

The fake test pilot's generation came too early to get into the modern space race. There were no opportunities for a 25 year old in aerospace, in 1999. Instead, our space race was Linux, we wanted to work for Linux startups & make world's fastest web server. By the time the 1st privately funded rockets started going up, we were over 30 & it was generation Y's domain.
Posted by Jack Crossfire | Jun 12, 2016 @ 07:07 PM | 6,194 Views
Musk rounded the internet with another interview. This one was not released in its entirety, on account of Jeff Bezos owning the Washington Post & being his arch enemy. Does Bezos even deliver Musk's amazon prime orders?


Taking him seriously requires assuming Yellen did enact double digit negative interest rates & millenials were dumb enough to think unlimited money was worth something. Well, we've got 1 out of 2 & 1 out of 2 ain't bad.

The hypothetical precursor missions involving sending Dragon 2's to the surface with paying scientific payloads have 1 problem: an experiment stuck inside a capsule is worthless. The experiment would have to climb out of the hatch or the capsule would need a completely different payload door. It would take a capsule completely different from what would carry humans, thus defeating the purpose of using a Dragon 2.

Anyways, Bezos's interviewer leaned more on the Falcon heavy & Dragon capsules being used for the whole Mars architecture rather than a new super rocket. Any colonial transporter would permanently stay in orbit.

Musk himself always insisted the Mars architecture would use a new super rocket. However, the size of the Raptor engine was continually shrunk & now would only be 200,000lbs of thrust.

Considering nothing larger than a basic trim, 5th generation, naturally aspirated, Honda SUV crossover has ever been put on Mars, no methane has...Continue Reading
Posted by Jack Crossfire | Jun 12, 2016 @ 04:45 PM | 5,853 Views
The next logical step was making a PID controller step the motor until it hit a desired hall effect sensor value. The motor position would thus be driven by hall effect sensor values rather than phase, eliminating cogging automatically.

Helas, this was way too slow to be useful in a brushless gimbal & the extra PID controller was another heap of settings to dial in. Once at the desired position, it oscillated very slightly while it hunted for the exact position. It did show promise in using the hall effect sensor to recover from pointing way off, but the tension wasn't as smooth as the stock motor.

It did result in a graph of hall effect sensor value vs phase. Useful for large scale motion, but small scale motion varies based on current.
Posted by Jack Crossfire | Jun 10, 2016 @ 12:07 AM | 6,053 Views
Watching Musk videos, he mentioned how today, there is technological a window for humans to become interplanetary, but the window may close if we don't seize it in the near future rather than wait for NASA's forever delayed schedule.

The rational was there were many times in the past when humans regressed in technology. Egyptians built the pyramids, then humans didn't build anything taller until the Eiffel tower. Egyptions had written language, but forgot how to read it. Romans had road & canal infrastructure, then lost it. Then of course are the well known tales of Greeks & Mayans having advanced technology, then losing it.

How can so many civilizations repeatedly go backwards & could it happen today? You could say the Apollo program was our Egyptian moment, but the technology to repeat it still exists, just not the money.

Perhaps the answer is what the government does when no-one can get jobs anymore. It prints enough money so everyone can get jobs again, without any innovation. The bar has been lowered now for 90 years of economic stimulus packages, from a time when loans were quite dear to a time when loans now pay the borrowers, with no point when the magnitude of innovation after 1 economic stimulus package exceeded a previous point.

It may seem like Facebook was a tremendous advancement over Myspace, but is it only because Snapchat was a lesser advancement over Whatsapp?

To be sure, the fake test pilot is not competitive & without the government would be permanently unemployed by the standards of innovation that existed 40 years ago, but the effect of so many of us not having to improve upon our work to survive must surely lead to a time of reverse innovation. After enough years of reverse innovation, it could become quite hard to read the equations that gave high density lithography, silicon doping, the transistor, the vacuum tube, & so on.
Posted by Jack Crossfire | Jun 06, 2016 @ 10:40 PM | 6,355 Views
Footage of the latest Falcon 9 shows quite a story of bent metal. Grids covering the gas generator exhaust are all warped. The hood panels are a lot less warped than they looked when it was on the barge. Engine insulation is all burned off, where previous rockets had bits of it hanging on. They had new tubes running into the engine compartment, maybe to pressurize the hydraulics when in transit.

Meanwhile, the hangar shows signs of creative housing reminiscent of San Francisco, despite the fact that any attempt to reduce housing prices merely causes the government to artificially raise prices again. The hangar photo shows quite a bit of empty interstage area they recovered. The 1st recovered booster has been cleaned up quite a bit.
Posted by Jack Crossfire | Jun 05, 2016 @ 09:26 PM | 5,937 Views
So driving the motors on The Feiyu with standard stepper motor waveforms didn't work. The motors moved unevenly & appeared to cog, but no amount of current made any difference & the torque was way above cogging. After swapping in a bunch of alternative motors & manually stepping through phases, 1 problem was keeping the pulse register always above 0. When enabling deadband, the 0 value jumps across the deadband. The deadband itself doesn't cut away any other pulse values or change the pulse frequency. It merely compresses all pulse durations except 0 to fit in a shorter time.

The proper way to adjust current is not adjusting the deadband but changing the maximum value of the pulse register.

That made stepper motor unevenness behave more like cogging. There were 2 ways to smooth out the motion: slow down the frequency until the motor made an annoying whine or increase the current until the MOSFETs got too hot. Helas, the MOSFETs got too hot to solve the problem by always increasing current.

An example waveform from the original Feiyu would solve everything, but the original firmware is gone. What is known is the Feiyu dynamically increases current as the motor strays farther from its intended position. It uses the lowest possible current when the motor is in position.

Someone in China was pragmatic about motor cogging not being solvable by higher current or mechanics, so they set about solving it through a complicated orchestration of the hall effect sensor, current sense resistors, IMU, & PWM, all in the name of eliminating cogging using the smallest possible size.
Posted by Jack Crossfire | Jun 04, 2016 @ 10:14 PM | 7,527 Views
Musk says we live in a simulation. A philosopher commenter circulating on the internet says it doesn't matter because whether reality is based on a simulation or fundamental particles of physics makes no difference in the final outcome. Nevertheless, it makes you wonder why anyone tries if nothing we do can happen in baseline reality.

Humans usually try to win Asphalt 8 even though it's not baseline reality, because it's fun. The mortal constraints of reality are a not fun, making it a lot easier for someone who believes in multiverses & simulated reality to do nothing. Musk would say it's ideal to live in a simulation because it's proof life became smart enough to do it. If we weren't in a simulation, life was extinguished before it could pull it off.

The blog suspects we don't live in a simulation because a civilization advanced enough to create a game indiscernible from reality would also be smart enough to realize it's a waste of time or would be smart enough to see it as immoral to torture simulated beings. Would we be 1 of many simulated war games the advanced civilization was trying to win? It makes sense that the multiverse would be not a cosmological property, but the manifestation of many other simulations being run.

The universe probably hasn't been around long enough for a civilization to become that advanced. We may be the most advanced civilization & have yet to create a perfect simulation. Valuations of technology startups are advancing exponentially because of the government, but the actual technology is not advancing as fast as Musk thinks.
Posted by Jack Crossfire | Jun 03, 2016 @ 11:14 PM | 8,096 Views
Quite a difference between the Falcon 9's of JCSAT & Thaisat. The Thaisat booster has divots in the legs where the crush zones are. They might not be divots but bulges because the crush zones would have expanded. The JCSAT booster has panels removed from the engine compartment. The panels are still in places for the Thaisat booster, but out of alignment. It's like some engines got shoved up into the fuel tank by the force of ground effect & combustion instability.

From far away, it's a marvel of alien technology, far beyond normal human experience. Up close, it's a dirty, beat up, soot covered machine with the hood panels of a Model T. Unlike a car, there's nothing but metal in the engine compartments. Hard to imagine a car being made of nothing but metal. Any other material would burn up. The panels allow good access to some of the outer engines, but fixing problems with the center engine is a bitch.

It would have made sense to use carbon fiber landing legs, but the divots reveal they're pure metal. Anything else would burn up from the heat of the engines. An enormous amount of metal mass in landing legs & grid fins was invested in recovery. Some payloads are going to require going without the landing legs & grid fins.

Now some enhanced videos. USLaunchreport is the only 1 providing any significant coverage of the booster recovery.

Falcon 9 lift with 4:1 timelapse & stabilization (4 min 14 sec)

Falcon 9 landing slowed down (1 min 30 sec)

Landing cam 2 slowed down (0 min 27 sec)

Posted by Jack Crossfire | Jun 01, 2016 @ 12:28 PM | 8,697 Views
For all the hype in the last 11 years, SOMA has never been known for the Autonomous Car Startup. Except for 1 other ACS which disappeared years ago, it's always been about the Classic Social Network Startup, which made this interview all the more fascinating.

We go riding with George Hotz and his $1,000 autonomous car (13 min 51 sec)

Once past the usual tired antics of the pitch, he dropped a few nuggets not in any other interview. His algorithm is based manely on machine vision, probably another convnet algorithm. Segments showed a front radar sensor & an external GPS antenna. It failed to detect a car in front of it. It started tracking an exit ramp, requiring him to take over. He claimed it detected a Botts dot lane marking which no other algorithm could track, but more realistically it detected the tire wear.

As usual, it's a very early prototype which can't change lanes. As with personal experience, he's trying to train the algorithm with videos of previous drives. Also matching personal experience, it didn't work at dusk. Either the sky turned white & the road turned black or it couldn't handle the shadows. He didn't say which was the case. He did say it worked at night, showing edge detection was probably 1 of the convnet stages.

Neither is there any information about how well it corrects a vehicle significantly out of the lane. Unless the training set involves a lot of drives off the road & in every possible offset from the lane markings, supervised learning algorithms are manely good at staying in the lane if they're already in the lane but bad at correcting if they go off.

Supervised learning not only requires many videos of driving, but a human must manually enter in where the lanes are. There's still no bulletproof solution to shadows, making any effort in manual training a waste of time.