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Posted by Jack Crossfire | Jun 09, 2008 @ 02:58 AM | 3,804 Views
Because T-Rex blade direction can be reversed & the tail rotor is so problematic, one idea was to make a tandem T-Rex.

2 computer failures in 3 weeks after 1 year with none is too suspicious. With the timing of the 2 crashes, everything points to the Hirose repair on http://www.rcgroups.com/forums/showthread.php?t=851112 .
Posted by Jack Crossfire | Jun 07, 2008 @ 08:52 PM | 3,562 Views
Having met many former aerospace engineers, we have uncovered the standard aerospace career path 4 U.

Aerospace -> unemployment -> Web 1.0 startup -> unemployment -> special effects -> poverty -> computer games -> more poverty -> Web 2.0 startup

Now the news.

http://blog.washingtonpost.com/the-t...d=sec-politics

News flash: someone in the media covered someone other than Ubama & Hill. The answer is McCain would freeze NASA's budget. Ubama would cut it and subsidize preschool entitlements with the money. A lot of people went to preschool and now hope to one day afford a 1 bedroom apartment. Best entitlement ever.

http://dvice.com/archives/2008/06/mo...&cat=undefined
http://www.spaceref.com/news/viewsr.html?pid=28234
http://www.spaceref.com/news/viewpr.html?pid=25594
http://www.onorbit.com/node/273
http://twitter.com/LRO_NASA

Next, we have more concept studies, stylish moon rovers, dot com/NASA relationships, astronauts who tried to climb Mt. Everest, & the next great NASA portal: twitter. Aerospace is a lot easier when U don't actually have to do aerospace. Should have stuck with dot com relationships instead of flying.

Strutless IMU seemed 2 work with the low RPM. Need a few more hours in the wind 2 B sure.

Actually fighting 2 kinds of vibration: high frequency vibration from the tail rotor & low frequency vibration from the mane rotor. Strutless IMU should now have low frequency problems.

Had yet another engine loss in autopilot. Definitely a software crash in the ARM this time. Got major tail wagging long before engine cutoff & no flight recording was written. The tail slowly started losing it, then suddenly entered a spin. Then the engine cut off.

Tail wag would have increased if the ARM crashed, but rate damping would have continued. PWM is programmed to shut down if the ARM crashes, so rate damping would have stopped next & allowed the spin. A partial flight recording would have been written if the ARM was still alive.
Posted by Jack Crossfire | Jun 06, 2008 @ 02:54 AM | 3,603 Views
Flying to Novay on Google flight simulator revealed 2 things. U can't boot a second copy of Google Earth to visualize your heading on a 3D globe & while there are many software globes, the world needs a physical LED globe which can plot latitude, longitude & heading. Google flight simulator is awful otherwise. Need a better flight simulator with a faster plane.

If you've got an army of free Chinese labor & unlimited home equity, U can build this LED monster:

3D LED Cube (三维显示器) (4 min 0 sec)


Well, it's a new world of not being able to test fly, make structural changes, & test fly. Now we get 1 structural change per day. Today's change has no tail struts & more lateral padding.
Posted by Jack Crossfire | Jun 05, 2008 @ 03:29 AM | 3,857 Views
1) Increased accelerometer trust: Doesn't work. Still need 0.001 accelerometer trust to handle any wind with the uBlox.

2) Increased I limit in attitude feedback: Recovers from gyro skew but not until after flying out of control for a minute.

3) Increased RPM: less gyro skew but not elimated. Unfortunately the RCE-BL35X doesn't have fine RPM selection. U get either too fast or too slow with variations depending on starting collective.

So our goal of making the Boeing A160 of Silicon Valley isn't going to happen. Stuck with high RPM & extreme noise because of the MEMS.

The next step is taking GPS acceleration back out of the accelerometer results & increasing accelerometer trust. It goes back to delaying GPS & recomputing the last 0.25 sec.
Posted by Jack Crossfire | Jun 03, 2008 @ 01:31 PM | 2,778 Views
So a T-Rex destroys itself just in 2 hours of normal flying. Port lighting strand failed & needed resoldering. Lighting plug stopped making contact & needed replacement. Slipped O-Ring needed reinstallation.

The answer to the latest roll anomalies is now: math errors & vibration. Discovered a bug in which position error magnitude was added to velocity magnitude to get lead compensation. U cannot add 2 magnitudes to get lead compensation, only vectors.

The idea was to fold lead compensation into the PID constants, but that's not possible. Position feedback doesn't use vectors. It uses magnitudes.

Remember the Jesus monitor?
http://www.rcgroups.com/forums/showt...=jesus+monitor

Well, it now costs $1700, 20% more than we paid for it. Inflation has actually outpaced electronics depreciation. The Jesus monitor was a unique case of raw materials comprising most of the cost, but never thought we'd realize capital gains on a gadget.
Posted by Jack Crossfire | Jun 02, 2008 @ 02:35 PM | 2,890 Views
Well, once again gyro bias was to blame for roll anomalies. The fact that deviations in position were aligned north & west is just because that's where the wind came from & perpendicular to wind was exactly where the tail rotor made the most noise.

Last time it was the accelerometer. This time it was the gyros.

Clearly tail rotor vibration can influence the oscillating masses in all piezo sensors. The effect is only 0.005V but huge in a super precise IMU. Probably have to replace the tail rotor blades & grips, clean the mane blades, grow a mane.

Depending on oscillating masses is a horrible way to determine orientation. IR sensors would add lots of weight. They need either a flybar or another microcontroller + IMU for rate damping.

Wish someone would invest in miniaturizing FOG gyros. These days it's not the limit of technology as much as getting people to invest in the obvious. Just getting someone to sell uBlox 5's mounted in a simple module is like reforming China.
Posted by Jack Crossfire | Jun 01, 2008 @ 02:20 AM | 2,772 Views
Any quest for automated takeoff & landing begins with an absolute altitude test. Recorded altitude for complete flights show more stable altitude than Sirf-III, but still can't detect when it's on the ground.

The takeoff algorithm would be hold horizontal velocity to 0 & vertical velocity to +2m/s until altitude is 10m above the minimum altitude of the session. Landing algorithm would be vertical velocity of -2m/s until engine shutdown. User starts & stops the engine.

So after 1 PIC died, the analog input code got debugged, collective gain was tuned, derivative terms were re-enabled in the PID loops, got another 40 min of flying in.

Happily, both collective & manual climb rate targets seem to be optimum. The uBlox took its first pictures. Unfortunately there was no longer enough light to get proper exposure.

Wind in the wind tunnel was high enough that she didn't have enough tail rotor authority to turn sideways to the wind. The wind screens were at full tension.

Now we have 3 ground views of hovering in the wind, 2 stationary views from the onboard cam in which the tail rotor couldn't overcome wind, 1 commanded dolly in autopilot, & 1 commanded impact into the ground to see if she would stay level.

Wind tunnel cam (2 min 21 sec)
...Continue Reading
Posted by Jack Crossfire | May 30, 2008 @ 03:16 PM | 3,730 Views
U can throw away your barometers, pitot tubes, washout filters, neural networks, sonar & Kalman filters. Just buy a uBlox 5.

Turned off the neural network and got solid hovering in the wind using straight PID feedback. Very fast response to wind gusts. There's no lag on any axis & it's dead accurate.

They're either using carrier phase smoothing or throwing a genetic algorithm at the CA codes. It really was just a matter of waiting for it to get cheaper.

All the missions have been navigation model 6. Altitude in ground effect is still very unstable. Above ground effect it's the most stable we've had. Still has vortex ring state & ballooning in the right conditions.

Sadly, we've probably seen the end of neural networks for navigation & 590 of our 600 Mhz are now wasted. There's still a neural network for cyclic, but with this level of navigation it's not necessary. Aside from autonomous takeoff & landing, the uBlox didn't leave many problems to solve.

VicaCopter under uBlox5 control (2 min 40 sec)
...Continue Reading
Posted by Jack Crossfire | May 29, 2008 @ 08:26 PM | 3,813 Views
uBlox5 is a monster. The latest positioning engines R way ahead of what we had a year ago in terms of latency & velocity readings. May have been a lucky satellite placement, however.

The barometer seems to be a dud. In the wind it detected pressure waves from which no meaningful climb rate could be extracted. Not a problem since the uBlox can beat it.

uBlox 5 is not based on an Atmel chip. Based on the stagnation of the Antaris line, they'll be handing out extra mortgage bailouts in San Jose today....Continue Reading
Posted by Jack Crossfire | May 29, 2008 @ 04:17 AM | 3,423 Views
The uBlox gods were dissapointed with our hand soldered Altoids creation, so they sent down a one of a kind module. PCB & integrated antenna, almost as compact as the EM406. Commute 1: figure out it's set to 38400 baud UBX protocol & not the default.

Neural washed up

The neural washout filter didn't go very well. The problem seems to be this is a recurrent neural network & back propagation doesn't work very well for a recurrent neural network. Time to go back to genetics. We do have the steady state filter processing barometer & GPS in all their unsynchronized glory.
Posted by Jack Crossfire | May 26, 2008 @ 10:26 PM | 3,763 Views
In a daylight expedition to the new test range, it didn't feel very close to the dumpy apartments but it felt a lot closer to the houses than on The Goog. Renters R one thing. Home owers R a different beast. Being $1 million underwater on a mortgage + copter noise = future Baghdad suicide bomber.

To integrate the barometer in the original neural network, would have to modularize the initialization code & have 3 modules, each handling 1-3 axes from an independant navigation source. Not planning on ever doing this.

The neural washout filter is priority 1. The neural washout filter will be trained on the ground. Want to combine all 3 axes in a single module. Even then, it's a complete waste of the 600Mhz CPU. Not an easy move. Maybe that CPU can train a neural PID replacement....Continue Reading
Posted by Jack Crossfire | May 25, 2008 @ 07:47 PM | 3,922 Views
Don't try it unless you've got tons of mortgage bailouts on the way, you really need to prove your manliness, or another EOS 5D is just 2 weeks of rent. Sewing thread works. It has to be clean & dry of course. It won't make the sensor spotless, but it can remove large spots that air alone can't. In exchange, U get a sensor full of lint which air can remove.

Unfortunately we seem to have a tiny chemical spot on the sensor....Continue Reading
Posted by Jack Crossfire | May 25, 2008 @ 04:23 AM | 3,921 Views
With gas now over $4.20, thinking more about ways to use the golf course instead of the park. Anything would have to be silent & invisible.

What we need is a flight box on wheels suitable for rough terrain. It would store a lead acid battery & laptop.

After reviewing GATech's T-Rex videos, have concluded the flight dynamics model probably has more mileage as an alternative to carrier phase GPS. Now playing with 2 ideas but no plan. 1 is to apply the barometer to the existing model.

The other is again shrinking the adaptive part by making more assumptions in the fixed part. The next frontier is the adaptive washout filter.

With the washout filter, angle of attack goes in & velocity change comes out, letting U model short periods of navigation without GPS. It needs a bandwidth & gain which change depending on payload & weather.

The neural network should have automatically developed a washout filter, but it didn't because we solved it the wrong way. To save clockcycles, it didn't take its own output as an input. Training it the right way would require filtering a bunch of past data points for 1 back propagation.

If it uses 30 sec of past data for each back propagation, that's 30*25=750 solutions. If it takes 7500 back propagations to learn how to fly, that's 5,625,000 solutions. If the Gumstix only does 15,000 solutions/sec, that's 6 minutes of flying to learn how to fly.

Definitely could not train a washout filter in flight.

Have our levitation portfolio.

Magnetic levitator compilation (3 min 47 sec)

Posted by Jack Crossfire | May 24, 2008 @ 05:48 AM | 3,830 Views
With 2% interest & tons of government aid, houses in San Francisco R now $10 million. That's enough for 20 suborbital flights counting inflation. The space traveler becomes famous & gets rich on book royalties & promotions. The home ower lives in the united version of Antarctica.

Meanwhile, have decided humans are programmed to obsess & brood, endlessly, over anything that hovers. Maybe some prehistoric ancestor millions of years ago was saved by something that hovered & every male organism since has kept the program to worship hovers.
Posted by Jack Crossfire | May 23, 2008 @ 04:52 AM | 3,862 Views
Magnet UAV Rides again (0 min 44 sec)


That's all we had planned for Magnet UAV. The rest is just getting the heater to heat the solution & maybe force some oscillation. Then it'll sit for a month.
Posted by Jack Crossfire | May 22, 2008 @ 04:18 AM | 3,802 Views
The solution to the PIC reset requirement is an analog circuit to pulse it. Analog computers R great fun. The reset pulse could have been generated by 555 timers of equal complexity, but this reuses our op-amp.
Posted by Jack Crossfire | May 21, 2008 @ 04:24 AM | 3,688 Views
Remembered the magnet UAV crashes any computer near it. Would make a good E bomb if it had any range. Also remembered the PIC needs a manual reset after powering up to work properly.

As for VicaCopter, adding pressure climb rate to the neural network is a buster. Creating training tables where the 2Hz barometer, 1Hz GPS, & 25Hz IMU R aligned is a buster.