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Jack Crossfire's blog
Archive for November, 2008
Posted by Jack Crossfire | Nov 30, 2008 @ 01:26 AM | 4,677 Views
2 minute flight times R killing us. It's like flying a rocket. Have enough credit again to upgrade propellers in the next 2 weeks.

Managed to stabilize altitude. It required higher collective limits. Altitude gains have been equal 4 all 3 UAVs. Horizintal velocity gains R identical to the T-Rex. The Corona needed 2.5x more horizontal velocity gain. Suspect it was because the Corona naturally damped horizontal velocities.

This was our first uBlox 5 test with fixed pitch. Fixed pitch rotorcraft give audible cues of collective response & the uBlox 5 is very fast.

Next, U need to align your IMU, magnetometer, & rotors or correct it in software. The result is inability to determine heading & starting lunges in horizontal velocity. Our IMU is off the rotors by a certain amount in pitch....Continue Reading
Posted by Jack Crossfire | Nov 28, 2008 @ 08:02 PM | 4,790 Views
Got the 1st video of the quad rotor flying itself 4 U. Altitude hold is still worthless. May need an MRAC 4 that one. Not enough flight time to do much testing between battery charges. Definitely need more power. This is about as good as the coverage gets when U only have 3 minutes of flight time. Cool the batteries after 3 minutes & U can get another 2 minutes before the quad rotor starts to tilt.

Autonomous quad rotor (1 min 17 sec)
...Continue Reading
Posted by Jack Crossfire | Nov 28, 2008 @ 06:42 AM | 4,711 Views
Now some test flights of 200Hz PWM. 200Hz PWM changed everything.

The stability with 200Hz PWM is freakish. Holy mother of molasses it's stable. It's like flying the Corona again. Full manual mode has returned. With that, the quad rotor was open 4 business.

Sideways lunges went away. Either it was the damping or binding in a motor. The starboard motor seems 2 have a damaged bearing. Got some more life out of it by lubricating it.

The quad did its first reasonable autonomous hover. Take a look at the Goog replay.

Quad rotor's first autonomous hover. (1 min 5 sec)


The hover was 170sec & condensed to 64sec 4 U home gamers. For the first 70sec, we had to command a 2m/s climb rate. Altitude hold doesn't work very well. 170sec was the limit of the battery.

Flight times R still real short. Even if it's balanced, the batteries get flaming hot within 3 minutes. Need better propellers before trying anything longer....Continue Reading
Posted by Jack Crossfire | Nov 27, 2008 @ 06:34 AM | 5,166 Views
Skip Mohatt died on Monday. He died at age 74 from injuries in a car accident. Drive safely.

We were the worst civics student in all history & he was the toughest civics teacher in all history. As far as Calif* civics education was "different" from what the rest of the world was taught, we were a Calif* civics dropout & still are, but Skip had 2 nuggets of information 4 U.

"People become politicians for 1 reason only: power." It's not about change, rescuing the economy, doing good, or making money. It's about power & only power.

The other nugget was "Most of your teachers are now women. In college, most of your professors will be men." That was the first time we ever heard that. Always knew there was something peculiar about gender roles, but this was like the theory of relativity. That was the beginning of the end of our fantasies about marriage.

Would have become obsessed with gender roles eventually, but Skip was really the single point were it began. Every heroine worshipping, heroine robot, heroine galaxy, heroine car, heroine statue, & heroine college, started there.

Now back to the blog.

Got the Suppo ESC's up to 200Hz. That's right kids. 200 Hz. Haven't heard of any castle creations doing that. Maybe a space shuttle main engine can do that. Looks like ESC's, unlike servos, use edge detecting microprocessors at very high clockspeeds. It makes sense because they need a lot more logic than servos to control shutdown modes.

At 200Hz, the quad was very stable on the vertical test stand.

The reason for this is we're getting sporadic sideways lunges in the test flights. Either the radio is dropping packets, the PIC memory is getting corrupted again, or it can't respond to wind. More rate damping is the easiest step.

Good news is the IMU without the Z accelerometer still works. No more IMU glitching in this dumpy apartment. Autopilot is a disaster. The computerized attitude hold doesn't have enough authority to recover from an autopilot malfunction.
Posted by Jack Crossfire | Nov 26, 2008 @ 04:42 AM | 4,670 Views
The answer is yes. The Z axis accelerometer is very problematic. Took a few years, but finally would say the Z axis alone is probably the main point of failure from high vibration. For vehicles which don't fly inverted, U can probably ignore the Z accelerometer & do better.

If the accelerometer shakes enough, it probably goes to maximum in both directions. Lowpass filtered, it probably washes out to 0g.

Unlike normal quad rotors, this quad rotor has so much surface area it actually can glide to a soft landing from a few feet.
Posted by Jack Crossfire | Nov 25, 2008 @ 04:29 AM | 4,905 Views
Well 4 U quad rotor fans, vibration is still as problematic as it was on the unicopters. The quad may vibrate less, but it's so freakishly more unstable than a unicopter, U need higher bandwidth filters. Plus, U need the attitude estimation to work fulltime. There's no manual override if the IMU starts drifting.

Designing a quad rotor from the ground up is like designing a T-Rex from scratch. Holy pile of work. Makes U wonder what those Chinese T-Rex designers consider a mortgage bailout. You're really best off buying finished & proven quad rotor electronics from someone else instead of developing your own.

Now today's discovery.

Suppo ESC's only go up to 2ms on the PWM. Slightly below 2ms, the ESC hits maximum power. If U go higher than 2ms, the ESC limits power to the maximum & shuts down after a certain amount of time, usually in flight. It emits a repeating beep to indicate signal lost & it disarms. Then if U pull back to 1ms it emits a different beep to indicate it's armed again.

The second time it arms, it normalizes idle to 1ms instead of 0.8ms, so U can't balance the quad rotor again until resetting it.

Got the quad rotor up again. Major oscillations resolved. Minor oscillations still there. Manual hover was going smoothly. Seemed 2 B plenty of power, thanks to some software tweeking. Autopilot tests were disasterous. Had some crashes due to the lack of space. For battery #2, had 1 slow heading drift. Then the random nose dives began. Some more crashes & that was it.
Posted by Jack Crossfire | Nov 24, 2008 @ 12:41 AM | 4,744 Views
As another day passes without any flights, it's another delay, another setback. This time, glitches in the IMU readout. The A/D converters were running too fast for the PIC to handle the data + the new rate damping code, so the IMU sampling had to go from 1600Hz to 800Hz. That broke rate damping.

The effect was an A/D interrupt handler getting 2 pins ahead of the A/D buffer handler, accelerometer readouts going into gyro slots, very hard to track down.

Not long ago, dreamed we achieved the wealth & power to own a 9' Steinway, but not the $3 million for the square footage to put it in, so hatched the ingenious strategy of putting it deep in a forest where no-one would hear it.

Sure enough, someone found a piano deep in a forest. Maybe it belonged to someone in the same situation. Maybe a renter who could afford the $3000/month for rent & the $5000 for an accoustic piano, but not the $5 million for a house, faced with the prospect of having his 401k confiscated for the common good, decided now or never & made a forest practice room. Unfortunately, U can't use forests as practice rooms in an age of taxpayers funding $100 million houses, so it was impounded.

http://www.cnn.com/2008/US/11/23/mas...ano/index.html
Posted by Jack Crossfire | Nov 23, 2008 @ 12:06 AM | 4,695 Views
Raytheon Active Kill System (1 min 3 sec)


So this video of a guided missile shooting down another rocket got us thinking, a missile that flies up, turns 90 deg, & flies sideways in a fraction of a second is a super high speed UAV. What else can U do with a super high speed UAV?

Maybe instead of massive vehicles with massive batteries & hour long flight times, U have tiny airborn robots that take off, perform tasks in a fraction of a second & land with just a tiny amount of energy.

Used to wonder if there was a way to launch billions of tiny payloads into space real fast, each payload consisting of maybe a fraction of a gram of raw materials & launched using lasers or some super cheap vehicle. Then these billions of tiny payloads would self assemble in space to form massive structures.

What if U could put a small rocket in a handheld launcher & make it fly out 1m, reverse direction & fly back real fast. Maybe U could make it fly out & back hundreds of times in a second. Every time it flew back to the launcher it would recharge. A perpetual 1m linear orbiting rocket guided by a handheld launcher. U could aim the handheld launcher & the rocket's 1m linear orbit would always point where U aimed it.

Maybe instead of a rocket, it was a mirror with some mode of propulsion & U beamed a high powered laser at it to make a laser saber that was bounded by the rapidly oscillating, flying mirror. Not as clumsy or random as...Continue Reading
Posted by Jack Crossfire | Nov 22, 2008 @ 03:57 AM | 4,853 Views
The quad rotor bailout isn't working. Time for drastic measures. Got to elect a quad rotor despot & implement more regulation on the PIC. We're going to need to nationalize not just all the subprime aircraft, but the prime aircraft too. That's right. All your functioning aircraft now belong to Jack Crossfire, to rescue the broken aircraft. Give em up.

Some photos of Oakland telescopes seem to have missed the Jack Crossfire show, so U still get some content, this time....Continue Reading
Posted by Jack Crossfire | Nov 20, 2008 @ 04:36 AM | 4,921 Views
The quad rotor finally got in the air. Not enough power to control altitude. Cyclic oscillation in the dumpy apartment is the same as in the air. A few seconds in the air with that oscillation & the IMU drifts too much, U start going sideways faster & faster out of control, flip, & engine shutdown. Looks like better propellers R a start.

Higher cyclic gains may reduce oscillations, but these R prone to flipping without more kludges.

Quad tests (0 min 56 sec)

Posted by Jack Crossfire | Nov 19, 2008 @ 03:14 AM | 4,524 Views
Depressed over the quad crisis, it's time to worship The GOOG.

It's time to look over The GOOG's Time Warner photo archive & compare great depression #1 with great depression #2. Mainly the family living in poverty. After photographing our dumpy apartment, in our age of endless propaganda about government safety nets, total regulation & centralization, was surprised to find the typical apartment of the modern 50 hour/week programmer looks exactly like the poverty stricken apartment of the 30's.

U know you're taxed at 70% when U work, under Oooobs consisting of 30% marginal taxes, 20% FICA, 13% sales tax, 1% property tax, assorted infrastructure taxes, & "recycling fees" on everything U buy.

During the unemployed times, & U R going to have a lot of unemployed times, you have no savings. Your purchasing power is provided by unemployment insurance & other government programs. The property, sales, infrastructure, & recycling taxes on those purchases may come out of entitlements, but they easily exceed the 30% of your income U had left during employment, so the total tax you're paying during your lifetime is over 100% of what U earned. U pay over 100% of your income in taxes.

Unlike depression #1, there R no private war chests to start businesses & hire people. That money, over 100% of your income, has been paid into government programs to eliminate the need to start businesses & hire people.

Now what do U do when U can't get yaw damping to work? U bring back the vertical test stand. Most people use lazy susans to test yaw damping, but we only have enough room for a single piece of aluminum which can be reused for a vertical test stand & wind screen. U know the wind screen.

Quad rotor vs. vertical test stand (1 min 31 sec)


Notice heading in the video is fixed except when commanded by the pilot. Cyclic damping is still in crisis.
Posted by Jack Crossfire | Nov 18, 2008 @ 04:30 AM | 4,688 Views
Now that we're not flopping anymore, can see the quad is still capable of nasty vibration. Propeller balancers will be in attendance.

Decided to forget about manual cyclic & begin implementing a full time orientation hold & switchable position hold on top of that. That is a buster to get all 3 modes to coexist simultaneously for quad rotor & single rotor craft.

With enough software functioning between commutes, test flight #2 was still disasterous. Cyclic rate damping is good enough for the computer to hold the attitude, but still not for a human. There is no yaw authority. Yaw damping is ineffective & it takes very large deflections for the computer to try to hold a heading, which it never quite does before 1 of the 2 motor pairs stops.
Posted by Jack Crossfire | Nov 16, 2008 @ 06:18 AM | 4,737 Views
Looks like all quad rotors have to overclock their PWM way above the usual 50Hz. Mikrocopter uses I2C to get still higher update rates. The answer is yes. Suppo/Super Simple ESC's can do 100Hz, but it requires shrinking the resolution. The standard resolution only goes to 60Hz.

Nonlinear feedback curves, lighter propellers, higher gyro bandwidth, & higher frequency PWM has all contributed a bit to stability. It's never going to be as stable as an articulated rotor.

In today's video, U can see the rate is damped enough for a human to hold the angle, but the stick response is prone to violent rotation.

Quad rotor rate damping 2 (1 min 35 sec)


Forget about having enough money for any new parts in November. The Suppos R what U get.
Posted by Jack Crossfire | Nov 14, 2008 @ 02:50 AM | 5,005 Views
Well, Microdrones raised the bar with an 8.5lb quad rotor capable of 50 minute flights on battery power. Dual redundant IMU's & flight computers. Must figure out how Germans got so loaded compared to US.

Anyways, back to bailing out SUV manufacturers.

Decided blogs based on user content R really boring now because no-one's buying anything but T bills, so here R some rate damping efforts. Unfortunately, Goo Tube audio synchronization doesn't convey the relation between movement & throttle changes & sure enough, Goog stock is only $300.

Quad rotor rate damping (2 min 35 sec)


See. No rate damping at all. Disappointed to find the "New 1000mm Quad Copter Design" was using Turnigy ESC's at only double the price, not the 10x price U would expect for the ESC to be the problem. The next step is really full time attitude hold. Everyone uses full time attitude hold. Disable lowpass filtering completely & U start to get some rate damping but it's very erratic.

Also, these props R 72% heavier than successful quad rotor props. Haven't sold the T-Rex yet.
Posted by Jack Crossfire | Nov 13, 2008 @ 04:29 AM | 4,750 Views
That didn't go so well. Throttle control isn't fast enough for rate damping to work at all. It's a complete, unflyable, quad disaster. The Suppo ESC's either don't have the response time or don't have enough throttle steps. That's what U get for being sucked into super low prices.

There's much less vibration in the quadrotor than the unirotor. With virtually no noise in the IMU, U don't have the drift anomalies that plagued us & U can probably use the accelerometer for some velocity estimation.

Not surprising that with all these advantages, Mikrocopter has solved most of the problems of autonomous VTOL in the last year & you'd now be hard pressed to bother with all we did when U can just buy a Mikrocopter. They're hauling in some serious dough with those parts.

Mikrocopter does it all on an 8 bit Atmel. It needs no Kalman filters, quaternions, ground based computing, crazy communication schemes, neural networks, or anything. Just straight gyro integration on all 3 axes, using integer math. Unfortunately the source code is in German & it depends on some crazy fixed point optimizations, so your hacking mileage may vary.

If the dynamic forces are low enough, a very high accelerometer blend & slow yaw rate can eliminate the need for a quaternion attitude estimate. High wind still might give U problems. Suspect quaternions & Kalmans will come to Mikrocopter soon enough, which is the biggest reason to still bother with VicaCopter:...Continue Reading
Posted by Jack Crossfire | Nov 12, 2008 @ 07:02 PM | 4,011 Views
When spare parts for our Corona dried up, it seemed Lite Machines was gone. They shifted completely to an extremely painful suppository shaped VTOL device that seemed doomed.

The biggest problem was the requirement for hand launches & landings. For years, no-one was willing to reach into the whirling mass of blades to grab it, but thanks to some recent bank layoffs, that's not a problem anymore & now the mighty Lite Machine VTOL lives.

Lite Machines' Voyeur VTOL UAV - the real thing (1 min 2 sec)

Posted by Jack Crossfire | Nov 12, 2008 @ 03:47 AM | 4,084 Views
PIC debugging complete. There was a bug where DAMPING_SIGN variables interfered with analog readings, but just moved the DAMPING_SIGN variables somewhere else & it started working. Maybe it'll explode over some yellowjackets.

IMU calibration complete. Throttle range calibrated. Rate damping & control directions tested. Engine cutoff & failure testing complete. Threadlocking applied. Ny-ties tied. LED's lighting. Went back to engine cutoff switch + throttle stick since there isn't enough off margin when the transmitter is on & the rate damping is active. Now those propellers R really off when they're off. Running out of things to do without flying.
Posted by Jack Crossfire | Nov 10, 2008 @ 02:49 AM | 4,447 Views
The answer is yes. There is now a yellowjacket hive behind the dumpy apartment complex. If U go there to photograph or fly, you'll be stung over 10 times by a swarm, mainly in the head & have excruciating pain for the next 6 hours, followed by bearable pain. You'll need to run back to the nearest water supply as fast as possible & spray yourself in freezing weather to try to get rid of the monsters.

Still had enough unaffected skin after the attack & extreme pain to finish the quad assembly. Engine testing is already disasterous. Propellers spin up randomly from gyro noise. Prop savers break. Nuts & washers R falling from the fuselage.

Quad rotors R real dangerous. Unirotors don't have any starting torque. Quad rotors can go from 0 to full RPM instantly. Battery connector is too close to the rotors....Continue Reading
Posted by Jack Crossfire | Nov 08, 2008 @ 07:24 AM | 4,285 Views
Getting the quad rotor powered up is going to take another week. Going to 4 engines makes things very complicated & unreasonable. It's a matter of commuting back & forth every 2 hours, learning as much as possible between commutes, getting a missing part or tool down in the valley. We have 1 defective prop saver.

To test the rate damping, need to unplug all but 1 of the motors & wiggle it bare handed with the propeller spinning. IMU mounting isn't going as well as planned either. The total cost is heading more into the $250's than the $132 envisioned....Continue Reading
Posted by Jack Crossfire | Nov 06, 2008 @ 04:23 AM | 4,312 Views
the quad rotor.

Motor mount & mockup #2 was sturdier but not perfect. Final assembly will be foam tape intensive. The plywood fuselage is soft indeed. Time to fabricate this: 4 hours & it's back in the car & back to Silicon Valley.