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Jack Crossfire's blog
Posted by Jack Crossfire | Feb 16, 2014 @ 02:48 AM | 2,445 Views
Posted by Jack Crossfire | Feb 15, 2014 @ 05:51 PM | 2,305 Views

After every attempt to revive it, the phone that ran in 2 Jesus Heroine races was finally replaced by a new copy of the same model & T-Mobile was voted off the island after 8 years. The best theory is salt got somewhere inside the touch screen area & couldn't be removed. It's still the only affordable phone.

There was hope to exchange parts from the new phone & stay on the old plan, but none could be exchanged. The mane board was drastically changed. The new version had nearfield communication & rearranged contacts. Maybe the old LED can be used in a flashlight.

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Posted by Jack Crossfire | Feb 13, 2014 @ 05:48 AM | 2,480 Views
The problem is it has erroneous oscillations above 0.5m, as the bank angle influences the detected movement more. Tried downsampling the readings to 10Hz. That did nothing. Tried throwing out readings of quality 0 like autoquad does. That did nothing.

Time for another stab at the raw data like autoquad does. The PX4flow must not do very good bank cancellation.
Posted by Jack Crossfire | Feb 12, 2014 @ 02:28 AM | 2,744 Views

So the phone returned from LG untouched. They didn't accept payment or try to repair it. None of the damage they reported was there. They probably can't really repair it, but either replace it or make up any excuse they can to do nothing at all.

Tried again to restore it by soaking the touch panel in water. Maybe it would dissolve salt from a gasket that was interfering with the sensor. Then tried scraping salt from the frame. It still didn't work.

This phone is now sold for $100 on Virgin. They have better plans, using the obsolete Sprint network. The obsolete Sprint network is still better than T-Mobile, which offers no data for under $40.

The parts could be used for a repair or the extra $5 could be paid for a Sprint plan. It would not be viable to pay for an unlocking code to stay on T-Mobile. Assuming no design changes, the mane board can be swapped.

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Posted by Jack Crossfire | Feb 11, 2014 @ 05:32 AM | 2,551 Views
Autoquad optical flow demo (2 min 39 sec)

Pretty good & frustrating demo of what the PX4flow can do. The obvious advantages are: large airframe, large propellers, lots of ground detail. Surprised the banking didn't throw off the optical flow. He used a unified kalman filter & did significant processing of the raw optical flow data.

Next, we have him recording a flight by walking around with the aircraft & playing it back. The next step would be copying parts of autoquad. It's probably what arducopter based its kalman filter on.

AUTOQUAD: Waypoint Live Recording V3 (WLR V3) (4 min 41 sec)
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Posted by Jack Crossfire | Feb 10, 2014 @ 02:57 AM | 2,413 Views

Decent pot arrangement. The trick is lots of hot glue & wood. A wheel would be better than a stick for steering.

Another iteration with production wood. Unfortunately, the steering stick has a finite number of gluings. There was no other way to attach it than with a giant blob of glue. The throttle stick wants to angle away from the camera, which would require a heavier piece of wood.

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Posted by Jack Crossfire | Feb 08, 2014 @ 03:02 AM | 5,488 Views

The buck converter was most efficient at 120Hz. It peaked at 9V 2.3A. To make that, it consumed 12V 2A for 82% efficiency.

The nominal use is 7.5V 1.5A. Lacking a real dummy load, it produced 7.5V 1.9A by consuming 12V 1.7A for 70% efficiency. The MOSFET still heated up over 75C. The efficiency was probably overstated because the load resistance was not accurately known.

The dropout voltage at nominal use was 3V. It's a much worse dropout voltage than an LM317. A pair of LM317's with a big heat sink would do the job in much less space. They have a 2.5V dropout voltage & heat to below 50C while providing 8V 1.7A.

A linear regulator would be 62% efficient. The circuit is definitely not the most ideal, probably owing to the MOSFET being extremely slow. The Castle 10A BEC can do a whole lot better in a lot less space, but this is the age of spare parts.

Would consider the lack of efficiency, weight of the inductor, size of the circuit & dropout voltage deal breakers for the buck converter.
Posted by Jack Crossfire | Feb 04, 2014 @ 09:08 PM | 2,671 Views
It's a problem as old as time, we all encountered eventually. Now that the venture capitalists have latched on to wearable computing, it's a problem we have to face, whether or not it's any more solvable.

Today's problem is proportional steering & throttle with 1 hand. It begins by tearing down a picco Z controller for sticks. It would be ideal, since it was rugged & used single axis sticks. There's no chance the 8 year old controller would ever be used again.

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Posted by Jack Crossfire | Feb 03, 2014 @ 10:36 PM | 2,660 Views

It's probably equivalent to where it was in Sep 2013. The rate of rate gyro feedback seems to have stabilized it, slightly. The barometer is disabled, giving it tighter but more twitchy altitude. The buster was a new manual control interface. That brought out a lot of deficiencies that don't come out in a waypoint playback.

After all the work copying the DCM, came to the conclusion that the DCM is worthless, indoors. Consider that the equilibrium is perfectly level, indoors. The only nonzero angles are from IMU drift. If it turns, the DCM is going to swap the roll & pitch angles, when in fact the roll & pitch should be unchanged since they're from drift in the copter frame.

The DCM is best suited for outdoors, where wind causes a real nonzero equilibrium. So everything needed to be reverted to the straight integration, with all the gyro biasing & floating point added to those routines.

For some flights, the IMU doesn't drift. For others, it drifts.
Posted by Jack Crossfire | Jan 31, 2014 @ 02:18 AM | 2,373 Views

It got a new installation of buttons & LEDs. The battery has some cable management which seems to work well. Comparing to the video

PX4Flow micro quad (1 min 16 sec)

from Sep 2013 reveals it's nowhere close to where it was. Not sure why this is. There's still a lot of IMU drift, but it's bearable.
Posted by Jack Crossfire | Jan 29, 2014 @ 09:44 PM | 3,293 Views

The RC car goes to heroic lengths to achieve just bang bang steering.

It doesn't completely stall the motor, despite the motor sucking very high current when at the limit. It uses an ingenious centrifugal clutch.

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Posted by Jack Crossfire | Jan 29, 2014 @ 05:00 PM | 2,535 Views

The Chinese fartbags once again stick it to the poor people of the world. The blog recalls that the LCD wasn't cracked & there certainly wasn't any of the damage listed. The problem was the touch sensor, which wasn't listed, & discoloration of the backlight, which didn't have to be fixed.

Just because the Chinese are the only people in the world who can make phones & the only ones who can invent things, they treat the rest of the world like snot. The Americans get poorer & the rich move on to the stars. That's how humans have always lived.
Posted by Jack Crossfire | Jan 28, 2014 @ 10:07 PM | 2,418 Views

So the PX4flow issue ended up being the UART overflowing. The floating point conversion must have slowed it way down. IMU drift still seems within limits. There are a few more UART routines to optimize for the higher latency, a few more glitch crashes.

After all that floating point rewriting, DCM conversion, & IMU hacking, the result was still pretty bad. Optical flow is still a sloppy method, especially outside the 1m fixed focus of the PX4flow.

It would scream if it had an autofocus based on the altitude data, but there's still no way to make a long macro lens with autofocus down to a price.
Posted by Jack Crossfire | Jan 28, 2014 @ 02:57 AM | 3,388 Views

Getting the video feed on Qgroundcontrol requires disconnecting the PX4flow from all other power sources except USB. Official Linux support for Qgroundcontrol seems to be gone. It's just Mac & Win, unless you want to make your own port.

The PX4flow is indeed broken. The camera works. The altitude readings work. The flow compensated readings are garbage. Moving it around a lot gets useful flow compensated readings to start showing. It reverts to garbage after a certain amount of time below a certain amount of movement.

The gyros would have to be broken, but no mems gyro has ever died. Some of it could be the UART dropping characters. The raw readings are quite erratic around startup & engine arming time.
Posted by Jack Crossfire | Jan 27, 2014 @ 03:32 AM | 2,532 Views

After a full day, the electronics were transferred to a new airframe with new motors & new propellers. The IMU drift, as it was known, was no more. So the motors should be considered gone after 1 crash.

There was 1 phase in the development where it was spontaneously getting thrusted into the floor by 2 motors going to full throttle. That might have done it.

The autopilot is now non functional. The PX4flow might be damaged. There was another reflex to put the sonar on foam, which probably doesn't work, either.
Posted by Jack Crossfire | Jan 26, 2014 @ 05:39 AM | 2,478 Views

After a 2 day process, an outboard IMU was fabricated.

A magic switch was installed to switch the UART between debug & IMU input. The bootloader started in 115200, then the mane firmware switched to 230400 for the IMU. That supported 1050 full readouts per second.

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Posted by Jack Crossfire | Jan 23, 2014 @ 01:59 AM | 2,398 Views

Hard mounting the electronics made all 3 axes drift for the 1st time. So the next strategy was to get as many axes stabilized as possible, then use an offboard gyro for the 1 remaning axis.

Returning to nearly the original battery mounting still resulted in drift in 2 axes. Also tried the hardware lowpass filter setting & increasing the full scale range.

That left going back to a very large offboard IMU in a heavily padded case.

Finally added feedback for the rate of the rate gyros that all the commercial quad copters seem to have. They call rate of rate feedback "stabilization P", while the rate feedback is "stabilization I". The feedback for angle & trim are the "self leveling P & I". A total of 4 terms are required.

It didn't have any obvious impact. The weight of the PX4flow is degrading the flight characteristics.
Posted by Jack Crossfire | Jan 21, 2014 @ 08:40 PM | 3,107 Views
It's quite annoying when everyone else in the world has a Turnigy microquad & yours is the only one with an IMU drift issue.

Decoupling the battery from the electronics caused drift in both directions. The only explanation is the battery was preventing drift in its long axis while not affecting drift in its short axis.

The others hard mount their stock KK board with the heavy LCD on the frame & always have the battery underneath.

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Posted by Jack Crossfire | Jan 20, 2014 @ 11:27 PM | 2,519 Views
The hunt for the IMU drift has been long & fruitless.

There was using higher quality ADXRS gyros, fitted with their own microcontroller.

There was more compliant foam.

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Posted by Jack Crossfire | Jan 20, 2014 @ 08:00 PM | 2,474 Views

A complete home entertainment system for FPV, but with the same old analog NTSC video.

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