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Jack Crossfire's blog
Posted by Jack Crossfire | Oct 08, 2013 @ 06:03 AM | 2,931 Views
So the microphone monitoring crisis evolved into a simple app which shows the microphone level. You can view it during a phone call to know if the microphone is working.

It can optionally feed the microphone to the speaker & add simple reverb. As usual for a JAVA SDK, compatibility with every version of Android on every phone is a hideous mess.

The minimum playback buffer reported is not always a multiple of the recording buffer, which requires recording 2 full buffers before playback can begin, creating an unnecessary delay. Sometimes it can be forced to use a smaller playback buffer than the reported size, but not consistently enough. None of the sizes are powers of 2, but strange numbers like 3712, 7526.

The free ride with Goog now ends at the Play store. It costs $25 initially to upload anything on the Play store. The Goog has so far not required an annual fee. Their history of making paid services free makes one reluctant to pay up.

Every programming job nowadays requires you to have something on the Play store, so it's caused lots & lots & lots of guys to pay the fee & upload millions of apps.

There are many microphone monitoring apps that look a lot better & have a lot more features, but none with useful level meters. Adding some more effects, a useless graphic EQ, & different options for the microphone routing would make it competitive, but it's a road of useless features for popularity.

The world just needs a microphone monitor for verifying the microphone is working. There are also microphone oscilloscopes which would have done the job.
Posted by Jack Crossfire | Oct 07, 2013 @ 07:15 PM | 3,130 Views
Having a self monitoring headset for the phone has been a long running battle. Commercial headsets don't monitor their own microphone.

Another attempt at a self monitoring phone headset failed. The phone's microphone connector appeared to be flaky, so making the headset use bluetooth was the next step.

Bluetooth sound quality was horrible. The absolute lowest samplerate is used. Microphone gain was too low. The stock microphone seemed to have much higher gain. The deal breaker was RF interference from the bluetooth chip coming out of the monitoring amplifier.

...Continue Reading
Posted by Jack Crossfire | Oct 04, 2013 @ 01:14 AM | 3,321 Views
Posted by Jack Crossfire | Oct 03, 2013 @ 01:24 AM | 2,706 Views
Px4flow waypoint navigation 2 (3 min 53 sec)

All fully autonomous flights with just the px4flow, sonar, & barometer determining position. That's probably the most aggressively something has ever flown itself using optical flow. Optical flow has previously just been used for aiding a human pilot in a hover.

With the maximum velocity limited to 0.3m/s, the horizontal navigation starts to scream. 0.25m/s is probably the upper limit for consistent navigation. 0.6 to 1.0m seems to be the useful altitude range.

There was an attempt to use just the gyro for heading. It was slightly better, but still not as consistent as a mast.
Posted by Jack Crossfire | Oct 02, 2013 @ 05:37 AM | 2,946 Views

AeroVironment (AVAV) Cuts Jobs in UAS Segment

Another one bites the dust. With $685,000 in severance packages, it's probably a large section of the company. Once, Aerovironment & Lockheed competed in a micro UAV competition.

AeroVironment/DARPA Nano Hummingbird UAV flying (1 min 45 sec)

Aero created a miniature ornithopter, a mechanical marvel, & won the contest.

...Continue Reading
Posted by Jack Crossfire | Oct 02, 2013 @ 01:49 AM | 3,018 Views

So the PX4flow has a very low top speed. 0.25m/s was the fastest it could move before it stopped detecting movement at all & flew either away or much farther than it was programmed to.

Your luck depends entirely on the type of carpet. Its top speed in the plush apartment carpet seemed to be higher than the finely colored office carpet. Its sweet altitude has been 1m over all carpets.

More Microquad Crashes (0 min 36 sec)

Then, there were issues with the maximum turn rate being real low before it exploded. Suspect the microquad has much better performance than this, but it needs very precise tuning.

The attempt to offset the magnetometer to compensate for motor current failed. The turns were still way off. The only solution is a mast with a 2nd chip, but it wouldn't be crash proof or aligned perfectly after repairs, making it still error prone. The mane problem is the limited velocity for position sensing.

The flight time with the PX4flow weighing it down was slightly better than the Syma X1 at 7 minutes.

...Continue Reading
Posted by Jack Crossfire | Sep 27, 2013 @ 11:48 PM | 3,442 Views
After many weeks of hacking gearboxes, the gearbox which finally had enough torque & hackability was the pololu 25D 75:1 gear motor.

Despite being enclosed, it actually unbolted. The pinion gear was removable without a pinion puller.

...Continue Reading
Posted by Jack Crossfire | Sep 27, 2013 @ 01:38 AM | 3,114 Views

It's every bit as crash prone & fragile as expected. Every day of flying requires a bag of propellers. The propeller mounts tend to break off.

Not sure exactly how to repair the motor mounts. Glue isn't very robust. You can't replace the motor mounts without replacing the entire frame, which takes 1 week to rebuild. They may eventually need plywood doublers. Discovered the propellers can sometimes be bent back into place, after a mild crash.

Microquad Crashes (1 min 1 sec)

A sudden tendency to flip over in normal flight appeared. A motor+ESC was replaced but found not to be the problem. Increasing the I2C speed to support the MS5611 was not the problem. The ESC's were not malfunctioning. The turboPWM wasn't too fast. The autopilot wasn't overflowing or byte wrapping.

The problem was tracked down to the attitude control feedback. The PID limits have to be extremely low, compared to brushed motors. It took recording the PID values & PWM values on the ground to notice at what offset a flip would occur.

Since the microquad was too small to mount on a test stand, the only way was to fly as low as possible, wiggling the cyclic to try to get it to flip, & accepting propeller damage.

The px4flow seemed to do a lousy job separating angular motion from horizontal motion. It uses a lowpass filter to get the gyro centers. It reads only 1 noisy gyro value for each frame. Then it has a complicated set of rules for...Continue Reading
Posted by Jack Crossfire | Sep 26, 2013 @ 09:22 PM | 2,985 Views
3D Robotics Announces $30 Million Series B Financing

Amazing how far the good old quad can go. That's probably the most any UAV startup has ever gotten. When Rotomotion, Adaptive Flight & Neural Robotics were in their prime, they were lucky to get $100,000 in contracts in a year. The Kamen & Procerus buyouts were only in the $5 million range. $30 million is probably more than any hobby store's value.

Jordi isn't nuking his credit cards for parts anymore. Now the trick is staying in the game until their shares vest. So many company founders get booted before their shares vest, the vesting time is specifically designed to get free labor in most cases.

The baby is out of the bag & now in the hands of the corporate managers. That kind of money is going to have to go to higher end products, just as makerbot had to shift to higher end machines. It's hard to see a future without 3D Robotics supporting some military programs.

Like it or not, quad copters are now the big leagues, just like Linux in 1999. You either ride the wave all the way to the top or let DJI take all the money & live in a world of DJI products. In the Linux craze, the key open source developers were compensated nicely with pre-IPO options. The key arducopter & PX4 people should make out well.

To be sure, if I knew where 3D Robotics was going to end up & how much the founders were going to be worth, I would have quit the day job in 2007, gone...Continue Reading
Posted by Jack Crossfire | Sep 24, 2013 @ 09:06 PM | 2,741 Views

The attraction to this gearbox was that it was open, allowing you to disassemble it more easily.

It turned out extremely tiny.

The motor was bolted on, but the gearbox doesn't come apart.

...Continue Reading
Posted by Jack Crossfire | Sep 24, 2013 @ 02:06 AM | 3,383 Views

The jesus barometer goes on.

& gets earplug foam insulation. Earplugs are decent sources of breathable foam.

The temperature compensated MS5611 output

...Continue Reading
Posted by Jack Crossfire | Sep 22, 2013 @ 05:36 AM | 2,719 Views
Bay bridge run (6 min 13 sec)

10 miles of a 21 mile day. The brushless gimbal fell over after 2 hours, making 90 minutes the longest it can go on 5 Ah without destroying the battery.
Posted by Jack Crossfire | Sep 20, 2013 @ 01:13 AM | 2,891 Views
Posted by Jack Crossfire | Sep 19, 2013 @ 05:46 AM | 3,348 Views

Sonar on the micro quad was decidedly worse than the Syma X1. The motors are noisier & there's more airflow. Attempts to move it closer to the center failed. It got stuck at 0.3m. EMI from the power distribution board could be jamming it or it could be unlucky airflow. Foam wasn't rigid enough to keep it pointing down. There is hope office carpet yields better results than apartment carpet.

The MB1240 runs at 20V & the highest you can go without serious electronics is 30V. A dual transducer at 30V might do better.

Then, compass interference from the power distribution board has returned. There is a config parameter which records the mag readings to a file, during a hold down test. That can be graphed & used to set mag offsets in the config file. The hold down test doesn't give the true offsets during a flight, so the numbers need some trial & error scaling.

Only moving the mag far away would completely eliminate the interference. That's not going to happen with the MPU9150.

Finally, the altitude given to the PX4flow is degliched but giving worse results than glichy altitude, so it needs to be tested. The PX4flow does a lousy job subtracting angular movement from translational movement, yielding roll oscillation.

It would probably give better results if the pixel flow was completely processed on the flight computer instead of relying on the PX4flow to convert the flow to meters. The sonar forwarding would go away.
Posted by Jack Crossfire | Sep 17, 2013 @ 10:07 PM | 3,232 Views
Comca$t finally closed the door on getting local channels in the digital format they are aired in. For now on, they'll be encrypted & only available via an official Comca$t box after paying for the digital service. If you don't pay for the digital service, you'll be reverted to the analog low definition quality last seen in 2001.

It's a horrendous regression in service. So many people must already be paying the $100+ for digital service that no-one complained. The good news is there wasn't anything worth watching on TV in years. It might have been amusing to see some of the recent shows or a really important sporting event in HD, but they have no value.

The 3rd party DVR's & home theater PC's keeping Comca$t's CEO out of the $5 billion club have finally been squashed in 1 swift stroke. Your only recourse is to drive within line of sight of sutro tower with a portable recording device.

The goog automatically searches for "BCM7002 datasheet" for you, because so many guys have already tried hacking in. There's no unencrypted transport stream exposed on a pin for you to capture. There's no way to rip off the keys from the chip. It probably does a handshake to ensure your account is paid for, then receives a new key.

The transport stream is probably buffered in the SDRAM. Some crazy Russian could probably extract it with a really fast logic analyzer or SDRAM sniffer.

After all the years of local channels being...Continue Reading
Posted by Jack Crossfire | Sep 17, 2013 @ 04:38 AM | 3,497 Views
PX4Flow micro quad (1 min 16 sec)

Micro quad flies some waypoints, then a position hold test over plush carpet, using a PX4flow modified to use an MB1240 sonar module.

Based on the previous video of the TCM8230 over carpet, the PX4FLOW is a huge improvement. It actually holds position quite well over plush carpet & below 1m. Replacing the MB1043 with an MB1240 & translating the serial protocol from cm to mm is required.

The sonar still has issues above 1m. It glitches to 5m when it can't detect a reflection. Sometimes you want it to send 0 when it reads 5m & sometimes you want it to repeat the previous reading when it reads 5m. It still glitches, despite this algorithm.

It's very heavy, so it handles the wind quite well. Crashes require a lot of repairs & propellers.
Posted by Jack Crossfire | Sep 14, 2013 @ 12:52 AM | 3,009 Views
Heroinesapien walking on carpet (2 min 15 sec)

Eons ago, back when Goo Tube was only 320x240, the NYSE was below 9000, & phones still had keypads, I got a robosapien for $50. It was the 1st "learning toy" of any note. Manually manipulate the arms & legs while recording & it could play back the manual motions with some level of accuracy.

Actually got it to walk around on carpet, way more than its design. It needed fully charged batteries. It under extended the motions because the pots wouldn't completely follow the limbs.

It had a timer which made it record a waypoint after a certain period of not moving. That recorded a lot of wrong positions if you didn't hit the right position on the 1st try. It had a fairly high threshold for being considered stationary, making the training motions ridiculously fast.

These factors made training it a very cumbersome affair. The training was an extremely exaggerated bunch of movements that resembled none of the playback. It ended up pretty boring & tedious, compared to programming movements from a computer. The novelty was supposed to be the fluid, biomorphic movements it could produce during playback, I suppose.

It did look pretty fluid compared to previous toys, but just like graphics in a computer game, the eye candy only went so far before the logic of the game & the ordeal of teaching it by hand took precedence. There are much less visually appealing games which...Continue Reading
Posted by Jack Crossfire | Sep 13, 2013 @ 01:02 AM | 4,671 Views
Posted by Jack Crossfire | Sep 10, 2013 @ 05:02 AM | 3,796 Views
Posted by Jack Crossfire | Sep 08, 2013 @ 11:27 PM | 3,395 Views

It's single sided PC boards, conventionally routed. No 3D printing, laser cutting, or anything else.

...Continue Reading