SMALL - espritmodel.com SMALL - Telemetry SMALL - Radio
Jack Crossfire's blog
Archive for September, 2008
Posted by Jack Crossfire | Sep 29, 2008 @ 12:13 PM | 3,208 Views
So crammed $280 of gas consumption into 1 week so now we have only 1 beach & some timelapse movies left. Need some fair weather clouds. Star movies over a few minutes R impossible because we don't have the lens heater to defeat condensation.
Posted by Jack Crossfire | Sep 25, 2008 @ 12:30 AM | 3,274 Views
Combine a 24000 bits/sec uplink with a pile of broken web 2.0 scripts from The Goog & U get hours & hours & hours of waiting & retrying. As expected, the defective Ubunt bunt xlib & gcc have been falling over constantly. Without your own technology, there's nothing but horses down here. A bit crazy that anyone could actually make a living down here & consider the green monster of fields & moss their home. Never found a job down here. Just went to school & left to jobs Francisco like everyone else. It's a green postcard.
Posted by Jack Crossfire | Sep 24, 2008 @ 01:04 AM | 3,460 Views
Got perfectly clear weather at night & such a dark sky it felt like
falling into space. Also, the quest to make a field look like it's worth $700 billion resumes with crazy lighting. It's the same crazy lighting we remembered from 8 years ago.
Posted by Jack Crossfire | Sep 23, 2008 @ 12:48 AM | 3,328 Views
Finally made it to the Fl*rida compound. Spent a lot of your taxes on the mortgage for it. Cell phone internet access is still the measly 48000 bits/sec down & 24000 bits/sec up of GSM way way way way way out here. It's so humid & hot, doubt VicaCopter would have worked. Her voltage regulators, & batteries would have surely exploded.

Fixed wings won't be doing takeoff & landing rolls here. U can't beat the star fields between the permanent clouds. Not...enough...bandwidth...for...photo....captions .
Posted by Jack Crossfire | Sep 20, 2008 @ 01:16 AM | 3,552 Views
until October. Unfortunately, couldn't qualify her for an aerial photography mission in time to order the first $200 of gear & we have a battery shortage, so there will be no Fl*rida shots.

Got the ground based autopilot tested in the gusty wind. Unfortunately the days of daylight are over. Still flying just like the Gumstix autopilot....Continue Reading
Posted by Jack Crossfire | Sep 19, 2008 @ 02:41 PM | 3,390 Views
The 2 tiny thumbnails from Aviation Weekly are the only record we have of the F-117 demolition. Everyone wants the most advanced aerospace technology, but we've got to pay off some mortgages.
Posted by Jack Crossfire | Sep 19, 2008 @ 04:07 AM | 3,405 Views
Following up on HP, NVidia dropped 360 engineers into the dead pool today. Who's next?

NASA wrote:
> The ISEE-3/ICE bit rate was nominally 2048 b/s during the early part of
> the mission and 1024 b/s during the P/Giacobini-Zinner encounter. The
> bit rate then dropped to 512 b/s on 9/12/85, 256 b/s on 5/1/87, 128 b/s
> on 1/24/89, and finally 64 b/s on 12/27/91.

Whew, & U thought your 20 year old 72Mhz transmitter was slow.

Speaking of bloodbaths, USB serial adaptors R going up in price like multi family housing. They're becoming novelties for the rich & famous, subsidized by giant government banking complexes. So could only afford 1 and sacrificed one of our 5V hacks.

The enclosed ground station is a disaster on the grass. Raising XBee & friends on merely a sheet of paper boosts the signal quality to 100%. Signal quality in flight was perfect.

Snagged a spot on flight in dead calm air with manual position control. She really needs tight attitude control, otherwise she gets into nasty circling oscillations.
Posted by Jack Crossfire | Sep 17, 2008 @ 04:45 AM | 3,286 Views
Looks like OQO did an HP.

http://dbmoore.blogspot.com/2008/09/changing-guard.html

People wanted a touch sensitive display instead of a keyboard. A real winner would be a pocket computer strapped to a transmitter.

Technology crashes are defined as 2 consecutive pops in 2 days. Time to start learning how to write teen barbie lottery web 3.0 scripts.

Still don't think people get as excited by pure software as they used to & as much as investors think they do. The Green Tech appeal may not be the greenness at all but the interaction of software & physics. Physical software.

Maybe it dates back to when programming meant having an electrical equivalent to every command. We humans naturally equate physical programming with value. Manipulating abstractions & interfaces doesn't feel as valuable as manipulating energy & mass. Maybe that's why humans aren't going crazy over standards based programming.

Since we can't find a ground station enclosure, U get more EOS excitement instead.
Posted by Jack Crossfire | Sep 16, 2008 @ 03:48 AM | 3,282 Views
HP's (latest) 25,000 mass layoff should get the message across. Jobs which don't have to be done near corporate headquarters can be done in Bangalore, and corporate headquarters are always in Calif*.. We predicted EDS in Dallas would be eliminated & it was. Well, half of them can still move to Bangalore.

Had a successful radio test. 8 hours without a failure.

Time to tabulate the radio settings that work & the radio settings that don't.

Good radio settings:
---------------------------------------
Ground:
115200 bps
40ms beacon interval


Copter:
57600 bps
3.3V - 5V comparator



Failed radio settings:
---------------------------------------
Ground:
115200 bps
21ms beacon interval

Copter:
115200 bps
3.3 - 5V comparator
Copter UART failed.
---------------------------------------
Ground:
57600 bps
40ms beacon interval
Ground XBee failed.

Copter:
57600 bps
3.3 - 5V comparator

Well, 57600 is a draconian reduction in bandwidth but it seems to be required to keep the PIC UART from locking up. The ground station seems to handle 115200. The 3.3V - 5V comparator did nothing. What a disappointment.

The XBee lockup has moved from the UART into the transceiver. Now feels like too many collisions at just the right time may lock it up. Maybe it was designed to wait for ACKs after broadcasting instead of having packets pushed into it.

Even though no-one uses all that mesh networking, their investors keep forcing it on us...Continue Reading
Posted by Jack Crossfire | Sep 15, 2008 @ 02:19 AM | 3,421 Views
So we're down to only testing radio, probably until October. Got a few crashes with the PIC receive even though it was supposed to be resetting the registers. Got a few crashes with the ground station XBee even though it was spacing apart the activity. Looks like reset & permanent configuration are going to be required. Never had this problem with the airborne Xbee.

It seems a number of circumstances may cause an XBee lockup, like using a high powered RF source nearby, using a microwave oven nearby, using the module for many hours, a stray packet coming out simultaneously with a sent packet. The reset pin seems to be the only solution & that means hard flashing the XBees with configuration, not fun.
Posted by Jack Crossfire | Sep 13, 2008 @ 08:06 PM | 3,250 Views
Leave the radio test on overnight & you're going to have a bad day. Looks like the XBees lock up on simultaneous full duplex UART again. All U can do to guarantee the XBees aren't doing 2 things simultaneously is cut out half the ground beacons & half the bandwidth (radio bailout mode).

Digi/Maxstream/??? has a note on full duplex operation.

http://www.digi.com/support/kbase/kb...tl.jsp?id=2037

Which basically means nothing for our problem. You're stuck running drastically below the capability of the $64 because of a firmware bug.

Narrowed down the PIC to suddenly not receiving UART interrupts. Only a corrupt register could cause that. Don't have the budget for a debugger & there's nothing which could corrupt a register.

Looks like the rule is just don't run analog over 120Hz but forget about knowing why. It could also be heating or power supply glitches.

Surprised that the chance of random noise passing a CRC check over many hours is quite high. The chances go up as the packets get smaller.

RADIO=fdf1 522d 0ef2 fcf6 SWITCHES=0000
RADIO=78eb 5d7d 30ec ddf5 SWITCHES=0000
RADIO=f3b4 ff7a 7efe 76df SWITCHES=0000
Posted by Jack Crossfire | Sep 11, 2008 @ 04:28 AM | 3,376 Views
Ground based autopilot has already exceeded the cost of a 400Mhz Gumstix because of mistakes, it's much more complicated, & it has endless bugs. The only good news is none of the extra expenses have actually been used.

A bit of oscilloscoping revealed that a packet timeout of 1 was causing the XBee to split packets. Setting it back to 3 caused the XBee to align packets as intended & the data rate suddenly surged to 100% error free. Still could not increase the frequency of ground beacons.

The oscilloscope also showed the downlink came roughly 1 beacon behind the ground beacons & overlapped ground beacons. Overlapping TX & RX was not crashing the XBee. No idea what crashes the XBee. It's related to fragmented packets, asynchronous I/O, & Uba Acka Bama Racka.

With the IMU packets up to 125Hz & the downlink grinding at 30000 bits/sec, we have a crash somewhere in the aircraft. The XBee still works. The PIC is still alive. Resetting the PIC recovers the downlink.

Also lost all of the 72Mhz feed once.

Next, we have swashplate training & a tiny magnet for solving the washout woes in swashplate training. This aspect is much easier since U can reconfigure the computer without disturbing the machine vision setup.
Posted by Jack Crossfire | Sep 10, 2008 @ 03:12 PM | 3,068 Views
So the LHS had $20 receivers but our attempt at finishing off 72Mhz problems ended in fried diode. That's how to get nothing for the price of a short range XBee. Goog says the diode can be replaced easily, but we're out of time in this commute.

For the cost of those GWS receivers, U can get a short range XBee, use it as a receiever only, & get the same range as an XBee-Pro in a fraction of the space of 72Mhz gear.

After the radio IMU test, no-one doubts it can fly itself. The issue is it's dropping more packets than it should. Once the USB dongles are replaced, we'll have spent more on ground based autopilot than the cost of a 3rd Gumstix.

PICs send a lot of bad bits at 115200 baud, but it turns out full duplex falls over below 115200. Because the XBee UARTs can't send & receive simultaneously, they need more time between beacons to transfer downlink packets.

There are strange interactions between CCPM, UART, timer2, timer3 modules on the PIC. U really only have timer0 & timer1 for user space.

The IMU is sampled at 1680Hz & lowpass filtered. The bandwidth is 1/256. Every 16th sample is sent to the ground for a 105Hz downlink rate.

The downlink rate is currently limited by PIC memory. It can probably do 120Hz. One idea is to send 120Hz & intentionally drop packets on the ground station until the dropped packet rate is always the same regardless of the downlink quality. The issue is timing. You're just filling gaps by copying packets from the wrong time slot.
Posted by Jack Crossfire | Sep 09, 2008 @ 03:48 PM | 3,487 Views
Good news: we're a lot better off than most people who R tied to their ground station.

Bad news: In the latest test, 72Mhz only reached 140ft. Fortunately, the 72Mhz part is the cheapest.

Finished the first full inertial navigation test by 600ft radio link. Amazingly, with all the dropped packets, the gyros didn't drift as much as feared. The dropped gyro contributions are just too small compared to all the other factors to make a huge difference.

Interpolating the gyro amounts to fill in dropped packets degraded the result. There's definitely more drift at 600ft.
Posted by Jack Crossfire | Sep 06, 2008 @ 09:12 PM | 3,157 Views
No-one ever ran an XBee in 2 threads before, we doubted it would work, & it didn't work after all. The XBee UART appears to freeze if U send data while it's sending. Running the XBee in 1 thread & so far it hasn't frozen anymore. Unfortunately U have no way of knowing if the XBee is about to send a stray packet just before U send something.

Like we said, humans R fascinated by sending more data farther. Did try the Airtronics receiver again with the HiTec transmitter & it was horrible. It only got 2000 bits/sec & was pretty unreliable. Maybe it has to be matched with the Airtronics transmitter or maybe the 80's weren't the Jesus decade.

Next, U may be able to get 8000 bits/sec over 72Mhz but it does reduce the range. Knew it in 2006 & rediscovered it again. Fortunately with the modulation routines all using hardware, the bitrate with the 2006 settings is up to 4700.

So today we learned those fixer uppers Northwest North Idaho really were worth $1 million & those ocean front condos in Phoenix really were ocean front condos. Can't wait for the Social Security Mae bailout, & the Barrack Mac bailout.

The funk has changed names again. Now he's Uba 'Ack. Uba 'ack, the ultimate savings & loanama with a free porshama for every cat. Pretty soon he'll figure out how to get it to 1 syllable 4 U lions.
Posted by Jack Crossfire | Sep 05, 2008 @ 02:28 PM | 3,094 Views
On the test range, managed to get receiver lockups every 5 minutes on the ground station XBee. Nailed it down to precisely the receive direction on the ground. Have only a half duplex test, running it in API mode, reducing the frequency of transmits left.

So currently we're using 2 serial ports on the ground station for the 72Mhz & 2.4Ghz channels. Could use 1 serial port & multiplex the 2 channels. That would eliminate a thread & $12 for a serial port.

It would require rebuilding the ground station board yet again & adding another chunk of assembly language for buffering. The PIC goes from $5 to $12. Weight & miniaturization isn't an issue on the ground. Heroine 2200 uses 2 serial ports & we never notice it. Mainly, serial ports are platform independant.

In other news, both our XCite Batteries puffed. They puff in temperatures over 90F & harden in lower temperatures. Thinking of keeping them around for winter use only....Continue Reading