Telemetry Radio
Jack Crossfire's blog
Posted by Jack Crossfire | Jan 04, 2008 @ 03:43 AM | 2,437 Views
Hopefully rchover will do a better job than helihobby. While lying awake for 6 hours in bed due to copter withdrawal, thought up some more inertial navigation ideas.

Notice in every professional UAV video how solid the tail is. The tail on the Corona, like the Trex the way we're going to fly it, was real loose. That probably destroyed the navigation quaternion.

In fact, combining big gyro drift + big wobble probably makes quaternions fall over, so now we're integrating the gyros directly on their axes. Many fixed wing autopilots are very successful like this.

With our favorite telemetry, it seems to cut drift. Least squares estimation is also showing signs of life.

Next, there's subtracting GPS velocity straight out of Euler angles. Most of the time, U can see the pitch angle try to jump back in line for every GPS update.

More of your favorite telemetry (0 min 59 sec)

This is not chromakeyed anymore. The HUD & aerial video are stacked in Java. So far Java really sux at video textures.
Posted by Jack Crossfire | Jan 03, 2008 @ 01:50 PM | 1,955 Views
30min flight time

logo 10
20min flight time
1150 mm rotor diameter
500 mm blades

logo 500
7 min flight time using 22.2V 5Ah
1150 mm rotor diameter
500mm blades

Looks flimsier than the Trex but longer flight time.
18min of flying on 14V 4.2Ah
950mm rotor diameter

9min flight time on 18V 3.2Ah
425mm blades
970mm rotor diameter

trex 450
18 min flight time using 11.1V 2.1Ah 2000rpm

So without the Corona, flight times R 2 short. The only way to do it now is the Saudi Arabian juice.

Can't afford a 500 size anymore.

The boss ate our paychecks to pay off his mortgage.

It's cheaper to make lighter electronics than buy bigger batteries.

The 450 has 98% of the Corona's blade size.

Don't anticipate increased value from long flights for another year.

We fly just about every day. Whatever comes now is going to desintegrate in a year.

In any case, the Waypoint Mode switch must become Engine Mode. Engine cutoff & spool up to flight speed. The flight computer needs CCPM mixing & a 5th servo header.
Posted by Jack Crossfire | Jan 02, 2008 @ 05:15 PM | 2,086 Views
Well, it's probably going to be the Trex 500. The Trex 500 was very popular last November on social networks but sold nowhere. Then it suddenly disappeared.

The 500 is probably the largest U can fly in Calif* without paying big bucks and driving 300 miles. The extra space for the TRex 600's is needed for the illegal immigrants.

A Trex 450 would require drastically reduced electronics weight, would definitely not move an HD cam, but would be the most convenient.
Posted by Jack Crossfire | Jan 02, 2008 @ 03:18 AM | 2,454 Views
Well, we're probably not going to spend any more time on HD video from space, but we will have a 7.2oz still camera to mount. With the autopilot, it's 14.7oz of payload. The Trex 450 may not have enough power to do the job even though it uses the same motor & battery as the Corona.

The Trex 500 has 4x the battery cost. In 2006 the 22.2V 4Ah battery was $170. In 2007 it was $230. Guess what it's going to be in 2008. trex 450SE CF + motor + ESC for $230

Autopilot weight:

Payloads of different copters:

What's probably going to happen is we're going to have a fixed wing UAV & a rotor wing UAV eventually. Fixed wings can take U far and high from the ground station for long periods of time, but they require special programming to handle constant turning. Copters can get U stationary timelapse movies near the ground station, but they require special programming.
Posted by Jack Crossfire | Jan 01, 2008 @ 09:10 PM | 2,500 Views
Discovered the tail rotor hub was cracked, the hard way. That explains the recent yaw control losses. Unfortunately this part is no longer available.

So it's time for a new airframe. The Corona was the last copter which could fly for 30 minutes on a battery charge but it paid for it in maneuverability. Economics dictate shorter flight times and better maneuverability in the new copters.

Looks like U can choose either short flight time + less stability on a Trex 450 or extremely short flight time + better stability on a Trex 600.
Posted by Jack Crossfire | Jan 01, 2008 @ 04:23 AM | 1,948 Views
Simulated the XMas flight recording again with the 14 state Kalman filter just for a sanity check. The Kalman didn't do much better than the algebraic methods even though it probably did slightly better. That flight recording contains a lot of horizontal acceleration.

HUD + video + Kalman filter (0 min 58 sec)

Eventually made an algorithm where the least squares approximation of recent drift rate was subtracted out of the latest gyro rates. Couldn't get the yaw drift to work but there wasn't any huge advantage with that method either way. Simplicity still seems golden.

There's probably a tradeoff between a larger copter or DGPS.

Now a summary of 2007.

2007 was pretty rough. Food got 50% more expensive. Rent got 10% more expensive. Electronic parts got 25% more expensive. Fell in love again. Lost 401k, vacation benefits, and 10% of our income. Copter autopilot wasn't as easy as expected. Our cash lost all of its value as far as mortgages are concerned. No good songs came out. No new HDTV movies were on broadcast TV.

The worst seems to be less and less new stuff. There's less original artwork, less original music, less original technology, but more copies of it.
Posted by Jack Crossfire | Dec 31, 2007 @ 02:47 AM | 2,617 Views
So the next best thing to a Kalman filter is a least squares approximation of all IMU results. Instead of averaging 99 gyro steps + 1 accel result, you feed 99 gyro steps and 1 accelerometer result to the least squares equation and it spits out the best estimate of the true current state.

BTW, Gumstix showed the 600Mhz board in stock for the first time since it went on sale a year ago.
Posted by Jack Crossfire | Dec 29, 2007 @ 08:01 PM | 2,822 Views
> light rain...rain....rain...very
> wet pattern from Thursday through Sunday
> with progressively wetter systems...
> hazardous weather outlook...

Have new techniques to waterproof Vicacopter using painter's drop cloth.

Video AHRS tests gave 2 conclusions:

Need more clockcycles to run a 14 state Kalman filter or need a better AHRS algorithm to use the existing clockcycles.

Need a better camera to get higher framerates.

Suspect the 14 state Kalman filter worked better than the 7 state because it accumulated history in the velocity stores. Another idea is to predict future drift from historic data.

One other thing. Amazon's touch pad finally died so a new laptop is back on the budget.

Now a word from our sponsor.

When Earth is not enough. (0 min 50 sec)

Posted by Jack Crossfire | Dec 28, 2007 @ 12:05 PM | 2,706 Views
Simulated another flight recording with HUD, video, & moving map. The idea is to find any evidence of GPS lag. Looks like the Aiptek does 8fps in HQ mode and 4.25 in low quality mode. The AHRS is still pretty awful. This was the uBlox, dynamic model 6, 1Hz.

HUD + video + moving map (0 min 58 sec)

Posted by Jack Crossfire | Dec 27, 2007 @ 06:29 PM | 2,687 Views
Finally have a way to plot flight recordings on a moving map. The uBlox autopilot tests are replayed. This was dynamic model 6, 4Hz. Underdamped oscillation clearly visible. Can't verify the GPS accuracy although it seems to lag too much for 4Hz to be useful. Time is compressed 3x.

Autopilot test on moving map (0 min 39 sec)

And this was dynamic model 5, 1Hz. Time is compressed 5x.

...Continue Reading
Posted by Jack Crossfire | Dec 26, 2007 @ 12:50 PM | 3,206 Views
2 Pedestrian - same as 3 Automotive

5 Airborn(e) <1g acceleration - increased delay

The answer is no. The dynamic model settings didn't do much except maybe add delay. The goal with the uBlox was to increase wind resistance but everything besides DGPS is still gravy. So we fought the uBlox for 1 month. 4Hz wasn't really there without DGPS. Don't want to devote that huge amount of space and weight to something which doesn't make much difference.

Well the video overlay HUD showed a serious influence of acceleration on AHRS and it leads back to better GPS to take it out.
Posted by Jack Crossfire | Dec 25, 2007 @ 10:24 PM | 2,989 Views
On the first sunny XMas in many years, finally got HUD overlays from the flight recordings. With every flight parameter + video stored on flash, we can simulate a ground station in the dumpy apartment.

It's a painstaking process, rendering the HUD & synchronizing it to the video. Just needs a few hours to capture the OpenGL output over AGP. Times like these make U wish U just wrote it in C using software graphics + YUV overlay. Overlaying on video this way is very fast. May never draw 3D graphics or run this in Windows.

HUD & video for XMas (1 min 39 sec)

Can finally see how bad the AHRS is.

Going through each uBlox model 1 battery at a time.

1 Stationary - no velocity readings
3 Automotive - noisy data
6 Airborne with <2g Acceleration - longer delay
Posted by Jack Crossfire | Dec 25, 2007 @ 05:51 AM | 3,390 Views
* 1 Stationary
* 2 Pedestrian
* 3 Automotive
* 4 Sea
* 5 Airborne with <1g Acceleration
* 6 Airborne with <2g Acceleration
* 7 Airborne with <4g Acceleration

It defaulted to "Automotive", so now we put it on "Airborne with <2g Acceleration". The logic seems to be more lowpass filtering the higher U go. Suspect the most sensitive model is "stationary" and the least sensitive model is "Airborne with <4g Acceleration".

Either way, high wind & rain will keep away meaningful tests for the rest of the year.

Got some good news. The bogus climb rates from the uBlox were actually a bug in the simulator. It was reading heading as climb rate, hence the range of -3.14 - 3.14. Also, the uBlox is randomly ignoring configuration lines, so it often generates garbage NMEA sentences. Climb rate is now in the meaningful range, if not actually useful.

XBee is paying off in this wind. Had 1 save which wouldn't have been possible on 72Mhz.

Well, got our first autonomous video from the Aiptek. Besides tons of manual altitude nudges, it actually maintained horizontal control in 5mph wind. The uBlox definitely has less delay.

Got 100 lousy seconds of video. Only hand stabilized 35 seconds for the viewers at home. The rolling shutter was in attendance.

Aiptek video in auto hover (0 min 36 sec)

Need a tiny camera with a real fast, manual shutter speed + full frame shutter. Next year's cameras R going to be 20% more expensive than last year's.
Posted by Jack Crossfire | Dec 24, 2007 @ 03:58 AM | 3,112 Views
Well, if U plot acceleration vs. attitude U don't get any correlation. The secret is still locked up in the neural network.

After more test flights in cyclic -> attitude mode, it looks like 4Hz without DGPS doesn't buy much. Attitude hold is also sensitive to wind. If 4Hz doesn't come through, we're dropping a few grams and going back to the EM406.

Cyclic -> attitude mode with hard coded angles is so stable it's tempting to just live on that. Can fly through trees in ways no IR stabilizer ever dreamed of.

The search for GPS noise continues. Put the antenna out from under the blades to measure blade interference. Put her on the ground and cycled the throttle from 0 to light on the skids to measure vibration effects. Got no obvious interference.

One thing is 4 sure. There are no blogs discussing DGPS experiences. Maybe Web 3.0. Have 1 more scenario with 4Hz before it's time to think about DGPS.

The latest batteries are now down to 13min of flying. The first batch was retired when it hit 8 minutes of flying. As recently as the current batch was doing 20 min.
Posted by Jack Crossfire | Dec 23, 2007 @ 04:46 PM | 2,828 Views
Have an F35 engine. Pratt 'n Whitney didn't release hi res versions of the most recent test firing although they have an older test firing.
Posted by Jack Crossfire | Dec 22, 2007 @ 05:15 AM | 2,725 Views
Lowpassing the GPS readings revealed a neat thing. Feeding the lowpassed velocity into the neural network gives back roughly the unfiltered velocity. So we have 25% bandwidth climb rate directly controlling throttle and 100% bandwidth ground speed + the neural network controlling cyclic.

So with the lowpassed climb rate, got better horizontal results but no altitude hold.

To that end, we're now pushing for another step down in neural network load. This should lead to a hard coded networks for attitude -> acceleration and acceleration -> attitude. Then, a realtime calculation of neutral attitude should be possible by feeding in current acceleration.
Posted by Jack Crossfire | Dec 21, 2007 @ 03:19 AM | 2,818 Views
Well, had enough pullback in the rain to resume test flights. Time to run the Rotomotion PID controller + uBlox scenario. This controller applies position error, integrated position error, and absolute velocity directly to attitude. As with the EM406, it was not even close to the Vicacopter PID controller. Suspect it could be tuned, but the Vicacopter PID controller would always be more stable.

The Vicacopter controller applies position error to target velocity. Then it applies velocity error to attitude.

This time the climb rate was out of control in the same spot it seemed stable on 12/16. It looks like altitude is the first to go back to 1Hz. Whether or not accuracy is to blame, there's a simple matter of throttle not being fast enough to keep up with GPS updates without causing yaw. Sudden yaw throws off horizontal control. That leaves only $133 of the uBlox's $200 tag intact.

The uBlox seems to be an EB85 of another kind. More and more it seems anything above 1Hz is going to require DGPS to give reasonable accuracy. The pros all use >1Hz GPS but they also use DGPS.

Stepped up the XBee telemetry rate yet again by reducing accuracy. The test video is still from the lousy pencam. Obviously the pencam is a bit tilted and we have a few radio dropouts.

Video overlay HUD #2 (1 min 15 sec)

Posted by Jack Crossfire | Dec 19, 2007 @ 05:23 AM | 2,782 Views
So after the sessions with straight PID feedback & GPS devestated AHRS, put the neural network back in the loop. With the neural network providing only a 1/4sec prediction and the increased cyclic gain, got good hovers pointing North. Pointing anywhere else was impossible.

The increased cyclic gain was the key to higher GPS speeds. The feedback rate & the GPS update rate have to resonate like a tuning fork. Of particular note, 4Hz climb rate on the uBlox is coming out pretty worthless. Climb rate probably has to be stepped down to 1Hz. Climb rate didn't have a problem on 12/15, making the different parts of the test range suspect.

Unfortunately lost the Gumstix flash again. It would not boot.
Posted by Jack Crossfire | Dec 18, 2007 @ 03:23 AM | 3,066 Views
Well, we have simulations with and without GPS assisted attitude calculations. The trick with this is GPS is delayed & prone to glitches. U have to dilute the GPS corrections over many output samples and delay the accelerometer readings.

The accelerometer reading corrected with GPS is blended with the gyro readings. We do not apply GPS corrections directly to gyros.

The corrected acceleration never hits magnitude 9.81 like it's supposed to.

The GPS corrections gave more accurate but seriously delayed gyro results. Finding the less inputs U put into the attitude, the faster and less accurate the result. The more inputs U put in, the slower and more accurate the result.

Should reduce blade pitch one of these days. Raised it to lift HD cameras, but it made wind very hard for even humans.


30" monitor: $1400
900Mhz video set: $200
Laptop: $600
Laptop video capture: $150
HD cam: $660

Have over $100 invested in worthless SD cards. The Canon A450 seems the most practical way to recover that investment with less crash risk. Still having post budget stress syndrome from the Canon TX1 crash. With official inflation at 4.3%, it's easer to blow cash & crash cameras.
Posted by Jack Crossfire | Dec 17, 2007 @ 02:55 AM | 2,730 Views
According to NOAA, we're done flying until 2008.

Have enough useless equipment to build a semi autonomous ground rover.

1 Functional 72Mhz radio set.
1 Partially functional 72Mhz set.
2 1Hz GPS modules
2.4Ghz video set
2 standard 360' servos
2 standard 180' servos

Not sure how useful it would be. There's not much to see from ground level.