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Gisela & Joe Noci's Discussions

MAP calibration algorithms - has any one done this?

Started this discussion. Last reply by Michael Johnston Jun 4, 2013. 1 Reply

Map Calibration using Affine techniques -Has anyone out there done any work on map calibration using 3 or more known points on a paper scanned map, or a Google Earth map? As you know, you cannot use…Continue

Tags: nampilot, calibration, Map

My Blog On Turret Gimbal obliterated by Moderator?????

Started this discussion. Last reply by Michael Pursifull Feb 5, 2013. 1 Reply

I posted a blog on a Ball turret Gimbal design and build It appeared in DIYDrones with only 2 of the nine photos, and the text all garbled in between!! The preview before posting it was fine .Was…Continue

Tags: SurVoyeur, Gimbal, Turret, Nampilot

Optimizing Wing Aerofoil for UAV long range flight ( not for endurance)

Started this discussion. Last reply by Marco Ricci Apr 3, 2013. 37 Replies

Good Day all,I have been spending a lot of time analyzing many different aerofoil profiles to optimize said profiles for a very specific flight regime. If there are any experts with good knowledge on…Continue

Inertial Sensor Temperature compensation and orthogonality offset corrections

Started Nov 4, 2012 0 Replies

Hi Chris, maybe Bill (P) and other sensor boffins..Is there any temperature compensation and sensor orthogonality offset ( measured on a rate table maybe) done on the APM series autopilots? Has any…Continue

 

Gisela & Joe Noci's Page

Latest Activity

Monroe Lee King Jr. commented on Gisela & Joe Noci's blog post Antenna, Feedpoint matching, Baluns, Turnstiles and why Complex homegrown antenna mostly do not work...
"Nikola Wonderful work your doing here. There is some estimates to be had using helicals http://www.daycounter.com/Calculators/Helical-Antenna-Design-Calculator.phtml I've been doing a lot of work with RF lately doing rocket telemetry and video…"
Saturday
Nikola Rabchevsky commented on Gisela & Joe Noci's blog post Antenna, Feedpoint matching, Baluns, Turnstiles and why Complex homegrown antenna mostly do not work...
"A short followup for my earlier posting about my intent to try circular polarized antennas.  The general results are either uninspiring or terrible.  For the 2.4GHz FHSS video link, I tried a set of Blue Beam Ultra.  These actually…"
Saturday
Nikhil Shetty commented on Gisela & Joe Noci's blog post EO-IR camera gimbal fitted to SurVoyeur mk-IIc - a new generation in Anti-poaching measures in Namibia.
"We are still at our analysis stage and haven't yet purchased a camera or accompanying lens. For this purpose based on your comments, I tried preparing a MATLAB script (Considering the FLIR Quark 640, 19mm lens, 120m AGL and 20m/s flight…"
Apr 17
Josh Potter commented on Gisela & Joe Noci's blog post Antenna, Feedpoint matching, Baluns, Turnstiles and why Complex homegrown antenna mostly do not work...
"Getting into FPV has caused me to learn a lot about RF design, and some of this stuff is over my head.  Great post, thank you for sharing. "
Apr 15
Gisela & Joe Noci commented on Gisela & Joe Noci's blog post EO-IR camera gimbal fitted to SurVoyeur mk-IIc - a new generation in Anti-poaching measures in Namibia.
"Nikhil, What camera are you using ( FLIR- TAU, Quark, etc) and what is the lens that you have fitted - From that info we can work out the field of view and therefore the ground coverage related to flight height AGL. This will give the ground…"
Apr 14
Nikhil Shetty commented on Gisela & Joe Noci's blog post EO-IR camera gimbal fitted to SurVoyeur mk-IIc - a new generation in Anti-poaching measures in Namibia.
"Thanks for the response. We are trying to build a UAV and are trying to figure out what is the fastest we can fly to have unnoticeable motion blur based on IR camera resolution of 640x480, 120m AGL and 7-9 fps ("slow video" due to export…"
Apr 13
Gisela & Joe Noci commented on Gisela & Joe Noci's blog post Antenna, Feedpoint matching, Baluns, Turnstiles and why Complex homegrown antenna mostly do not work...
"Will post this evening Albert - The Coax collinear works well, but not easy to trim - you will need an SWR meter..but there are better - later.. Joe"
Apr 10
Frejus commented on Gisela & Joe Noci's blog post SurVoyeur mk-II - From the Nampilot..
"Hello Gi-Joe ;-) I am creating a photogrammetry pro activity and school in the south of France, with all due certifications... I may be interested in purchasing / reselling the MK2 + NX1000 Can you pls contact me ? Thank you "
Apr 10
Albert Pienaar commented on Gisela & Joe Noci's blog post Antenna, Feedpoint matching, Baluns, Turnstiles and why Complex homegrown antenna mostly do not work...
"Hi Joe I love this elusive topic and your help. I recently searched for antennas with high gain and a flat radiation pattern. I found something called a CoCo, coaxial collinear, apparently it can be end fed or center fed. Could you please let us…"
Apr 9
Gisela & Joe Noci commented on Gisela & Joe Noci's blog post EO-IR camera gimbal fitted to SurVoyeur mk-IIc - a new generation in Anti-poaching measures in Namibia.
"Hi Nikhil, I am not to sure what effect you are referring to - there is certainly blur related to the camera frame rate and the rate at which the ground features pass in front of the camera, but flying at 18m/s and at 100meters AGL we do not notice…"
Apr 9
Nikola Rabchevsky commented on Gisela & Joe Noci's blog post Antenna, Feedpoint matching, Baluns, Turnstiles and why Complex homegrown antenna mostly do not work...
"Thanks for that response, Joe.  That helps a lot.  I recently was range testing a FHSS video link (125mW output and 5dB antennas) and I could only get 500 meters with it on level ground.  I had previously tested the rig at a different…"
Apr 8
Nikhil Shetty commented on Gisela & Joe Noci's blog post EO-IR camera gimbal fitted to SurVoyeur mk-IIc - a new generation in Anti-poaching measures in Namibia.
"I had a question regarding the functioning of the IR camera. I was wondering if you experienced any motion blur from the IR footage and if you did how did you rectify it. Also would you happen to know what factors effect motion blur on IR cameras?"
Apr 8
Ross McGowan commented on Gisela & Joe Noci's blog post Antenna, Feedpoint matching, Baluns, Turnstiles and why Complex homegrown antenna mostly do not work...
"Joe, I would just like to add my thanks for the time you are investing in this conversation. As a budding FPV'er this has to be one of the hardest subjects to grasp, and one of the most important. I am all ears! Ross"
Apr 6
Gisela & Joe Noci commented on Gisela & Joe Noci's blog post Antenna, Feedpoint matching, Baluns, Turnstiles and why Complex homegrown antenna mostly do not work...
"Hi Nikola; Hope this post did not double - it seem to disappear..had to re-enter it.. You are quite correct in your analysis. You don't really lose signal, rather the signal cancels itself out..Assuming open line of sight between the two…"
Apr 5
Nikola Rabchevsky commented on Gisela & Joe Noci's blog post Antenna, Feedpoint matching, Baluns, Turnstiles and why Complex homegrown antenna mostly do not work...
"Fascinating (and frustrating) stuff.  I have a related question and it's more about real world than theoretical.  Most folks are doing FPV on a UAV.  What about a rover?  I've played around with Friis equation solvers…"
Apr 5
Gisela & Joe Noci commented on Gisela & Joe Noci's blog post Antenna, Feedpoint matching, Baluns, Turnstiles and why Complex homegrown antenna mostly do not work...
"@iskess' Have a look at my comments to Justin on TX/RX bandwidths and mutual interference. By default, the low cost of the modules used in this typical application means that many compromises have been reached in their design and…"
Apr 5

Profile Information

About Me:
Software/Hardware Engineer, Aircraft designer.
Please tell us a bit about your UAV interest
UAVs in civilian aerial photography and Anti-Poaching applications
Hometown:
Swakopmund

Gisela & Joe Noci's Blog

EO-IR camera gimbal fitted to SurVoyeur mk-IIc - a new generation in Anti-poaching measures in Namibia.

Posted on January 18, 2014 at 1:36pm 25 Comments

We have developed a version of the SurVoyeur mk-II, the 'c' version, which has a new nose housing a gimballed, stablized EO and IR camera combination.

This gimbal houses the FLIR QUARK 640 X 512 pixel Thermal camera, fitted with a shutter to enable flat field correction,  and also…

Continue

Etosha Natiola Park, Namibia, receives first UAS and Pilot completes training.

Posted on December 21, 2013 at 1:30pm 8 Comments

Gabriel Shatumbu, A qualified Pilot, receives his competency certification for the SurVoyeur mk-II UAS .

Etosha National Park in Northen Namiba received their first Wide Horizons SurVoyeur mk-II UAS yesterday. The Pilot completed his training on Friday. The system consists of the 2.6meter wingspan SurVoyeur mk-II aircraft , stabilized steerable Infra-Red gimballed camera ( FLIR TAU-2) and an 18mpixel stills camera also with video…

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Mission Planner Legal use of Google Maps/Earth content

Posted on November 22, 2013 at 10:30pm 38 Comments

How have the Mission Planner Developers managed to get around the Restrictions laid down by Google Earth regarding the use of Google Earth/Maps imagery and geo data for the Mission Planner software?…

Continue

Comment Wall (24 comments)

At 4:56pm on September 22, 2010,
T3
William Premerlani
said…
Hi Gisela,

We have made good progress with wind estimation. It is now incorporated into MatrixPilot. The theory is described here.

With respect to the cross-coupling of the acceleration into pitch estimation during a launch, we have not addressed the issue yet, it is not high up on my list. Paul Bizard did a lot of simulations, and found values of the PI feedback gains that were a reasonable compromise between rejection of gyro drift, and rejection of acceleration on takeoff. I think the time constant is between 10 and 15 seconds.

Beyond that, there are many things you could do, including turning off the PI roll-pitch compensation during high acceleration. There are many people who are using this approach.

Finally, you might want to take a look at the uavdevboard website, or join its discussion group.

Best regards,
Bill
At 5:05pm on September 22, 2010,
T3
William Premerlani
said…
Hi Gisela,

One more thing I forgot to mention, I don't recall whether it is mentioned in the "DCM document":

You can approximately adjust the accelerometer value along the axis parallel to the fuselage by computing the forward acceleration from the stream of GPS velocity reports. Although this does not help much during high acceleration launches, it will do a reasonable job once the plane is in flight, because the errors caused by the GPS dynamic behavior as the plane accelerates and decelerates tend to cancel each other out.

Best regards,
Bill
At 12:03pm on October 2, 2010,
T3
William Premerlani
said…
Hi Gisela,
You asked:
"(1) ...I assume that in a normal body axis convention (as in ArdIMU as opposed tp MatrixPilot ie X is +ve forward - this would be the fisrt column - rxx, rxy, rxz)?"

You are correct.

"(2) You mention that the plane must change attitude for this to work - and then refer to the denominator of Equ6. Now Equ6 computes the estimated airspeed, and if the denominator is zero, this cannot be computed. Is this the reason behind your statement?"

Yes.

" If in fact I have a measure of airspeed - via a pitot - and hence do not need to compute equ6 - can I then be computing regardless of the planes change of (or lacl of chnage) in attitude?"

Yes.

Best regards,
Bill
At 3:25am on October 3, 2010, Gisela & Joe Noci said…
Hi Bill
Thanks for the answers above. I would like to take these questions further, relating specifically to the use of GPS CourseOverGround to determine Yaw Gyro Bias

In the DCM theory document on page 21, you comment that the assumptions made when using GPS CourseOverGround (as opposed to actual Aircraft Heading – the direction in which the aircraft is actually pointing) are violated in the case of strong wind. This I understand.

However, if I am prepared to accept that the value of “yaw” as will be computed from the resulting DCM matrix is in fact a “course over ground” as opposed to an “aircraft heading”, and that the prime purpose here is as accurate a determination of yaw gyro bias as possible, that this is achieved irrespective of wind?

(The advantage of this would be that we would not be contaminating the errorYaw vector with what can only be a best estimate of wind. As this vector gets combined with the errorRollPitch vector to compute the final correction vectors, I assume any inaccuracies in the errorYaw vector will affect all gyro bias values – not only yaw).

Regards,
Gisela
At 4:01pm on October 9, 2010,
T3
William Premerlani
said…
Hi Gisela,

Regarding the effect of the wind on yaw gyro drift correction, the wind is relevant only during turns.

If your flight plan involves mostly long straight paths with turns only once in a while, you do not need to account for the wind if you use GPS course over ground to compensate for yaw drift. The controls will rotate the plane the exact amount needed for the wind.

However, unless you somehow measure and account for the wind in the navigation calculations, there will be a temporary yaw error after a turn, that will gradually dissipate.

An example might help. Suppose the plane is flying along at 10 meters/second airspeed with a cross wind of 5 meters/second. It will be crabbing into the wind with an angle of 30 degrees. Then suppose the navigation controls decide to make a 90 degree turn into the wind. In other words, navigation commands a change in course over ground of 90 degrees. It will rotate the plane by 90 degrees. However, all that is needed to turn directly into the wind and to change the course over ground by 90 degrees, is a 60 degree turn measured by the IMU, so with a 90 degree turn, the plane will wind up flying with a 30 degree error in course over ground. That will show up in the GPS course over ground, and the drift compensation algorithm will respond to it, but it will take 10 or 20 seconds to do so. During those 10 or 20 seconds, there will be a difference between the desired and actual course over ground.

So, if your flights will involve frequent turns, it is best to account for the winds in the navigation calculations. You can either estimate the winds using the method I have suggested, or you can use a magnetometer to be able to distinguish between course over ground and the direction the plane is pointing.

You can also simply ignore the wind if you are willing to tolerate temporary course errors.

Best regards,
Bill
At 4:44pm on October 10, 2010,
T3
William Premerlani
said…
Hi Gisela,


Actually, cross coupling between the earth and body frames of references reduces the drift of the yaw gyro, without any negative effect on roll and pitch. Tests have proven out the theory of an interesting effect. Consider an extreme case, either as a thought experiment, or as a real test, to see what is going on:

1. Start up your IMU close to being level, without any GPS or magnetometer connected for yaw drift. Program it to perform roll-pitch drift compensation only. During initialization, gyros will be approximately zeroed. After some time, the accelerometers will perfectly lock the roll and pitch. Yaw will slowly drift, at a small residual rate, because there is not any yaw feedback.

2. Rotate the IMU by 90 degrees, either by rolling or pitching, so that the axis of the Z gyro is horizontal instead of vertical.

3. Wait a few minutes. During this period of time, the accelerometer information is zeroing the Z gyro! During the same period, one of the other gyros will not receive any feedback, but it will be close to be perfectly zeroed, so its drift will be low.

4. Rotate the IMU back to level. The Z gyro is now zeroed, although the yaw angle is random.

There is another effect that you might be interested in: the bottom row of the direction cosine matrix is independent of yaw, so any yaw drift does not impact it. The reason for this is that the bottom row represents the earth frame Z axis as seen in the body frame. Because the earth frame Z axis does not contain any yaw information, it appears the same in the body frame, no matter what the yaw angle is. In fact, if you are only interested in roll and pitch, you only need to compute the bottom row of the matrix, which can be computed using only the bottom row information, and all three gyro signals. The fact that the Z gyro may have some drift is irrelevant, it all works out ok.

Best regards,
Bill
At 11:47am on October 11, 2010,
T3
William Premerlani
said…
Hi Gisela,

I think I see what you are missing, but it is going to take some thought on my part to figure out a way to explain it.

In the meantime, here is another data point for you:

There is a roll-pitch-yaw demo program available along with MatrixPilot. I use it routinely for testing purposes. I run it without any sort of yaw compensation, I set the yaw error to zero. The bottom row of the matrix perfectly tracks roll and pitch, no matter what is going on with yaw. The other elements are more or less ok, except there is a slow yaw drift.

I will see if I can think of another way to explain why things work out so well. In the meantime, here are some factors that may be involved in explaining the discrepancy, perhaps you will be able to explain it:

1. MatrixPilot and the roll-pitch-yaw demo software record the gyro offsets during power up, so once the DCM algorithm gets running, the residual drifts are rather small.

2. If the board is level, yaw drift has no impact on roll and pitch. In other words, if roll and pitch are zero and roll and pitch rate are zero, there is no way for yaw to change roll and pitch.

3. If the board is not level, there is enough information from the accelerometers to compensate for yaw drift, so there will be yaw lock.

4. If GPS is available to achieve a strong yaw lock, there may be a phase angle error in yaw, but the yaw rate error will be zero.

5. It is true that all three gyros are involved in computing the bottom row of the matrix. However, there are linear combinations of drifts that will not impact roll and pitch.

I think what may be going on in your simulations is that possibly you are not including the effect of roll-pitch compensation and/or you are introducing arbitrary yaw gyro errors?

As long as the yaw gyro error is a small offset (a few degrees per minute), everything should work out ok.

I have run out of room in this message, I will send you another later.

Best regards,
Bill
At 2:39pm on October 11, 2010,
T3
William Premerlani
said…
Hi Gisela,
Perhaps the amount of Z gyro offset that you were using was too large. That will result in numerical errors due to neglect of second order terms, followed by an effect I call "coning" that is caused by in interaction of the second order terms with normalization, followed by a failure to achieve roll-pitch lock.
Otherwise, the theory says that yaw compensation is orthogonal to roll-pitch compensation, as long as roll-pitch lock has been achieved. Here is why:
The roll-pitch rotation error vector is computed by taking the cross product of the last row of the matrix, with the gravity vector measured by the accelerometers. Since gravity is vertical in the earth frame, the computed roll-pitch error vector is in the horizontal plane of the earth frame.
The yaw rotation error vector is computed by taking the cross product of two vectors that are both in the horizontal plane of the earth frame. The result is parallel to the earth frame vertical.
Therefore, the yaw rotation error vector and the roll-pitch rotation error vector are orthogonal in the earth frame. Therefore they are orthogonal in the body frame. Therefore, an error in the yaw compensation does not impact the accuracy of the roll-pitch compensation.
Best regards,
Bill
At 2:51pm on October 11, 2010,
T3
William Premerlani
said…
Hi Gisela,

Another thought...in case you have not seen them, you might be interested in Robert Mahony's papers. He goes into more mathematical detail.

The point I was trying to make in my previous comment is that:

1. When the IMU is not level, the drift compensations compute rotation corrections that are applied to all three physical gyros, because each gyro receives a weighted sum of the three elements in each rotation error vector.

2. When roll-pitch lock has been achieved, the roll-pitch rotation compensation error vector is orthogonal to the yaw rotation compensation error vector, in any frame of reference. So, when the two rotation error vectors are transformed from the earth frame into the body frame and mapped onto the physical gyros, they should not interfere with each other.

I think I understand your question, which I think boils down to, "Do errors in the yaw rate gyro create errors in roll-pitch values". If that is the question, my answer is that, provided the rate errors are not so large as to break lock, the roll-pitch values should not be impacted by yaw error.

Best regards,
Bill
At 2:27pm on October 12, 2010,
T3
William Premerlani
said…
Hi Gisela,

How much discrepancy in roll-pitch are you seeing? There are a number of known sources of small errors, including:

1. Forward acceleration.
2. Linearization of the non-linear update equation.
3. GPS filtering.
4. Side slip introduces errors in centrifugal compensation.

Are you running simulations?

Best regards,
Bill

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