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Gisela & Joe Noci's Groups

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 Antonie Kruger Aug 24. 38 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

Autopilot System for full Inertial Guidance and platform stabilization -The NamPilot System-

Started this discussion. Last reply by Gisela & Joe Noci Mar 1, 2013. 6 Replies

This Autopilot system is the system fitted to the various UAV's designed and flown in Namibia for nature conservation and to support the anti-poaching programs there.Have a look at the postings under…Continue

 

Gisela & Joe Noci's Page

Latest Activity

Antonie Kruger replied to Gisela & Joe Noci's discussion Optimizing Wing Aerofoil for UAV long range flight ( not for endurance)
"Hi Joe, I'm very late to this discussion. I curious to know what foil you settled(if there is ever such a thing) on. Cheers, Antonie"
Aug 24
Gisela & Joe Noci left a comment for Manuel Mayr
"Hello Manuel, Let me know what you wish to do and I will try to help...New legislation is happening here at the moment, and presently all UAV flights in, around or over and national park areas are forbidden, unless executed by the Ministry, etc.…"
Aug 5
Gustav Kuhn commented on Gisela & Joe Noci's blog post More 433 MHz antenna - the 1/2wave Ring Radiator
"Hi Joe, I tried to calculate what the physical size on FRG would be, but gave up, and just made the first one as per free space measurements. That one came out at about 750 MHz. From that I factored a correction in, and it came out on 868 MHz ! As…"
Aug 4
Gisela & Joe Noci commented on Gisela & Joe Noci's blog post More 433 MHz antenna - the 1/2wave Ring Radiator
"Looks Good Gustav! What did you use for the dielectric constant for the FR4 to start with? I find its normally around 4.2 to 4.4. I do prefer the Jpole - easier to set up, and it is easy to add a phased section on top to get another 2 to 2.5dB …"
Aug 4
Gustav Kuhn commented on Gisela & Joe Noci's blog post More 433 MHz antenna - the 1/2wave Ring Radiator
"All Joe's Fault.... After I figured out that a "SlimJim" (Google is your friend) might just be the easiest omni antenna for the "test instrument deprived" to make, I wanted one for my new XUAV Talon. The base station one was…"
Aug 3
Kev W. commented on Gisela & Joe Noci's blog post More 433 MHz antenna - the 1/2wave Ring Radiator
"  Hi Joe and fellow antenna dabblers I did make a couple of the 1/2 wave ring radiator antenna's, I was aiming for 459MHz, but the results were not what I was after :( A couple of issues, first being trying to locate a cylindrical former…"
Jul 28
Gustav Kuhn commented on Gisela & Joe Noci's blog post More 433 MHz antenna - the 1/2wave Ring Radiator
"Oops, did I say 915 MHz ? 3DR modems, easier to get. Will be using your Planar Ring design shortly, just received my miniVna Tiny :-) With 15000 mAh @ 16 m/s my Talon just might do 120 minutes, but that is with only a GoPro :-( Love to see some…"
Jul 27
Gisela & Joe Noci commented on Gisela & Joe Noci's blog post More 433 MHz antenna - the 1/2wave Ring Radiator
"Hah! No guys or Gals responding???  Thought I better then...Hi Gustav. Nice RL on that Slim Jim, but how come you are on 915MHz? - Thought that was a no-no in RSA...Are you using those Digi-Modems? We use the 868MHz Xbee Pro's - 300mW and…"
Jul 27
Gustav Kuhn commented on Gisela & Joe Noci's blog post More 433 MHz antenna - the 1/2wave Ring Radiator
"Hi guys/girls, I would like to present the return loss picture of a 915 MHz "SlimJim" antenna I made for my base station :-) "
Jul 22
Gisela & Joe Noci left a comment for Daniël Bakker
"Hi Daniel, I have mailed it to you at the adr you gave. Joe"
Jul 4
Gisela & Joe Noci commented on Gisela & Joe Noci's blog post Video and Datalink Antenna for airborne and ground tracking systems
"Hi Daniel, PM me and I will send you the PDF files. Regards Joe"
Jul 2
Daniël Bakker commented on Gisela & Joe Noci's blog post Video and Datalink Antenna for airborne and ground tracking systems
"Hi Joe, I'm trying to find some more information on the diamond antenna, unfortunately the PDF file you posted on the previous page of comments is no longer available. Could you point me to an information source? Thanks, Daniël"
Jun 27
Gisela & Joe Noci left a comment for Martin
"Hello Martin, Martin, no, we have not done large areas with our SurVoyeur system. It tends to become impractical depending on the required GSD. For example, with a 22mpixel camera, APSC format sensor, 22mm lens, you would achieve around only 10cm…"
Jun 10
Gisela & Joe Noci commented on Thorsten's blog post u-blox M8N - ground planes, antennas and positional accuracy
"More on GPS performance and GPS Antenna Thorsten, and all others interested in doing tests on GPS performance, etc ... GPS received Signal to Noise ratio is probably the most important parameter and affects many GPS performance criteria. If the…"
Jun 7
Kev W. commented on Gisela & Joe Noci's blog post More 433 MHz antenna - the 1/2wave Ring Radiator
"Thanks for the detailed response, a nice little project for me to get stuck into :) I will repost to the blog with pictures/details of my antenna once I have it tuned to my satisfaction. All the best, Kev. "
May 17
Gisela & Joe Noci left a comment for Kev W.
"Hi Kev W  -  I have replied to your query on the 459MHz antenna - pardon the belated response - the blog gets lost down the way and I don't see the posts - only saw when you messaged me.. Joe"
May 16

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

Etosha National Park, Namibia, adds more to its Anti-Poaching UAV Arsonal.

Posted on September 11, 2014 at 7:00am 17 Comments

After after almost 9 months of application of the SurVoyeur MKII UAV system in the Etosha National Park here in Namibia, The Park and Ministry have added further to their capabilities. Two more Pilots have also completed there training this week, each on both the…

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Laser Rangfinder for Auto takeoff and Landing - 25kg Composite Pusher UAV Project

Posted on August 3, 2014 at 10:00am 18 Comments

Pictured above is a twin tail boom Pusher Composite UAV made by Paramount Advanced Technologies. It was fitted with our autopilot and flight control software and we spent a few weeks flight tuning the system and implementing full auto takeoff and auto landing modes.

About 4m wingspan, pusher…

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More Laser Rangefinder based landings - from the NamPilot

Posted on June 26, 2014 at 6:59am 5 Comments

Seeing Andrew Tridgell's post on the SF02 LRF used for landings on APM, I thought I would post some flight logs of our landings using the same rangefinder.…

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Comment Wall (25 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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