William Premerlani's Discussions
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As i understood,the RMarix outputs measure values of the roll, pitch and yaw which corrected by GPS and acc.
I want to add a "fly by wire" function into DCM.
Following is my PID algorithm.
//From RMarix get corrected values of roll,pitch and yaw.
Me…
Fantastic, that's what I have been testing with various gyros. I have a bunch of temperature-drift profiles for about 6 gyros types. The one I am trying to use is the LPR530. The LISY300AL is surprisingly temperature stable though. The ADXRS601 has…
Hi Daniel,
We found the LISY gyros to have more noise than the Analog Devices gyros, so we raised the sampling rate by a factor of 10, and used a decimation filter, when we switched to the LISY gyros.
Regarding temperature corrections, there have…
Thanks again Bill. I am actually porting this to a 12-bit ADC platform to see how things work out, hence the questions. I've found that the ADC samples can be quite noisy on my board (what appears to be up to 5-10mV of noise on the samples). I am al…
Hi Daniel,
The RollPitch demo was developed for the green board only. It was quickly superceded by the RollPitchYaw demo, which runs on either the greenboard or the redboard.
The RollPitchYaw demo will also serve as a RollPitch demo. You do not ne…
Thanks Bill. I have looked at the new RollPitchYaw demo and that does make sense now. I cannot, however, find an updated RollPitch demo. Is there one? Or can I just remove the adj_accel, yaw_drift and perhaps some other functions from the imu_demo t…
Daniel,
Sorry, the posting that you refer to is an old one that I forgot to update. The first version of the board, the so-called "green board", used Analog Devices gyros. The link that you followed is for one of the earliest demos for that board.…
I am looking at the RollPitch Demo files posted in the link above - assuming that this works with the UAV Dev Board (which uses the LISY300AL or the ADXRS401). But looking at the analog2digital.c file, I am a little confused. First of all the pin as…
Profile Information
- About Me:
- I am the designer of a UAV controller with GPS, 3 gyros, and 3 axis accelerometer, being sold by Spark Fun Electronics.
- Hometown:
- Schenectady, New York
William Premerlani's Videos
William Premerlani's Blog
Waypoint firmware for the UAV DevBoard is revised
Sigh....I am going to give Peter Hollands an award for finding the "juiciest bug" in the released waypoint firmware for the UAV DevBoard. The bug has been fixed, and the firmware has been re-released as version 1.8b.
The bug was in the yaw drift gyro compensation calculation. It would only show up for waypoint legs with a heading between 327 degrees and 360 degrees. The result wa… Continue
Posted on October 29, 2009 at 2:48pm — 44 Comments
AileronAssist versions 1.7 and 1.8 released
UAV DevBoard pilots:
This is an update of a previous post.
I deleted version 1.6 of AileronAssist firmware and released version 1.7.
The reason is that I noticed that the firmware fail safe does not work in version 1.6. Although the commanded return to launch will work just fine in version 1.6, loss of signal return to launch does not. If you turn off your transmitter, and if your rad… Continue
Posted on September 17, 2009 at 3:30pm — 16 Comments
Altitude hold for UAV DevBoard
UAV DevBoard pilots,
I am putting the most recent releases of MatrixNav and AileronAssist back on line. I briefly reverted to the previous releases while I investigated a system issue that I just ran into.
I just bought an EasyStar, ready to fly, with radio, servos, ESC, and radio already installed. I did some flying with MatrixNav. Most of the time it worked fine, but once in a… Continue
Posted on September 2, 2009 at 2:26pm — 10 Comments
ICD2 for programming the UAV DevBoard is back in stock
If you have a UAV DevBoard, but you are waiting to purchase an ICD2 PIC programmer from SparkFun in order to program it, please be aware that they are now back in stock.
Best regards,
Bill Premerlani
Posted on August 17, 2009 at 3:02pm — 7 Comments
UAV DevBoard firmware progress report
UAV DevBoard pilots,
This is an update on a few UAV DevBoard related activities.
There is a new release (1.6) of MatrixNav, that now includes rudder-elevator mixing, and yaw stabilization in both stabilized and and RTL mode. It is available under the UAV DevBoard tab.
Ben Levitt just created a couple of groups in the DevBoard… Continue
Posted on August 13, 2009 at 4:51pm — 4 Comments
Comment Wall (29 comments)
- At 6:57am on February 28, 2008,
Chris Anderson said…
- William,
Welcome! Your board and especially your documentation are VERY impressive. Would you like to do another one of our Q&A interviews here to explain to everyone your thinking behind developing the board and some of the things people have done with it?
Best,
Chris
- At 3:24pm on January 7, 2009,
Nathan said…
- Bill, I'm interested in using your older 2-axis board for an application. Do you know of any discussions dedicated to it? Awesome documentation, BTW. Having thought myself for long hours on how to do all of that in PIC assembly, I know what a monumental task it must have been.Thanks.
- At 11:06am on April 27, 2009,
Tom Yochum said… - Hi Bill,
I am very impressed with the work you have accomplished. My own project is in many ways an effort to duplicate your results (cheap IMU as an AHRS for micro-UAV control). I am currently tackling the problem of initial alignment of the AHRS. I have skimmed through the DCM paper and did not see anything there. I haven't looked through your code yet either. Could you give me a quick idea of how you did the initial alignment?
Thanks.
Tom
- At 6:13pm on July 29, 2009,
Roy Brewer said…
- Thanks for getting back to me with this. This would be great news if it pans out. Let me know.
BTW, would that be 6 HW PWM outputs, or would some of those be in s/w?
- Roy
- At 6:52pm on September 21, 2009,
Justin said…
- Hi Bill,
My apologies...this has been my fault all along. I assumed I had the wires connected to the board correctly becaues I was measuring a positive voltage between the outside pin and the middle pin. I didn't think I would be able to detect a voltage from the signal.
In your previous comment when you said that I should measure a voltage with respect to ground for the signal I went back and did some futher testing and realized I simply had them plugged in backward.
The RollPitchYaw demo is working great now! I'll load up John's heli code and give that a test as well with the receiver properly connected and I bet it will work just fine.
Thanks again!
Justin
- At 7:41pm on September 28, 2009,
Frank Hermes said… - Hi Bill,
No I do not mind (publishing), but I appreciate your asking - as you can tell, I am very ignorant in this area, and humbled when i read through all the guys out there that are so knowledgeable, but doing my best to learn...I appreciate your patience...
You know, I thought after reading your paper on DCM that I was right back to where I was in regards to the gravity thing and the accelerometers, but since you addressed that aspect regarding using them anyway to correct the gyro drift that maybe I once again just didn't understand - I thought somehow since you were collecting continuous data that you were able to integrate the accelerometer only (no appreciable gravity influence) data into the gyro data - yikes, WRONG, again!
I would appreciate any thoughts from you or readers...this thing is really starting to bug me for a solution (reasonable one!) and I am willing to invest as long as I know there is some chance of success, particularly in regards to the COS since all I need there is data output - obviously the "canarderon" thing will take some mechanical magic as well...
I really do appreciate your time and thoughts, Frank
- At 11:39am on September 30, 2009,
Frank Hermes said…
Hi Bill...
I have a graph taken from one of the simulation programs we use to design the rockets (RockSim); it represents a typical rocket flight from liftoff to apogee...thought it might help you get a sense of the forces involved...
Curious as to your thinking that the GPS velocity may be useful in some way - my understanding of the accuracy of the GPS position would not lend itself to a rocket which is changing its postion so quickly, but you indicate it might do quite well - is the designed-in inaccuracy of the GPS signals their absolute position, but the position change is quite accurate? Accurate enough to track something going 1.5+ mach?
It seems as though, based upon what I have learned so far, and your coments, that none of the typically available sensors are free from the need to reference/sensing gravity except the IR, and maybe the magnetometers?
Could we use a magnetometer for the basic reference? Model rockets typically do not utilize a lot of ferrous material, and other than their time sitting on a big metal launch pad/rail, their environment is pretty metal free...could calibrate away from the pad for the baseline, then once it leaves, it is "free" once again...
How do the "big boys" get around the gravity issue?
Thanks, Frank
- At 5:07pm on October 3, 2009,
automatik said… - Hi Bill,
I am re-reading your paper "Direction Cosine Matrix IMU" ([pdf] Draft 5/17/2009). I think there is a typo in Eqn. 20 (or there is a chance that I am not getting something). Vector notation, for Z row of the matrix, is represented as follows [rxx, rxy,rxz], and I think that it's a typo as Z row , as I understand it, should be [rzx,rzy,rzz]. What do you think?
- At 4:54pm on October 5, 2009,
Frank Hermes said…
- Hi Bill,
Thanks for the further thoughts...I follow you until you get to the magnetometer and the issue of the single vector availability...so even though you have two or three magnetometers available you still only get one real ref - I guess that is due to the resolution capability of the sensors...
I ran across a guy who told me about a project at Utah State that if you have not seen you might be interested in as it relates to the rocket thing:
https://chimaera.usu.edu/
If you go to the documentation page, there are some papers descibing their work (see Attitude Control, p.95 in the Flight Readiness paper)...they used a MicroStrain commercial IMU for attitude reference - no GPS...one excerpt from the Navigation section particularly interests me:
A SINS (strap-down INS) works by measuring the accelerations and angular rotation rates of the rocket using an Inertial Measurement Unit (IMU), and integrating these measurements directly to find the velocity and position of the rocket. The IMU measures the sum of all specific surface forces applied to the rocket, including motor thrust and drag, but cannot measure the gravitational force. To account for this, the equations of motion for the rocket
must include the gravitational force before the SINS can integrate and find the rocket velocity and position. SINS is a particularly good measurement device for the thrusting phase of the rocket’s flight, when the motor thrust
varies unpredictably.
A Kalman filter is a mathematically optimal state estimator. It takes multiple measurements, along with their statistical characteristics, and outputs the most probable state of the rocket and its statistical variance. It is unique, in that it is a time-domain filter that requires no system to store previous state data. These qualities make it ideal for inclusion in the navigational algorithm, so that the rocket state is not dependent on a single measurement device.
Sounds to me they just use an estimate for gravity? Thoughts...
Regards, Frank
- At 12:49pm on October 6, 2009,
Frank Hermes said…
- Hi Bill…
The initial goal is to provide a signal (based upon degrees of tilt of rocket tip from vertical) to either inhibit, or possibly trigger, second-stage (sustainer) motor ignition after burnout of the first-stage (booster) motor. The effort is to maximize the coast period between burns. [I attached a flight simulation graph to an earlier email to you to help paint the picture, but I think it may have been reduced to useless by your blog program. If there is a direct email address you can release to me I can resend that graph.]
During booster burn, we expect acceleration along the rocket’s vertical axis to range between 0 and <18 g. After burnout, during coast, deceleration along the rocket’s axis will range from about negative 1.5 g to about 0 g. All other accelerations (both linear and angular) are likely to be quite small since rocket the does not spin much and tips over very slowly.
Booster (first-stage) burn would be between 4 and 12 seconds. The coast period may be from 10-15 seconds. Therefore, the total duration of the sustainer upward flight prior to ignition is less than 15-25 seconds, so indeed long term drift of the sensors may be a minor concern.
In regards to using a magnetometer, the launch rail is typically 10-14’ high and made of steel. I suppose you could calibrate the sensor(s) away from the pad, then mount the rocket, then launch it – once away, there are negligible iron effects. The lull between placing the rocket on the rail and launch could be up to 10 minutes or more.
Further use might include adaptation of the IMU into a vertical-trajectory/vertical-stabilization system to control flight all the way to apogee, which could be as much as one minute flight time.
Regards, Frank
© 2009 Created by Chris Anderson
