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Mike,
Regarding the computation of acceleration, equation 25, the units come out just right.
As you point out, acceleration is in meters per second per second.
Rotation rate is in radians per second. Radians is a dimensionless angle measurement.
V...
Bill-
The actuators for my system are pretty fast, so I think not a problem... 3-4 seconds, full scale movement.
Question on the A centrifugal calculation in Eqn. 25... how is an acceleration m/(s*s) computed from rad/sec * m/s?
Mike,
By the way, one of your big challenges with your trim tabs is going to be to move them quickly.
The sailboat project I am working on uses a DC motor driven jack-screw with a 12 inch stroke, for controlling the rudder. Its rather slow, it tak...
Mike,
Actually, equation 25 requires only 2 multiplies.
Now, to your question. Assuming the craft (air, sea, or land) is moving in the direction that it is pointing, the sideways acceleration measured in the frame of reference of the craft is eq...
Hey Mike,
Congratulations on getting the DCM lite running. That's great.
Refereeing to your question (3) above, If you look at my post I wasn't suggesting that you use ACOS to find your angles, I was letting you know what each of the lower DCM el...
Bill -
I'm trying to control pitch and roll of a boat (fishing boat, speedboat) thru the use of 2 DC motors that adjust plates along the left and right of the stern of the boat. adjusting the plate position (trim tabs) causes different amounts of...
Mike,
Its good to hear that you have "DCM lite" working, I am sure there are lots of other applications for it. I will be by your house some day for that slice of pizza.
Regarding your questions:
(4) There are no further "orthogonality issues"....
Brian and Bill -
Like I said, I owe you guys a pizza each! Thanks to your help, "DCM-lite" seems to be working now. The problem was, as I believe you both suggested, a simple sign thing... the polarity of one of my three gyros is different from t...
Mike,
I took a quick look at your plots. I'm still a little confused about units and variable names, but it almost looks like you've got x and y rates swapped. If you have you IMU pitched up 45 degrees then yaw it around this orientation you shoul...
Mike,
It just occurred to me that my code may have confused you...the axis conventions I use in my firmware are not the "standard" conventions that I used in the documentation that I wrote concerning DCM. I wrote my firmware before Paul Bizard set...
Mike,
The fact that a yaw of 360 degrees brings you back to your starting point is a great clue because:
1. It proves that you have the right gyro gains.
2. It greatly narrows down the suspects. There are only a few ways for that to happen. My m...
Brian and Bill -
Thanks so much for spending the time to try to help me out. I already owe you both a pizza, on me, should you ever happen thru Elkhart, Indiana!
Brian - yes, I'm following most of your algorithm almost exactly. The only part I d...
Mike,
I replied to your last post, but my reply seemed to have disappeared. In the meantime, I took a quick look at your code.
In one of your previous posts, you mentioned that you were going to update only the last row of the matrix. I am rathe...
Hey Mike,
I'm at work so don't have time to look at your code real close right now, but a quick glance and it seems more complex than it needs to be. It's probably close, but I'll have to spend more time looking. In the meantime I type up a genera...
Thanks Brian and Bill for your quick responses. I appreciate very much.
I'm still having no luck getting my device to correctly track a fixed pitch and roll angle when I spin in on a test fixture. It does seem to track fairly well when I change j...
Comment Wall (1 comment)
- At 4:21pm on July 14, 2009,
William Premerlani said…
- Hi Mike,
Regarding your question about forward acceleration compensation in the DCM algorithm, and equation 26 of my DCM "primer"..
It would not hurt to compensate for the forward acceleration by computing the time rate of change of the GPS velocity, but I do not think it will make much practical difference, unless you are talking about a moon launch.
The gains on the roll-pitch drift compensation are rather low. As a result, the compensation does not respond much to accelerometer noise or transients. Only continual accelerations can lead to major error, such as during a turn.
Centrifugal acceleration can be sustained indefinitely, so it must be taken into account.
Forward acceleration and deceleration is transient, so it really does not do much to the DCM algorithm.
One data point on that is that I do hand launches of my GentleLady, with stabilization turned on, no forward acceleration compensation, and pitch stabilization does not even twitch, and I am throwing very hard. Basically, the plane goes from no velocity to full speed in a split second. The acceleration is high, but the duration is short, so the drift compensation controller filters it out.
Recently, I began to wonder whether I might improve the pitch accuracy during long duration parabolic trajectories, by adding the forward acceleration compensation, using the total "3D" velocity, so I finally implemented in the version of the firmware that I am working on now, but there was no difference in performance that I could see.
Having said all that, at the end of the day, I do recommend that you do the forward acceleration compensation, because it won't hurt, and if for some reason you want to turn up the drift compensation gains, you do not have to worry about creating a pitch error due to forward acceleration.
Best regards,
Bill
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