"Hi Justin,
I agree with you. In the latest version of MatrixPilot, wind related computations have been moved to the navigation layer. The computation of the direction cosine matrix elements is now "pure".
We have worked out a way to…"
Henry Fletcher's Discussions
Project Meteor
Started Nov 14, 2010 0 Replies 0 Likes
A small team of young engineers is working on Project Meteor, aiming to develop a highly capable AUAV for various different operational scenarios. The main initial drive of the project is to get a…Continue
Overly Complex?
Started this discussion. Last reply by Chris Anderson May 18, 2010. 6 Replies 0 Likes
Hello all,I'm thinking of using the following for an autopilot:Arduino Mega connected to:9 Degrees of Freedom - Razor IMU - AHRS compatibleSerial Servo Controller -> connected to at least 3 micro…Continue
Henry Fletcher's Page
Latest Activity
Justin commented on Henry Fletcher's blog post Switching from DCM to Quaternion"I would like to drop in a comment about the need for wind estimation in or around DCM.
I believe the original design of DCM was to *let the wind yaw the matrix*, in this way the UAV began to compensate for the wind, and could still navigate. How…"
bernienepper commented on Henry Fletcher's blog post Switching from DCM to Quaternion"EE 71 - You guys are super math gods - thanks for letting me follow you discussions -"
William Premerlani commented on Henry Fletcher's blog post Switching from DCM to Quaternion"Hi Roy,
In the past, I have used CORDIC functions, table lookups, and low-order Taylor series, any of them could be used. I think that for this application I would use a combination of a table lookup and a low order Taylor series. I would use a…"
Roy Brewer commented on Henry Fletcher's blog post Switching from DCM to Quaternion"Hi Bill,It seems we are thinking along similar lines, although I am more focused on quaternions (and related parameterizations, at least for the moment) and you are sticking with rotation matricies. Once you know omega and delta_t, you can find the…"
William Premerlani commented on Henry Fletcher's blog post Switching from DCM to Quaternion"Hi Roy,
Hi Roy,
I am delighted to continue this discussion with you. You are exactly correct in your comments.
1. I am counting 0*x^2 as the second term in the expansion. Sorry about that. In any case, it is the x^3/3 term that is the correction.…"
Roy Brewer commented on Henry Fletcher's blog post Switching from DCM to Quaternion"HI Bill,(sorry I'm so late in my reply)I created the figure you recommend, and I think I see what you are getting at. Let me see if we are on the same page:With a first order (linear) approximation to the kinematic integration soultion, we…"
William Premerlani commented on Henry Fletcher's blog post Switching from DCM to Quaternion"Hi Roy,
One more comment in response to your comment: "- Although (ortho-)normalization is necessary for quaternions and DCM, the process can actually be a source of error. There are other, more exotic quaternion-like representations (rodrigues…"
William Premerlani commented on Henry Fletcher's blog post Switching from DCM to Quaternion"Hi Roy,
Yes, I eventually plan to eliminate two linear approximations. The first one is the integral of the kinematic equation, to use the exact nonlinear formulation of a finite rotation. That one is a high priority for me. The second one is to use…"
Roy Brewer commented on Henry Fletcher's blog post Switching from DCM to Quaternion"Great discussion, guys!I would just like to make the following points and ask some questions. Please correct me if I am mistaken on any of these.- No one, especially not control specialists, should disparage linear approximations! They are very…"
Yuan Gao commented on Henry Fletcher's blog post Switching from DCM to Quaternion"I think this grammar needs some explaining: "the old clunky DCM implementation". The "clunky" part of this paragraph refers to the "old implementation", not the "DCM". In this sense we are talking…"
DeveloperPete Hollands commented on Henry Fletcher's blog post Switching from DCM to Quaternion
"For those reading this thread that are completely new to the maths for representing orientation ( e.g. DCM and Quaternions and Euler Angles ), I have found this book ( 3D Math Primer for Graphics and Game Development ) to be helpful. It is for…"
Paul Bizard commented on Henry Fletcher's blog post Switching from DCM to Quaternion"Yes, because today you still need to switch back and forth between the quaternion and the DCM representations for feedback purpose, the DCM algorithm is not so "clunky" !
And thank you Bill for having given DCM to all the DIY Drone…"
Henry Fletcher commented on Henry Fletcher's blog post Switching from DCM to Quaternion"Oh yes! Woops, good spot Bill. 3x3 is 9 but the DCM is a 3x3 matrix ... !Yes, perhaps "clunky" wasn't the best word there! I just got a little carried away with the fact I had got my gyro updated variables down from 9 to 4, I guess it…"
William Premerlani commented on Henry Fletcher's blog post Switching from DCM to Quaternion"Hi Henry,
Very well said, a good description of the situation. The only statement that I would take issue with, it must have been a typo, was:
"The DCM is a 9x9 matrixThe Quaternion is a 4x1 vector."
I am sure that you meant to…"
Henry Fletcher commented on Henry Fletcher's blog post Switching from DCM to Quaternion"This is a good discussion! I have been following it closely :) I can always learn a thing or two about hardware interfacing! I wrote much of the DCM code and the quaternion implementation we are now using, and I have already had it scruntinized by…"
Profile Information
- About Me:
- Cambridge University (UK) Engineering Undergraduate
- Tell us a bit about your UAV interest
- General...been into RC aircraft for a while now, and want the ability to go out of visual contact ( even if I can't on account of legislature!)
- Hometown:
- Oxford UK
Henry Fletcher's Blog
Switching from DCM to Quaternion
Posted on January 6, 2012 at 9:24am 35 Comments 0 Likes
We've recently made the move from the old clunky DCM implementation to a new Quaternion approach, and it seems to perform better, or at least the code is much smaller and takes almost no time at all to execute on our 72MHz 32-bit flight controller. I'll be writing an article on the Quaternion method as part of our series on Engineering Insights.
We've also added MAVLink support, and full integration with QGroundControl GCS. This helps greatly with debugging, and of course enables…
Continue 'Engineering Insights - Lesson 2: Testing and Tuning Always takes Ages!
Posted on December 27, 2011 at 8:00am 3 Comments 2 Likes
Video of ROFL Tuning Session with spectacular crash when we deliberately detune one of the PID values! No quadcopters harmed (much) in the making of this video. Video of stable flight below.
By the way, the ROFL quadcopter kit is still on sale on my website:…
Continue Engineering Insights - Lesson 1: Problems with Prototypes!
Posted on December 10, 2011 at 6:30pm 5 Comments 3 Likes
Seraphim is our sensor board for the quadcopter, it includes accelerometer, gyroscope, magnetometer, barometer, GPS and micro-SD card slot. With the exception of the GPS unit, all of these components are a complete pain in the backside to solder properly, and there are some consequences of not…
UAir: Integrated Wireless Comms - Making life soo much easier!
Posted on September 11, 2011 at 3:03pm 3 Comments 3 Likes
Here you can see the little guy we have just begun to use and will be releasing for sale in early October. The black Forebrain board is what was running the autopilot code in ROFL up till now, 72MHz ARM Cortex-M3 microcontroller, measures 66mm*23mm. The longer Hivebrain board is what we will switch to and will…
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