Roy Brewer
Roy Brewer
  • 44, Male
  • United States
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Roy Brewer commented on Denny Rowland's blog post 'ROWLAND F1-535 nears production status'
Looks very solid. What is the frame made of, and what are its dimensions? - Roy
Sunday
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Roy Brewer commented on Igor van Airde's blog post 'ArduCopter: Changing from PI to PID to improve stability'
As Robert Lefebvre and I said earlier, it is not a good idea to integrate the rate feedback term as you have it shown. If you want to see what a good control loop architecture looks like, try…
Feb 8
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Roy Brewer commented on Ellison Chan's blog post 'Swarm of Quads!'
Alex, So, are you the "K" with Daniel providing the "Mel" of KMel Robotics? Can you give us any technical details about these vehicles? Are they for sale? Thanks Roy
Feb 2
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Roy Brewer commented on Chris Anderson's blog post 'Check out this open access robotics journal'
@Anish - I've found in my limited experience that the papers are not as high quality as other more traditional sources, in general, but there are exceptions. You have to admire their open source spirit .@All,You may want to check out their…
Jan 25
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Roy Brewer commented on Igor van Airde's blog post 'ArduCopter: Changing from PI to PID to improve stability'
Although both the current and the proposed architectures can be made to work, I think they both needlessly complicate the tuning process - which is complicated enough on its own. Also, the gains and some of the signals do not mean what you may think…
Jan 20
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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…
Jan 18
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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…
Jan 16
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Roy Brewer commented on Jason's blog post 'Motor Efficiency'
As was mentioned, those curves are for an unloaded motor. The torque-speed relationship for a propeller is actually quadratic, not linear. It also depends on the airspeed of the vehicle. The same holds true for the thrust.Check out this document for…
Jan 13
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Roy Brewer commented on Riccardo Kuebler's blog post 'UavDevBoard and MatrixPilot join the quadrocopter world'
Thanks Bill.If I understand your architecture correctly, I'd call the "virtual quad" a command model. I assums your feedback objective will be to make the error DCM equal to the identity matrix (or, equivalently, to make I - DCM_error…
Jan 13
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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…
Jan 11
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Roy Brewer commented on Riccardo Kuebler's blog post 'UavDevBoard and MatrixPilot join the quadrocopter world'
Thanks, Bill & Ric.It sounds like you have attitude command in the pitch and roll axes and rate command in the yaw channel, and direct thottle with some vertical damping. Are you using direct feedback of elements of the DCM for your…
Jan 11
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Roy Brewer commented on Riccardo Kuebler's blog post 'UavDevBoard and MatrixPilot join the quadrocopter world'
Fantastic stuff, as we've come to expect from the UDB / MatrixPilot team! I have two questions: 1) What is the control mode - attitude command? Rate command? Something else? 2) The scenery is also pretty impressive. Where was this video…
Jan 9
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Roy Brewer commented on Paul Feely's blog post 'Top 5 Small Robots of 2011'
It apparently is controlled like a single blade of a helicopter, with virtual "collective" and "cyclic" pitch on the flap actuator "Development and Flight Validation of an Autonomous Mono-Wing…
Dec 27, 2011
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Roy Brewer commented on Geoffrey L. Barrows's blog post 'Wide field 4D optical flow odometry using Arduino and Stonyman image sensor'
Great stuff, Geoff! So, now you have 4 of the 6 DOF. Can you use some sort of trapezoidal distortion to estimate pitch & roll attitudes or rates? What are the next highest dimensions of optical flow? - Roy
Dec 17, 2011
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Roy Brewer commented on George Tarrant's blog post 'Offer of help with tuning PID loops'
George , I totally agree.   See my comments here for some interesting papers on the subject: http://www.diydrones.com/profiles/blog/show?id=705844%3ABlogPost%3A265363&commentId=705844%3AComment%3A268042   A more powerful processor may…
Jul 19, 2011
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Roy Brewer left a comment for robert bouwens
Hi Robert. No, I have not looked in detail at the implementation
Jul 13, 2011

Roy Brewer's Blog

Roy Brewer

Parallel programming on the Arduino with Occam

Posted on June 17, 2010 at 9:11am 0 Comments

Looks like these folks are implementing the parallel programming language Occam on the Arduino.

http://answers.oreilly.com/topic/1624-parallel-programming-arduino-and-the-good-kind-of-trouble/

They specifically mention a UAV project on running on ArduPilot

- Roy
Roy Brewer

Complementary filter demo

Posted on February 16, 2010 at 10:30am 2 Comments









This is a demonstration of complementary filters on pitch and roll attitude using 3 gyroscopes and 3 accelerometers running on a custom Quadrotor controller board. Filters are coded in Python on the laptop with VPython rendering of spinning 3D cubes. Sensor processing code is running on the ATMega644p-based controller and is written in C. For Python code, see:… Continue
Roy Brewer

New 9 DOF sensor for $99

Posted on December 4, 2009 at 10:28am 12 Comments



Its means to be interfaced to a PC over USB, but it appears to provide 9 DOF (accelermeters, gyros, and magnetometers). The device apparently can output the raw sensor values and/or Kalman filtered quaternions



http://www.pnicorp.com/products/all/spacepoint-fusion



Too good to be true?



-… Continue
Roy Brewer

Accelerometer question for IMU Experts

Posted on August 7, 2009 at 8:09am 44 Comments

I'm sure there's plenty of experienced IMU builders on this board who can resolve this question (see here: http://www.diydrones.com/forum/topics/gyrospes-vs-acceleometers?x=1&id=705844%3ATopic%3A85220&page=1#comments (starting at the 5th comment) and here:… Continue

Comment Wall (4 comments)

At 1:52pm on July 29, 2009, William PremerlaniWilliam Premerlani said…
Roy,
A recent idea from Ben Levitt has caused me to reconsider an answer that I gave for one of your questions.
Ben has suggested that one of the spare pins on the UAV DevBoard, RE8, could serve as an extra PWM input. It just might work! Ben is going to try it. If it does work, then the spare pins on the UAV DevBoard could be used to expand it from 4 PWM inputs and 3 PWM outputs to 5 PWM inputs and 6 PWM outputs.
Best regards.
Bill
At 7:25pm on July 29, 2009, William PremerlaniWilliam Premerlani said…
Roy,

The 6 PWM outputs total would split up as 3 PWM hardware outputs and 3 PWM software outputs. Obviously, the hardware outputs would work the same way they do now: you write to duty cycle registers.

The software outputs could be implemented without too much trouble using a couple of spare timers and their interrupts, using a technique that I used on the first PIC board that I built a long time ago. The first timer generates interrupts every 2 milliseconds, creating ten 2 millisecond "time slots" for the software PWMs within which pulses are generated. Ten times slots are more than enough, only three of them would be used. A simple scheduler would decide which pulse was being generated, and start the front edge of the pulse. An interrupt generated by a second timer would control the falling edge of the pulse.

The entire process could be packaged up in such a way as to be transparent to the programmer, who would see a simple duty-cycle interface to the three additional software PWMs.

Its on my list of things to do soon, if someone else doesn't get to it first.

Best regards,
Bill
At 2:22pm on August 29, 2010, William PremerlaniWilliam Premerlani said…
Hi Roy,

Regarding "DCM lite", I will give you the short version now, the longer version when I have some time.

The bottom row of the direction cosine matrix contains all the information you need about pitch and roll. It is possible to update the bottom row without using any of the other rows, if you take a look at the details of the computation. Updating the bottom row involves multiplying the update matrix times a vector equal to the bottom row. Then, the roll-pitch drift compensation can be computed from the bottom row, and the accelerometer values.

If all you want is pitch and roll, you can stop there.

If you also want yaw, there are several ways that I can think of that you could use to do that. One way is to integrate the yaw rate, which you can compute from the elements of the bottom row plus the gyro rate values.

Best regards,
Bill
At 8:41am on May 19, 2011, Caleb ChamberlainCaleb Chamberlain said…

Hey Roy,

I'm happy to answer any question you have.  Email might be the most convenient way to do it: my personal email address is voiceafx [at] gmail.com

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