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Old Jan 07, 2009, 02:58 PM
Chris Anderson
San Francisco/Bay Area
Joined Mar 2007
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Another(!) new Sparkfun autpilot board: dsPIC + 3-axis IMU

Another day, another new autopilot from Sparkfun! (They must be gearing up for their autonomous vehicle competition in April.) Today they released Bill Premerlani's new IMU-based autopilot development board. Uses a 6 DOF IMU, faster processor, other nice improvement from previous board. And the code is now in C (rather than assembly)! $299 w/out GPS.

We're hosting his home page here.

Features:
  • Connection for a 20-Channel EM-406A SiRF III GPS Receiver (not included)
  • PIC dsPIC30F4011 Controller (with onboard 3.3V and 5V glue logic)
  • dsPIC runs at 120MHz with 16MHz resonator and PLL
  • MMA7260 three axis accelerometer
  • 3 ADXRS401 gyros
  • 4 Input, 3 output PWM points
  • 6-Wire ICSP debug header
  • 2 Separate colored status LEDs
  • 3 General purpose switches
  • On board 3.3V and 5V regulators (150mA max)
  • 10m Positional Accuracy / 5m with WAAS
  • GPS Outputs NMEA 0183 and SiRF binary protocol
  • Spare USART connection for debugging
  • 4 Spare digital I/O pins for debugging
Dimensions: 1.5 x 2.75 x 1.0"
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Last edited by zlite; Jan 07, 2009 at 07:41 PM.
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Old Jan 07, 2009, 05:20 PM
Registered User
Joined May 2004
176 Posts
Nice looking board....

It needs a modem and magnetometer to be perfected....and maybe switching regs.

Also only 5 dof imu (no mag).

Amazing what sparkfun is cracking up! Give me a board with the above listed and I'm sold!
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Old Jan 07, 2009, 10:42 PM
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Joined Jan 2009
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Quote:
Originally Posted by rbeall
Also only 5 dof imu (no mag).
6 DOF means 3-axis accelerometer and 3-axis gyro, which it has. Sparkfun also sells a PNI 3-axis magnetometer for $60, which requires a simple SPI interface. The magnetometer should be on a separate board in any case, as the further you can place it away from other sources of magnetic and electrical noise, the better...
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Old Jan 08, 2009, 02:12 AM
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176 Posts
yeah you are right! I was being retarded. I was just running through the Psi determination and realized that you can't get psi from this unit and then made crazy remarks. I stand corrected. I guess you could get Psi from gps but most of my work assumes little to no gps.

Fun little unit would like to get in touch with the designer for sure and see if he's going to go any further. I just finished up a similar board but its got a mag and modem as well as pitot statics and switching regs. Cant wait to get them in and start working. I only have the proto board tested minus the gyros because the non soldermasked board was shorting the gyros. One more week and they will be in!
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Old Jan 13, 2009, 11:52 AM
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Joined Jan 2009
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degrees of Freedom

Hi all,

I am pretty sure that you can determine a fair approximation of the orientation of a plane from GPS, 3 accelerometers and 3 gyros, although you might have to incorporate a model of the plane and use GPS, accelerometer and gyro information to get an accurate estimate of bank angle. Pitch and yaw should be no problem in any case. The GPS that I am recommending provides a very accurate 3D velocity vector based on Dopler shift. Together with gyro, accelerometer information, and a model of the plane, you can make a very good estimate of the orientation of your plane. The only caveate is that since GPS gives course over ground, if for some reason you prefer to navigate and control the plane with respect to the air instead of the ground, you will have to estimate wind velocity some how. Anyway, my goal for the spring is to perform aerobatics under autonomous control. I'll let you know how it works out. I will publish the firwmare.

With my previous board that had GPS, and only 2 accelerometers, and 2 gyros, I was able to construct a fairly accurate model-based (I had to include actual rudder and elevator deflections in the algorithm) estimator of yaw, pitch, and bank of a sailplane. I used it this past summer to provide pitch stabilization and a come-home feature for my Gentle Lady. Performance was very smooth with no problems during 100s of flights. The source code on the DIYdrones website is a simplified (I finally decided that I got better performance without bothering with mixing and bank angle) port of this firmware from the previous board to the new one.

You might be interested in reading some of the material I wrote on the subject of control and navigation algorithms, its available at www.sparkfun.com on the page for the first version of my board, which by the way is now on sale for half price. If you are considering a sailplane, you might do well to buy the previous version of the board. The code for it is in assembly, but it is my understanding that there is a free C compiler available from MicroChip that is compatible with the 18F2520 PIC that is used on the board, if you have any interest in rewriting the firmware in C.

I invite anyone who wants to, to get in touch with me here.

Best wishes to all who read this.

Bill Premerlani
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Last edited by premerlani; Jan 13, 2009 at 12:02 PM.
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Old Jan 13, 2009, 05:54 PM
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By the way, a GPS, 3 gyros, and 3 accelerometers can be used to provide control and navigation for a car, a boat, or a plane. Anything that continually moves more or less in the direction that its is pointed. However, for anything that can hover or move backward, like a helicopter, you will also need a magnetometer.
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