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Re: [Paparazzi-devel] Reply to:"Re: ArduIMU and Tiny autopilotcontinued

From: David Conger
Subject: Re: [Paparazzi-devel] Reply to:"Re: ArduIMU and Tiny autopilotcontinued (David Conger)"
Date: Thu, 02 Dec 2010 20:31:55 -0800

Hi Steve,

Thank you very much. This is good news then. When you say "I tried to read it at 50hz ... reading at 40hz seemed to work ok". Where did you change the code to do this? I would like to try this and see if that helps. My FunJet has the IMU and autopilot mounted to black foam about 9mm thick which is mounted to thin plywood. This board is then mounted on another plywood plate fixed to the airframe. This allows me to quickly and easily remove and replace the autopilot and IMU from the airframe by just unplugging the wires. Here's a photo:

I hope with the changes and a very balanced propeller I can fly with this setup. I have only done one test flight in manual so far. I did learn never to paint a plane all black and try and fly at sunset. It was a short flight with a very hard landing. This photo was take after I glued the front back onto the back of the fuselage so it seems my wiring and setup is very durable. :)

On Dec 1, 2010, at 1:53 PM, Steve Joyce wrote:

I took a look at this too after it was posted on the Wiki.  As I understand the code, the attitude solution is calculated at 50Hz,  It is just that it is polled from the module on the paparazzi side at 15Hz. 
I tried to read it at 50Hz, but it didn't work (probably overloads the processor with I2c interrupts or has some other timing problem).  But reading at 40Hz seemed to work quite OK.  It was a noticable improvement in the control response in Auto1.
It flew my plane with the same control parameters I use for IR sensors.  The only thing I noticed was a pitch-down on acceleration and pitch-up on deceleration, which is to be expected.
----- Original Message -----
Sent: Wednesday, December 01, 2010 9:25 PM
Subject: Re: [Paparazzi-devel] Reply to:"Re: ArduIMU and Tiny autopilotcontinued (David Conger)"

Does anyone know how fast the gyro integration is done in the arduIMU (Atmel). (DCM propagation)

15Hz attitude data is sufficient for stable flight (slow of fast) but the lower bandwidth sensor also means you need to reduce the gain compared to 60Hz attitude, especially when flying fast (extra phase gives smaller gain margin).

But 15Hz integration is very very low on anything as small and agile as a Funjet. If the weather is smooth enough I do believe this will work, but it's also extremely easy to make is not work anymore by adding vibrations, turbulence, etc...

Even with a very efficient fixed-point implementation, a 20MHz 8-bit micro is "a bit" weak...


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