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[Paparazzi-devel] Paparazzi TWOG and Tiny13 tested with low cost IMU

From: Prof. Dr.-Ing. Heinrich Warmers
Subject: [Paparazzi-devel] Paparazzi TWOG and Tiny13 tested with low cost IMU
Date: Fri, 23 Jul 2010 22:04:03 +0200
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Same news for Bremen,

We have tested a low cost Sparkfun IMU ( RAZZOR IMU 6DOF Razor - Ultra-Thin IMU)
with the paparazzi hardware.  Five month ago we tested the tiny13 with or quadrocopter code successfully . We were a little bit surprised, that we can fly our quadrocopter with low cost MEMS sensors.

The price of the sensors is about 9.9 euro and 6.99 euro in single quantities ( The quality is not as good as the ADXRS610 but we found no significant differences in fly with it since the drift is compensated. For the quadrocopter we use our  Klaman-filter (run time is 7.5 ms)  and for normal plane we use a filter interdruced by  William Premerlani, and Paul Bizard:  

Direction Cosine Matrix IMU:Theory, William Premerlani, Paul Bizard,05.17.2009,

We take this filter for normal plane configurations and integrate it to the Paparazzi autopilot system  by the use of a small planar sensor pub with new MEMS rate sensors form STMicroeletronics
LPR530AL (pitch and roll) the LY530ALH (yaw) and the ADX335 (Analog Device) acceleration sensor. The rate sensors have high vibration frequencies (over 20kHz) and a high vibration resistance. After exact bias calibration of the sensors we found out that the DCM filter with PI-Controller is very robust by low computer cost. The run time is only 0,59ms for the LPC2148 ARM7 micro controller running at 60 MHz. The only small disadvantage is that the controller after power up needs about one minute to stabilize on zero pitch and roll angle  We made automatic flights with a 400mm and 800mm span with delta (up to 17m/s. wind speed).  Compared with the old IR-sensors attitude estimation these solutions give all weather compatibility and a better performance in flight dynamics.

The kinematic equations are integrated in a notation of the DCM 50 times per second. To save orthogonality of the DCM for every integration step small adjustments of the matrix elements are applied. For bias and drift error correction a PI  feedback controller is used. To estimate the errors the acceleration data and the GPS ground speed is taken into account.

 The price of the new sensor set is lower than the old IR system. For the twog the resistors to ground had to be extracted.  A low cost system consist of  69$   for the twog   (I fetched it for this price currently 125$)  35$  for GPS and 90$ for the IMU.  If you can solder the imu self it will cost less than 35 $.  You have to short the high pass filter on the rate signal for better performance of the RAZZOR IMU. Currently a paparazzi compatible planar pcb is under development  with this sensors (30mm*57mm) with normal servo connectors to fly quadrocopters and normal planes.

 It will need a few weeks to document the work since most of our team members are in vacation.  We will do this soon as possible. The changes on the code are marginal.



Attachment: Warmers_Tiny_IMAV2010.pdf
Description: application/empty

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