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About ashishtbm
since
06-04-2021
07-01-2021
ashishtbm
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06-30-2021
08:30 PM
I agree with you that MEMS sensors currently available are not military/tactical grade ones. But I have purchased one BMI088, one of the recommended applications is drones. It is true that INS needs very accurate sensors especially in GPS denied environments, but implementing an AHRS should not be an issue. Even if drone is a toy class, for autonomous flying all three euler angles needs to accurate enough (especially roll and pitch) and without any major drift. My only point was in case of long duration external accelerations, accelerometer cannot be trusted for absolute attutude estimation hence there will be nothing to stop the drift in estimated angles. If we see the current scenario, all the flight controller boards use these consumer grade MEMS sensors. So, I just wanted to understand the basics behind the drift problem in case of external acceleration. I would be grateful if you can refer to some books/papers which I can refer to and understand basics.
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06-27-2021
07:23 PM
I was going through theory of INS and trying to understand attitude estimation, velocity and position and estimation. Theroy can be summarized as follows, 1) Gyro is integrated to estimate the attitude/orientation, with initial orientation as the initial condition. 2) Accelerations measured in body frame are converted to inertial frame using orientation given by gyro, and then acceleration in inertial frame is integrated to get velocity and again integrated to get position. Initial velocity and position are the initial conditions. So, above two steps are quite clear. But now the doubt/problem comes into picture, 1) Any gyro, however accurate it is will have bias and moreover changing bias, which will mess up the estimated attitude for sure. In this scenario, estmation of postion and velocity will definitely be erroneous. 2) Error in position and velocity can be tackled by GPS, but what about attitude? How to restrain drift in estimated attitude within acceptable limits? 3) Lets assume a scenario in which a small UAV is going in tight horizontal circiular motion for extended period of time. In this scenario, accelerometer cannnot be used to correct for drift, as there is constant acceleration in addition to gravity. How to tackle this problem? Whether this problem is solvable at all in case of MEMS IMUs? I understand that fusion softwares are proprietory solutions but I am not asking for any code here. I just want some explanations about how things are done in this respect. Thank you.
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06-07-2021
07:02 AM
I have already gone through the code and what I can see is, only thing is to bring accelerometer in active mode (unless we don't want to change ODR and range) and after that we can read the data. In my case, I have confirmed the written register, and temperature data is coming correctly. Infact I have checked all the register values, before and after writing. Even sensor_time register is not incrementing, it's LSB is showing value of 54 and not changing. Other two higher bits are showing 0. And as I said, all 6 registers of accelerometer is being read as zero. But acc_bit is being set, which I have confirmed by reading corresponding register.
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06-04-2021
09:57 PM
I have recently bought BMI088 IMU and started interfacing work with atmega2560. I have written my own I2C routines to perform communication task and UART routines to see the output on serail terminal. Rotines are functioning without any issues as I am able to read gyro data and temperature data (from accelerometer). Now only problem that I am having is that acceleration data being read is 0 in all three axes and there is no change at all. What may be the reason? I have few points, 1) In device initialisation procedure, it says to only write 0x04 in ACC_PWR_CTRL(0x7d) which will bring devide in normal mode. I have written this register, checked it by reading it as well. As temperature reading are coming proper, it signifies that accelerometer has been brought to active mode. In this scenario, accelerometer should also spit out correct reading, but it is not. 2) There is one more register ACC_PWR_CONF(0x7c), reset value of which is 0x03 which corresponds to suspended mode. And this need to be written with 0x00 to bring accelerometer in active mode. There is no mention about this register in initialisation procedure. Although I have written this register to 0x00 but still acceleration output reads 0. Any help is appreciated.
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