MultiWii

Hi Ziss_dm,

I am interested to run FFT on my BMA020 but I am not a specialist of C language. I f you can supply the software required, I will be happy to run the FFT.

Regards,

Phebus

Hi, Ziss_dm To do a spectrum analysis of brushless motor vibrations on my Tricopter, I have made a new simple test setup that can easily be reproduced. Equipment required: -1 PC running Windows XP, -Nunchuk clone with pcb cut around the ADXL335 3-axis analog accelerometer, wires connected to Gnd, Vc...

Hi Ziss-dm, The ADXL345 data sheet Rev C indicates that due to i2C communication speed limitations, the maximum output data rate when using 400 kHz I2C is 800 Hz (page18) corresponding to a bandwidth of 400Hz (table 7 page 14). Applying to the ATmega 328 microcontroller with 2mS cycle time or 500Hz ...

Hi Ziss-dm,

On your recording, what is the maximum output data rate of the ADXL345, what is the unit for the cycle time, what is the maximum output data rate to the GUI ?

Regards,

Phebus

Hi Ziss-dm, I have tried foam tape with little results. Because of the low weight of the electronic board, the foam tape needs to be very soft to get a low resonant frequency to filter the vibrations. Then the board wobbles at the resonant frequency and you get more noise on the gyros. Best results ...

Hi Ziss-dm, All my measurements are made with my tricopter at rest on the ground, motors at idle (3900rpm). Would you detail how you get 153W. On my vibration abacus for a sine wave with frequency 750Hz and 2G max acceleration I get a maximum velocity of 4.3 mm/s and a peak to peak amplitude of 0.01...

Hi Ziss_dm, I have checked, with motors running and test accelerometer not touching the central plate, that the accelerometer output is flat showing that there is no electromagnetic interference from ESC’s. This is confirmed by the HMC5883L digital compass heading output not moving at all with motor...

Hi ziss_dm When I have done my tests, I have recorded the vertical acceleration with only one motor on at iddle. The settings are : Y= 200 mV/division = 0.6 G/division, X=2mS/division. Tricopter, one motor on.jpg On this picture of my oscilloscope, the switching of motor poles is at 750 Hz correspon...

Under is the picture missing.

In order to confirm that high frequency motor vibrations saturate the BMA020 A to D converter when G range is set to +/- 2G, i have glued on the central plate of my tricopter a +/- 3G ADXL335 analog accelerometer with its first order low pass filter set to 500 Hz. With motors running at min. throttl...

This only affects BMA020, right? I did TRUSTED_ACCZ on my hardware with adxl345 as I was curious if AccZ would change ... and it was fine even at max throttle. Hi dongs The ADXL345 works fine because in the Multiwii software the acceleration range is set to +/- 8G (register 0x31, 0x0B) and thus the...

Hi Ziss_dm I have done the following modifications in the BMA020 section of the Multiwii software : control = control | (0x00 << 3); //Range 2G 00 replaced by control = control | (0x02 << 3); //Range 8G 00 and to get acc_1G = 255 in the GUI, ((rawADC[1]<<8) | rawADC[0])/64 , ((rawADC[3]<<8) | rawADC...

The decrease of AccZ while powering up the motors seems to be due to saturation of the BMA020 input. When motors are running, the maximum amplitude of high frequency motor vibrations may exceed the +/- 2G range of the BMA020 A to D converter because the 20 Hz low pass filter is after the A to D conv...