Calculating speed of the rocket using MPU9250 and may be BMP280

[Nursik]

I am new to this forum and I think this is suitable place for this question.
I wanted to calculate speed of the rocket using those two above mentioned sensors. I did some research before and understood that I could do integration method using the altitude that I could get from BMP280 or do some stuff with angles using accelerometr, but most of them are giving incorrect values most of the time.
So if you ever calculated the speed of the rocket such that you had +- 10 m/s accuracy, could you tell your method?

 

[waltr]

If starting from altitude you need to differentiate. Disadvantage is the Velocity is noisy and if vector not straight up.
Veln = Veln-1 + [Altn - Altn-1]/dt

Where:
Veln is current Velocity
Veln-1 is the previous Velocity
Altn is the latest altitude
Altn-1 is the previous altitude reading

If starting with Acceleration you need to subtract Earth constant then integrate. Advantage is Vel is cleaner since integration filters noise. Disadvantage is if Vector not straight up.
Veln = Veln-1 + [Accn+Accn-1]*dt

If you have data from both sensors then calculate Vel from both.

There are more complex methods that obtain more accurate results.
Search the forum here from info on these other methods.

 

[Spacedog49Krell]

First a couple of very basic questions, what CPU are you using? How fast are you sampling your sensors? To achieve good velocity values from the BMP280, you need to sample it between 50 - 100 samples/second. I recommend sampling rates between 200-400 Samples/second for the accelerometers and gyros. I have flown the older MPU-6050 with great success.

 

[Chad]

The flightsketch firmware is open source and it used the bmp280, you may be able to read through this and get some ideas. look at the function starting at line 1887

https://github.com/flightsketch/firmware/blob/master/main.c