+ Post New Thread
Results 1 to 8 of 8

15th June 2016, 17:00 #1
 Join Date
 Feb 2011
 Posts
 45
 Helped
 2 / 2
 Points
 1,320
 Level
 8
How to measure linear acceleration?
Hi!
We know that accelerometer measure acceleration due to motion and gravity? The question is how we can obtain acceleration measurement due to motion alone?Last edited by helmi_mjd; 15th June 2016 at 17:06.

15th June 2016, 17:00

15th June 2016, 17:37 #2
 Join Date
 Mar 2005
 Location
 California, USA
 Posts
 3,570
 Helped
 779 / 779
 Points
 18,622
 Level
 33
Re: How to measure linear acceleration?
You mount your accelerometer along the axis of motion, or buy a multaxis accelerometer. If you do the most basic of searches you'll find accelerometers that do what you want. Try searching "accelerometers".

15th June 2016, 18:50 #3
 Join Date
 Sep 2013
 Location
 USA
 Posts
 6,033
 Helped
 1478 / 1478
 Points
 26,543
 Level
 39
Re: How to measure linear acceleration?
A quick review of the wiki pages on both motion sensing and accelerometers yields that accelerometers make somewhat poor motion sensing devices, as they measure acceleration only not motion.
e.g. if you have an object that moves at a constant velocity in a direction that is perpendicular to gravity an accelerometer won't sense it's motion as there is no acceleration on the sensor. This is why an accelerometer in free fall measures 0.

15th June 2016, 18:50

15th June 2016, 19:08 #4
 Join Date
 Feb 2011
 Posts
 45
 Helped
 2 / 2
 Points
 1,320
 Level
 8

15th June 2016, 19:26 #5
 Join Date
 Mar 2005
 Location
 California, USA
 Posts
 3,570
 Helped
 779 / 779
 Points
 18,622
 Level
 33
Re: How to measure linear acceleration?
I would suggest you look at the data sheet for both the DF Robot part and the ADXL345 which it's based on. Usually with a 3axis device like this you orient one axis (say, Z) along the gravity direction. Sometimes the device automatically compensates for gravity so that when it's mounted this way, the x and y axis outputs are zero at rest. If not, then you'll have to calibrate out the gravity term.
1 members found this post helpful.

15th June 2016, 19:26

15th June 2016, 20:12 #6
 Join Date
 Feb 2011
 Posts
 45
 Helped
 2 / 2
 Points
 1,320
 Level
 8
Re: How to measure linear acceleration?
Thank you barry. I will study on this. For now, this is what i have from the IMU:
X: 0.16 Y: 0.59 Z: 8.67 m/s^2
X: 0.20 Y: 0.55 Z: 8.63 m/s^2
X: 0.12 Y: 0.59 Z: 8.63 m/s^2
X: 0.16 Y: 0.55 Z: 8.63 m/s^2
X: 0.16 Y: 0.55 Z: 8.63 m/s^2
X: 0.16 Y: 0.59 Z: 8.63 m/s^2
X: 0.12 Y: 0.59 Z: 8.63 m/s^2
X: 0.16 Y: 0.59 Z: 8.63 m/s^2
X: 0.08 Y: 0.55 Z: 8.63 m/s^2
X: 0.16 Y: 0.55 Z: 8.59 m/s^2
X: 0.12 Y: 0.59 Z: 8.67 m/s^2
X: 0.16 Y: 0.55 Z: 8.55 m/s^2
X: 0.16 Y: 0.59 Z: 8.59 m/s^2
X: 0.16 Y: 0.59 Z: 8.63 m/s^2
X: 0.12 Y: 0.63 Z: 8.67 m/s^2
X: 0.16 Y: 0.59 Z: 8.59 m/s^2
X: 0.12 Y: 0.63 Z: 8.55 m/s^2
X: 0.20 Y: 0.55 Z: 8.59 m/s^2
X: 0.16 Y: 0.55 Z: 8.55 m/s^2
X: 0.16 Y: 0.55 Z: 8.59 m/s^2
X: 0.12 Y: 0.59 Z: 8.59 m/s^2
But I'm not really sure why the z is not ~9.81 m/s. I will look in this matter also.
Thank you again.

15th June 2016, 21:49 #7
 Join Date
 Mar 2005
 Location
 California, USA
 Posts
 3,570
 Helped
 779 / 779
 Points
 18,622
 Level
 33
Re: How to measure linear acceleration?
My first guess would be that you don't have your device mounted exactly perpendicular to the earth. That would explain the values you are seeing.
1 members found this post helpful.

16th June 2016, 08:27 #8
 Join Date
 Feb 2011
 Posts
 45
 Helped
 2 / 2
 Points
 1,320
 Level
 8
+ Post New Thread
Please login