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**Discussion forum for the BasicX family of microcontroller chips.**

I'm a new user of basicx

currently i have a biaxial accelerometer, can i use it to get the

position of a robot?

**_____________________________**

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currently i have a biaxial accelerometer, can i use it to get the

position of a robot?

to tell if one wheel tilts too high on one side or the other.

-----Original Message-----

From: b... [mailto:b...]On Behalf Of

hankybanky123

Sent: Monday, September 25, 2006 8:26 PM

To: b...

Subject: [BasicX] Can I use accelerometer to get position?

I'm a new user of basicx

currently i have a biaxial accelerometer, can i use it to get the

position of a robot?

> I'm a new user of basicx

> currently i have a biaxial accelerometer, can i use

> it to get the

> position of a robot?

>

> good mornin

ya surely u can use that but confim first whether it

is workin properly or not? if any qurries then do

reply ok:)

>

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(i.e. where is Down?), but not where the accelerometer is related to its

environment (where am I?) except as part of a Dead Reckoning algorithm.

Google "accelerometer applications".

http://www.memsic.com/memsic/pdfs/an-00mx-001.pdf

http://www.analog.com/en/cList/0,2880,764%255F%255F43,00.html

http://www.xbow.com/Support/appnotes.htm

Tom

>

> I'm a new user of basicx

> currently i have a biaxial accelerometer, can i use it to get the

> position of a robot?

>

Yes, if you integrate acceleration once you will get velocity (V). If

you integrate the measured acceleration (A) signal twice, you can get

position (P). Be sure that the robot is at rest when you start

integration though because it needs known initial conditions of

position and velocity (which in this case is P(0)=0 and V(0)=0). You

will need to sample the acceleration at a known small time interval

(DT. i.e. DT=0.01 sec).

Here is a reasonable way to compute the first and second integrals to

yield velocity and position respectively at each time sample, k:

V(k)=V(k-1)+A(k)*DT

P(k)=P(k-1)+1/2*A(k)*DT*DT

These should look familiar to you from your physics text book. You

need to compute these equations for each axis to get Px and Py from

your dual axis accelerometer.

An important thing to note about getting position from an

accelerometer is that the error in position "integrates" What this

means is that if the noise or error in your accelerometer follows a

normal distribution (overestimates and underestimates equally) then

your position estimate should be reasonable. If however, the

accelerometer is biased (tends to overestimate more than

underestimate or vice versa) then the error in your position estimate

will grow exponentially. Any error is kept in your calculation

thtough the iteritive integration, so calculating position the

accelerometer can have large errors. But it still is a valid way to

get position. Give it a try!

Sami.

inaccurate very quickly.

_____

From: b... [mailto:b...] On Behalf Of

Sam

Sent: Wednesday, September 27, 2006 12:01 PM

To: b...

Subject: [BasicX] Re: Can I use accelerometer to get position?

--- In basicx@yahoogroups. com,

"hankybanky123" wrote:

>

> I'm a new user of basicx

> currently i have a biaxial accelerometer, can i use it to get the

> position of a robot?

>

Yes, if you integrate acceleration once you will get velocity (V). If

you integrate the measured acceleration (A) signal twice, you can get

position (P). Be sure that the robot is at rest when you start

integration though because it needs known initial conditions of

position and velocity (which in this case is P(0)=0 and V(0)=0). You

will need to sample the acceleration at a known small time interval

(DT. i.e. DT=0.01 sec).

Here is a reasonable way to compute the first and second integrals to

yield velocity and position respectively at each time sample, k:

V(k)=V(k-1)+A(k)*DT

P(k)=P(k-1)+1/2*A(k)*DT*DT

These should look familiar to you from your physics text book. You

need to compute these equations for each axis to get Px and Py from

your dual axis accelerometer.

An important thing to note about getting position from an

accelerometer is that the error in position "integrates" What this

means is that if the noise or error in your accelerometer follows a

normal distribution (overestimates and underestimates equally) then

your position estimate should be reasonable. If however, the

accelerometer is biased (tends to overestimate more than

underestimate or vice versa) then the error in your position estimate

will grow exponentially. Any error is kept in your calculation

thtough the iteritive integration, so calculating position the

accelerometer can have large errors. But it still is a valid way to

get position. Give it a try!

Sami.