Re: Location Detection

I've heard about using accelerometers to detect movement (like in the 
new PowerBooks) but my general perception is that it can get fairly 
complicated to implement and if it's not done correctly, can have 
serious accuracy problems. With the resources I have available to me, 
precise measurement and calibration isn't easy. I'm more of the "Stick 
it on with some duct tape" philosophy.

However, I've been wondering if an optical mouse might work for tracking 
movement... Just mount it on the bottom of the robot and plug it into 
the gumstix... Shouldn't be too hard to figure out how the X11 mouse 
drivers work and hack it up to just record (x,y) coordinates starting at 
(0,0) when the robot is powered on. This seems like it would be a fairly 
high resolution way of detecting motion and would be a lot 
cheaper/easier than a gyroscope or accelerometer arrangement.

--
Jeremy Grosser
www.runemonkey.com

Aleksandar Matijaca wrote:
> Self - calibration --- why not just place occasional RFID tag (extremely 
> short range antenna) on the floor,
> and those can be used by the robot as a calibration point when it runs 
> over it??
>
> Regards, a.m.
>
>
> On 7/9/05, *Athanasios Anastasiou* <thanos@xxxxxxxxxx 
> <mailto:thanos@xxxxxxxxxx>> wrote:
>
>     Hello Jeremy
>
>     I also had the idea of using several ultrasound fixed beacons and
>     deriving the position from these BUT there is a much easier solution to
>     this which is used as an alternative navigational aid.
>
>     It is called Inertial Navigation and it breaks down to basic principles
>     of Kinematics.
>
>     You just mount an accelerometer on your robot and calibrate it before it
>     sets off moving around. The calibration is just setting the starting
>     point. Lets suppose that this is A(0,0). When the robot starts to move,
>     the accelerometer records the dx, dy and dz of the robot chassis and
>     updates the starting point. So after integrating the accelerations you
>     get a new point B(x,y).
>
>     Ofcourse there are a few caveats in this method, one of which is that if
>     your robot moves towards a direction, under the threshold of detection
>     of the accelerometer, its movement will not be recorded and its
>     position
>     not updated. But this is not so serious in robots that have 4 wheels and
>     move in interior spaces (probably more of a problem for marine robots
>     using this method.).
>
>     The second problem is that you have to make sure that the accelerometer
>     is always vertical in respect to the chassis of the robot (otherwise you
>     need to correct the accelerations for the angle of movement). If you are
>     absolutely sure that the robot is not going to get tilted you can use a
>     single accelerometer...If not, you need an extra accelerometer just for
>     measuring the angles and thus adding three more degrees of freedom
>     (movement in three directions plus roll pitch and yaw angle).
>
>     STMicroelectronics sells some very interesting accelerometers that can
>     give you the three basic accelerations (dx,dy,dz) over serial or I2C
>     buses. In an application note i noticed that a single accelerometer can
>     also be used to provide angular position as well. I am not so sure
>     about
>     that...
>
>     Could there be any other alternatives to correcting the values that an
>     accelerometer returns except mounting it on super slick gimbals and
>     gyroscopic mechanisms??????
>
>     I hope this helps
>
>     All the best
>     thanOS


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