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Alok, Have your team put the ultrasonic sensor block within a time loop and
also use a switch.  That way you can make it either detect the object/wall
correctly or have it quit the loop after specified time, whichever happens
first.

Sachin Aradhey
#3629 Nanobots
Harrisonburg, VA.

On Fri, Nov 19, 2010 at 9:10 AM, Alok Jain <[log in to unmask]> wrote:

> Hi!
> My team realized that ultrasonic sensor is not consistent when used with
> the wait block. Sometimes it seemed to be not stopping at all. I am talking
> about big objects and the side wall. I did a little experiment and there
> seems to be a difference of 15 cm (at power level 60). i.e. if I want the
> robot to stop at 30 cm, it actually stops when distance is 15 cm.
> I tried changing the sensor and also putting the sensor lower, but still
> the same result. The reading in the sensor, when robot is stopped, shows up
> correctly. It is only while stopping it is acting up. At power level 75 and
> higher it totally misses the stop point. Did anyone else face this problem
> in the past? Am I doing something wrong ?
> Here are my questions:
>
> 1) how high should the Ultrasonic sensor be placed from the ground?
> 2) Is there something I need to caliberate or change in the program ?
>
> My team is competing on Sunday, so any help is highly appreciated.
>
> Thanks,
> Alok
>
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