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November 2010

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From:
Tom Bove <[log in to unmask]>
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Date:
Fri, 19 Nov 2010 14:47:05 +0000
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We encountered the same situation, but the sensor was within a loop block.  The height of the sensor didn't seem to be a factor.  Approaching objects at other than a 90 deg angle seemed to be the major issue.  Also, I had not sanded the wood borders of our practice field, and after smoothing the problem area, the accuracy improved.  We did insert a stop motor block upon exiting from the loop to avoid coasting issue.

At the competition, it worked fine.

Tom
Coach of Team #2280- The Blockheads


-----Original Message-----
From: Jamie Diamond [mailto:[log in to unmask]]
Sent: Friday, November 19, 2010 09:16 AM
To: [log in to unmask]
Subject: Re: [VADCFLL-L] Ultrasonic sensor - not behaving accurately

Do you have a motor or move stop block to force the move or motors to stop after the wait block? The wait block does not in and of itself stop the motors, it just transfers control to the next block after it when the condition is met. If the wait until ultrasonic sensor is the last block in your program then it will overshoot as the motors coast to a stop.

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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