Need advice on Lego NXT Ultrasonic sensor use.

[Jim DiNunzio]

I’m getting my bot ready for our RSSC’s contest, the Can-Do Challenge on Feb 14 (https://www.rssc.org/can-do-challenge.html), and need some advice on use of the Ultrasonic sensor use.

 

I’ve attached two pictures of my bot. I’ve used this sensor before successfully for at least 2ft in contests a long time ago where I mounted it horizontally. However, in this design I thought vertical would be better to detect a can. I tried horizontal first, but it didn’t work any better.

 

https://www.youtube.com/watch?v=dNbv3ONI3cU&list=PLmb0WjGtyZZS9qjUYhY4bdeh4ZQYx7BYS

Each tile has 12in (30cm) sides

 

I can reliably get good distance measurements when a can is within 1-2 feet (30-61cm), but I need a 3 feet (91cm) range for the contest.

The sonar seems to be very sensitive to its pitch and if pitched a small angle too low it strangely sticks to reading 23cm, some point on the floor. If it is slightly too high then it misses the can entirely. The further away the target is the smaller the sweet spot angle.

 

But keeping it exactly level on a moving platform is challenging. I’ve tried adjusting its pitch very slightly but it has not resulted in an improvement. My earlier bot design was a little more stable and maybe kept the sensor more level?

 

I do have a second ultrasonic sensor and am wondering if I should mount it as well. Both units behave the same when mounted in the position shown.

 

Thanks,

Jim

 

[camp .]

    It could be worse. At least you're trying to find something cylindrical. With the TABLEBot Challenge, I've taken to using a 3.5" tube as my "block" because ultrasonic waves spang off flat surfaces, never returning to the receiving transponder.

Enjoy,

Camp

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[John Davis]

My suggestion is foam-tape off a lower section of the transmitting sensor and aim slightly below the optimum. That way, if the robot tilts upward it may still see the can but the nearby floor will not be illuminated. If it tilts downward, the floor reflection may still be reduced sufficiently while the normal cone still strikes and reflects from the can. I think the lower 'eye' is the transmitter on your robot.

John F. Davis
(310) 961-2196 (cell)

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