Content in “sensor”

can any1 pls xplain d working of ULTRASONIC SENSOR?

or working of anyother environment independent sensors? 

Hi all, I am so excited about this. It may not be much to anybody else, but to me it is!

You all know how we only have the IR's or the Ultra sound to work with when we want to check distance? Yeah, if we have millions we can also get a camera or two, and laser range finders..

However, I wanted something cooler.

This is not that, I am sorry.

However, I am working on something cooler (I hope, but it may be far fetched), and when doing so, as a spin off I made this. 

And it is pretty wicked, I think.

Hi, I'm pretty much new to robotic, even though I've worked with kit like fischertechnik and Lego NXT.

I know the base of it, and i'm good with electronics.

but here it is i want to build plane that coud fly by itself using rangefinder (Ir or ultrasonic) to keep a distance from the ground, but i've read that IR sensor aren't good outside and that ultrasonic doesn't work good on absorbant material (Grass).

Since it's a plane I also have to consider weight in my choice.

Wich sensor would be the best for this task ?

I need help in using an optical mouse as a sensor for my mini-sumo. i read from some place that it could be used to let the robot know that it is slowing down and will react to it. Does anyone know how i could use a mouse to do this?