How accurate are the ultrasonic sensors??

I’m thinking about buying a few to try some basic room navigating stuff… just need to know what they are accurate to… the web page says 1.5 to 115 inches… so does that mean its only good at 1.5 inch increments??

I’d like to be able to place it at ground level and have it basically go in a circle(measuring every 4 degrees as thats the limit of the optical shaft encoder) and then look for gaps to move through.

Thanks guys…

from my personal experience the ultrasonic sensors are good for finding large objects(walls, Atlas balls). I belive that the ultrasonic sensor works from 1.5" tp 115 on any increment. to calculate the values given use the print to screen function and watch the values given. Start the sensor touching the wall and slowly back away at equal increments. In my own experimentation i found that the value change is most easilly noticed in about 1/2" increments.

The timing resolution is far better than it needs to be for a VEX robot. Depending how you have implemented the software, resolutions of better than a millimeter are possible.

However, you might want to research how altitude and humidity affect the speed of sound if you want accuracy on that kind of scale…



Well, I am looking for accuracy of something close to an inch. I do plan to do a bit of experimenting with it to see what all I can get out of it. The ideal goal would be very rough 3d composites from the front only kinda thing.

IE, if I put a ball infront of it it gets results in say a 10x10 grid with the numbers inside being the ultrasonic results then I could at least look at it and go “Oh, that could be a cup.” etc etc…

Just wanna see how well it works. using optical shaft encoders to get at least somewhat accurate readings on where the sensor is pointing.

One thing to keep in mind on the ultrasonic sensor is that the beam width is quite wide - nearly 15 degres. That means for any direction, you get the distance to the nearest surface within 15 degrees of the sensor pointing angle. This sensor is not very good for mapping of any sort. See the good writeup at

FX Govers

Dangit your right i forgot about it!

Man… we need a laser range finder lol.

You could use a Panasonic IR range finder. They are cheap (~$12-15), narrow beamwidth, and good for ~5ft of range.

(OOPS, I meant Sharp, not Panasonic)

I’ve got the Sharp GP12D2 IR ranging sensors working just fine on my Vex robot – use them as analog inputs. They are good out to about 4’ and have a very tight beam. see for details.

That is my plan rightnow :wink: gonna order some tonight I think. Thanks again :slight_smile: