Sonar sensor crosstalk

[carrillo694]

Our team is considering employing the distance measurements offered by the KOP MaxBotics ultrasonic sensor. However, we are also concerned about the possibility of "crosstalk" with other robots using this sensor, whereby we might accidentally read the ultrasonic pings of nearby robots around us who are also using the sonar sensor.

To what extent is this concern justified? Have other teams experimentally observed the effects of this phenomenon, or had experience with ultrasonic ping sensors that have been interfered with by other robots' ping sensors?

[WileyB-J]

Do you know how the retro-reflective tape works? The sonar sensors work in a similar fashion. The communication band is rather narrow and unless another sensor is VERY close to yours, it should not interfere. The sonar wavelength "cone" is small enough to make background noise negligible.

[StevenB]

I worked with several of the MaxSonar EZ1 sensors back in 2007. I found that they generally worked very well, but did occasionally interfere if the sensors were parallel to each other and between roughly 1 and 2 feet apart. Unsurprisingly, there were also problems if the sensors were pointed directly at each other.

In general, the sensors worked very well, and I wouldn't worry much about interference. We were using them close together for sensing game pieces (and chose to use Sharp IR sensors instead) but for navigation-level sensing, the MaxSonar sensors are an excellent choice.

As with any sensor, you should filter the input, especially if a result is going to cause irreversible actions. For example, instead of driving until you get a reading less than 8 feet, drive until you get three successive readings under 8 feet. It's the real world, so expect a bit of noise in the readings!

These links might be useful:
http://maxbotix.com/performance.htm
http://maxbotix.com/articles/012.htm

[carrillo694]

Originally Posted by StevenB

I worked with several of the MaxSonar EZ1 sensors back in 2007. I found that they generally worked very well, but did occasionally interfere if the sensors were parallel to each other and between roughly 1 and 2 feet apart. Unsurprisingly, there were also problems if the sensors were pointed directly at each other.

In general, the sensors worked very well, and I wouldn't worry much about interference. We were using them close together for sensing game pieces (and chose to use Sharp IR sensors instead) but for navigation-level sensing, the MaxSonar sensors are an excellent choice.

As with any sensor, you should filter the input, especially if a result is going to cause irreversible actions. For example, instead of driving until you get a reading less than 8 feet, drive until you get three successive readings under 8 feet. It's the real world, so expect a bit of noise in the readings!

These links might be useful:
http://maxbotix.com/performance.htm
http://maxbotix.com/articles/012.htm

Thanks for your help! I think your comments about personal experience, as well as the documents you have linked us to, have answered our question.

[rEgonicS]

Does the sonar only detect (or at least supposed to) the reflective tape? I wasn't sure how it worked so I tried testing its accuracy by putting a block of wood and metal in varying distances in front of it. The results were rather discouraging.


Also, I think I read somewhere that connecting the sonar through a digital input is more accurate than analog. Is it worth switching the output method?

[EricS-Team180]

rEgonicS,
The sonar is a sonic range finder, the camera will be used to detect light from the retro-reflective tape. Please take some time to investigate the sonars on the MaxBotics site. Over the last 5 years they have introduced a series of them for different applications. The EZ1 may not be the best for singling out the objects of the size you were testing. Our experience with them - using the analog input - has been very similar with StevenB. Last year we used it as one of two sensors for hanging tubes in autonomous (the other being the yaw rate sensor). Once we picked out the right sonar for ranging to the rack, we were able to hang very consistently. ( At first we used a sonar with too wide of a beam, and kept ranging on our alliance partners. That caused us to stop short of the rack.) I would expect to be able to range to the fender or the backboard this year, if it proves to fit our strategy. It might also be used to determine the distance between 'bots. The trick is to know when to pay attention to it's output and when not to