Reducing noise on the MaxBotix ultrasonics?

[trycatch]

Happy mid-build season, all.

This is our first year trying to use the MaxBotix ultrasonic, and we're getting a *lot* of jumping around and noise. Admittedly, I don't have a big totally open room to test in yet, but it seems like there's got to be some way to do some smoothing to minimize reflections? Any suggestions?

[codetheweb]

As long as the sensor is fairly parallel to the wall, there shouldn't be too much noise (±0.5-1 cm). How are you reading the value? Over the analog output?

You might try accumulating 5-6 readings then taking the median.

Are you currently using a single sensor? We tried using two, but gave up because of the noise.

[trycatch]

Just one - I was doing it in a kitchen, so I was probably catching a lot of stuff inside the cone being emitted, rather than the wall I was pointing at. That gives me hope it'll be cleaner on a practice field. Our goal is to zero in on when we're in gear-peg-release-distance.

[codetheweb]

You might want to have a look at this.

[dk5sm5luigi]

Given the noise we had seen in the past we switched to IR Rangefinders and probably won't go back. We found one that does up to 18 feet and the noise was easier to work with than the ultrasonic.

We listed them here: http://findrobotparts.com/sensors/ca...es/13/tags/635

[tr6scott]

Originally Posted by dk5sm5luigi

Given the noise we had seen in the past we switched to IR Rangefinders and probably won't go back. We found one that does up to 18 feet and the noise was easier to work with than the ultrasonic.

We listed them here: http://findrobotparts.com/sensors/ca...es/13/tags/635

Have you tested them for placing the gear? We are having issues with vision targets messing with the IR readings.

[dk5sm5luigi]

Originally Posted by tr6scott

Have you tested them for placing the gear? We are having issues with vision targets messing with the IR readings.

We haven't tried yet. Weather is killing us. We have only met 2 days a week for what is going to be 3 weeks now. (We usually only meet 4 days a week)

[tr6scott]

Originally Posted by dk5sm5luigi

We haven't tried yet. Weather is killing us. We have only met 2 days a week for what is going to be 3 weeks now. (We usually only meet 4 days a week)

Well good luck with the weather, and might want to have a plan B in your pocket.

[trycatch]

Originally Posted by tr6scott

There was a team that posted their solution in previous years... I don't have link saved... but it boils down to, make x samples, sort the values, throw out the the a few of the largest, and a few of smallest, then average.

example, take 10 samples, throw top 2 and bottom 2 out, average over the remaining 6.

In the past these sensors have proven pretty good when used this way. The problem is when they are off, they are way off, so even a simple average data gets skewed.

Ooooh, that's pretty clever. I hadn't considered that!

Originally Posted by dk5sm5luigi

Given the noise we had seen in the past we switched to IR Rangefinders and probably won't go back. We found one that does up to 18 feet and the noise was easier to work with than the ultrasonic.

We listed them here: http://findrobotparts.com/sensors/ca...es/13/tags/635

That's also a possibility!

Does taking it out of continuous mode help? I would think so, but haven't messed with it much yet.

[golf_cart_john]

Originally Posted by dk5sm5luigi

Given the noise we had seen in the past we switched to IR Rangefinders and probably won't go back. We found one that does up to 18 feet and the noise was easier to work with than the ultrasonic.

We listed them here: http://findrobotparts.com/sensors/ca...es/13/tags/635

We ran into some inconsistency in range with those. They seemed to report a range of a few inches when the wall is perpendicular to the sensor, then over a foot when the wall is still a few inches away but several degrees away from a "square" approach.

If I'm not mistaken, they judge range by reflection brightness, rather than time of flight or angle. So they're super sensitive to the reflectivity of the target. Since the wall of the airship is prime for specular reflections, its reflectivity varies widely based on how perpendicular the sensor is to the wall.

Did you find this to be an issue as well?

[Knufire]

This might be of interest to a few of you: https://www.sparkfun.com/products/14032

Documentation states that the laser is Class 1, which should make it FRC legal.

[tr6scott]

There was a team that posted their solution in previous years... I don't have link saved... but it boils down to, make x samples, sort the values, throw out the the a few of the largest, and a few of smallest, then average.

example, take 10 samples, throw top 2 and bottom 2 out, average over the remaining 6.

In the past these sensors have proven pretty good when used this way. The problem is when they are off, they are way off, so even a simple average data gets skewed.

[ScottW of MaxBo]

Hello, this is Cody Carlson from MaxBotix Inc.,

I saw your forum post, and I would like to lend some assistance.

You state: This is our first year trying to use the MaxBotix ultrasonic, and we're getting a *lot* of jumping around and noise.

I apologize as I'm unsure of which MaxBotix ultrasonic sensor you are using. We did send an MB1013 to every team in the First Robotics completion this year. This sensor has a relatively wide beam pattern. As such if there is clutter around the edge of its detection zone, you would see range readings jump. Two options that you could employ would be using blinders to narrow the line of sight of the sensor or test a less sensitive sensor like the MB1023, MB1033, or MB1043 where each is less sensitive than the previous model.

If you would like to look at making a blinder. This is, in general, a large flat object that runs parallel to the sensor to restrict its beam width. Some customers even attempt to make horns to restrict the beam width, but this is a more involved solution.

If you would like any help with sensor selection please let us know.

Sensor Selection Guide: http://www.maxbotix.com/SelectionGui...tion-Guide.htm

Please let me know if you have any questions.

Best regards,

Cody Carlson
Technical Support
of MaxBotix Inc.
Phone: (218) 454-0766
Fax: (218) 454-0768
Email: techsupport@maxbotix.com

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