[Dprglist] ultrasonic positioning systems

[John Swindle]

Correction:
I like all but one spec: 1 to 3 percent accuracy. That is terrible. And I don't understand why it exists.
In my case, the accuracy does not depend on distance. If the receiver can hear enough emitters with acceptable SNR (which initially is negative SNR), then the result is accurate, no matter whether the separation is 2 inches or 20 feet.

-----Original Message-----
From: John Swindle <swindle at compuserve.com>
To: pondersome64 <pondersome64 at gmail.com>; dprglist <dprglist at dprg.org>
Cc: swindle <swindle at compuserve.com>
Sent: Thu, Feb 20, 2020 11:37 AM
Subject: Re: [Dprglist] ultrasonic positioning systems


Wow! The Marvelmind specs and videos look great! Looks like they've been incorporated since 2016. Specs are almost exactly what I am trying to do. Very neat. Thank you for pointing me to that!
They are doing 3D trilateration. Cool. 3D geometry always bumfuzzles me so I haven't even tried it.
They only require 2 beacons for 2D, and 3 beacons for 3D, so they are doing time-of-flight (as their website says) based on the radio synchronization. I'm doing difference in time-of-flight which does not use a radio and does not require synchronization but which requires 3 beacons for 2D. The radio idea is better and faster, but I never found a radio that had a communications stack with low jitter. Radio is not my thing, so I'm sure there are radios that can do the job that I don't know about.

Since their beacons are ultrasonic, they require line-of-hearing which is essentially line-of-sight between the beacons and the robot. The localizer I demonstrated operated at audible frequencies and was not affected by most obstacles, so my line-of-hearing is much more than line-of-sight. People rightly objected to my localizer's audible noise, so I switched to ultrasonics, which have all sorts of problems, such as line-of-sight requirements and absorption.
I am surprised that the range is 30 meters or more at ultrasonic frequencies. The absorption in air (not the 1/r spreading) is huge at those frequencies, far worse than the spreading. For one of the outdoor DPRG contests, I estimated I'd need powerful emitters (50 watts or more each) in order to cover a 150 foot square arena with ultrasonic frequencies. I abandoned the experiment. Neat that Marvelmind solved that problem.
I've been trying to keep the frequencies low to avoid both the line-of-sight and the absorption problems, and to make omnidirectionality easier. Maybe I will continue to work on that. Otherwise, it seems Marvelmind has solved the problem! Good stuff.
Later,John Swindle


-----Original Message-----
From: Karim Virani via DPRGlist <dprglist at lists.dprg.org>
To: dprglist <dprglist at dprg.org>
Sent: Thu, Feb 20, 2020 9:32 am
Subject: [Dprglist] ultrasonic positioning systems

Does anyone have any opinions about the MarvelMind Indoor Navigation system? 
https://www.superdroidrobots.com/shop/item.aspx/ips-indoor-navigation-positioning-system-dsp-starter-set-nia-v5-07/2664/_______________________________________________
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