Acoustic Location System


#101

What has happened to this forum?

It was so good.


#102

Barry,

thanks for your interest. I continue to work on this project, but have been working on Trident data integration at the moment and will get back to signal processing shortly. See: Software Exploration - DDS and the Trident #2 for the Trident integration work.

I do have code that runs on a micro-controller (even an ESP-32) that will sample analog data points and send them as JSON to the Raspberry Pi that runs on the Trident via wi-fi (need to test wi-fi from an external housing to Trident in underwater conditions). I could do the signal processing on the RPi and then merge the data (time difference of arrival values) into the Trident data stream. That along with depth data should be enough to calculate location relative to the surface acoustic transmitters. I have also been looking at sensor fusion approaches (attended a MATLAB sensor fusion workshop that was interesting) which would combine acoustic data with IMU and other pertinent data.


#103

As a long time mostly-lurker on Open ROV I’m very interested in this thread. We are finishing a small, battery powered acoustic transmitter for use in diving applications. We are transmitting data, not location, at least for now. We have tested both the receiving and transmitting functioning from several hundred up to 1,000 feet in water. We are using the same Steminc SMC26D22H13111 cylindrical element cited here.

What I’m wondering is if anyone has come up with a reasonable source- or has alternative suggestions- for the potting material for the transmitter. The Conathane EN-12 that is mentioned in some of the literature seems inaccessible to ordinary mortals. At least, I have been unsuccessful in sourcing it. I received a quote for an alternative that was comically expensive- $975 per oz…

Great thread!


#104

Ron,

I used Clear Flex 50 from Smooth-On ( https://www.smooth-on.com/products/clear-flex-50/ ). The vendor no longer sells trial kits from their web site, so the smallest quantity is one-gallon ($281). The trial kits (1.5 Qt for around $35) are available from distributors. One California distributor I just checked with is:
Douglas and Sturgess
1023 Factory Street
Richmond, CA 94801

Smooth-On has many other distributors listed on their web site.

I was curious about your data transmission application and what type of encoding you are using. If you are willing to share your approach (open source sw and/or hw) others have been interested as well. I could test it through the electronics I have shared on this forum if you like.

Jim


#105

Not sure if it is the quantity or type you are looking for but Blue Robotics sells a potting compound.

https://www.bluerobotics.com/product-category/cables-connectors/tools/


#106

Thanks for the replies. Good to know you have successfully used the Smooth-On product, I have used various products from Smooth-On quite a bit in the past for casting instrument housings and prototypes, and there is a distributor near us in the Seattle area.

I did get a response from one of the adhesives/ potting distributor technical representatives (Ellsworth Adhesives, they were very helpful). They suggested a castor oil based urethane as the chemistry that would be closest to sea water as far as the speed of sound transmission. He said this material, Resinlab® UR3010 Clear, was commonly used in underwater acoustic transducers. It is not too expensive.
Water @ 20°C — 1482 m/sec
Sea Water, 3.5% @ 20°C —- 1522 m/sec
Castor Oil — 1474 m/sec

https://www.ellsworth.com/products/by-market/consumer-products/encapsulants/polyurethane/resinlab-ur3010-urethane-encapsulant-clear-50-ml-cartridge/

We are developing a commercial product, but at this point only need to access prototyping quantities and even in production we will be very low volume. I’m going to check with Smooth-On regarding the chemistry of the Clear Flex 50 and get some to test against the UR3010.

Our application involves sending a small amount of sensor data (60 bits) every few seconds, using a very basic amplitude modulation scheme. I’m functioning more on the mechanical design side, so I only know what I am told about the electronics and firmware. Our present business arrangement prevents us from (at least for now) sharing code, unfortunately I need to tread lightly there. I’ll be happy to share results of transmitter configuration testing as we progress.

Our receiver is a wrist worn device, so the receiving side needs to be very compact and enclosed in a durable housing- we are currently using a small, >10 mm piezo disc receiver in an aluminum housing. While we have a source for the receivers and they work well, we would prefer to be able to assemble them ourselves if we could find a cost effective source for the piezo ceramic elements- standalone, not already assembled. That’s one of the things I’m working on now.


#107

Ron,

thanks for the info. I like the fact that the Ellsworth Adhesives product is available in the cartridge - even though one 50 ml cartridge is about the same cost as the 1.5 Qt Smooth-on kit. For prototyping the cartridge is great since no need for mixing (just use disposable mixing tips) and less of an issue with shelf life as compared to opened containers. Maybe I need to figure out how to load Smooth-on into cartridges and store the product that way.

I also have gotten samples from another vendor with good results for potted transducers - similar characteristics to Smooth-on product.

Contact info:

Epic Resins

S7515-01

Product Datasheet

Description

600 Industrial Blvd.
Palmyra, WI 53156
Phone: (262) 495-3400 Fax:(262) 495-3410
Email: customerservice@epicresins.com

Revised 1/29/2015

EPIC S7515-01 is a two component aliphatic urethane doming compound. S7515-01 is designed to provide exceptional U.V. resistance and fast tack-free time at a convenient 1 to 2 by volume mix.

Jim