Hi all. Not only am I a newbie but am also a complete electronic Neanderthal. I'm actually a photographer. I do extensive work with marlin underwater and am looking for electronic help for a new project. We do not catch the marlin but use teasers (big lures with no hooks) pulled behind the boat at around 10 miles an hour to bring them up into photo range. Right now there is almost no data on the maximum speed, acceleration, g-forces and bite force on any of the 5 species of marlin. Current tagging protocols prove tricky because of the lack of two anchor points in the fish to secure the tag at a fixed axis. Also the data I want is not long term PSAT (POP OFF SATELLITE TAG) data but very short term hi-resolution data. My idea is to put an accelerometer and magnetometer into the cylindrical solid resin head of the teaser, a space probably an inch and a half in diameter and about 4 inches long. We will then drag the sensor behind the boat. Once the fish strikes the lure it will force a high speed angle change, I hope giving some if not all the data I'm looking for?

My question is this, I need to embed the accelerometer and magnetometer into the cast resin head with power supply, access points for charging (these we can place behind waterproof seals) data storage and some way to retrieve the data. The bite force recorder would be a big bonus. The marlin force their prey into the corners of their mouths and crush it before swallowing. I was wondering if there was some sort of soft fluid filled sensor that could run from the back of the lure head into the soft silicone skirt the makes up the back of the lure? That way on biting down on the teaser, the force used by the fish could be measured in the lure head.

Any help would really appreciated. As alway budget is a big concern to get this project moving. Many thanks.

 

Sounds possible but a task for an expert.
Can I assume that the electronics will be chewed, swallowed and destroyed by the marlin? What effect would a small lithium coin battery have once ingested by the marlin?

 

No, there is no ingestion of anything. The lure head and silicone skirt are attached to the boat with 130 lb line and have a 30' 400 lb test leader via a rod and reel running around 30 lb of drag. The fish strikes the teaser, causing the vector change I'm looking for, it holds onto the lure until it feels resistance from the line. The lure is pulled from the marlin's mouth or he spits it out. The leader material and clear resin head are scratched up because the marlin's bill is highly abrasive (the reason for the 400 lb leader) but there is no ingestion of any of the parts. Once we get a strike I want to wind back the lure unseal the data transfer ports and transfer the data to some sort of software for analyzing. Here is a video showing the process.
http://www.youtube.com/watch?feature=player_embedded&v=sPaR-KMAxOg

 

I would probably go for a completely sealed system, perhaps in some kind of rubberized silicone. The unit would be battery powered and will transmit its data in real-time via bluetooth to a data logger on board on the boat. A flexible unit may allow you to include some strain sensors to measure pulling forces.

 

I'm in agreement. The idea was to cast the components in the resin head as a single solid unit with an o ring sealed port to access the battery and data. We would need access to charge the battery and remove the data. This is what I'm looking for:

power source
data strorage
magnetometer
accelerometer

Bonus would be:
bite force sensor and recorder

There is a mountain of individual components at electronic outlets for just a few dollars. I would have no idea how to put the whole lot together, power it and store data.

I like your BT or network idea but the lure travels in and out of the water up to 200' behind the boat. We do run a router on the boat for a network but we are dealing with connection issues while the lure is a foot below the surface. I've attached some pix of a lure head and skirt.
http://www.fathomoffshore.com/lures/xl-extra-large/queen-anne-s-revenge.html

 

At 200' behind the boat that strikes out bluetooth.
I'm not too keen on the idea of an o-ring cover. I would rather put a rechargeable battery and bring out a 4-pin water proof connector for charging and data access. This way the whole unit is sealed and waterproof. We use high vacuum epoxy to seal connector pins in high vacuum bulkhead connections.

 

Another option would be to house the unit in a waterproof container, which would become the teaser. After reeling it in, the unit can be removed completely from the container/teaser. Use a mini USB port for both downloading the data and charging the batteries.

 

I can understand your need for the accelerometer. What specific data are you collecting with the magnetometer?

hgmjr

 

Because the teaser is moving forward at a non constant rate (in and out of the water causing changes in drag) I was advised to include the magnetometer to give me the vector from the accelerometer relative to it's position and direction of travel?

I like the idea of the USB port/charging plug being available through a waterproof cap. O ring seals are something I know enough about. I not sure it's necessary for the whole unit to have to be removed.

 

Because the teaser is moving forward at a non constant rate (in and out of the water causing changes in drag) I was advised to include the magnetometer to give me the vector from the accelerometer relative to it's position and direction of travel?

I like the idea of the USB port/charging plug being available through a waterproof cap. O ring seals are something I know enough about. I not sure it's necessary for the whole unit to have to be removed.

I believe you may be able to get all of the force vector information you are looking for by using a 3-axis accelerometer. That will provide you with x, y, and z axis data at the same time. The trick will be to sample the data at a rate commensurate with the speed of the event to give you adequate data resolution. There may be a way to trigger the data capture from one of the accelerometer outputs.

These are all off-the-cuff suggestions. I am not an expert on accelerometer applications.

hgmjr

 

Have the unit totally sealed, i.e. no o rings or caps or whatever.

Transfer data via bluetooth you'd have to store it in memory while it is out on the line and transfer it when you reel it in after a strike of course.

Charge the unit via inductive coupling like almost every electric toothbrush in the world.

 

Have the unit totally sealed, i.e. no o rings or caps or whatever.

Transfer data via bluetooth you'd have to store it in memory while it is out on the line and transfer it when you reel it in after a strike of course.

Charge the unit via inductive coupling like almost every electric toothbrush in the world.

I like that.

 

Many thanks, simpler makes me happier. Where do I get a 3 axis accelerometer which will record the correct data frequency and how do I power, recharge, store and access data in a small 4"x1.5" cylinder?

The data event will in total run about 4 or 5 "sessions" of about 5 to 10 seconds each (as the fish repeatedly hits and looses the lure) over a total time of about 2 to 3 minutes until he looses interest and swims away. The peak or highest rate/degree of change during each of those 5 to 10 second interactions is what I'm looking for. The fish may displace the lure head anywhere for a few inches to several feet depending on the type of strike. Would a magnetometer give me the distance of displacement from "rest" or can I get that info from the the 3 axis accelerometer as well?

 

You're talking about a data acquisition system with a processor, memory, D/A converter(s) for the accelerometer, communications, power manamgement, etc. There are a few ready to go systems on the market, but considering your space constraints, you'll probably need a custom system. It won't be easy or cheap to have one built. The you'll need to write the software for controlling the system, recording the recovering the data. Given that you said earlier that you know little about electronics, you'll probably need to farm out all the work.

 

Many thanks, can anyone point me in the direction of someone who could at least quote me on getting something like this done?

 

Here is a youtube video link demonstrating an MEMS IMU. An IMU (Inertial Measurement Unit) is a more sophisticated device since it provides acelerometer and inertial data in real time. Certainly small but probably not cheap. There would still need to be some sort of microcontroller and a data storage memory needed to log your data. The technology for implementing what you need is definitely out there. You may want to contact this company and explain to them what you are trying to do. They can probably hook you up with an engineering design company that will take on your challenging project.

It would not surprise me if the company can take on your design themselves. They would probably like the chance to use your project as a show-and-tell for advertisement purposes. They may give you an attractive price for your endorsement.

hgmjr

 

Much appreciated!