Other quad-copter, dragonfly dipper ideas:
1) A quad-copter carries around a hollow sphere containing an accelerometer, and the sphere is suspended on a thin supple data cable. The copter dips vertically at a controlled rate, the sphere hits the water, the cable goes slack, the sphere sinks, the logger records the time between the water impact and the impact on the bottom. The sphere has known buoyancy and sink rate.
Mud sticking to the sphere/probe could be a problem. Applying something like NeverWet may keep it clean...
I like the idea of the air boat. About steering, the commercial "Alligator" says "Twin air rudders with adjustable single link between steering servo and rudders for fast, powerful response". I'm not sure how that works. I'll have to find time to follow the links for DIY airboats. You're right, there are a lot! How about a quad-copter props turned up to horizontal?
Two variable pitch propellers each mounted 45 degrees off axis would give nearly omnidirectional control. Variable pitch would not be a necessity but it would give finer control.
I like the raft/airboat with transducer idea best. It is simple, cheap and reliable. Sounds like a fun project.
Was there a reason that the depth sounder would not work? If it is because the depth is too shallow then you could raise the transducer and fill in the gap with an appropriate medium.
The quadcopter ideas are neat but I don't think they are practical for the number of measurements that need to be made. An airboat could do it faster and cheaper with far less risk.
Call it another crazy idea - but how about "employing" some descent size fish and attach to their belies a pressure + GPS data logger?
After a day or two of free swimming in the rice paddy dish them all out of water to retrieve all the data you need.
Then after clearing the data you can reuse the fish cohort over and over again until you're done with other water reservoirs.
To speed up the data collection (and to satisfy quad advocates) you can circle a single quad low above the water level around your area of interest just to scare the hell out of the fish so it can disperse quick and dive in panic as deep as possible
Thanks for the ongoing suggestions. There is so much creativity here! I'll be able to meet soon with one of the principals on this project, so I'll have an opportunity to summarize the suggestions and to ask questions. I often have the nagging thought that someone must have done it already, but am often surprised by how off the mark that thought can be. This is a very specific niche to fill and there are specific constraints, many of which I still finding out.
Propability and JohnS, a merger, the quadcopter with the long landing gear could be replaced by a heron or other long-legged water bird that slowly circumnavigates the paddy (collecting data) while trying to catch the fish.:thumb:
Rich, the air boat is still high on the list, if it turns out that they really do want a walkabout kind of survey. The air boat would serve to avoid wheels on and in the mud. It would have to drop or dip a blunt upsidedown T probe to determine depth. My results with the ultrasound have been minimal so far. Medical ultrasound uses sound frequencies of 1MHz or greater to allow detection of small structures close in. The structure here wouldn't matter, just distance, but it would take some R&D to make it happen. I do have a nice depth probe, based on direct Q-xfr capacitance to digital, that could be dipped with a simple actuator.
Just a thought. You can buy waterproof stereo earbuds very cheaply. They're designed for swimmers who need their tunes while doing laps. I wonder if they could be used for the standing-wave approach, with one operating as transmitter and the other as receiver. I'm sure the mechanical impedance is designed for a relatively dry ear canal, but the sound doesn't have to travel far in the water.
Interesting possibility, the earbuds. With a wavelength of 5cm, that is a frequency of ~30kHz (1500m/s / 0.05m), so 1/2 wavelength at ~15kHz which would be within reach. 1/2 wavelength would fit with velocity nodes at the water surface, almost a perfect reflector, and the bottom, a relatively squishy boundary. There is also PVDF material, often used for hydrophones.
Comments
Mud sticking to the sphere/probe could be a problem. Applying something like NeverWet may keep it clean...
Two variable pitch propellers each mounted 45 degrees off axis would give nearly omnidirectional control. Variable pitch would not be a necessity but it would give finer control.
Was there a reason that the depth sounder would not work? If it is because the depth is too shallow then you could raise the transducer and fill in the gap with an appropriate medium.
The quadcopter ideas are neat but I don't think they are practical for the number of measurements that need to be made. An airboat could do it faster and cheaper with far less risk.
Call it another crazy idea - but how about "employing" some descent size fish and attach to their belies a pressure + GPS data logger?
After a day or two of free swimming in the rice paddy dish them all out of water to retrieve all the data you need.
Then after clearing the data you can reuse the fish cohort over and over again until you're done with other water reservoirs.
To speed up the data collection (and to satisfy quad advocates) you can circle a single quad low above the water level around your area of interest just to scare the hell out of the fish so it can disperse quick and dive in panic as deep as possible
Propability and JohnS, a merger, the quadcopter with the long landing gear could be replaced by a heron or other long-legged water bird that slowly circumnavigates the paddy (collecting data) while trying to catch the fish.:thumb:
Rich, the air boat is still high on the list, if it turns out that they really do want a walkabout kind of survey. The air boat would serve to avoid wheels on and in the mud. It would have to drop or dip a blunt upsidedown T probe to determine depth. My results with the ultrasound have been minimal so far. Medical ultrasound uses sound frequencies of 1MHz or greater to allow detection of small structures close in. The structure here wouldn't matter, just distance, but it would take some R&D to make it happen. I do have a nice depth probe, based on direct Q-xfr capacitance to digital, that could be dipped with a simple actuator.
Just a thought. You can buy waterproof stereo earbuds very cheaply. They're designed for swimmers who need their tunes while doing laps. I wonder if they could be used for the standing-wave approach, with one operating as transmitter and the other as receiver. I'm sure the mechanical impedance is designed for a relatively dry ear canal, but the sound doesn't have to travel far in the water.
-Phil