Hi guys,

I am a student working on a project: an underwater camera that follows a swimmer from under to film him. I am doing so by having a robot move up and down on a wire using motors and an arduino board. I want this robot to move at the same speed as the swimmer. Therefore, I need to find a way to measure the distance between the robot and the swimmer in order to adjust the speed of the motor.

I was wondering if there are 2 device (1 on the robot and 1 attached on the swimmer) that can measure the distance between each other and send it to the arduino board.

In summary, I am looking for a device that can:
- work underwater
- measure the distance between the robot and swimmer (can be a 2 piece device, 1 on the swimmer and 1 on the robot)
- can output this distance to an arduino board
- be in a student's budget (so nothing above $100)

 

Welcome to AAC!
An echo-sounder is a high-tech , but expensive, solution.
So how about a really low-tech, cheap, solution? Use a length of shirring elastic with one end attached to the swimmer and the other end attached to a force sensor mounted on the robot. Adjust the speed of the robot to keep the elastic tension constant-ish.

 

Unclear... move up Δ and down ∇... do you mean instead, along the swimmer direction forth and back ?
The video camera 'on-a-cable-car' to grab onto the wire for wheeled propulsion or just for guidance using propellers ?

The distance measurement can be the same equipment as in ultrasonics distance measurements on air, derated for 4.5 times the propagation speed; and waterproofed. Interfacing to Arduino, I do not know. ----> https://www.aliexpress.com/wholesale?SearchText=ultrasonic+distance+measurement&opensearch=true

Waterproofing motor shafts is not simple, prepare for frustrating tests.
Very hard to accomplish if you do not have a pool very nearby at nearly all times.
Have you investigated if you will be allowed to anchor the 'wire' to a pool walls/bottom ?

Highly doubt that budget will do it. Rental of scuba equipment will eat a good chunk of it.

----> https://donaldmiralle.wordpress.com...erwater-cameras-at-rio-2016-olympic-aquatics/

----> http://www.nytimes.com/2012/08/01/s...otographers-make-their-underwater-moment.html

----> http://money.cnn.com/2016/08/08/technology/olympics-underwater-robots-getty/index.html

----> http://www.poolview.co.uk/swimpro-cam

---->

 

Unclear... move up Δ and down ∇... do you mean instead, along the swimmer direction forth and back ?
The video camera 'on-a-cable-car' to grab onto the wire for wheeled propulsion or just for guidance using propellers ?

The distance measurement can be the same equipment as in ultrasonics distance measurements on air, derated for 4.5 times the propagation speed; and waterproofed. Interfacing to Arduino, I do not know. ----> https://www.aliexpress.com/wholesale?SearchText=ultrasonic+distance+measurement&opensearch=true

Waterproofing motor shafts is not simple, prepare for frustrating tests.
Very hard to accomplish if you do not have a pool very nearby at nearly all times.
Have you investigated if you will be allowed to anchor the 'wire' to a pool walls/bottom ?

Highly doubt that budget will do it. Rental of scuba equipment will eat a good chunk of it.

----> https://donaldmiralle.wordpress.com...erwater-cameras-at-rio-2016-olympic-aquatics/

----> http://www.nytimes.com/2012/08/01/s...otographers-make-their-underwater-moment.html

----> http://money.cnn.com/2016/08/08/technology/olympics-underwater-robots-getty/index.html

----> http://www.poolview.co.uk/swimpro-cam

---->

Hi,

Thank you for your quick response! Just to clarify, the $100 budget was only for the measuring device. Instead of using an ultrasonic device (which would be hard to program), I was thinking of a 2 part device (mounted on both the swimmer and robot) that measure the distance between each other and output it.

For the rest, I have solutions for:
- I will use a waterproof brushless motor to move the robot
- the cables will be tied at both ends of the pool using special suction cups.
And yes, when I mentioned about UP and DOWN, I meant going up and down the pool lane. I also live in a house with a pool.

Best

 

Welcome to AAC!
An echo-sounder is a high-tech , but expensive, solution.
So how about a really low-tech, cheap, solution? Use a length of shirring elastic with one end attached to the swimmer and the other end attached to a force sensor mounted on the robot. Adjust the speed of the robot to keep the elastic tension constant-ish.

That is a very interesting solution but I would rather not too many things attached on the swimmer so that it doesn't affect his technique.

Do you think there may be a way to attach a device on the swimmer that measures his speed and sends this information back to the robot to adjust the speed of the motor?

Best

 

An example of this kind of 2 piece device would be: https://www.nanotronshop.com/nanoloc-ranging-kit-ii-p-17527.html ,however, this is way out of my budget and doesn't work underwater.

The link you have are interesting but they cameras are only for photography, not filming (which is what I am looking for). I am trying to develop my own system instead of buying a professional one used in the olympics

 

The "cable car" can house a movie camera instead of a photo camera...
The first link includes laser ranging gadgets, not only ultrasonics...
The brushed or not condition for the motor does not change the need to waterproof shaft/bushings.

Out of the box... Explore if the motion can be instead, following the shade of the swimmer projected at the bottom of pool. Tricky, but a light sensor could command the motor.
Out of the box... a LED, infrared or not on the belly button/trunks could be traced by the camera with some imaging following software to command the cable rail car motion... Until the swimmer does his thing belly up

And up and down is then, definitively wrong, that would be surfacing/sinking. It is forward and backward.


Edited: The mindset "measure the distance" could be replaced by a 'follow' the swimmer.
---->

 

MaxBotix has sonar sensors in your price range. See here where they discuss using them under water.

 

Waterproofing motor shafts is not simple, prepare for frustrating tests.
Very hard to accomplish if you do not have a pool very nearby at nearly all times.

It is pretty straight-forward actually. I'm not sure what troubles you've had in the past, but I work with subsea equipment and we do it all the time. Last year I designed an experimental kit to turn a 1hp SurplusCenter gearmotor into an oil-compensated subsea torque assembly. Using these super-cheap double lipseals, the modified motor passed all hydrostatic tests with flying colors down to a simulated depth of 600ft (the highest pressure our hydrostatic test chamber can do).

 

Hi strantor... Any sources you may know for 2, 3, 4, 5 mm shaft diameters, with stainless garter spring and in silicone ?

 

Hi strantor... Any sources you may know for 2, 3, 4, 5 mm shaft diameters, with stainless garter spring and in silicone ?

Why do you specify in Silicone? Silicone is not typically a good material for this application. It is too soft, and not oil resistant (and subsea motors are typically oil-compensated).

These sizes are much smaller than I am used to; my typical application is 20-40mm shafts. But I did find some small ones from AXV seals
2.32mm
5mm

AXV was just something I used for an experiment. The seals we typically use for subsea motors are NMF type MAC. I don't have a catalog anymore - you would have to ask a vendor if they go down that small.

 

I would imagine that this would not be a too-difficult image processing task to have the processor simply examine frames from the video being captured and decide where the swimmer is and then adjust to keep them centered in the frame. You could probably make it almost trivial by just having the swimmer wear a very distinctive color swim suit that contrasted highly with whatever else was in frame.