I am working on a project that involves developing a wearable sensor that measures the speed of the user in a swimming pool. Work will go into encapsulating the device etc to make sure it is water proof, but my question is in regards to what will be needed to make this possible.
All that needs to be measured is the horizontal speed of a swimmer so that it can be displayed/visualised in some way.
Can I do this using just an accelerometer? If not what would be needed/what alternatives can be achieved using an accelerometer?
Any feedback or ideas are much appreciated.
Thanks!
If this is in a swimming pool then the best solution would be an overhead camera.
Trying to waterproof a device and attach it to a swimmer without affecting their performance will be a horrendous task unless you have megabucks. Look at the depth gauges, compasses and decompression meters worn by divers, big bulky things even when there are no electronics.
ardly:
If this is in a swimming pool then the best solution would be an overhead camera.
Trying to waterproof a device and attach it to a swimmer without affecting their performance will be a horrendous task unless you have megabucks. Look at the depth gauges, compasses and decompression meters worn by divers, big bulky things even when there are no electronics.
Hey, Thanks for your reply!
It really doesn't matter much if it is obtrusive. Its more just a prototype to see if such a system would actually be useful in theory and worth pursuing if I did have the "megabucks" like you say. For this the performance doesn't need to be great.
Just need to find a way to get some sort of data about the speed/change of speed across the distance, and would be mounted around the waist of the swimmer.
Apart from the overhead camera you'll not find useful sensors, Speed over ground is possible in theory, but only works for airplanes or ships which do not bend like a swimmer. It will be hard even with a ship, which will yaw and roll over ground with the waves. For the same reason the relative speed (in water) can not be determined reliably. Better results may be obtainable from a buoy, dragged by the swimmer within some distance.
Using an Accelerometer to get usable data would be difficult I think.
You may be able to do this with a water pressure sensor, similar to how an airplane measures airspeed using a pitot tube. It wouldn't be terribly accurate, what with a lot of water turbulence and whatnot, but over time average readings may be useful.
DrDiettrich:
Apart from the overhead camera you'll not find useful sensors, Speed over ground is possible in theory, but only works for airplanes or ships which do not bend like a swimmer. It will be hard even with a ship, which will yaw and roll over ground with the waves. For the same reason the relative speed (in water) can not be determined reliably. Better results may be obtainable from a buoy, dragged by the swimmer within some distance.
And, short term, a swimmer's speed varies all over the place. It's slowest at the beginning of a stroke, fastest at mid stroke, and slow again at the end of the stroke.
@ajmurray, Accelerometers all the way!
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3D tracking of movements will be vital in evaluating how a stroke deteriorates over time, and how movements in certain dimensions impact overall speed. Gyros on the same $1 or less module would add a lot more detail. All components can be easily made waterproof, they are small, and even powering can be kept watertight with inductive charging.
All of this in a super-tiny package, powered by something like a tiny 600mAh LiPo, dipped in anything from silicone to epoxy to resin, etc. would rival any super-expensive professional rig.
These could be used for any sports application, or any place in harsh environments where measuring motion/speed/Gs in 3 dimensions is vital.
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I was a USN NavET when we used actual gyros and ESGMs to measure velocity. Inertial navigation is your accurate, waterproof, and cheap friend!
And to be fair, the OP didn't give enough information to begin ruling solutions out. Things like budget can swing the accuracy equation wildly, as would distance/time durations, etc. Even unrealistic expectations can be achieved with an unrealistically high budget...
I have not looked at dive computers for a while. The Suunto does look good but it is over $1000 and most diving gear is pretty clunky. Using an Arduino the swimmer would need a box strapped to their waist and converting an Arduino prototype into something like the Suunto would be very expensive.
What about sonar?
The swimmer wears a device that has an accurate real time clock and 'pings' at specific times.
Microphones at both ends of the poll listen for the pings and can calculate the distance to the swimmer based upon the time the ping is heard?
Unfortunately the speed of sound in water is about 1,500m/s so a ping would take 0.0333s to travel the length of a 50m pool and half that for 25m pool, so I am not sure if this is practical?
Sonar looks practical when the senders are stationary, at both ends of the pool (power consuming!). The swimmer sensors pick both pings, with their time delay telling the relative distance to the senders. With a known pool length the swimmer's position can be determined, and from that its speed.
This model can be reversed, so that the swimmer sends pings which are received and processed at the ends of the pool. Then the size of the ping sender battery will determine the size of the device at the swimmer. Other senders may be feasible, like a mechanical
(spring loaded) clock unit could produce loud enough ticks for the pings.
You are right Dr. If the swimmer sends pings there is no need for the swimmer to have a realtime clock, the time difference beween the pings being received at both ends of the pool lets you work out the distance. Given the high speed of sound in water though, 1500m/s, is this practical?
Putting a pinger in a waterproof case sounds like it could be practical. The only problem being it would need to be loud enough to be heard clearly 50m away.
DrDiettrich:
Sonar looks practical when the senders are stationary, at both ends of the pool (power consuming!). The swimmer sensors pick both pings, with their time delay telling the relative distance to the senders. With a known pool length the swimmer's position can be determined, and from that its speed.
This model can be reversed, so that the swimmer sends pings which are received and processed at the ends of the pool. Then the size of the ping sender battery will determine the size of the device at the swimmer. Other senders may be feasible, like a mechanical
(spring loaded) clock unit could produce loud enough ticks for the pings.
I think water turbulence would give all kinds of erroneous readings.
