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I'm trying to create a small scale, dumb-downed version of the pitch tracking systems used to detect the speed and direction of baseballs.

I'm currently working with an HC-SRO4 sensor and an Arduino, but I'm unsure how to expand because a single sensor can't track an object that's not moving linearly (ie rising or falling as it moves). My team's idea was to make a grid of multiple HC-SRO4's connected to one Arduino, but we're worried that the delay will be too large if we try to turn them on sequentially to avoid interference.

How can we use ultrasound to track a moving ball?

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    I wouldn't worry too much about the path of the ball not being straight. If you assume it goes straight and it gets off-track by 8 degrees (which is quite significant), your speed calculation will be off by only 1%. And you probably won't be more accurate than that anyway. I would worry about the limited range of the HC-SR04 though. – Edgar Bonet May 22 '17 at 12:20
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Yes you can use ultrasound to track a moving target, but I really doubt it could be done with an Arduino.

You need to be able to ping the object at least 3 times in the time it takes to move your beam width. 3 times because if you know where it is with the centred ping you need to calculate the direction of travel by pinging either side of the centre to see if it is there.

You then need to track it in three dimensions. To do this you will need multiple sensors ideally at least 3 for 2D and 3 for 3D, so at least 6. 3 sensors in a plane will give you a reasonable degree of accuracy, but you beam width is key to this, the narrower the better.

Now you have to triangulate the position of the object, well actually work out the area of probability (for both planes) you never 'know' where it is really.

Oh and all 6 sensors need to have different frequencies to prevent interference, you then need to add in reflection processing to reduce false signals.

Its just much easier to buy a Pixy camera and download the software that they have for visually tracking your balls.

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