0
\$\begingroup\$

I am working on a performance art project in which I want to track the position of juggling balls as they are thrown in the air. The idea is to output a sonification of the ball's position in the air as an alternative to seeing the pattern being juggled. Note that because this is not scientific, I am only looking to generate any output which changes intelligibly in response to juggling patterns.

I think that having a beacon/transmitter/receiver resting on the floor would be a good idea, making all the calculations relative to this beacon. The props would be a maximum of 2-3 meters away from the beacon when at the top of a throw.

Props being juggled

Ideally balls, less than 100mm in diameter. That being said I could adapt to using larger ones, or to use juggling clubs instead.

Already tested approaches

  1. Bluetooth accelerometer data from wii controllers embedded in juggling clubs. This didn't produce very interesting results because the acceleration hardly changed once the club was in the air.

  2. Computer Vision detection of colored juggling balls. This approach created very interesting results but requires a large amount of setup, space, and was very sensitive to lighting conditions

  3. Mounted infared sensor detecting closest object. The beam was too small to accurately pick up small juggling balls at a distance

Ideal results

Below are two examples of suitable final results

  1. Wireless distance detection from the props to the beacon (digital)
  2. Props interfering with field which is detected and then output by beacon. (analog)

What suggestions do you have about solutions to this problem?

It could go one of two ways: 1) Each prop generates position data and outputs its own audible output through speaker 2) Each prop interferes with some kind of field from the beacon. All output comes from a speaker connected to the beacon.

Thanks in advance, Max

PS I am aware that this question is very general. I am open to all suggestions about different approaches to the problem.

\$\endgroup\$
  • \$\begingroup\$ Put a battery, ultrasonic transmitter, and components to generate a pseudorandom modulation in each ball. Each ball uses a different PR sequence. Use an array of 4 or more ultrasonic receivers, and solve GPS stylee for the pseudoranges and hence position of each. You might need several transmitters per ball, what with the narrow beams - doh, probably won't work, unless you restrict the apertures to spread the beams out more. \$\endgroup\$ – Neil_UK Apr 14 '17 at 10:13
  • \$\begingroup\$ Active Theremin system: small coils in the balls driven at a frequency, maybe the 125kHz of lowend RFID, being detected by a reciever on the floor? Not sure if the near field is quite large enough for this. \$\endgroup\$ – pjc50 Apr 14 '17 at 10:42
0
\$\begingroup\$

Bluetooth accelerometer data from wii controllers embedded in juggling clubs. This didn't produce very interesting results because the acceleration hardly changed once the club was in the air.

Well, that's to be expected! You know, gravity's pull is rather constant on earth!

So the interesting thing here is the rotation (since basically, you could pretty well simulate how your cub flies as soon as you know how you've accelerated it with your hands). Alltogether, given a proper system model and a sufficiently fast accelerometer, that's a good approach.

You'd have to know the initial position (and assume initial zero speed) of the cub, but from that, a Kalman filter would usually be used to calculate the position of the cub.

\$\endgroup\$
  • \$\begingroup\$ He needs the whole IMU which will give orientation, accelerometer. \$\endgroup\$ – ammar.cma Apr 14 '17 at 10:43
  • \$\begingroup\$ @ammar.cma the accelerometer he uses is a three-axis one. That should suffice for position. \$\endgroup\$ – Marcus Müller Apr 14 '17 at 11:15
  • \$\begingroup\$ @ammar.cma though you are generally right, without info on the rotation and angular velocity of the cub, it would be impossible to know the position, my guess is that one can make reasonably good assumptions on the rotational axes that might occur when juggling, and avoid putting the accelerometer on those axes, so to reduce the error down to a degree that might be manageable, if one fuses the accelerometer data with knowledge on juggling moves \$\endgroup\$ – Marcus Müller Apr 14 '17 at 14:12
  • \$\begingroup\$ Thanks for answer Marcus, good idea. Its a bit difficult to get multiple wiimotes sending data to the programs I am programming in. Ill have a go though \$\endgroup\$ – Slidon Apr 14 '17 at 18:40
0
\$\begingroup\$

Put a magnetic pulsar in each ball. Different carrier frequencies.

And have a receiver coil, or 2 or 3, pick up the carriers.

With lots of thermal noise, and various bandwidths to accept or reject that random noise, perhaps with a control board to adjust noise in realtime, you have a commercial product.

\$\endgroup\$
  • \$\begingroup\$ This sounds cool but I'm having a bit of trouble understanding. A pulsar seems to be a type of star?? I'm not very knowlegable about analog electronics so a bit lay information would be really appreciated :P \$\endgroup\$ – Slidon Apr 14 '17 at 18:43

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.