Hi guys

How can I measure displacement?

Say I throw a ball up in the air in an angle (0 - 90 degree), how do I measure the displacement between where I stand to just before the ball land (or anywhere while the ball is still in the air?)

Say the displacement is between 10 to 20 meters, accuracy/precision is not so important, say up to +/- 4 meters(?), Resolution is within 4 meters(?).

I am not sure how realistic of my above specs, hence the (?), but those are the minimum specs that I would like to have, if possible.

Thanks guys

Added on 18/09/2013 12.34PM NZ Time:

The idea is, I want my device to do something after I toss/launch it in the air, from a certain distance from me/launch point.

eg. I am standing at Point_Toss, my device/ball will land at Point_Landing, between Point_Toss and Point_Landing, there is a Point_X (still in the air), so I want my device do something (flash a LED?) when Point_X - Point_Toss = Y_meter (+/- error).

Maybe this might help, These need to be in a 3D environment.

 

With practice, you should be able to eyeball 10-20 meters with 4 meter accuracy/precision.

Good luck.

 

With practice, you should be able to eyeball 10-20 meters with 4 meter accuracy/precision.

Good luck.

Lol, I did not see this one coming , but anyway, I am thinking in term of electronics device.

Maybe I should change my question to, what sensor/s do I need to achieve above specs, if you think +/-4m is too easy, I am also interested in the range of 15-30m, +/-1m too.

Thanks guys!

 

It's actually likely to be pretty complicated. You could do it with two TV cameras and locate the ball by triangulation.

Is this system going to operate in a specially built environment? If you could use a white ball and make sure that the background was black, it might not be too difficult to locate the ball in the cameras' visual field. But if you want to operate in an uncontrolled outdoor location, that's much more difficult.

 

It's actually likely to be pretty complicated. You could do it with two TV cameras and locate the ball by triangulation.

Is this system going to operate in a specially built environment? If you could use a white ball and make sure that the background was black, it might not be too difficult to locate the ball in the cameras' visual field. But if you want to operate in an uncontrolled outdoor location, that's much more difficult.

Sorry, it's my bad again.(by not being specific enough in my question), the device need to be in the ball as I mention above, or the ball is actually the device.

And yes, it's in an uncontrolled outdoor environment.

Thanks guys!

 

Oh, that's different.

How about setting up multiple audio sources, and have a microphone in the ball with a digitizer and storage device. Then you'd record the waveforms of the audio signals as received by the ball, and using doppler effect etc and calculation of the range to each sound source, figure out the path of the ball.

Or you can get multiple accelerometer packages for not too much money these days. Store sequential acceleration readings, then integrate the numbers later to get velocity and rotational position. Maybe a device like this?
https://www.sparkfun.com/products/10937

 

Use a heavy square ball (brick), and soft ground for landing.

Then it will not roll from where it lands, and you can use a tape measure.

 

Oh, that's different.

How about setting up multiple audio sources, and have a microphone in the ball with a digitizer and storage device. Then you'd record the waveforms of the audio signals as received by the ball, and using doppler effect etc and calculation of the range to each sound source, figure out the path of the ball.

Or you can get multiple accelerometer packages for not too much money these days. Store sequential acceleration readings, then integrate the numbers later to get velocity and rotational position. Maybe a device like this?
https://www.sparkfun.com/products/10937

Could you explain a bit more about how to do it with accelerometer please?

 

Use a heavy square ball (brick), and soft ground for landing.

Then it will not roll from where it lands, and you can use a tape measure.

Lol, didn't see that one coming neither, but this is not going to do what I need.

 

Well, dip the ball in paint before tossing, then do it on your mother's patio. She will know where it lands.



Alternatively look up engineer's chalk and chalk lines.

 

I'm also quite serious.

You will need to calibrate any measurement system so you will need to think out of the box.

Other possibilities include.

Using a sand pit for landing.

Pegging out with string or grass lining a grid of 1m squares for landing.

Describe the project requirements in more detail for help with the tracking system.

 

Model rocketers use altimeters. An option.

Without knowing what you're doing, I'd consider using a ground based measurement of initial velocity and angle. With just a few measurements for calibration, you'd be able to construct a model for estimating projectile height for any combination of angle and velocity.

Heck, with the low accuracy you need and the low velocity, you could probably just calculate the height based on the physics. Air resistance would just be a small error.

 

I've suggested this elsewhere on these forums: have a system that sends out a radio pulse and a sound pulse and a receiver that starts timing when the radio pulse arrives and stops timing when the sound pulse arrives - the difference is due to the speed of sound and so is proportional to distance

 

Cool, but that gives elevation how?

Oops, my mistake. The OP does indeed just want distance away from the source. Huh.

Can you (the OP) wait until the ball actually hits the ground? I think an onboard accelerometer would be able to estimate distance to within your specs. A ground strike might not be necessary to accomplish that, but I think it would simplify things.

 

Can you toss it with low/no spin and weight one side? That side would have an ultrasonic transducer, and you could get some accurate readings out of it.

 

Model rocketers use altimeters. An option.

Without knowing what you're doing, I'd consider using a ground based measurement of initial velocity and angle. With just a few measurements for calibration, you'd be able to construct a model for estimating projectile height for any combination of angle and velocity.

Heck, with the low accuracy you need and the low velocity, you could probably just calculate the height based on the physics. Air resistance would just be a small error.

Ideally, all the electronics and device need to be in the ball, if that's possible.

 

Oops, my mistake. The OP does indeed just want distance away from the source. Huh.

Can you (the OP) wait until the ball actually hits the ground?

Hi wayneh,

Thanks for your reply, the distance need to be obtained before the ball hits the ground.

 

I've suggested this elsewhere on these forums: have a system that sends out a radio pulse and a sound pulse and a receiver that starts timing when the radio pulse arrives and stops timing when the sound pulse arrives - the difference is due to the speed of sound and so is proportional to distance

Hi sirch2,

Thanks for your reply, all the sensors and electronics need to be in the ball, if that's possible.

 

Can you toss it with low/no spin and weight one side? That side would have an ultrasonic transducer, and you could get some accurate readings out of it.

The projectile is more like a rocket, actually, the ball can be replaced by a rocket, if that make more sense.

So the ball/rocket will spin, but it only spin with the projectile as the center line (hope I am making sense here, in not, please ask for clarification)

However, how do you get some reading with a ultrasonic transducer in your suggested solution, I am interested.

 

A Tri-axial accelerometer in the ball and a small uC to act as a data logger (also in the ball) might work. Mems accelerometers are real cheap, so are uC's. Lotsa number crunching ahead.