Rotational Axis Measurement

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PaulyGirl1
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Rotational Axis Measurement

Post by PaulyGirl1 » Sun Aug 31, 2014 11:43 am

Have been tinkering with this idea for a while and now want to commercialize it.
The idea is to be able to read the spin axis of a rotating ball as it travels through the air. The spin axis will help to feedback information relative to how much movement (curvature) the ball will have.
Here are the components I need:
1. A small relatively shock resistant wireless chip that will send a signal that will indicate the axis of rotation. This chip would be embedded in the center of a ball
2. A remote handheld battery powered meter that will display the rotational axis. Remote definition would fall into the range of 5--60 feet from the chip.

I have accomplished reading spin axis with other methods but they are very slow and not user friendly methods......so any help is appreciated.

jremington
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Re: Rotational Axis Measurement

Post by jremington » Sun Aug 31, 2014 7:22 pm

Why not tell us how you have determined the axis of rotation, and with respect to what reference?

skimask
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Re: Rotational Axis Measurement

Post by skimask » Sun Aug 31, 2014 8:26 pm

And what kind of ball...
And how the O/P plans on getting this unit inside the balls without wrecking aforementioned ball...
I ignore "one post wonders".

jremington
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Re: Rotational Axis Measurement

Post by jremington » Sun Aug 31, 2014 8:31 pm

Also, could you take a moment to explain what you mean by this?
The spin axis will help to feedback information relative to how much movement (curvature) the ball will have.

PaulyGirl1
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Re: Rotational Axis Measurement

Post by PaulyGirl1 » Mon Sep 01, 2014 3:13 am

In the past I have measured spin axis using high speed video and special markings on the ball for tracking purposes....it is a bit crude and not the instant feedback I am looking for.
I am using this application in fastpitch softball pitching....but would also be applicable to baseball....or any other type of ball.
One of the most important criteria for ball movement is the axis of rotation. The ball moves perpendicular to the axis of rotation.
The idea is to have the chip inserted into the center of the ball during the manufacturing process.

Hope this clarifies some of the early questions.

jremington
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Re: Rotational Axis Measurement

Post by jremington » Mon Sep 01, 2014 8:00 am

There is no "chip" that will do what you want. It is conceivable that an IMU could provide some useful information, but you would have to think carefully about the data output rates in relation to the flight time of the ball. Of course the IMU would have to be coupled with a microprocessor, a transmitter and a battery, so this is a pretty ambitious project.

Dave Mueller
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Re: Rotational Axis Measurement

Post by Dave Mueller » Mon Sep 01, 2014 8:06 am

PaulyGirl1 wrote:A small relatively shock resistant wireless chip
"Shock resistant" doesn't even come close to describing the forces experienced by a baseball when hit by a bat.
If you limited the device to pitching practice only, you'd still have to make the electronics (with battery!) perfectly balanced in 3 axis (axii? axises?) to avoid introducing negative effects.
It's a neat idea, but I don't think it's practical to implement.

jremington
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Re: Rotational Axis Measurement

Post by jremington » Mon Sep 01, 2014 8:56 am

Another problem is that with IMUs, the accelerometer is inaccurate if the device is rotating rapidly. So, you lose your reference to the down direction. I agree that this is probably impractical.

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Ross Robotics
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Re: Rotational Axis Measurement

Post by Ross Robotics » Mon Sep 01, 2014 9:47 am

How you are calculating the spin is how the professionals do it today. I would imagine with unlimited funds that the pros have, they would have already tried this.
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PaulyGirl1
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Re: Rotational Axis Measurement

Post by PaulyGirl1 » Mon Sep 01, 2014 11:01 am

Well there is a great product that's been on the market for 6-7 years now....it has a chip inside a ball and measures the spin rate of the ball in revolutions per second. The product is called RevFire. It is used just for pitching practice/training and is very durable. It seems like a logical progression to be able to read the rotational axis.

jremington
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Re: Rotational Axis Measurement

Post by jremington » Mon Sep 01, 2014 12:25 pm

Cool product! I'll bet if you take apart the RevFire ball, it will have a small PCB with a rate gyro, accelerometer, microprocessor, transmitter and a battery.

To determine the direction of the axis of rotation, you need an Earth-frame directional reference. An IMU will include a magnetometer for a North reference. You need one more direction and in principle, an accelerometer can be used to define "down". But as mentioned they are confused by rotation.

This company http://www.x-io.co.uk/ is doing state of the art research on IMU development and applications. Check out the video of footstep tracking at http://www.youtube.com/watch?v=6ijArKE8vKU

Mee_n_Mac
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Re: Rotational Axis Measurement

Post by Mee_n_Mac » Tue Sep 02, 2014 8:18 pm

PaulyGirl1 wrote:Well there is a great product that's been on the market for 6-7 years now....it has a chip inside a ball and measures the spin rate of the ball in revolutions per second. The product is called RevFire. It is used just for pitching practice/training and is very durable. It seems like a logical progression to be able to read the rotational axis.
Measuring spin rate is easy, a 3D gyro will do that. Measuring true velocity (sans radar gun) is a bit harder. It depends on the level of accuracy you want. Pinning those to some Earth fixed reference frame so you can know up/down spin vs lateral spin is where it get's hard. Embedding the electronics in a pitched, not hit, ball seems easy enough. Keeping those electronics "happy" after being hit should be do-able but don't expect good "inertial position" data from the ball, in flight, after it's been hit.

From the RevFire FAQ I infer that they don't measure velocity but rather deduce it from an assumed distance and an measured time. That time being from release by pitcher (G's go from X to 1G) until catch (Gs go from 1G to Y). Also there's no mention that they know the orientation of the spin axis wrt Earth, thus a sinker could be a curve ball as far as the collected data goes. The observation by a coach must play into this.

So there's the new problem to be solved ... to get that orientation ?

PaulyGirl1
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Re: Rotational Axis Measurement

Post by PaulyGirl1 » Mon Sep 08, 2014 5:42 pm

"So there's the new problem to be solved ... to get that orientation ?"

Yes, that is the mission.......there is always more than one way to skin a cat......I just have to find that way.

Mee_n_Mac
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Re: Rotational Axis Measurement

Post by Mee_n_Mac » Tue Sep 09, 2014 10:38 am

As said above you can try using a magnetometer, I'd be careful to look at it's frequency response to see if it can keep up w/the expected spin rates. Or do the reverse, generate the magnetic field within the ball and sense it externally, as was done here ...
http://hackaday.com/2014/09/08/tracking ... ic-fields/

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