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Computing total velocity of broomstick - Impact of distance from I.C. to sensor

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gordonjudd
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Computing total velocity of broomstick - Impact of distance from I.C. to sensor

Post by gordonjudd »

Noel,

This is question that I hope will make sense to you as I am a bit hazy on how to apply the principles of rigid body dynamics.

Looking at how the instantaneous center (I.C.) moves relative to the butt of the rod where the sensor is located (see I.C. Flow video example I am wondering how you should compute the total velocity of the tip of the broomstick (shadow beam).

For reference purposes let A be the position of the sensor, and B be the end of the shadow beam. I.C. would be the location of the instant center of rotation measured for the butt section of the rod (the blue dot location on the video).

I assume that taking omega x rod length will give the relative velocity (Vb/a) from A to B that you used to compute the velocity of the shadow beam.

Will taking the vector distance (from the I.C. to A) x omega give the velocity of point A (Va)? Consequently Vb= Vb/a+Va where the velocities would be added as vectors.

From the video the distance from the I.C. to point A is quite large at the start of the cast so its impact on Va could be significant (although omega would be smaller at that time point.) Even when the angular velocity (omega) is near its maximum the I.C. is near my elbow so Va could have a significant y component at that time point.

Thanks.
Gordy
"Flyfishing: 200 years of tradition unencumbered by progress." Ralph Cutter
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