Vinyl Spinning Physics Problem

[Jacob Roman]

I already posted this in the math forum with no answer.

I'm making some turntables in 3D using DirectX8. I just figured out mathematically how to get the vinyls to spin exactly 33 1/3 rpm clockwise.

Now here's my problem. If I were to make it to where you click and hold the mouse down on the vinyl, which will cause it to stop, and after doing some scratching, I toss it by hand either forward or backward (Force). Tossing it forward will cause it to go faster, then cause it to slow down back to 33.5 rpm. Tossing it backward (counter clockwise) will cause it to play backwards briefly, some torque then come into play and pull it back forward slowly to 33.5 rpm. What physics formula do I need to pull this off? Thanx in advance.

[Cade]

Well speed would be relative to the distance between the current mouse xy and the mouse xy when you clicked. Not so sure about the rest yet, sorry

[BodwadUK]

To move forward and back review the mouse position and work out how many pixels represent seconds in music if that makes sense. The faster and further back you push the cursor the more effect it has on the music (Same for forward)

To slow it down have a resistance value in RPM and apply that instead of your acceleration.

For you acceleration problem you need to make a decision as to how many RPM gain you get per second and then calculate it by adding up until you reach that rpm

I think thats what you want anyway

[wossname]

Is the record being viewed directly from above or from an angle?

[Jacob Roman]

Any angle. Don't worry bout the mouse coordinates. Got that covered. The angle of the record doesn't matter here. It's all based on clockwise/counter clockwise rotation physics with some torque coming into play. I'm not exactly a physics guru but any physics help will be awesome.

The rpm of the vinyl with the sound playing at normal speed is 33 1/3 rpm, which is 3.333333333 rotation speed per frame. Multiply that by 60 FPS and 199.9999999999999 degrees per second.

[BodwadUK]

You should use a type of timer not the frame count or am I not understanding you correctly

[Jacob Roman]

I'm using Time based animation

[Jacob Roman]

Ok i found this to obtain Torque

http://shark.comfsm.fm/~dleeling/physics/torque.html

Torque = Force × Distance to fulcrum × sin (Angle)
Torque = Force × Distance to fulcrum × sin (90°)
Torque = Force × Distance to fulcrum × 1
Torque = Force × Distance to fulcrum

For those who don't know, the fulcrum isthe central point about which the system turns.

So now all I need to do is figure out the force I need to pull the vinyl to 33 1/3 rpm whether it went too fast or too slow.

[bat711]

Isn't it dependent on the power of the turntable motor, to make it realistic anyways? I thought manufacturers list that?

[Jacob Roman]

The motor has nothing to do with the software part I'm doing. It's the torque it puts out. That's what I'm trying to figure out mathematically.

Now my problem right now is figuring out the amount of force for when you spin the vinyl by hand (errr mouse actually) and releasing it, causing it to spin fast on its own, while the torque slowly pulls it back to 33 1/3 rpm. Same goes for when you stop it briefly, the torque will slowly pull it back to 33 1/3 rpm. The more torque there is, the faster it can pull back to 33 1/3 rpm.

[Edit] I think I found the key but still trying to figure it out:

http://departments.weber.edu/physics...s_rotation.htm