Need equation for modified sine curve for a cam.

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    Cam Curve Sine
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Discussion Overview

The discussion centers around finding the equation for a modified sine curve used in cam design. Participants explore the theoretical underpinnings and practical applications of this curve in creating cam shapes.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant expresses a desire for the specific equation from the "Cam Design Handbook" by Harold A. Rothbart without purchasing the book.
  • Another participant suggests that the modified sine curve is likely just a literal interpretation of a sine curve, noting its infinitely differentiable nature which avoids discontinuities in accelerations and forces.
  • A different participant agrees that the modified sine curve is a good starting point unless a specific design requirement dictates otherwise.
  • A more detailed explanation of the modified sine curve is provided, outlining how it divides the event length into three subsections with corresponding lift expressions for each subsection.
  • One participant recommends conducting a Google search for "modified sine curve," indicating that portions of Rothbart's book can be accessed online, including relevant equations.

Areas of Agreement / Disagreement

Participants generally agree on the utility of the modified sine curve for cam design, but there are varying levels of detail and specificity regarding its implementation and the need for additional resources.

Contextual Notes

The discussion includes specific mathematical expressions for the modified sine curve, but the assumptions and conditions under which these expressions are valid are not fully explored.

sgt_rock
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I am looking for the equation used to create the cam shape using a "modified sine curve".

I am pretty sure the information is in the "Cam Design Handbook" by Harold A. Rothbart but I don't want to buy the book for just one equation.

Any help would be appreciated.
 
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It's more than likely just literally a modified sine curve. Nice thing about sine curves is that they are infinitely differentiable, so there are no discontinuities in accelerations/forces, etc.

Unless someone else has designed cams before.
 
Yeah, modified sine curve is a good starting point unless you're doing something particular.
 
The modified sine curve divides the complete event length, beta, into three subsections and uses a separate lift expression over each subsection. They are as follows:

For a total lift of h ...

for 0<theta<beta/8 .....y=(h/(4+pi))*(pi*theta/beta-(1/4)sin(4 pi theta/beta))
for beta/8<theta<7*beta/8 ..y=(h/(4+pi))*(2+pi*theta/beta-(9/4)*sin(4*pi*theta/(3*beta)+pi/3))
for 7*beta/8<theta<beta ...y=(h/(4+pi))*(4+pi*theta/beta-(1/4)*sin(4*pi*theta/beta))
 
Do a Google search on "modified sine curve" and you will find several entries, one of which is from GoogleBooks. There you can read a portion of Rothbart's book where you can find these equations on p. 75.
 

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