Hi All,

i want to move a solid in a motion analysis as shown in the Picture.

Because of the resolution limitation maybe the quality of the picture is not good enough.

If you need a higher res. picture you can download it here http://dl.dropbox.com/u/1362871/Motion%20Plot.png

My Problem is the expression formulation because of the timesteps.

For the first timestep (0 - 0.55sec) its easy:

(10*((TIME/0.55)**3)-15*((TIME/0.55)**4)+6*((TIME/0.55)**5))*0.720)

But now i have no idea how to add the other timesteps (2-7) into the expression.

The only way i have found is to use the IF function. But thats a terrible solution.

I do not want to use the interpolated method.

Hopefully you can help me.

Thanks

Hi Christian,

This looks like you can get close using a step function for each stage. There are additional interpolations, but with a step function you specify the start time, start value and then end time and end value. Step functions are cumulative, so the next function will be relative to the first. As an example:

STEP(TIME, 0, 0, 0.55,720)+STEP(TIME, 0.65,0,0.95,-150)+STEP(TIME,0.95,0,1.25,150)+STEP(TIME, 1.35, 0, 1.95,-720)

If you look in the help you'll find the following:

The

STEP(function returns a smooth step function applied to an expressiona,x1,y1,x2,y2)afor time or for a result. The smooth cubic function starts rising at (x1,y1) on the horizontal axis, and levels off at (x2,y2). Use this function in expressions for forces or motors.## Format

STEP(a,x1,y1,x2,y2)## Arguments

atime.x1y1x1.x2y2x2.## Step Function Equation

The

STEPfunction approximates the Heaviside step function with a cubic polynomial.FunctionDefinitionSTEP (a, x=_{1}, y_{1}, x_{2}, y_{2})y_{1}a ≤ x_{1}y_{1}+ (x_{2}- x_{1}) *z^{2}·(3-2*z)x_{1}< a < x_{2}y_{2}a ≥ x_{2}=z((a - x_{1})/(x_{2}- x_{1}))The other alternative you have is to just import this data as datapoints (save the function data as csv or txt and load it into motion.

Cheers,

Ian