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[Jan Stránský <question706302@xxxxxxxxxxxxxxxxxxxxx>]

Question #706302 on Yade changed:
https://answers.launchpad.net/yade/+question/706302

    Status: Open => Answered

Jan Stránský proposed the following answer:
Hello,

yes, you can use TranslationEngine to simulate any velocityVector(time) function, and therefore any trajectory.
Use PyRunner and set translationAxis and velocity of the TranslationEngine:

###
O.engines = [
    TranslationEngine(...,label="translation"),
    PyRunner(iterPeriod=1,command="setTranslation()"),
]
def setTranslation():
    t = O.time
    a = ... # any function of time
    v = ... # any function of time
    translation.translationAxis = a
    translation.velocity = v
###

Specifically for circular motion (with variable velocity):
###
r = 5
sph = sphere((r,0,0),1)
O.bodies.append(sph)
O.engines = [
    ForceResetter(),
    TranslationEngine(ids=[0],label="translation"),
    PyRunner(iterPeriod=1,command="setTranslation()"),
    NewtonIntegrator(),
]
O.dt = 1e-4

def setTranslation():
    x,y,z = sph.state.pos
    angle = atan2(y,x)
    v = sin(angle) + 1.4
    a = Vector3(-sin(angle),cos(angle),0)
    translation.translationAxis = a
    translation.velocity = v

view = yade.qt.View()
view.eyePosition = (0,0,20)
view.lookAt = (0,0,0)
###

Note that here a tangent of sphere is specified at each step, so
technically the result is not exact circle, but "little" spiral.

Cheers
Jan

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