Inconsistent nParticle/Instancer Motion Blur (Maya2017 Update 3)

[thebenp]

I am having trouble getting particle instance motion blur to match the original particle motion blur, it seems to be exaggerated.

Windows 7, Maya 2017 Update 3, mtoa 1.4.2.2, Arnold Core 4.2.16.3

I am unable to upload a scene, but here is a mel script that will create a repro scene from a blank scene, with a cube emitting nParticles with an Instancer attached.

Be aware, running the script will automatically try to create an nParticle cache.

Run the script in an empty scene, then hide the Instancer and render the nParticles.

Looking good.

Now hide the nParticles and render the Instancer. The motion blur is quite extreme in comparison, in fact I am not sure which one is correct.

Any clarification of this behavior would be appreciated.

//nParticle_Instancer_motionblur_test_scene

CreatePolygonCube;
select -r pCube1 ;
move -r 0 5 0 ;
emitter -type omni -r 100 -sro 0 -nuv 0 -cye none -cyi 1 -spd 1 -srn 0 -nsp 1 -tsp 0 -mxd 0 -mnd 0 -dx 1 -dy 0 -dz 0 -sp 0 ;
nParticle;
connectDynamic -em emitter1 nParticle1;
setAttr "nParticleShape1.radius" 0.06;
setAttr "nucleus1.usePlane" 1;
setAttr "defaultArnoldRenderOptions.motion_blur_enable" 1;
setAttr "nParticleShape1.particleRenderType" 4;
CreatePolygonSphere;
select -r pSphere1 ;
setAttr "pSphere1.scaleX" 0.06;
setAttr "pSphere1.scaleY" 0.06;
setAttr "pSphere1.scaleZ" 0.06;
particleInstancer -addObject -object pSphere1 -cycle None -cycleStep 1 -cycleStepUnits Frames -levelOfDetail Geometry -rotationUnits Degrees -rotationOrder XYZ -position worldPosition -age age nParticleShape1;
select -r nParticle1 ;
doCreateNclothCache 5 { "3", "1", "48", "OneFilePerFrame", "1", "","0","","0", "add", "0", "1", "1","0","1","mcx" } ;
currentTime 40 ;
setAttr "persp.rotateX" -4.5;
setAttr "persp.rotateY" 35;
setAttr "persp.rotateZ" 0;
setAttr "persp.translateX" 8.3;
setAttr "persp.translateY" 3;
setAttr "persp.translateZ" 10.7;

[mspeer]

Hi!

Arnold + nParticle Render Type Sphere or Points = only 50% Motion blur (wrong, don't know why)

Arnold + nParticle with Instances = 100% Motion blur, correct

If no one else has a better idea,

please report this problem (bug?) to Autodesk.
Help -> Speak Back -> Report a Problem

[thebenp]

Thanks for confirming. I have submitted a bug report.