Heli rotor - strange mblur with VRPhysCam

[Morne]

Hi all

As you can see in this short clip, there seems to be some odd mblur on my heli blades. The animation makes it seem like the main rotor is hectagonal and the tail rotor is a pentagon. With mblur it is suppose to seem round while turning. At the moment the mblur makes it seem asif the blades are blurred sideways instead of circular. Hmmm I hope that is clear.

heli_mblur_test.mov

VRPhysCam is set to mblur and samples is 10. Exposure in cam is switched off. ISO is 100, f-stop is 16, and shutter speed is 30. Scene is lit with 1 directional light for the sun and in VRenvironment I have override switched on (default skylight override).

Any ideas how to fix the mblur?

Regards,
Morne

[Neilg]

I've not watched the clip yet, but it sounds like you're just sampling the blur between 2 points.
Select the rotor blades, right click and go to vray properties, uncheck 'use default motion blur samples' and change it from 2 to something like 6, see how that works out for you.

When it blurs, think of it as making copies of your object along its movement path between frames and blurring between those - that number sets the number of copies it uses, so while 2 points is fine for most things, anything that rotates at speed will need more.

It will slow the render down a lot more though, but it's the only solution.

[Morne]

noise?

Thanks that worked great! Now how can I get rid of the noise the mblur seems to be making?

[Morne]

noise kinda fixed

ok I upped the samples of mblur in cam settings to 16 and to 6 in object settings. It looks much better now. (but rendering went up from 11 secs to just over 1 min) O well it looks better at least

[Neilg]

You should think yourself lucky...
I had a scene which was rendering at 20minutes a frame, but the wheels of my cars had that issue. After fixing it the times went up to over an hour, which was great fun to re-optimise a couple of days before the deadline, haha.

[vlado]

You can change the number of motion blur geometry samples locally just for the rotating objects from the V-Ray object settings dialog - there is typically no need to change the global geometry samples for everything.

Best regards,
Vlado

[Morne]

You can change the number of motion blur geometry samples locally just for the rotating objects from the V-Ray object settings dialog - there is typically no need to change the global geometry samples for everything.

Best regards,
Vlado

Vlado so what you saying is that in my VRPhyscam I should leave the default of 6 samples, and instead of in the VRay object mblur samples which is default 2 (I changed it to 6) I should increase object mblur to something like 16 and leave 6 on physcam?

[Morbid Angel]

here is a trick we used to do for chopper shots: if you have a constantly rotating blades, you can fake motion blur, by making the objects appear motion blurred via texture with feather mattes. Then it will be a super fast render and yet look good.

[Morne]

the problem then is that in some shots the blades are not constant, and also I'm using hair and fur which has a bug with opacity in Max 2009.