Michael, I've gone back to 3ds having tried obj and run into problems that I couldn't solve.
My interest and use of SimLab Composer is for the simulation of mechanisms designed in Moi for 3D printing.
At the very beginning of my use of SimLab I imported .obj files but had difficulties that I couldn't resolve and didn't know whether it was my incompetence with SimLab, errors in my (Moi) design or what. In desperation I tried another file format and chose 3ds, for no particular reason.
Problems eased and I managed to produce several satisfactory simulations.
I'm inclining towards doing 2 simulations per mechanism. One early on in the design as a 'proof of concept' and one at the end of the design to pick up the (all too many) errors that I've made.
On my latest project I'd done the 'proof of concept' simulation shown in the attached 3D pdf.
Then, during the course of the design I received your recommendation to use obj format - for better render performance.
So back to obj having by that time largely forgotten my initial struggles with it in SimlLab and I just couldn't get the simulation of the final mechanism to work. Eventually I realised that I'd used 3ds files for the concept and was now struggling with obj files.
Back to 3ds files and happiness.
I've sought comment from SimLab and their recommendations regarding the best file types to import for simulation and though that I should post here to for your comments and for the information of others following a similar path.

Mike.

Just received this advice from SimLab:
"For simulation it is better to use an nurb based format like ACIS or STEP
while OBJ and 3DS will bring better material appearance.

ACIS and STEP will include inertia information, to get more accurate results.

So my suggestion to you is to try ACIS and STEP from MOI for simulation."