Rotation & angle of universal joint?

[N. W. Perry]

I managed to come to a working method, but it is based on a successive approximation method, far from optimal... (attached).
Note that I haven't found the 853/956 Auto chassis on the OMR, but it's available on Eurobricks. Needed it for basic geometry... but the universal joints are slightly wrong there, the middle connections are badly placed.

So, what you're saying is…this one actually is as tricky as it seems? 

There is also an 853 model at Technicopedia; it looks to be a different one from the Eurobricks model, but your own solution looks at least as accurate!

The other thing compounding this issue is that real plastic is flexible and digital brick are not. This means that what fits in real life may not on your computer. The single angle u-joints often are off by a few ldu, the double angle u-joints often have a significant length gap.

This model actually has a few such instances, as do some others from that early Expert Builder period, where connections are made that depend on the natural tolerance of the plastic and the spaces between bricks. I've been meaning to ask in another thread how others have gone about modeling these instances (for example, in the 850 Fork Lift, I made my own custom 2x2 brick that is 1 LDU too short and mixed it in with proper-sized ones, to allow a connection with one beam that's misaligned with another).

I don't have the time to go in to details at the moment, but you might want to look at my 8860 animation script (included in LDCad's examples).

It does realtime frame depended universal placements.

I actually looked at the 8860 script for piston rod/crankshaft placement as well. I recognize that the answer is in there somewhere, but I will probably need some help translating what I'm reading there. 

Meanwhile, I'll see how close I can get with successive approximation—I'll probably try setting the angles in Bricksmith, since I can repeatedly apply an incremental rotation of my choosing until it's as close as can be.