Complex objects

I can't find a way to make multiple linked objects into one object. I am building a tricycle, and the steering columb is a linked set of prims, including the wheel. I need them to move together as one, while the rest of the trike is a separate group of linked prims. How can I take both linked sets and make them into one object that moves together, yet leaving them separate so the handlebars rotate independently?

I also want to be able to do this with doors, making a group of doors and a frame one movable object, while having the doors themselves swing or slide.

What you're describing is akin to a hierarchy link-set system. Unfortunately, this is not yet possible in SL. Once any collection of prims and objects are linked together, they are all lumped as a single object. End of story. Any manipulation of child prims must be done on an individual basis.

You can "fake it" through various methods, but the drawback to that is that it's both very complex to pull off and you're never going to get the movements of the prims to be in perfect unison (due to outside causes like server lag).

For now, the best work around I would suggest is to try and make your components out of as few prims as possible - i.e. with sculpties. A single prim handle bar made out of a sculpted prim would be a lot easier to manipulate in a link-set.

I was just looking at a set of cars on slexchange that looks like the wheels individually rotate down and the car flies like that. Should I assume that the wheels are all single prims then? And is it common in vehicles to have wheels that turn?

More than likely yes, the wheels are probably single prims. It's fairly common for single prim wheels to turn, but it's really up to the designer. However, with something like wheels, they could be multiple prims and still be easy to manipulate.

Here's why:

Say for example you wanted to use a torus for the tire and then a cylinder inside for a hubcap. Both prims would generally have the same xyz coordinates and the same general rotation (give or take 90 degrees for the torus). So if a command was sent to positioning scripts within them, they would snap to the same relative location.

So independent prims within a link can still move independently of each other with scripting, but still move with the whole object when the object moves?

Yep, you've got it. Although, it should be noted that these whole-object movements are associated with the root prim, which means that this one main prim cannot be so easily told to move without moving everything else.

ok heres an idea. why not have the handlebars as an attachment that the avatar puts on.. so when he turns his keys left or right the animation moves him and turns the bars left or right.. while the bike is still controled .. just a thought

Thanks for the help, guys. I guess the rest of my questions here should be posted in the scripting forum.