Placing bones on objects that move on a loop...

[Kelley]

I think this is sufficiently different to warrant a new thread:

 

[1] I'm installing a single bone that will move the same [left and right] plate on both treads. On a previous attempt, I installed the bone in the right hand tread plate, on the Z-axis. Some of the plates developed a twitch wherein the bone rotated 180 deg. and the left plate flopped over to the far right of the right plate. I suspect it was because of the oblique angle the bone occupied at the points where the plates moved over the major drive wheels at the front and back. [tho' I'm not certain]

 

This time, I'm installing the bone along the X-axis. The question is: at the points where the plate moves across those acute angles, is there any advantage to setting the roll handle at 90 deg. to the plate itself?

 

[2] As I placed the bones in the wheels, I notice that each bone comes in at a slightly different rotational angle. I set them all to X=180/y=0/z=0 for consistency's sake, but is there a key to hold down that will constrain them to 0/45/90 or 180?