From Google search:
Apparently, Quaternion is the default rotation mode for new Armatures.
I want to use the X Rotation of a bone as a driver. Well, them dang quaternions are weird lookin’! So, I converted to Euler and I feel much better now.
Why do quaternions scare me so much? Do other animators take my approach and convert? Can I set Euler as the default?
Thanks,
Cal
“Quaternions came from Hamilton after his really good work had been done; and, though beautifully ingenious, have been an unmixed evil to those who have touched them in any way, including Clerk Maxwell.” William Thomson, first baron Kelvin, 1892
Can I set Euler as the default?
I do not know but this might help you
I think you can also write this in a driver:
radians(90) …blender should convert 90º to radians
or… degrees(1,5708) …would convert the other way around.
Euler is great until you hit gimbal lock… once you do, you’ll immediately understand, and never go back to Eulers again 
Life is mostly made of bad compromises …
TBH very few people understand quaternions and I’m not sure I even met a CG artist who knows how they works. Personally like most people I don’t.
On top of that I think it’s nearly impossible to edit animation curves with them especially when you don’t understand them which is probably the case for 99% of artists 
But !
Euler also comes with some flaws and as you’ve seen there are a bunch of possible combination : XYZ,YZX,ZXY …
The big problem with Euler is called Gimbal lock and that could make animation really unpredictable…
Interestingly enough objects are defaulted to XYZ Euler, bones to Quaternions, probably because bones are more prone to arbitrary rotations/orientation …
TBH when providing a rig to animator we switch all controllers from Quaternion to Eulers, but I can understand why quaternion can be a good default choice. It’s weird, limited, but reliable.
I feel much better now. I’m glad I’m not the only one who finds them troublesome.
Thanks everybody !
Yes some times they are a “necessary evil” due to gimble locks but that is not always the case.
I have used many drivers to continuously rotate bones for wheels (backwards/forwards speed control etc along a track) with drive control objects and found it impossible to get working with quaternions, with euler it works with no problems.
Fun fact:
The Mad Hatter scene in Alice in wonderland is said to be a reference to quaternion rotations and the work of William Rowan Hamilton (discovered quaternions in 1843)
Just a bit more of useless information that stuck into my head when I attempted to understand them. I still can not even spell them correctly without checking 
Oh, and to make things even more complicated radians are not the same thing as quaternions (they are more similar to Euler)
Thanks for sharing this link, really interesting reading 
Here’s a nice interactive site making a valiant attempt at explaining quaternions. I can’t say it helped me wholly understand them, but I can say that I don’t understand them slightly less after seeing this.
Yes same here, they are the best vids I have seen on the subject.
Me too.
I use (CMU) BVHs on MakeHuman Characters a lot, and sometimes I need to tweak stuff.
Now I don’t feel like I’m “cheating” by switching to Euler.
Thanks again.
(PS - Still making stuff loud? Remember… “No higher than 11!”)
Louder as time goes by
Do not worry nobody has complained.
It seems ALMOST intuitive. Like it’s not vastly removed from the usual Euler coordinates, but with an extra arbitrary angle in there to help further define it’s position in space.
It’s kind of like a combination of local and global coordinates, where Q represents a universal Z, where 1 is up, and 0 is down, and I, J, and K, are an object’s local X, Y, and Z as rotated so many degrees around Q.
Yea SEEMS. it’s that fourth dimension that gets me.
It’s just…man, math makes me so mad.
I loved algebra, but after 1 or 2 calculus classes I said “Nope. This ain’t for me”. 
It’s worth noting that gimbal lock is purely an issue of representing rotation over time. The problem isn’t with the mathematical representation, but how we decide to interpolate between two values. With quaternions, even a naive lerp (linear interpolation) of the quaternion components yields usable results. (We don’t actually do that though. We use slerp (spherical linear interpolation))
Some people have the misconception that a quaternion is just a fancy combination of an axis and and angle. While that’s not the worst way to think about it, it’s incorrect. Quaternions cannot be used to reliably encode rates of rotation. They “crap out” at rotations of 180 degrees or more, flipping the rotation direction and such. The end-result is the same, but any intermittent states aren’t what you want. If you want to describe inertia or spinning, one should use angular velocity (rotation axis vector scaled by magnitude of rotation) or angle + axis.
As for quaternion animation curves: unless you are doing some extremely specific mathematical animation, they are useless. Quaternions are still the default though because while few understand the math, it’s easier to explain to someone the steps they need to do to apply its rotation to a vector than with euler angles where you quickly get in arguments over the order in which they should appear and which of them is the pitch, which one the yaw and which one the roll.
I think that sums it up.
Again, thanks everyone !
Cal
