Any 4x4x4 rubik's cube consists out of 24 centrepieces, 24 edgepieces and 8 cornerpieces. One of the main differences between the revenge cube and the normal cube, is that there is no fixed centerpiece on the bigger one. That's why two centers can swap, something that is impossible on the 3x3.
Although many aspects of the notation of the 3x3 are the same on the 4x4. However, some parts are confusing. The basic notation (the capital letters) represent an outside layer turn. So R means to turn the outer right face clockwize. And, of course, the ways to determine which way to turn the face are adopted from the 3x3 as well, so R' means a counterclockwize right turn, and R2 means a double right turn (in any direction).
The best thing you can do is remember the standard notation of the 3x3, but forget the speedsolving notation. It'll become very confusing in a moment, so make sure you don't even think about the speedsolving notation of the 3x3 anymore.
We might want to turn the inner layer, while the outer layer stays in tact. This is represented by a lowercase letter. For example, you want to turn the inner right face, while leaving the outer one. This is represented by an r. Other inner layer turns, include r', r2, f, f', f2, u, u', u2 etc.
Although we can now indicate every move possible, we're not done with learning the notation yet. Sometimes, we want to turn both the inner and the outer layer in the same direction. Then, we could write r R for example. But this is so commonly needed, that a * is added behind the capital letter, to indicate that both layers should be turned. So R* would be the same as r R, and r would be the same as R* R'. Other double layer turns include R'*, R2*, F*, F'*, F2*, U*, U'*, U2*, etc.
The confusing thing is that a lowercase letter on a 3x3 represents a double layer turn, while it represents an inner layer turn on the 4x4.
The locationing system of the 4x4 remains almost the same as the one used on the normal rubik's cube, however some changes are needed.
When we want to indicate a cornerpiece, we use the exact same locationing system used on the 3x3.
When we want to indicate an edgepair, we use the same system aswell. However, when we want to indicate an edgepiece, we add the lowercase letter of the side it's nearest to. See the examples for some more clarification.
When we want to indicate a centerpiece, we write down the side it is on, and then add two lowercase letters of the sides the centerpiece is nearest to. See the examples for more clarification aswell.
Note the difference between UFr and Ufr. The first one is about an edgepiece, while the second one is about a centerpiece. You can recognize which sort of piece I'm talking about like this:
- A cornerpiece is indicated with 3 capital letters;
- An edgepiece is indicated with 2 capital letters and 1 lowercase letter;
- A centerpiece is indicated with 1 capital letter and 2 lowercase letters.