the hand is stiff

If I may ask you something Wayne 

right now we have 4 set of bones (DEF-MCH-FK-IK)

deformation bones are used to attach to the mesh and make it move 

MCH bones are there to attach to deformation bones to control it and make the move of both the mesh and deformation bones 

what I don't understand what is the point of FK/IK bones, Why do we need them?and to which bones they get parented and constrain?

let me give an example of what I will be dealing with 

mainly I model hard surface assets like hard surface characters ,mechs ,robots 

If I want to use DEF-MCH and CTRL bones only.

will that be enough to make animation friendly rig or not?

and thank you so much 

FK and IK are 2 different ways of moving an armature. FK is kind of like posing an action figure where every little part has to be moved independently of everything else. Rotate the shoulder, the elbow, then the hand, so on until you get it all like you want it. IK on the other hand lets you grab the hand control and position it and all the other bones will move where they need to go. Some animations work better with one while others might work better with the other, which is why there's 2 sets.

First, IK and FK are two different types of animation...Paths for a lack of a better word. FK or Forward Kinetics is you move the shoulder bone, then move the upper arm, lower arm, hand, etc. IK or Inverse Kinetics is where you move the IK control bone, and the IK chain (The MCH Bones) is calculated for you. Moving the hand moves all the way up to the shoulder including bending at the elbow. Arms are normally done using FK, but if you need the hand to stay put like when doing push up then IK is preferable. Why? Because you can position the hand on the ground then just move the upper body up and down and the arms will be automatically calculated (the MCH bones). Robots have very stiff and limited movement, which means you will want to lean more towards IK than FK. 

Second, the IK and FK bones are the control bones. They just handle the movement differently and depending on the animation action as to which one you use. 

Third, the MCH bones are used to facilitate the actions of other bones. Like the IK chain. The IK control bone is what the animator interacts with, but the MCH bones are what blender uses to calculate the movement and in turn moves the DEF bones. Another example: A mounted gun on a mech can be setup as a targeting MCH bone. Then the target bone would be the control bone. The animator would simply move the target bone to where the gun should point at, and the MCH bone then moves the gun to point at the target or tries to if the gun has enough movement to actually point at the target. Another common use of MCH bones is when you need a stand in for another bone to prevent Cyclic errors. Like a parent bone being a child of one of its child bones.  

so for a a whole body part like movement of a limb I will use IK bone, for a limited movement of a body part I will use FK bones. I hope that I got that right 

for the MCH bones I understood that we use them to facilitate the working of the other bones in the rig but if we don't need them we can discard them, did I get that right?

I have attached two examples of meshes I will be dealing with to give you an idea of stuff I will be working on 

https://www.dropbox.com/scl/fi/e8bzog9riqsv8xa4p8bf5/example-for-you.rar?rlkey=wkedo77rxkdxd1v58rjou65kz&st=ys3gjlgt&dl=0

I understand that this course is extremely advanced for me

so do you suggest that I use the rig made on wrangler for my hard surface character? Or should I keep studying that course?

and thank you so much guys for your help and explanations, it really opened my eye 

and from your explanation in the video I understand that constraints will never be assigned to fk or ik bones 

only deform or mch 

Except in rare cases or if you are combining roles of bones, then yes you never assign constraints to control bones.(IK or FK) By combining roles: I mean like if you use it as both a control bones and a deformation bone. This is common with game rigs. 

On the MCH bones, yes if they aren't needed then delete them. 

On movement, it's more if you need the end point, a foot or hand, to stay at a set position while the body is moving. The feet are constantly stopping at the ground while the rest of the body continues to move. This is why legs default to IK. Where hands swing with the arm. Which is why they are commonly FK. However if you do certain actions like a windmill or round house kick, it is easier to animate those using FK. If you have a character using their hand against a wall to guide themself in the dark. Then It would be easier to animate using IK. That's why IK/FK switching is so common in character rigs. I'll have to look at your example when I get home from work. Robotic characters usually have limited movement which usually makes setting up IK a little more complex, but makes animating a lot easier. Unless you want to give more organic movement to your robot/mechs which is common in Korean or Chinese anime. Less so in Japanese or American anime. 

hi wayne 

thank you for the video 

forgive me and I am sorry for not combining the hard surface character before sending it, it is not several pieces, it is one mesh composed of several pieces.

I am still working on it, it is the high poly version of the low poly game asset that I will build but the shapes, silhouettes are the same 

so what I go back to is should I keep studying the course and try to understand the "complex rig" you are teaching in order to be able to rig this character or what should I do in that problem I got myself into xd?

the problem that I am dealing with right now is the relationship established between ( DEFORMATION-MECHANISM-FORWARD Kinematics-INVERSE KINEMATICS)

if u can please please make a video clarifying the parent relationship between these bones and constraints ties and which ones go with the other I would be very very very extremely grateful for your enormous gigantic titanic help 

what I am struggling with is why and what bones get glued to the other and the logic behind it

if I understand that my problems will be solved

again thank you so much for your help and commitment to help me man 

really  appreciate it 

For a character like that, yes you should continue this course, but before doing this course you should complete this course:

CORE Fundamentals of rigging

This should answer a lot of questions for you. Now I'll try and clear somethings up. 

Think of rig as layers. 

DEF bones are the ones that connect to the mesh. Vertices and/or objects are connected to these bones. When they move something on the mesh moves. It can even be the entire object/mesh. Each bone will correspond  to a different part of the mesh. 

Then there's the base control bones. In most cases this starts as a copy of the DEF bones and is used as the controls for the animator when they are animating. Basically they move each joint(AKA bone) into position. For example: reaching for a door handle to open a door. The upper arm is moved then bend at the elbow(AKA rotating the forearm). Then positioning the hand. Then wrapping the fingers around the door handle. Control bones use FK movement. 

The linking is that the control bones are parented to each other in a logical manner. For example you want the head to move forward when the character bends at the waist not when the hand rotates. Then control bones are linked to the DEF bones through constraints. Constraints can be turn off thru influence slider or they can be overridden by a constraint higher in the stack. This allows for animating shape keys, corrective bones, situational bones, and of course switching from FK to IK. 

IK setup is only used for areas where It can make animating easier. Like arms and legs. Also along the spin. I believe Wayne covers this in this course. An IK setup is made up of 2 parts. The mechanism bones(MCH) and the control bones. Most of the MCH bones are used to link to the DEF bones through constraints. They are parented to themself and the top parent then is parented to next logical control bone not apart of the IK chain. Like a chest bone for the arm IK. Control bones are usually parented to the root bone or highest body bone. Commonly the hip. Bone. Sometimes this will be setup as switchable. In which case it will have no parent and instead be linked through constraints. 

As an additional note: can you just use the DEF bones to animate? Yes. However it will make animating more difficult and time consuming. Take a simple thing like stepping forward. Just a step, not a full walk cycle. Every time you make an adjustment to the bend of the knee you have to then move the upper leg so the foot is still on the ground. When you pull the body down you have to adjust the legs and foot to keep the foot from going through the ground. This is called counter animating. This is why IK is such a game changer. You plant the foot on the ground or up in the air and then when you move the hips down the leg automatically bends and adjust to keep the foot where it's at. 

With a robotic character like your example, could you just use DEF bones and apply IK to the DEF bones? This depends on your animation style and needs, but technically yes. However this limits your animation possibilities and teaches habits that will make it harder to adapt to other 3D software where bones are called joints and controls are separate objects. This is important if you are planning to go pro. For hobbyist staying in Blender, it's a good option. 

I was going to say there's actually also exercises earlier in the RIG course. If you just watched the videos but didn't do the exercises, I'd highly recommend doing those exercises. They show how things work in a simplified setup.

thank you guys for your thorough explanation of things 

and yes Wayne I took the core course 

I will try to study the course over and over until I understand the concept right