arm deformation

Arm is deforming strangely is there anyway I can improve it?

The weight’s of that bone are painted like that:

May be your bones axes are pointing into different direction. Go to edit mode with armature select Ctrl+n and choose the direction you want.

Naah it’s not that I just need some tweaks for arm deformation but don’t know how to do it

The arm wont actually rotate at the elbow joint like the first picture.

When you rotate the arm like that, the parts you want to deform is the top_arm/shoulder_joint or the forearm/wrist, both parts of the arm can rotate individually.

Twist is usually solved by adding extra bones to the arm parts (4 bones instead of 2), then weighting the mesh to it.
Or by using shapekeys controlled with drivers, the hand/wrist bone controlling the forearm/wrist twist for example.

Heres two examples.

Wrist Y Negative 90 shapekey (uses driver so may have to load as trusted).

4 arm bones.

The shoulder and hip joints are usually the most complicated to solve.

It’s a game model so I cannot allow to add any more bones. What is most importamt for me is actually shoulder deformation (see third post). Can it be solved by using shapekeys? Or maybe some other way like modifiers or something?

There is the Preserve Volume option on the Armature Modifier. If not already enabled, this may improve the deformation.

Shapekeys can help with the shoulder, though they can take time to setup correctly, also there are different ways to control them with Drivers.

Hook modifiers with empties and a vertex groups could be used.

There are different ways to get round this deform problem, though I only know a few, and I dont know what options you are limited to.

Thx for answer it is useful for mesh deformation but as I analyze my model deeper there seems to be something wrong with the arm joint or something.

As you can see when my arm is near the chest it’s like half of the arm is inside of the chest mesh. I know my chest mesh is wide but the way of how much of the arm mesh is inside the body means that problem lies elsewhere (at least that’s what I think). A lot of people here have experience with rigging and skinning different body types with different clothes so maybe someone can help me with that?