Separate all those pieces into separate objects (Edit mode, `P`, Loose Parts). Center their origins inside their bounds (Select them all, right-click, Set Origin, to Geometry). Add your armature w/root bone at the world origin, stretch it up to the belly joint-ball. From there, extrude bones using Shift+S snapping tools to create bones that run from each ball-joint to the next (e.g. in object mode select a hip ball, `Shift+S 2` Cursor to Selected; enter Edit mode on the armature, select the belly joint-ball, E extrude a new bone from it, `Shift+S 8` Selected to Cursor).
Then go through all the parts and parent them each to a bone that runs through them (enter Pose mode on the armature; one at a time, select a bone, then select the matching piece(s) in the Outliner pane, `Ctrl+P` to Bone). Doesn't technically matter whether the joint-balls are parented to the bone ending in them or rooted in them, but might matter artistically.
No; the ball joints are where the ends of each bone should be, they should not get bones themselves unless you need very special animation properties out of them; and even then, it would be easier to create the effects I can picture by using auxilliary bones influenced by the bones on each side.
I'm not sure how to orient the bones. Do I connect the chest/torso bone to the arm bones? Or do I create a separate bone and just move it to each respective arm and extrude?
Your armature should look something like this. Extrude from the end ball of each armature bone to automatically create parenting relationships. All of the armature-bone "balls" will line up with your model's ball joints, except the leaf points (fingertips, toetips, top of head) and the root bone's origin.
https://i.imgur.com/yUl1Smd.png
When I try to rig the model, certain parts of it stretch when it should remain solid. Could this be because the legs are too close together and the arms are too close to the body?
Show a screenshot of the stretching, and the modifiers on one of the model mesh objects. That should not happen if you are only rotating the bones when in armature Pose mode, not moving them; and you are also using bone parenting, not the Armature modifier.
The most realistic way to do it would be to create a skeleton made of bones for each rigid part, and a joint for each modelled joint.
Then, on the skinning part, each vertex would be influenced by a bone completely (100% on weight value). In a model like this there is not bending of the wood, the wood just rotates on the joints without bending, so the same must be shown in the rig.
If you want it to move like a mannequin, dont use bones, you dont need them for this.
Do it parenting each piece to its joint, and have the origins/pivot of the joints in it's center, so they rotate correctly from the joint, is quicker.
Separate all those pieces into separate objects (Edit mode, `P`, Loose Parts). Center their origins inside their bounds (Select them all, right-click, Set Origin, to Geometry). Add your armature w/root bone at the world origin, stretch it up to the belly joint-ball. From there, extrude bones using Shift+S snapping tools to create bones that run from each ball-joint to the next (e.g. in object mode select a hip ball, `Shift+S 2` Cursor to Selected; enter Edit mode on the armature, select the belly joint-ball, E extrude a new bone from it, `Shift+S 8` Selected to Cursor). Then go through all the parts and parent them each to a bone that runs through them (enter Pose mode on the armature; one at a time, select a bone, then select the matching piece(s) in the Outliner pane, `Ctrl+P` to Bone). Doesn't technically matter whether the joint-balls are parented to the bone ending in them or rooted in them, but might matter artistically.
When I add a bone for each part, does that include the joints?
No; the ball joints are where the ends of each bone should be, they should not get bones themselves unless you need very special animation properties out of them; and even then, it would be easier to create the effects I can picture by using auxilliary bones influenced by the bones on each side.
I'm not sure how to orient the bones. Do I connect the chest/torso bone to the arm bones? Or do I create a separate bone and just move it to each respective arm and extrude?
Your armature should look something like this. Extrude from the end ball of each armature bone to automatically create parenting relationships. All of the armature-bone "balls" will line up with your model's ball joints, except the leaf points (fingertips, toetips, top of head) and the root bone's origin. https://i.imgur.com/yUl1Smd.png
When I try to rig the model, certain parts of it stretch when it should remain solid. Could this be because the legs are too close together and the arms are too close to the body?
Show a screenshot of the stretching, and the modifiers on one of the model mesh objects. That should not happen if you are only rotating the bones when in armature Pose mode, not moving them; and you are also using bone parenting, not the Armature modifier.
Could I DM you the blender file instead?
The most realistic way to do it would be to create a skeleton made of bones for each rigid part, and a joint for each modelled joint. Then, on the skinning part, each vertex would be influenced by a bone completely (100% on weight value). In a model like this there is not bending of the wood, the wood just rotates on the joints without bending, so the same must be shown in the rig.
When you say a skeleton for each rigid part, do you mean one bone or a full on skeleton?
Sorry, a bone for each part in the same skeleton
when the teacher made us do the mannequin we started from stomach up, then hip down, parented stomach to hip.
If you want it to move like a mannequin, dont use bones, you dont need them for this. Do it parenting each piece to its joint, and have the origins/pivot of the joints in it's center, so they rotate correctly from the joint, is quicker.