Q1: How many DOF are in the human hand? Can you control each of them independantly? 

A1: I wrote in a previous blog post for Unit 2 that there are 19 DOF in the human hand. In hindsight, since I don't think it's true that each one of the DOF can be moved independantly, I may have been wrong. The endeffector of our hands are our finger tips, and at least on myself, I can't move just my finger tips without first moving one of the other knuckle joints that precede the endeffector's joint on each finger. I can very slightly move the endeffector joint but to get the entire range of motion I have to first control the other muscles in series. Each finger & thumb can move: up / down & side-to-side. THe human hand my only have 10 DOF in that case. 

Q2: Which of the two joint types we discussed, rotational and prismatic, is more commonly found in biological bodies? Can you think of examples of specific animals?

A2: Prismatic joints are by far the most common in the biological word because every muscle functions as a linear actuator. Take your arm for example, to bend your arm at your elbow joint your bieps muscles (actuator) contracts (pulls in a linear motion) and your tricep muscle relaxes, the inverse is true when straightening you arm out once again. Even the shoulder joint (which is technically a rotary / ball & socket joint) on humans requires muscles that can only pull in one direction, in that case it has muscle fibers surrounding the entire joint enabling healthy individuals to move their arm in almost any direction. There may be some exceptions that I'm not aware of. 

Q3: Are astronauts suits exoskeletons? What about a lever-controlled backhoe?

A3: I don't think that astronaut suits are technically exoskeletons. Their main function is to provide the wearer protection, but they don't provide extra strength or dexterity, and although the user is technically controlling it without using a controller, it is not that different then as if you were wearing a heavy full bodied snowsuit (as far as I'm aware of).

A lever controlled backhoe is more of an exoskeleton than the astronaut suit. It provides the user with lots of additional strength and provides the user protection. From my limited knowledge, they don't have too many sensors related to their endeffectors. You don't actually wear it though so I could be wrong on this. I think the definition of an exoskeleton in robotics is too loose.

Q4: Imagine an exoskeleton which has its own sensors, makes its own decisions, and acts on them. This is definitely a robot, yet it is also controlled by a human and attached to the human's body. Can you imagine where this could be useful

A4: This could be most useful when it comes to safety of the wearer of the exoskeleton and surrounding people. Whatever purpose the exoskeleton may serve, with the ability to make it's own decisions, it could have increased reaction speed and general awareness at all times. A worker without this ability could become fatigued or complacent and possibly hurt themselves or others accientally. Although I don't think it's technically a exoskeleton, I'm thinking of a tesla car, which could potentially prevent a deadly accident by making it's own decision (opposed to that of a tired driver) to stay in it's own lane or slow down etc. 

Q5: Robotic dogs, if the two hind legs are lowered so that they are driving / steering, and the two front legs grasp & kick the ball, then: What are the endeffectors of the dogs in that case? Are the dogs now purely mobile robots?

A5: This seems like a strange question. The end effectors would still be the ends of the arms that are hitting the balls, and the ends of the back legs would no longer be the end effectors if they are not actually doing the work or causing an effect on it's environment. If the dogs now moved with wheels instead of their legs propelling them similar to how a real animal would walk, then yes they would technically be robots vehicles and not dogs.