How are the claws used in Starstruck used so far opened and closed? Like here:
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You’re in the wrong channel. This should be in the General Forum channel.
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The “giant claws” that have made waves in Starstruck are either powered by good old-fashioned motors or pneumatics (through the use of air cylinders). The one in the video you linked uses pneumatics, as indicated here:
http://image.prntscr.com/image/44dd671f77b541bdbe30b4951fdf52ce.png
Among world-class robots, you probably will see pneumatics 60-75% (just estimating) of the time. At lower-level stages, you likely will see claws being powered by motors most of the time.
I disagree. I think that a claw can be just as effective when powered by motors, and you do not need to abide by the 40 shot limit. As somebody had calculated before, with a 2 double acting piston claw you get 40/(2*2) reps, so 10 reps. Doesn’t quite seem like that will be sufficient enough for higher level competitions. Even if you only used single acting pistons, its 20 reps (right?). Also doesn’t seem like enough for the world class level. I could be wrong, though.
You should be able to get more reps with a second reservoir, then an extra more reps with a pressure regulator that regulates the air just right… So if you have single acting cylinders you should be able to get around 30-50 reps which will allow you to last through the match…
For world class, I believe that it depends if you chose to be smart on what you consider. I believe that you will do insanely well during beginning competition with pneumatics. But later on, it’s best to chose motors for the claw if you want to extend outward to sweep the stars off the fence, which will probably be needed in order to do well at worlds.
But maybe the claw idea will change to something else when it reaches time 
Harboring some master plans, are we? 
Noooooo… Of couurse not
But back on subject, with claws, they would basically have frictional force that is enough where the claw is able to oppose gravity. If you want more information on how and what happens, look at “Pinching Claw” on VEX Curriculum: http://curriculum.vexrobotics.com/curriculum/object-manipulation/manipulators
I also have to disagree here. Of the top 6 clawbots on the world skills standings, 5 of them have motorized claws. 7700R is the only pneumatic one.
The biggest difference between the two designs is range. With a pneumatic claw, you’re limited by how wide outwards it can extend. Also, they are usually limited to two positions, completely open or completely closed. However, they do actuate very quickly, apply a good amount of force, and allow you to use pneumatics elsewhere on the robot.
With a motorized claw, you can get many different widths depending on how many objects you are going for. In our testing, we could consistently grab the back 3 stars head on. However, they are definitely slower at closing and heavier. The weight of two motors and a gear assembly means that you won’t be able to use an incredibly fast lift ratio, like 1.6:5, and still do a hang.
I think the question of whether pneumatics can last a whole match or not is not relevant; multiple teams have proven that pneumatics can easily last a whole match.