yes they are fragile. thats why you equip them with bullet proof, explosive proof(to a certain degree), water proof, airtight, coverings.
sure to do this at the joints the proofing material would have to be flexible. but it can be done.
if it could be done we'd be doing it already.
There is a reason it took damn near 30 years with the help of
engineering experts to create a robot that could walk on two feet
without falling over, and that's with a massive battery on its back
and several computers off to the side calculating its every step, making sure
The machine doesn't fall over and cause very costly damage.
The things we do with ease (thinking for ourselves,fine movements of the fingers,
walking on two feet with etc.) is stuff that's incredibly hard to implement in a machine.
A four legged robot that can move like a cheetah or dog can is even more difficult
not including the sort of coding, testing,hardware and just plain smarts it would require.
Just something simple as distinguishing who is and isn't injured or who is on its side on the battlefield is monumentally difficult. There is a reason all the robots in the field have human pilots and the robots that aren't used for combat have whole teams behind them, it's because the technology isn't that sophisticated yet.
A lot of ground would have to be covered before we're 800 pounds of thinking steel,mounted with guns and armor terrorizing the enemy.