Learn English – “I won’t be attending” or “I won’t attend”

I'll switch the "goal" to something a little more specific...

If you say "I am trying to eat more fresh fruit", the normal implication is you're making that effort right now. It doesn't say much about how long you've been trying, or how successfully. So most likely there's also the implied meaning that you haven't reached your goal of eating sufficient fresh fruit yet.

If you say "I try to eat more fresh fruit", the normal implication is that by habit, for some significant amount of time, you've been eating more fresh fruit than you would have done if you hadn't bothered to make any effort in that direction. So must likely the implied meaning is you do in fact eat enough fresh fruit, but you're aware (and are reminding someone else) that it requires some effort for you to achieve this.

OP's "I try to calculate the minimum angle..." would therefore be an unlikely thing to say, because you wouldn't normally be in the habit of doing this. That's not to say it's an invalid construction - it's perfectly grammatical. But you'd probably only use it in some contrived "narrative" context chronologically and sequentially describing each thing that you do, as you do it.

In the first case, the first statement is hypothetical (using the conditional mood), so considers a hypothetical situation where the machines would need to work, and weren't going to work without energy.
The other is a basic true statement (using the future tense) that simply states that the machines won't work without energy. I should note that this statement doesn't mean they can't work without energy, only that they won't. This is more to do with the idea of free will: consider a person who is able to work without biscuits but refuses to.

The second case is a lot more fun. Saying a machine can't (or cannot) work without energy sort of states that the machine couldn't work without energy even if it wanted to. In this case, because machines aren't sentient, it is identical to saying they won't work without energy.

However, the first sentence in the second group is either conditional or imperfect. In the case where it is conditional, it talks about a hypothetical situation like before. If, however, the tense is imperfect, it implies that the machines, in the past, weren't able to work without energy, but now supposedly can.

Note 1: Machines need energy to work. Fact of physics.

Note 2: I have no way of knowing what tense 'couldn't' is in. Normally you'd need to use the context to work it out.