Short answer for hero pickups:
We don't know the algorithm. It appears to be random, but it is dictated by a few rules.
- You can't have more than one hero on your team outside of Heroes vs Villains
- There are respawn timers on Hero pickups similar to vehicle pickups.
Long answer on vehicles:
I recently tested this in Walker Assault and confirmed a few things. The vehicle and power-up drops do, definitely, reoccur in the same locations. An AT-ST would respawn about 20 seconds after the last user dies in it (or abandons it). In Walker Assault they will spawn in certain locations depending on where the game's progress is.
There are limits to how many vehicles are available, but it depends on the map. Your team can, as an example, grab both x-wings in phase 1 of Walker Assault and make them live the entire game. If both a-wings from phase 2 survive, in phase 3 your rebel team could have 6 starships in the air at once (2 airspeeders are available in phase 3). Other game modes have a hard limit on number of vehicles and starfighters because the pickup will not regenerate until the last user dies or ditches the vehicle.
EA recently released patch notes that give us a small glimpse into how it works, but we'll never really know their algorithm. They recently added a little buffer to the respawn times:
- Starfighters pickups have a 20 second respawn delay
- T-47 Airspeeder pickups have a 10 second respawn delay