The timpani are something of a special case, since they are the only percussion instrument present in nearly all orchestral music, and they are played by a specialist player who will not normally play any other percussion instrument.
After that, there may be any number of percussion instruments in a composition. It is important that the composer or orchestrator pay attention to the physical requirements of the section, and in particular the choreography of both players and beaters. A common mistake is to allow insufficient time for players to change instrument or pick up new beaters.
Use the menu above to sample various percussion scorings from the Philharmonia's recorded archive.