Non-transposing, always in bass clef.
Detailed and precise notation of the dynamic behavior of the timpani part is recommended due to the instrument’s enormous dynamic range. It must also always be borne in mind that the timpani can drown out other instruments.
Since the middle of the 19th century instructions as to the type of mallet to be used have become increasingly common in scores. In the 20th century changes of mallet began to be precisely indicated by individual symbols. This system applies not only to the timpani but to all the other percussion instruments as well.
Until about 1800 timpani were transposing instruments. The notes were notated in bass clef as C and G with no accidentals, regardless of the key the piece was in. At the beginning of the score the actual sounded notes of the timpani were written: timpani in C and G, Bb and F, D and A.
This made sense for as long as the timpani only played the tonic and the dominant; it was also the reason for which the large kettledrum was also called the G drum while the small one was known as the C drum. When other notes began to be demanded – from Beethoven – composers began notating the actual pitch.