I am a woodwind player and not a percussionist, but here goes. First, although virtually all timpani or kettledrums (or, if singular, a timpano) are strictly bass clef instruments, the piccolo timpano can reach middle C. Each individual drum is set to a specific note (although the notes can be adjusted through the pedals), and many orchestras use multiple timpani for a wider variety of notes. Standard timpani consoles usually consist of four drums that range from low D to the high A (an added piccolo timpani is often used to create a five drum console). Drums usually range in size from 32 inches to 23 inches (a piccolo timpano is 20 inches). Different tones can be attained depending on which part of the drum is hit and by the type of mallet or stick used:
The tone quality of the drum can be altered without switching sticks or adjusting the tuning of the drum. For example, by playing closer to the edge of the head, the sound becomes thinner. A more staccato sound can be produced by changing the velocity of the stroke or playing closer to the center of the head.
Normal playing tones are created by hitting the head appoximately four inches from the edge of the drum. Timpani rolls are designated in musical charts or scores by "tr" (timpani roll). Unlike other drums,
... timpanists do not use multiple bounce rolls like those played on the snare drum, as the soft nature of timpani sticks causes the rebound of the stick to be reduced, causing multiple bounce rolls to sound muffled.
It is also possible to change the pitch of the drum with the pedal while playing, known as a glissando. This portamento effect is most effective "from low notes to high notes and those performed during rolls."