As a composer I often make use of the timpani on my Sibelius software. It sounds terrific digitally but often may be completely impractical for the human percussionist to play considering all the different notes he/she would have to play. I M using more than just the tonic and dominant. What other percussion drums cud be used as an alternative to the timpani? Help!
The timpani is a membranophone, which is to say a fitted and stretched membrane vibrates somewhere on the instrument, causing it to produce sound. But note that not all membranophones are drums. A kazoo is a membranophone!
An alternative to the timpani might be the tabla, another membranophone from India and the surrounding areas.
But what makes the timpani so special is the possibility for the performer to rapidly adjust the tuning in performance (the tabla can't do this, as far as I'm aware). This means that the timpani is an incredibly versatile instrument in the hands of a capable performer.
As such, I'm pulled towards two unfortunate conclusions: either your writing is unrealistic for the timpani, or your performer is incapable of performing it. Thus there are two options for where to go here:
Provide a score example of your timpani part for individuals here to look at and address.
Consider taking your work to a both a composition teacher and a percussion teacher. Try to find a college professor for both if possible.
If you're writing music intended for human performance then you're constrained in lots of ways. Sibelius can play chromatic semiquaver runs on a timp sample - but you couldn't play that on a real timp. Also, timps are expensive - you're more likely to have two than five. Also, they're relatively large, so one player can't physically reach more than about five. And your performer may have only hand timps, which take far longer to change pitch than pedal timps.
So your challenge is to achieve the effect you like using the forces you actually have; synthesizing a sound using an acoustic ensemble.
You may be able to approximate the effect using a large orchestral bass drum for the attack, doubled with low-pitched bass instruments, like bowed or pizz double basses, or low brass. Or you may be able to get away with playing some of the timp part using a low tom, reserving the timps for those parts that have to be pitched.
I'd suggest going to a local amateur orchestra, wind band, brass band or percussion ensemble and talking to the percussionists there. Or if you're composing for a specific ensemble, workshop your ideas with them.