small revolving drum with knobs
鼗 refers to a specific type of small hand drum that has knobs or pellets attached by strings, which strike the drumheads when the drum is revolved.
鼗 combines 鼓 (drum) with 兆, which likely contributes a phonetic element. The character describes a small revolving drum with attached knobs, a specific ancient instrument.
The bottom part 鼓 is a drum, and the top part 兆 looks like a pair of knobs on strings. Imagine spinning the drum so the knobs fly out and strike the drumheads.
For トウ, picture a small drum spinning on your toe: toe -> トウ, and the knobs rattle against the drum.