whip, flog, strike
撻 centers on striking with a whip or similar implement: whipping, flogging, or striking as punishment or to drive forward.
撻 combines 扌 (hand) with 達, which likely contributes the sound and may suggest reaching or arriving, giving the idea of a hand reaching to strike with a whip.
The hand radical 扌 holds a whip, and the right side 達 suggests reaching the target. Picture a hand lashing out with a whip to strike.
For タツ, imagine the sharp crack of a whip: 'tatsu!' The sound tatsu cues タツ as the whip strikes.