转 has two pronunciations: zhuǎn (to turn, to change) and zhuàn (to revolve, to spin). In 转动, it's zhuǎn when meaning 'to turn something' and zhuàn when meaning 'to spin/revolve'. Both are acceptable for this word.
usage
转动 emphasizes the physical rotating motion. Compare with 转变 (zhuǎnbiàn, to transform/change) and 转移 (zhuǎnyí, to transfer/shift).