kidsgen

http://www.kidsgen.com/fables_and_fairytales/indian_mythology_stories/brahma_and_gayatri.htm

Vanamali

http://www.vanamaliashram.org/Gayatri.html

Chakra

1. The reason for having 24 spokes on the Dharmachakra is  Puranas mentioned that only 24 Rishis wielded the whole power of the Gayatri Mantra representing the 24 letters of Gayatri Mantra in which Vishvamitra is first and Yajnavalkya is last who governs the religion (Dharma). 
2. Also known as Samay Chakra in which all the 24 spokes represented 24 hours of the day and symbol of the movement of the time

http://en.wikipedia.org/wiki/Dharmacakra
https://www.youtube.com/results?search_query=Dharmacakra