Do not attempt to make your own black powder !!!!!
Leave motor making to the experts.
Model rocketry was started in the first place to get away from the "basement bombers", where young budding "scientists would mix all types of chemicals together and suffer serious personal injury.
I'm sure that you can come up with a better and safer science project.
I would strongly suggest that you visit the Estes web site
www.estesrockets.com, and, click on the educational link.
Or better yet, call the Estes director of Education Ann Grimm at 1-800-525-7561 hit "0" ask the operator for the Director of Education
We want you to have a safe model rocket experience.......