2 Stage Water Rocket

This is a summer holiday product, I wanted to create 2 stage water rocket.

Additional Required Parts:

2x set Water Rocket Basic rocket kit from amazon jp (【科学工作】力学 超飛距離ペットボトルロケットキット)
1x sping - you can get it from a ball pen
1x syringe - cut it to about half, it depends on the lengh of your spring, the strange of the spring is not very important as in this design you can use the external rubber band to adjust the tension
1x nail and the shalf to replce the plastic syringe shaft
a lot of rubber band
8x M2x12 Screws
8x M2 Nuts
4x M5 Screws