This is my shot on a Nerf Hyperfire Mod.
I was inspired by this design by Ultrasonic2:
https://www.thingiverse.com/thing:2460171
I replaced the original motors and motor cage with two brushless DC motors and a custom designed motor cage.
The motors are powered by two BLHeli lightning 30A which are controlled by an Arduino nano that uses the Servo library.
I made some adjustments on the ESCs settings via BLHeli Suite using the Arduino nano as prgrammer.
The settings of the ESCs as well as the Arduino code are available in the Things Tab.
Useful links:
Download BLHeli Suite:
https://blhelisuite.wordpress.com/
Tutorial Programming ESCs via Arduino nano:
https://youtu.be/61bjFxJyOLU
Buy Brushless DC motors:
http://s.click.aliexpress.com/e/uJ2vnEy
Buy ESC:
http://ali.onl/19H5