It uses a spring motor that is activated by pushing up the pin on the bottom (after being cranked) to fling shrapnel to distances not achievable by your average run-of-the-mill grenades...or should I say blunt throwing objects...*cough cough*. On average, this grenade can fling various shrapnel (green rods, ball joints and connectors, etc...) up to 25 feet. The best feature of the grenade, besides its blast radius, is how YOU DON'T NEED TO REASSEMBLE IT; you just reload the shrapnel, and toss again.
I also have a slightly different version of this that can be fired from a Knex RPG launcher!!!!! (coming later this year, because the M4 is using most of my pieces).
Step 1: Parts List
Also, the invisible object next to the "=2" is a blue small gear
All black ball joints can be substituted by tan clips or similar pieces
Step 3: Begin construction
1. Add yellow rod pieces to a bottom plate
2. Add the motor
Step 4: First Layer
1. All parts
2. Pay careful attention to orientation of pieces
3. Top it all off
Step 5: Second Layer
Step 6: Third Layer
Step 7: Keep it together
2. Attached (like in the past steps make sure all the ball joints are turned the correct way)