You must first unlock the Editor mode, details here Builder in Crazy Machines ElementsAll you will need for this method is 2 Cannons and a Candle!
1. Place a Cannon facing one way
with a lit fuse (
on Dpad)
2. Place another cannon facing the other way so they are directly next to each other touching barrels
with no lit fuse3. Rest a Candle
with a flame (
on Dpad) on top of the Cannon
without the lit fuse4. Press
to start the machine and watch the magic happen
Your setup should look something like this
Here's a video