Step 2: So How Does it Work?
The remote control receiver needs to have 12v to enable it to trigger the relay. I used 2 X 9v batteries to do the job and it works fine but you could potentially use a small, 12v battery; the same used in the remote.
As the rocket launcher uses 18V to activate the sprinkler valve, I was able to wire up the receiver so when the relay was closed (activated by the remote) it used the power from the 2, 9V batteries to trigger the sprinkler valve.
If your device that you want to power uses a different voltage then the receiver, then you can also rig it up so it uses a different power source.