The 2 drawings attached show the different ways that the receivers can be wired. The first is if you want to use the same power source as the receiver, and the second is if you want to use an alternative power source. For the Compressed Air Rocket I used the first option.
There is also an on/off switch added to the receiver. I found that the receiver slowly leaks power (it's always on) so you will need to add a switch to make sure you can turn it off when your not using it
I have also included a drawing of how the relay works. For more info check out this website
- its really good at explaining how they work.