The radio is kind of a pain, what works well is SIMPLE hand signals.
For years now, my son operates the GSE and I'm near the pad looking for a fill. Our simple hand signals are;
1) Pump, a straight hand 'pumping up and down', he hits the fill for one second. I then go out to the rocket, look listen, feel for leaks, does everything seem right?. This is a good time to see if there is nitrous coming from the nozzle (their shouldn't be), is there gas coming from the vent (there should be), are there any 'leak noises coming from the tank or fill hoses.
2) Hold, arms crossed above my head, stop filling, don't dump but stop filling. This is useful if something doesn't seem right, or if you are not sure if the tank is filled, plus if there is a range concern that you want to make sure is clear (someone went out on the range, aircraft sighted etc) .
3) Fill, straight arm going in a circle, fill until you see some other command
4) Dump, 'hand 'cutting' across my neck, dump, and abort
5) Fire', hand above head thumbs up, plus me moving farther from the rocket, 10 second count as long as my hand stays up, hand down hold.
These commands are easy to see from 1,000 feet (the longest one of my cables), and each one is clearly different than the others, simple and has worked well.
He has 'passed gas' for some other people, they use the same hand signals.
As far as making your own GSE, not too hard but my suggestions are,
A) Use a solenoid saver, funny thing this is most important for the vent. During fill the solenoid actually gets cooled by the nitrous, during vent, if you hold the vent open too long you can fry the solenoid. I use simple capacitor / resistor.
B) Use good hardware (and buy extras), pressure rated stuff from McMaster dont use the home depot stuff.
c) Think it through before you start assembling stuff, sounds simple but things like how much clearance do you need to get a wrench on the tank with the valve guard in place can make a difference.
D) have the vent point down, not to the side.
e) For hoses, get a long hose AND a short hose and connect them together, the hose closest to the motor gets beat up pretty bad, not just from exhaust but from the hose whipping after launch. Change out the short hose (cheep) and keep the long hose (not cheep) in better shape. Plus then the long hose acts like a spare if the short hose gets damaged.
F) buy a wrench, really, buy the right size wrench (1 1/8 for my setup) not an adjustable wrench but the real one you need. makes it easy to put the valve on and off, without leaks or rounding off the flats.
Lots of ways of doing this, just wanted to share a simple way of doing things.
Mike K
P.S. I plan to launch more this year than last year at Lucerne, im not there every month, msg me if you want to use my GSE at the launch.
P.P.S. Nitrous is going to be a bit harder to get this year one of the larger plants is down for a while
https://nypost.com/2016/12/16/fatal-explosion-leads-to-whipped-cream-shortages-across-country/
