LUNAR Launch Systems
From LUNARwiki
I built the current mid- and high-power pads in use at LUNAR. An article describing the design of the pads is at The New LUNAR High Power Pads
We have also expanded our high-power design to our low power pads, changed to a single cable (to the rack of 6 pads) design, and built, at-the-pad continuity checkers for all the pads. I will be happy to discuss whatever you are interested in, what worked, and, more importantly, what didn't work.
Our current setup uses a single launch controller that handles 4 racks of 6 pads each for a total of 24 pads. We normally set them as 12 low power 6 mid power, and 6 high power pads. The low power pads are directly connected to the launch controller using one extension cord going to each pad. These pads are fired directly from a car battery. There is a 0.5 ma continuity checker at the launch controller which tests whenever a pad is enabled. Pads are individually enabled with a toggle switch, which allows us to have drag races with multiple rockets. We have tried firing all 24 at once, but I think the most that went were 15. We have since added at-the-pad continuity checkers to all the low power pads. Users can press a button to test the local continuity after they have setup. This has saved a lot of time by reducing most of the no launch due to bad continuity problems.
The mid and high power pads are both wired the same. They utilize a local-remote controller system to reduce the amount of wire we had to haul around. Each rack of 6 pads has a remote controller built into a tool box. It is connected to main controller via a cable made up of a 3 wire 16 ga. extension cord for power and a cat 5 cable for control. The two cables are taped together and use a single connector at each end.
Upgrading the LUNAR Launch Pads
This cabling system has worked nicely, allowing us to unroll one 100 foot cable, plug the next cable into the cable reel and continue. At the remote end, the launch controller consists of a 1 farad capacitor and a bunch of relays. During setup, the capacitor is discharged and the launch circuits are dead. When the rack is enabled, the capacitor charges and an alarm starts sounding. The relays each enable a pad via a toggle switch on the launch controller. Continuity can be checked at the launch controller when a pad is enabled. When the launch button is pressed, a 7th relay closes which disconnects the continuity checker and shorts the capacitor across the launch clips. As the capacitor drains, power also starts flowing from a car battery via the launch controller, but is limited by a 10 ohm charging resistor. This system will easily fire 6 good quality Estes or Copperhead igniters though it sometimes will not fire a marginal copperhead (one with micro shorts that need to be burned off).
When the capacitor is discharged, the launch circuits in the remote controler are dead and any welded relay cannot cause a launch. There is power in the remote box but that is to operate the 0.5 ma continuity checkers. When a rack is enabled, the 1 Farad capacitor is charged through a 10 ohm resistor. We needed the resistor to keep from melting wires when charging the capacitor. It takes about 30 seconds to charge or discharge the remote launch controller. There is an alarm on the remote launch controller and an led on the control panel that indicate when the capacitor voltage is above 2 volts and it is unsafe to be near the high power pads..
We also looked at putting a motorcycle battery at each remote pad but that takes a lot more circuits to insure safety (that is, that a relay has not welded). But, you can deliver a lot more power to the igniters with that system. You also have a lot more batteries to take care of. Our current system runs off of one lawn tractor battery, 24 pads and our pa system. After two days of launching, a hygrometer test says the battery is still fully charged though we top it off anyway after every two launches.
As much as possible, we have tried to make things interchangeable to handle problems. All our launch rods can be used on any of our pads and the electronics for our mid- and high-power pads are interchangeable. All our cable reels are identical so we can swap them around as needed.
If you have any questions, just let me know.
Bill
