Launch panel innards

[caveduck]

A rare look at the back of the hardwired DART launch controller, near the end of its 3rd year of service. Just upgraded to an SSR from the original mechanical relay, which was starting to get flaky after several thousand flights. No electronics other than the SSR and the LED indicator lights.

 

[Sooner Boomer]

Got schematics for that? Local club is looking for a new controller.

 

[caveduck]

I don't have a drawing of it, but the circuit is actually just that of a very simple launch controller, but with a 20x fanout for selectable pads. It uses a relay to short out the continuity light rather than dumping all the current through the firing button, which would have been the weak link in the chain for current carrying capacity.

Here's an Autocad layout of the front panel, will post a photo after I dig one up.

 

[Exactimator]

Here's a pic of the front.

 

[Honest John]

So could you give a brief tutorial of how the controller operates for us neophytes? I've never actually been to a club launch...

 

[Glasspack]

I could build a schematic for that one if anyone is interested …..Let me get started on Digikey

 

[Glasspack]

Did you build that Cave duck ?? Looks very nice

 

[Glasspack]

I built one but only for 4 pads...… High Power and low power model rockets

looks like the same style Pelican case.

 

[cwbullet]

That is pretty nice.

 

[caveduck]

@Glasspack - yes I built the DART panel. Here is the schematic as promised...drew it up hastily in OmniGraffle. I had a bill of materials from the planning phase but looked it over and it doesn't represent the as-built very well so I'm not posting it.
@HonestJohn - TLDR operation tutorial:
Toggle switches are pad selectors
Insert key and turn on key switch - power light comes on.
Flip up arm switch cover and turn on switch underneath - "arm" light comes on and continuity LED will light if you have continuity
Press "Fire Missiles" button to launch

Parts - case is a Seahorse 520 (Pelican clone). There are no case penetrations so it's water- and dust-tight. Get a good key switch (I used Eaton) and an SSR. We wore out a vanilla mechanical auto relay in several thousand launches. Use E-Switch or Eaton toggles from Digi-Key. Cheapo switches will not have the life. We did use 1/4" plugs/jacks from the Amazon 20-packs. You have to solder the center stack of the plug since from the factory they are just crimped and go flaky right away, but after doing that they have been solid for 3 years. Battery life is amazing...we can do 1000 flights on 50% charge of a 3 Amp-hour LiPo.

Planned upgrades:
* brighter LEDs - the ones we have are not too good in sunlight
* add piezo "armed" buzzer in parallel with the arm LED
* (maybe) change power inlet connectors to PowerPole
* Change toggles 16-20 to spring return momentary for MPR/TARC pads to disallow multi-select

 

[Glasspack]

is this pretty accurate ? this is one I put together from the photos...……using Digikey software Before you posted your schematic from OmniGraffle
And also I didn't see a continuity LED on the Panel …..

 

[caveduck]

Close BTW the continuity light is the one above the "fire" button in the photo. The one thing I see with your version is that once the arm switch is on, you have +12VDC on one clip of every selected pad with no resistance in the way, so large current will flow if that clip manages to touch anything else that is grounded, even to earth. In my circuit the continuity light and relay are on the hot side so that no DC+ reaches the pad until the launch button is pressed; you can ground either or both of the clips at the pad - even if the pad is selected - and nothing bad will happen. Only the ~20 mA continuity current will be carried to the ground.