Connecting electronics..dumb question.

[timothyterpsalot]

This is going to probably sound very dumb to many of you...But, I'm wanting to start doing DD and am wondering if all the electronics need to be connected before bringing it out to the rail or once you're there. Or is it that you just can't turn them on before you get out there? thanks...

 

[rcktnut]

Of course you want everything ready to go. Once you got your bird on the launch pad, then all you have to do is turn on your electronics.

I don't think you would make to many friends if you would take your bird out to the pad and then prep your electronics!!!!!

 

[n5wd]

...am wondering if all the electronics need to be connected before bringing it out to the rail or once you're there. Or is it that you just can't turn them on before you get out there? thanks...

Most folks (though, of course, not all) will have everything set up and packed together so that when they get to the pad they only have to turn on the electronics (either by a built-in switch or twisting the power wires together), and then inserting the igniter, hooking it up, and signaling to the LCO that you're ready to go once you're out to a safe distance.

 

[quickburst]

Turn your avionics on after your project is on the rail, is always the best practice. Some avionics will fire if the rocket is turned or moved quickly. I have seen a slight breeze set charges off (Murphy finds a way).

As Bruce Lee used to say "The best defense for a blow ..... is don't be there".

So play it safe, power up at the rail, not beforehand.

 

[sylvie369]

At MWP7 I saw two rockets blow both their charges out at the pads, one while sitting on the ground waiting to be loaded, the other while sitting on the rail waiting for launch. I don't know what happened, but I'm glad it happened out at the pads and not next to my car back in the prep area, or in line at the RSO station. It's fine to have your ematches connected and so on while you prep, but you definitely do not want to walk around with your electronics powered up. Be certain that they're turned off.

 

[dixontj93060]

Sylvie369,

That was my Performance Rocketry Little John that fired on the rail (after sitting there by itself for 10 minutes) !!!!

Every altimeter/electronic device works a bit different--tough though to know every combination... I was using a Transolve P6K that I had used in that rocket in that same configuration a number of times. As it turns out though, I had an intermittent break in one of the twisted pair feeding the power. You can power up the P6K multiple times over and over and not set off a charge if your off time is greater than one second--but glitch it and you are toast. I didn't know that (and didn't know that I had a faulty wire either) until afterward when debugging via email with John at Transolve. Frankly, you could survive a glitch with some other altimeters and never have a problem, but then other altimeters likely have other hidden fault event scenarios.

In any case it does pay to play around with your electronics with LED's or even e-matches hooked up in a safe workshop environment. Go through recommended and even unexpected power up / power down, low voltage and brown out conditions. I used to do this 20 years back when designing high speed chips, I've done more of it in the past 3 weeks or so than I have in years (with my P6K and my ARTS2 and my G-Wiz LCX and my Parrot). What do they say about having your friends close, but your enemies closer... The outlier events are your enemy.

-Tim

At MWP7 I saw two rockets blow both their charges out at the pads, one while sitting on the ground waiting to be loaded, the other while sitting on the rail waiting for launch. I don't know what happened, but I'm glad it happened out at the pads and not next to my car back in the prep area, or in line at the RSO station. It's fine to have your ematches connected and so on while you prep, but you definitely do not want to walk around with your electronics powered up. Be certain that they're turned off.

 

[sylvie369]

Tim -

Well, much better to have the glitch while sitting on the rail than before (in the prep area) or after (in the air). I'm sure it wasn't fun, but it was safe.

 

[dixontj93060]

Oh yah, you're right.. I do though turn on my electronics "under the tent" but only to check e-matches briefly and before loading the charge wells. After that, its on the rail and before initiator insertion.

Tim -

Well, much better to have the glitch while sitting on the rail than before (in the prep area) or after (in the air). I'm sure it wasn't fun, but it was safe.

 

[sylvie369]

With no BP loaded it's obviously safe, but make danged sure that you've turned things off before bringing out the BP (obviously).

 

[patelldp]

This is going to probably sound very dumb to many of you...But, I'm wanting to start doing DD and am wondering if all the electronics need to be connected before bringing it out to the rail or once you're there. Or is it that you just can't turn them on before you get out there? thanks...

Really not a stupid question. I have seen what I consider the equivalent of "connecting the electronics" at the pad, and I would consider that a bad design. When I prep my electronics bays, I make it so I can take these steps:

1. Insert battery into altimeter, screw altimeter to standoffs, and connect the permanent e-bay wires to the altimeter. Then, I close and seal off my e-bay. At this point, I do not need to access the altimeter anymore.

2. Prepare ejection charges with e-matches. I then test continuity by powering on the altimeter with the matches attached, away from anyone just in case they pop. This way I can isolate a problem if my altimeter is not beeping out what I intended it to (for example: "beep beep beep" for an RRC2 stating it has continuity on both channels). At this point I have confirmed the altimeter is ready for black powder and final assembly.

3. Measure out and add black powder to the e-matches.

4. Hook up recovery system, finish prepping rocket.

5. Set-up on pad, and last thing before I walk away is to turn the switch on the electronics bay, listen to the beeps as a confirmation that I didn't mess up the e-matches while adding and packing black powder. If it's telling me what I want to hear, it's go time!

 

[FredA]

Some altimeters (ARTS comes to mind) MUST be armed on the pad in launch position....
The ARTS seesm to sample gravity only at power up and not prior to launch as is a much better practice.
Because of this, you must power up an ARTS in launch position.

I'm sure other altimeters have this failure mode.
Just unsure of which ones document their behavior and which must just pass down this user-trap via tribal knowlege.

I disagree with arming as the last step.
The last step should be inserting the igniter.
If for some reason the motor lights early, you want the avionics armed to control the flight.

ARM FIRST, then install the igniter and walk away.

FredA

 

[Handeman]

Fred,

I second that. Arm first, Igniter last.

As for the ARTS powering up in launch position, isn't that because of the use of Accelerometers instead of just a baro senser? I don't think my HiAlt45 cares at all what position it's in at powerup, although I've always powered it up while the rocket is on the rail.

 

[quickburst]

Fred,

I second that. Arm first, Igniter last.

As for the ARTS powering up in launch position, isn't that because of the use of Accelerometers instead of just a baro senser? I don't think my HiAlt45 cares at all what position it's in at powerup, although I've always powered it up while the rocket is on the rail.

You are correct, the HA 45 doesn't care which end is where.

 

[fox_racing_guy]

I disagree with arming as the last step.
The last step should be inserting the igniter.
If for some reason the motor lights early, you want the avionics armed to control the flight.

ARM FIRST, then install the igniter and walk away.

FredA

This is great advice! I was at a club launch this past early spring and I loaded 1 of my rockets on the rail then separated it to arm my Chute Tamer. I then inserted my igniter then rubbed the clips together to be sure all was good. Next I wrapped 1 igniter wire around the clips then I started the next, I had the 2nd wire in the clips and had just started to wrap it around and guess what? I357 (blue thunder load, I.E. instant ignition) lit 10" in front of my face.
I was 100% unharmed along with the pad manager who was 3' away but it sure did wake me up in a hurry and my ears were ringing. The club had set out all the equipment the day before and it rained overnight, apparently condensation got inside 1 of the controllers and caused it to intermediately short out. Had I not armed my electronics the rocket would have came in with a flat spin.

 

[bobkrech]

Depending upon the pad and the rocket, I have a slight disagreement on when you should install the igniter.

If you have to move or tilt the rocket at the pad to install the igniter, this must be done before you arm your electronics. What you don't do to the igniter is to unshort the leads and hook up the clips until after you have armed and verified the electronics are working properly. The after insuring that the clips are not powered, connect the igniter to the clips, check the continuity, and then walk away.

Bob

 

[UhClem]

As for the ARTS powering up in launch position, isn't that because of the use of Accelerometers instead of just a baro senser? I don't think my HiAlt45 cares at all what position it's in at powerup, although I've always powered it up while the rocket is on the rail.

It is because of a design decision made by the manufacturer.

Measuring the 1G offset of the accelerometer accurately is vital to correct operation of the apogee algorithm. Which is integrating the difference between the current accelerometer reading and this 1G offset. Any errors in the 1G reading add up and result in apogee time errors.

The offset of the sensor varies with time and temperature so you can't just measure it once. It must be measured just before flight. Most altimeters use an algorithm that is constantly updating this 1G offset until just before launch detect. This will handle any offset shifts from temperature changes while waiting on the pad.

The ARTS altimeter goes a different way and measures the offset just once after power is applied.

 

[FredA]

Bob,

Totally agree....
Do NOT move the rocket once armed.
Attach the clips last.
Do what you need to acomplish both of these.

Do to the STUPID (IMHO) stingers on OROC rails, we need a wood block (or something) under the rocket to hold it up so the bottom rail button doesn't fall out of the bottom of the rail. This usually allows easy insertion of the igniter.

But, yes, now that I think about it, I usually install the igniter with the leads shorted. Then arm the rocket. Then, once the beeps are confirmed to be correct, attach the launch system clips to the igniter as the last step.

Sorry for the previous "bad" advice.

 

[THarrison]

As an added precaution, I always hook the clips up to the ignitor while the ignitor is outside the motor. Tapping the clips together and looking for a spark safety check is usually adequate, but sometimes it is difficult to see anything in the sun. Actually hooking up the clips to the ignitor to doublecheck is a smart decision IMHO. I had a very close call once with a faulty club launch relay and don't want to have an M motor go off at close distance again.

Todd Harrison