Is this controller going to work?

bkardon

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We’re gearing up for our first rocket launch, and I wanted to test our Estes launch controller, so I got out my voltmeter.

I figured I’d probably see zero volts across the clips until I had both the key in and the button down, at which point I’d see around 6-7 V and a light.

That is not what happened, and I’m trying to understand if this is not a valid way to test it, or if there’s something wrong with the controller.

What I saw was this:

No key or button: 0 volts, no light
Key alone: 5 volts, no light
Key and button: 6.5 V, no light

I’ve attached photos. My top two theories are that (a) the circuitry is more complicated than I’m imagining, and the presence of the actual starter affects its behavior, and it’s actually working fine, or (b) the controller is malfunctioning.

Thanks for your feedback!
 

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bkardon

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Oh, and I should mention that we only have two starters and two motors, which is why I’m not just trying it with a starter to test it.
 

neil_w

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That's all correct.

With key alone, voltage is applied in series with the continuity light, so it's dropped a bit. The resistance of the meter is very high, so it is not detected by the continuity circuit, which expects a pretty low resistance. To test this, try touching the clips together while the key is in, *don't* push the button. You should see the light.

When the button is pushed, it bypasses the continuity light so you get the full 6.5V. If a starter were in there, it would fire (although it could still take a couple of seconds, always hold the button down for a while before giving up.)
 

smstachwick

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Oh, and I should mention that we only have two starters and two motors, which is why I’m not just trying it with a starter to test it.
Definitely get your hands on an extra igniter if you can. Your local hobby shop will probably carry them, or perhaps another rocketeer near you will be willing to part with one or two.

One trick that’s especially popular is to dip the igniter tip in silver Testor’s paint. The aluminum powder produces a more energetic flame than the stock pyrogen will by itself. Entirely optional, obviously, but if you’re short on igniters it will reduce your odds of a misfire.

Three rules for a successful launch will always be valid though:
  • Fresh batteries
  • Clean clips
  • Lean on the button for a good two (or five) seconds. Only give up when it’s clear that it’s not going anywhere.
 
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bkardon

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Ok, great, thanks for the answers and tips! Your test does indeed result in the light turning on.

I’m still not sure I understand why pressing the key down without the button results in more than zero volts across the clips, but I’m happy to hear that’s normal.

I’ll post a photo when we launch later today!
 

neil_w

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I’m still not sure I understand why pressing the key down without the button results in more than zero volts across the clips, but I’m happy to hear that’s normal.
When you put the key in, you have the battery connected in series with a bulb or LED+resistor, and then to the clips. So you see the voltage there at the meter. If you put a starter in there, then a small current will flow, limited by the continuity light: enough current to light it up but not enough to fire the starter. With a starter in place, if you looked at the voltage between the clips you'd see less than 1V; the rest of the voltage is dropped across the continuity light.

When you push the button, it bypasses the continuity light with a short circuit. So then, all* the voltage is dropped across the starter, which produces a high current and the starter fires (hopefully :)).


*OK, not *all* the voltage is dropped across the starter, but most of it should be. The wire has some resistance and the batteries have internal resistance.
 

prfesser

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For testing, try separating a single strand from some thin (18 ga or thinner) stranded wire. Attach the clips with about 1/4" of the strand between them. I think that will have enough resistance to burn thru when the button is pushed.
 

jrap330

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When you put the key in, you have the battery connected in series with a bulb or LED+resistor, and then to the clips. So you see the voltage there at the meter. If you put a starter in there, then a small current will flow, limited by the continuity light: enough current to light it up but not enough to fire the starter. With a starter in place, if you looked at the voltage between the clips you'd see less than 1V; the rest of the voltage is dropped across the continuity light.

When you push the button, it bypasses the continuity light with a short circuit. So then, all* the voltage is dropped across the starter, which produces a high current and the starter fires (hopefully :)).


*OK, not *all* the voltage is dropped across the starter, but most of it should be. The wire has some resistance and the batteries have internal resistance.
To add to Neil's answer, when you depress the launch button...you have shorted out the buib, or LED allowing all the current to flow to the ignitor causing it to get hot. You mistakenly believe until the button is press you do not have a complete circuit, you do have a complete circuit but too much total resistance which is not enough to fire the ignitor. It is a simple circuit but until you see the diagram or have it explain you can get confused. Remember current not voltage causes the ignitor to get hot.
 

ArthurAstroCam

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This is all abut current. To ensure the best flow, pack the controller with fresh, name brand alkalines. Before doing so, use a good contact cleaner like Deoxit, or CRC. Use some, while you're at it, on the igniter clips.
 

smstachwick

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To add to Neil's answer, when you depress the launch button...you have shorted out the buib, or LED allowing all the current to flow to the ignitor causing it to get hot. You mistakenly believe until the button is press you do not have a complete circuit, you do have a complete circuit but too much total resistance which is not enough to fire the ignitor. It is a simple circuit but until you see the diagram or have it explain you can get confused. Remember current not voltage causes the ignitor to get hot.
Here’s a diagram. I don’t pretend to be an expert with electrical stuff, but this looks right to me.

8A2D73AE-66B1-4CBA-A2D7-CD2788AA3F83.jpeg
 

bkardon

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Thank you all for the suggestions, tips, and info!

I now understand what I was not understanding before - I assumed the circuit would be completely open until both key and button were pressed, but I understand that the circuit is closed by the key, but without the button shorting out the light, the current is too low for ignition. Makes sense now!

We did launch, and it worked great! I've attached a slo mo of the launch :) We had a lot of fun!

Unfortunately, despite being in the middle of a large field, it ended up sailing about 1/2 mile and getting snagged in a tree. We did follow the NAR guidelines for wind speeds under 20 mph, but even so we probably should have waited for a calmer day. Hoping the parachute line it's snagged on will break and we can recover it soon.

Thanks again!
 

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neil_w

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Unfortunately, despite being in the middle of a large field, it ended up sailing about 1/2 mile and getting snagged in a tree. We did follow the NAR guidelines for wind speeds under 20 mph, but even so we probably should have waited for a calmer day. Hoping the parachute line it's snagged on will break and we can recover it soon.
Matching your flights to the prevailing conditions (i.e., "flying the field") is something you learn with practice. Two guiding principles:
1) Start with smallest possible motors to judge conditions, with least chance of losing it.
2) Always bring at least two rockets to a launch. :)
 

smstachwick

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Thank you all for the suggestions, tips, and info!

I now understand what I was not understanding before - I assumed the circuit would be completely open until both key and button were pressed, but I understand that the circuit is closed by the key, but without the button shorting out the light, the current is too low for ignition. Makes sense now!

We did launch, and it worked great! I've attached a slo mo of the launch :) We had a lot of fun!

Unfortunately, despite being in the middle of a large field, it ended up sailing about 1/2 mile and getting snagged in a tree. We did follow the NAR guidelines for wind speeds under 20 mph, but even so we probably should have waited for a calmer day. Hoping the parachute line it's snagged on will break and we can recover it soon.

Thanks again!
The NAR Code is to guarantee a measure of safety. Guaranteeing successful recovery is up to the flyer, who should exercise judgement within the rules set by the code.

Very high-flying or far-drifting rockets are best flown with wind under 5 miles per hour.
 

neil_w

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Very high-flying or far-drifting rockets are best flown with wind under 5 miles per hour.
Thank you, I should have added that as my #3. NAR says <20 mph, but that is considered an absolute maximum. I would personally never fly anywhere close to 20 mph. I start getting itchy at around 10 mph, to be honest.

I don't know what the winds actually were for the @bkardon 's launch, though.
 

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Welcome bkardon. Glad you had fun. Rocket eating trees have befuddled us all from time to time. How high up ? Extendable poles used for painting can be had at your local big box home improvement store. Fisherman ? Cast a line around the branch and yank it down. As you get more flights under your belt at your favorite field you will learn the best locations to set up your launcher based on prevailing conditions.
 

smstachwick

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Matching your flights to the prevailing conditions (i.e., "flying the field") is something you learn with practice. Two guiding principles:
1) Start with smallest possible motors to judge conditions, with least chance of losing it.
2) Always bring at least two rockets to a launch. :)
Neil is correct about having a fleet ready to go. I have a fleet of 5 airworthy at any given time, set up for different motor casing sizes. Four of them flew at ROC this month.
 

samb

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Next time you find yourself on the range with a little wind try reefing the chute.

reef.JPG

Taping the shroud lines prevents the canopy from opening all the way, effectively reducing the parachute diameter.
 
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I suspect the skill code includes recovery. The counter argument is the PSII E2X Majestic that's considered Beginner with an anticipated altitude of 2000ft on a F15.

My son bought me this for Christmas to retrieve rockets. I also have old tent poles with a small rake at the end to snag the shock cord. @kuririn successfully used it to pull his rocket out of the tree last Sunday. He didn't need the extra tent poles because he was able to stand on the baseball bleachers. Stupid me forgot to bring my camera.

These make great continuity lights. They're rated for 12v with integrated resistor to protect the LED.

 

bkardon

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The surface winds were around 10 mph that day - I knew it was a bit on the high side, but we were very eager to launch. I'm going to go back out there soon and see if it's come down on its own yet. If not, maybe we'll look into long poles or ropes or chainsaws or something :)

I'm now rigging up a Raspberry Pi Zero with a camera so we can get some onboard footage for the next launch.
 

smstachwick

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The surface winds were around 10 mph that day - I knew it was a bit on the high side, but we were very eager to launch. I'm going to go back out there soon and see if it's come down on its own yet. If not, maybe we'll look into long poles or ropes or chainsaws or something :)

I'm now rigging up a Raspberry Pi Zero with a camera so we can get some onboard footage for the next launch.
Read this before attempting a tree recovery.

 
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