New Homemade Launch Controller

[eastvolt]

But I don't understand voltage and amperage as well as I need to to make proper use of your efforts.

Use the water analogy

Volts is the "pressure" of the water
Current is "how much water is flowing"
Resistance is "size of the pipe" (lower resistance = larger pipe)

V = RI

For a given water pressure (voltage), by varying the pipe size (resistance), you can change the "amount of flow" of water.

Think of that LED has a one way valve with a water wheel inside of it.
Your 12V battery is a water tank say 12 feet above the LED. Let the water flow downwards and start spinning the water wheel (LED makes light). If the pipe is too large (not enough resistance), the water wheel spins out of controls and fails. Therefore, you need to limit the water flow by using resistance (or decreasing the size of the pipe to decrease size of flow)

hope this makes sense

 

[paparoof]

Use the water analogy

Volts is the "pressure" of the water
Current is "how much water is flowing"
Resistance is "size of the pipe" (lower resistance = larger pipe)

V = RI

For a given water pressure (voltage), by varying the pipe size (resistance), you can change the "amount of flow" of water.

Think of that LED has a one way valve with a water wheel inside of it.
Your 12V battery is a water tank say 12 feet above the LED. Let the water flow downwards and start spinning the water wheel (LED makes light). If the pipe is too large (not enough resistance), the water wheel spins out of controls and fails. Therefore, you need to limit the water flow by using resistance (or decreasing the size of the pipe to decrease size of flow)

hope this makes sense

GOT IT. Thank you as well. That is going to help me a lot in understanding what it is I'm trying to do with this project.

Its embarrassing being so uneducated about something in a group of very educated people. It's worth it though; seeing the rockets go up is hell of a good time, but I get an even better kick out of the learning process.

Plus everything is funner when you made it yourself.

 

[mike_bar]

Its embarrassing being so uneducated about something in a group of very educated people. It's worth it though; seeing the rockets go up is hell of a good time, but I get an even better kick out of the learning process. [Snip]

Don't worry.

NASA has some good stuff about model rocketry on their website too.

I get embarrassed every time I go there; it's on their K-12 site (for kids).

I keep learning every day.

Regards,
Mike

 

[paparoof]

I get embarrassed every time I go there; it's on their K-12 site (for kids).

That right there's what they call "common ground"!

:beer:

 

[bobkrech]

Bob's attachment:
https://www.rocketryforum.com/attachment.php?attachmentid=41308&d=1183483911


Hi Bob,

I like all the safety features in that relay controller.

Two questions:

1. What is below the "Warn LED" on the Pad Unit circuit? Is that a small battery?


2. What happens if the relay contacts are welded close AND the "Test" button is pressed AFTER the igniter is installed? Will this launch the rocket? This may be a dumb question but I have seen dumb things happen.\

Thanks in advance.

Mike

1. It's a ground symbol which is not necessary.

2.) No. If the relay is welded, the igniter will go off as soon as the igniter is connected to the clips if the pad power is on. That's the one flaw with this design. It could be fixed by rearranging the power so that you add a parallel arm switch and 1000 ohm resistor in series with the power to the relay contacts. A 10 ma current would pass through a welded relay which could trigger a waraning but not provide enough current to fire an e-match. The arm switch in the on position would short out the resistor and allow full current to pass through the relay contacts.

Bob

 

[paparoof]

Okay I read and understood the whole Estes PDF that MikeBar linked to above, went back and RE-read EastVolts explanations and I think I can safely say I get it now. I truly appreciate your patience with me.

Especially the continuity test. It's about sizing the resistor properly to make the resulting amperage:

1. enough to light light
2. not enough to fire the ignitor

Pressing the launch button gives the already closed continuity circuit a second option, a path of less resistance. Lower resistance in the circuit equals higher amperage, enough to fire the ignitor.

Pretty much everything else is just more lights and different ways to interrupt the flow of electricity. Switches and safety keys, etc.

Am I finally up to speed? Is Radio Shack open on July Fourth?

AGAIN: thanks everyone for your all your input.

 

[paparoof]

2.) No. If the relay is welded, the igniter will go off as soon as the igniter is connected to the clips if the pad power is on. That's the one flaw with this design. It could be fixed by rearranging the power so that you add a parallel arm switch and 1000 ohm resistor in series with the power to the relay contacts. A 10 ma current would pass through a welded relay which could trigger a waraning but not provide enough current to fire an e-match. The arm switch in the on position would short out the resistor and allow full current to pass through the relay contacts.

EVEN THAT MADE SENSE! SWEET!

This is almost as exciting as the day the OSI Model finally clicked in my head.

 

[eastvolt]

You'll need to add a diode across the relay contacts to protect against voltage spiking when you turn off the relay.

Also, if you want an idiot light to check against a welded relay, just add an LED in series with a resistor from the 20A fuse to the relay directly. If the relay is fused at this point (assuming your igniter is good and installed), the LED will light indicating a welded contact.

Personally, its a bit overkill. You could literally think of a hundred different failure modes here (what if the fire switch contacts stick?, etc....) that could launch a rocket inadventantly.

Key is that you need to remember who the system is being designed for. You aren't designing a firing control system for NASA or the military here.

If you want to mitigate risk for the welded relay contacts, just purchase a high quality relay (NOT radio shack), that is rated at least 200% the continous current you'd expect during a short at the igniter. If you are using a 20A fuse, then a 40A relay minimum, and make sure its rated at that current for the voltage you are using.

EXTREMELY IMPORTANT. Relays rated for 20A at 120VAC will not work as well as a relay rate for 20A at 12VDC!!! When contacts separate at 120VAC (or any voltage AC), you do have a period where the voltage is 0 volts during the AC waveform. This basically will extinguish any arc that could exist between contacts and fuse them together. At DC, you will draw a continual arc (especially under high current) as the contacts separate.

 

[Handeman]

EVEN THAT MADE SENSE! SWEET!

This is almost as exciting as the day the OSI Model finally clicked in my head.

If you got that seven layers to "click", the basic electronics of a launch controller is a piece of cake!

There are some really great controllers explained here. I would like to build one like them someday, but....

I launch my big stuff at club events and only use my controller for Estes type BP motors, small APCP reloads and some 2 to 6 motor BP clusters.

I built a simple controller with a phone plug as a safety key, a LED and switch for continuity test and a momentary pushbutton for launch. It's all mounted in sheet metal on the top of a wooden box that contains a motorcycle battery. I use two pieces of flat metal and a piece of mop handle to make a handle on the box and two coat hooks to wrap the wire on.

I charge the battery and with 70 CCA it will work all day for what I use, even with the 50 feet of extension cord type wire between it and the pad.

The first battery was given to me (it wouldn't start a motorcycle anymore), when that died after a couple of years, I waited till the auto parts store had a sale and got the cheapest one they had for $20. The box could be much smaller now, this battery is only 2.5" x 5.5" x 5.5".

Anyway, it's easy to carry and use, self-contained, and works great.

If you're just looking for a LPR/MPR upgrade to a basic Estes controller that has more juice and staying power, but is still inexpensive, self-contained, and simple/quick/easy to use, you might want to consider something like this.


Here's a pic

 

[paparoof]

the basic electronics of a launch controller is a piece of cake!

They are once you have them properly explained to you.

I like your box idea (certainly easier to tote around and setup/take down), but I want the controller to be small enough for the kids to hold it in their hands, so all the "big" stuff is gonna sit out at the pad. Probably in a wagon.

 

[Handeman]

If that's the case, the relay type controllers are definitely the way to go.

Since you're using a wagon, I assume you don't have to pack everything in the car/truck to get to a launch site. Wish I could say the same.

Have fun with the "build". I know I enjoyed building the launcher and pad as much as some of the rockets.

BTW, any ideas on mounting the launch rods/pads on the wagon too. It should be stable enough to just pull it out to the launch pad, pull the hand controller away, and start launching.

 

[bobkrech]

You can use inexpensive automotive relays for a launcher.

You have several dozen under the hood of your car. They cost only a few dollars at most automotive stores or from allelectronics. Please note that the current ratings are extremely conservative. The relays are derated substantially to insure that they survive well over 100,000 cycles. The actual current required to weld the contacts is ~150 amps so this type of relay will handle just about any cluster combination provided you have a good 12 volt gell cell.

https://www.allelectronics.com/cgi-bin/item/RLY-351/500700/12V_SPDT_30_AMP_AUTOMOTIVE_RELAY_.html

For wiring you can purchase prewired relay sockets.

Simply use wirenuts to complete the connections.

https://www.allelectronics.com/cgi-bin/item/SRLY-2/525/SOCKET_FOR_AUTOMOTIVE_RELAY_.html

Bob

 

[Tom Riddle]

Personally, its a bit overkill. You could literally think of a hundred different failure modes here (what if the fire switch contacts stick?, etc....) that could launch a rocket inadventantly. [/B]

In The Handbook of Model Rocketry Harry depicts a lanch controller consisting of a battery, connected to a door bell button, out to 2 clips. The next diagram he shows a 'safer' controller with an interlock in series with the door bell button. If the 'fire' button sticks shut, you won't launch the rocket until the interlock is replaced.

The relay simply replaces the door bell button.

Now, if your design has a interlock in series, as it should, you won't have your face at the motor when it ignites {because the relay is welded shut}.

 

[RimfireJim]

In The Handbook of Model Rocketry Harry depicts a lanch controller consisting of a battery, connected to a door bell button, out to 2 clips. The next diagram he shows a 'safer' controller with an interlock in series with the door bell button. If the 'fire' button sticks shut, you won't launch the rocket until the interlock is replaced.

The relay simply replaces the door bell button.

Now, if your design has a interlock in series, as it should, you won't have your face at the motor when it ignites {because the relay is welded shut}.

For a welded relay contact safety, the interlock-in-series would have to be at the pad box, so even though you wouldn't have you face at the motor, you would still most likely be within a very short distance of the rocket when you re-engage the interlock. Probably better to know beforehand that it is safe to connect the igniter.
I put a low current piezo buzzer in parallel with the igniter in my launcher. If it is sounding, the igniter leads are "hot". It's loud enough to hear at the pad, but not loud enough to be obnoxious at the controller if the motor ignites. If the motor doesn't ignite, I can hear the buzzer faintly from the controller, which tells me the launch system is working fine and that the problem must be with the igniter. It took some doing to get the buzzer to work without giving a false continuity indication, IIRC. Have the schematic at home; I think there's a Schottky diode in there somewhere.

 

[RimfireJim]

EastVolt: thanks for going through that detail - that WILL help eventually. But I don't understand voltage and amperage as well as I need to to make proper use of your efforts.

I need to go read a book.

Another good source of explanations is https://www.allaboutcircuits.com/
Just note that they use the scientific convention for current flow direction rather than the engineering convention. They explain the difference and why, but it still throws me off.

 

[paparoof]

Another good source of explanations is https://www.allaboutcircuits.com/
...

STRAIGHT into the bookmarks.

Thanks!

 

[new2hpr]

Simply use wirenuts to complete the connections.
Bob

Wirenuts? :lol::surprised::rotflol:

If you're going to the trouble of making your own controller, please don't kludge it. Solder or screw terminals and insulate properly. Wirenuts are for locations that don't move, vibrate, or get bumped (like your house).

Do it right. Do it once.
-Ken

 

[paparoof]

Since you're using a wagon, I assume you don't have to pack everything in the car/truck to get to a launch site. Wish I could say the same.

Have fun with the "build". I know I enjoyed building the launcher and pad as much as some of the rockets.

BTW, any ideas on mounting the launch rods/pads on the wagon too. It should be stable enough to just pull it out to the launch pad, pull the hand controller away, and start launching.

Nah, still gotta drive to the site. But we setup in very different places depending on wind conditions, and sometimes that means walking 400 yards from the car to launch from "the other side" of the field. 400-yard walk + full size boat battery = wagon.

I'm actually planning on building the wagon as well. So your idea about incorporating even the launch pad into the wagon has my little tiny brain just whirring with activity. That's a GREAT idea.

 

[paparoof]

Solder or screw terminals and insulate properly.

Oh yeah. I'm an over builder by nature, so no worries there. My current home-build launcher has all connections soldered then all the wiring and in-line stuff (like the resistors) are all glued in place to reduce the chance of anything wiggling lose. This one will be the same.

 

[darkhelmet]

Wirenuts? :lol::surprised::rotflol:

If you're going to the trouble of making your own controller, please don't kludge it. Solder or screw terminals and insulate properly. Wirenuts are for locations that don't move, vibrate, or get bumped (like your house).

Do it right. Do it once.
-Ken

I think that was a little overboard on the criticism. Wirenuts aren't that bad of an idea; they're used in many industrial installation with high vibration.

A solder joint is worse for high-current paths. A poor solder connection will heat up before any other part of the circuit, causing the solder to melt. If there isn't also a mechanical connection, the wires will fall apart and short somewhere else. If the solder melts, and a bead of it drops, it can end up in other circuitry.

The best interconnect for high-current paths is a crimped lug with an optional thin braze of solder. The screw-type crimped lug is better than compressing the wire under a screw head, which also has the chance of leaving a stray strand hanging around to short somewhere. The "fast on" type spade lugs are also very good for low-resistance, good mechanical connections.

 

[new2hpr]

The key phrase there is "poor solder connection". Any poor connection has the potential to heat up or arc. Remember the fun of aluminum wiring? Sorry about all the smilies... the novelty has worn off now. My choices for connections would change if there was some future need to disassemble it. For a permanent connection, a good solder joint with the wires folded over beforehand, enclosed in adhesive-lined heatshrink tubing. Overkill, yes. Gonna fail? Not before the wire does. For a removable connection, screw terminals, screw-crimp lugs, and spade lugs are all reliable. For a little insurance, dab some liquid electrical tape over it.

Sorry if I offended. It just bugs me to see things done halfway.

-Ken

 

[DaveCombs]

Just wanted to throw this one in there... I was taught as part of my L1 that when you're at the the pad, you really ought to try touching the igniter clips together before hooking up the igniter. If they arc and spark, then you know they're hot and you should wait until that situation gets resolved.

 

[paparoof]

As long as you do it real quick-like, I think that's a good idea. I've seen plenty of people doing that right before hooking the clips up to the igniters.

I hope to get somewhere on the new design this weekend. The kids are at their mothers house and my girlfriend (and her grumpy old dog) are outta town, so it's nothin but sleep late, work on rockets and go to bed early! Oh wait - still have the unfinished tree house to work on and the boat motor to fix and the stone steps off the deck. Nuts.... Guess I better work on the launcher design while I'm still at work today

 

[bobkrech]

Sorry if I offended. It just bugs me to see things done halfway.

-Ken

No offense taken, but I wouldn't expect an EE to know about wire nuts. There's a huge difference between what's required to maintain nanoamp/volt noise level connections and that for transmitting 10's of amps at 12 volts dc or 120/240 VAC for that matter.

Wirenuts have been used in dual voltage industrial motors for decades. They are vibration proof especially when taped and it's not a halfway method for making reliable high curent connections, indeed it's the only way in a significant fraction of industrial machinery.

Soldering is fine for thin wires involved in low current applications, but when you solder heavy wires you have to supply a lot of heat and this frequently ruins the insulation. For this reason almost all high current industrial connectors are crimp connectors. The inexpensive modular Anderson connectors are used in many low voltage high current applications where a genderless conector is required. They were even used on Apollo/Soyuz to obviate connector gender issues. https://www.mcmaster.com/pdf/113/0744.pdf

Check out the wiring connectors used in your automoble to see what connectors are used for high current applications. Locking push-on connectors are almost universally chosen over screw terminal connectors in automotive application because of their vibration resistance, and you won't find a solder connection anywhere under the hood of a car unless it was done by someone who didn't want to spend the money for a proper crimping tool and crimp connectors.

Bob

 

[new2hpr]

Yeah, those modular genderless connectors are pretty cool and save a lot of headaches. I may have to try some in the next tester I make.

BTW, I've wired 4 houses and several cars bumper-to-bumper, so I've seen my share of wirenuts, spade lugs, callused fingers, crimpers, etc. No heavy industrial machinery, though.

Now, back to our regularly scheduled program. </hijack>

-Ken

 

[mike_bar]

Just wanted to throw this one in there... I was taught as part of my L1 that when you're at the the pad, you really ought to try touching the igniter clips together before hooking up the igniter. If they arc and spark, then you know they're hot and you should wait until that situation gets resolved.

I do this at the low-power pads. It seems like a good practice.

 

[darkhelmet]

No offense taken, but I wouldn't expect an EE to know about wire nuts. There's a huge difference between what's required to maintain nanoamp/volt noise level connections and that for transmitting 10's of amps at 12 volts dc or 120/240 VAC for that matter.

Oh, now don't jump to conclusions about EE's not knowing about wire nuts. Some of us aren't as narrowly educated as a typical physical Chemist. But, I'm glad you agree that high-current solder connections are bad.

One way to make the interconnect non-important is to limit the continuous current. All we need for an igniter (or cluster) is a large short-term current (several seconds at most). A continuous current allows significant heat transfer, melting poor connections followed by the wiring. A relatively inexpensive auto-reset thermal breaker will prevent this from happening. They come in standard package styles for automotive use, with two fast-on type spade lugs. After 10 to 20 seconds with greater than rated current, it break the circuit. After 20 to 30 seconds (typically) it closes again. They are available for a couple bucks.

 

[ben]

I do this at the low-power pads. It seems like a good practice.

I would be more inclined to do it at the HPR pads :surprised:

M in face vs. C6 in face :vroam:

Ben

 

[mike_bar]

I would be more inclined to do it at the HPR pads :surprised:

M in face vs. C6 in face :vroam:

Ben

Ben,
I agree that an M motor is more powerful.
Did you mean to say that model rocket safety is no concern for you?
Or is it less concern for you?
Mike

 

[paparoof]

I think what Ben meant was that it would be even more useful to do the "touch the clips together" thing at the pad to avoid an M going off in your face. Certainly would be worse than a C going off in your face. Not that they wouldn't both be bad, but if forced to choose between the two....