Electronics 101

[UPscaler]

Can somebody give me a lesson here? It was being discussed on my 6x alpha thread, but I decided to post it here, since I am a beginner.

Attached is a CAD drawing to scale of the altimeter bay for my 6x alpha. On the left, a Perfectflite MAWD, on the right, a Missileworks RRC2 mini, both to scale.

I was told by Daveyfire, to just put the switches in the AV bay body tube ring. Simple enough. I have also determined that I need three 1/4" vent holes in the band as well.

That's where my knowledge ends. I have no clue about the wiring, I don't even know what the switches are actually used for. I am convinced it has something to do with powering up the altimeters on the pad. Is 1/4" all thread good, or should I go bigger? What wiring goes where. Generally, My dad and I know nothing other than how to build the AV bay (excluding the all thread question above),and how to buy the altimeters...

Please... enlighten!:D

-Braden

P.S. The red on the picture is the band around the bay. I'm not sure why I made it go into the bay it's self. However, the switches will be on each side of the ring.

[Rex R]

well I have no experience with what you are doing...but some experience w/ munitions :). the switches are to disarm the pyrotechnic charges until just before flight (fighter aircraft have all sorts of 'remove before flight' streamers attached to safing keys, in place they disable, remove and things can happen;bombs drop etc.). your altimeter manuals should tell you how to safe the charges(type of switches). hth
rex

[ScrapDaddy]

*Subscribes to thread* I'm intrested in this too.

A good place to start would be looking up the manuals for the altimiters.

[Zeus-cat]

There are six switches on the MAWD. They are in a DIP switch array just to the right of the beeper (denoted as F anf G from this photo from the Perfectflite website) A DIP switch stands for dual in line package or something. That really is not important.

The switches are numbered 1, 2, 3, 4, 5, 6. Switches 1, 2 and 3 control the deployment altitude of the main parachute. All switches off (towards the numbers) means the chute will deploy at 300 feet. You can add extra altitude to the main deployment in 200 foot increments by turning on or off switches 1, 2 and 3 in specific patterns. This is covered in the manual for the MAWD.

Switches 4, 5, and 6 cover the Mach delay which is an advanced topic so I will skip it.

Item H is a capacitor that will keep the altimeter operating for up to 2 seconds if a sudden shock to your rocket momentarily causes the battery to loose contact with the battery holder.

To the right of the capacitor are two terminals for the battery that you need to supply to power the altimeter. I recommend mounting the battery very securely somewhere in the rocket; preferably away from the altimeter if possible. You really don't want a 9 volt battery slamming into your altimeter if you have a violent parachute opening, or even worse a violent ground impact. Anyway, you need to run the + and - wires from the battery to the altimeter. The terminals are marked + and - so you should be able to connect it up without a problem.

You also need to add a switch to your rocket that controls power. The switch needs to be accessible from OUTSIDE the rocket. In my designs I put the switch on the same plywood sled that I mount the altimeter to and then drill a hole in the rocket so I can insert something that will turn off the switch. You need to do this so you can make sure the altimeter does not fully activate (detects a launch) while your rocket is just sitting on the launch pad.

When you turn on the MAWD it runs through a series of diagnostics. It checks the battery power and reports the apogee from the previous flight. This all takes about 30 seconds and then the MAWD goes into standby mode and waits to detect a launch. The MAWD is a barometer based altimeter and when it detects a change in altitude of 80 feet it fully activates. You can fool the MAWD by opening or closing the altimeter bay while the rocket is still on the ground. The change in air pressure may be enough to cause the MAWD to fully activate. This is very dangerous as the altimeter will fire the drogue pyro charges when it detects apogee and then the main pyro charges when it detects the rocket is less than 300 feet from the original launch altitude. Once the pressure in the altimeter bay equalizes the MAWD will think apogee has been reached because the air pressure is not decreasing. When apogee is reached it will fire the charges. This means part of the rocket is probably in your hands when the charges go off. I hope this convinces you that you need a power switch.

For ground testing you can bypass the switch by simply putting one end of the same wire in each terminal. You shouild never do this for an actual launch unless you are only using the MAWD to log data and not to fire any pyro charges. By the way, the Perfectflite website sells a kit that shows you how to make pyro charges out of old Christmas lights. If you get this kit you will also need FFF or FFFF Pyrodex. I buy mine at a local Gander Mountain store, but other gun stores should have it too. I do not recommned FF as this is not fine enough for rockets. I have found you really need to pack the charges tight when making them using the Christmas light way. You don't need much powder, but make sure it is tightly wrapped. Do lots of ground tests before you launch tomake sure you are using the right amount of powder and that your charges are reliable. I also double up my main pyros just in case. I'm glad I did as only one of my two main pyros went off during my last launch.

And the terminals for the switch are the two that are on the side of the altimeter that are closest to the power terminals.

The other two pairs of terminals denoted as E are for the main and drogue pyro charges. You will need to run wires from the MAWD through the upper and lower bulkheads and then to whatever pyro charges you will be using. Since you do not want to have ejection gasses enter the altimeter bay you MUST seal the holes you run the wires through.

So in summary here is what you need to wire up a MAWD:
1) a MAWD
2) a method to securly mount the altimeter, a switch and a battery (the sensor on the MAWD must be open to the atmosphere)
3) wires from the battery to the MAWD
4) wires from the switch to the MAWD
5) wires from the MAWD to the drogue and/or main pyro charges
6) a way to turn the switch on and off from outside the rocket
7) small hole(s) in your altimeter bay to allow the MAWD to detect pressure changes as the rocket climbs

[UPscaler]

Zeus! Thank you for explaining this to me. I wasn't sure if I needed to mount an outboard battery. I could drill holes in the sled, and mount the battery holders on the back side, or is that just over complicating things? I assume the RRC2 is similar enough, except for the whole LED read out system. I'll figure that out once I get the altimeter.

If I remember someone explaining this correctly. The mach delay shuts the altimeter off for the set amount of seconds so it begins detecting altitude after the rocket hits mach. Because at that speed the pressure is constantly changing regardless of the altitude and the apogee/main charges will fire, correct?

[cjl]

Well, it doesn't shut off the altimeter. It just prevents it from firing charges.

[Zeus-cat]

I always try to mount the battery on the back side of the sled if possible. Of course, that said I am just now working on a sled where the battery will be immediately above the altimeter. I have a wooden barrier for the battery to rest on and then I will use a cable tie to hold it in place. The bay is 5.5 inches long by 1.15 inches in diameter. I simply can't put the battery on the back side of the sled as it won't fit in the bay if I do that.

[UPscaler]

I always try to mount the battery on the back side of the sled if possible. Of course, that said I am just now working on a sled where the battery will be immediately above the altimeter. I have a wooden barrier for the battery to rest on and then I will use a cable tie to hold it in place. The bay is 5.5 inches long by 1.15 inches in diameter. I simply can't put the battery on the back side of the sled as it won't fit in the bay if I do that.

Well, as shown in the picture. There is plenty of space on this sled. I think I will put a couple 9V battery holders on the back, they are only a dollar and change from missileworks.

[UPscaler]

Also, where do you guys stand on this situation (see attached photo)

Option A seems logical to me, because should my drouge tangle, or something else happens that causes the rocket to go haywire, and the main fires. It wouldn't zipper the tube as easily.

However, I was told that I should change it to nose blow in stead.

Pros? Cons?

Thanks!:cool:

[SpartaChris]

When you say switches, are you referring to the dip switches on the altimeter, or arming switches to actually turn the thing on?

The perfectflite is one of the easiest altimeters to use. I highly recommend reading the manual cover to cover. You can download it from perfectflites website.

As for your DD question, I set all my DD rockets to have the drogue come out of the back end of the rocket and to blow the nose cone off with the main. Knock on woods, but I've never had a problem.

[SpartaChris]

Something else I recommend you do is make a baro chamber to test and get to know your perfectflite before you fly. I made a simple one using a glass jar from a container of spaghetti sauce, a switch, couple of terminal blocks and a nipple used to connect a tube to a large hobby syringe to suck the air out. Make sure to seal everything so you don't have any leaks.

I wire the altimeter as if I were doing dual deploy, connecting the power switch, apogee and main wires to their respective terminals on the altimeter. I connect Christmas lights to the terminal blocks on the cap of the glass jar and simply watch for them to flash as I slowly push the air back in from the hobby syringe I used to withdraw.

Simple, works well and gives you a feel for how your altimeter works.

[UPscaler]

Something else I recommend you do is make a baro chamber to test and get to know your perfectflite before you fly. I made a simple one using a glass jar from a container of spaghetti sauce, a switch, couple of terminal blocks and a nipple used to connect a tube to a large hobby syringe to suck the air out. Make sure to seal everything so you don't have any leaks.

I wire the altimeter as if I were doing dual deploy, connecting the power switch, apogee and main wires to their respective terminals on the altimeter. I connect Christmas lights to the terminal blocks on the cap of the glass jar and simply watch for them to flash as I slowly push the air back in from the hobby syringe I used to withdraw.

Simple, works well and gives you a feel for how your altimeter works.
That sounds simple enough Chris! I'll try to get one together!

As far as the bay goes, Do I need to epoxy one of the bulkheads in? The switches I am talking about are the external ones, such as these ("http://www.missileworks.com/index.php?main_page=product_info&cPath=2&products_id=3).

Here is another drawing, showing the front and back of the sled where the altimeters/battery holders will be