Altimeter Switch Mount.

Ok, I know there are build threads of circuit boards for Altimeter bays, but the search stuff isn't bringing anything useful up.

can folks please post how they are mounting thier altimeter switches in the AVA bays?

I am looking for either an access hole for a pushbutton switch, or the "remove before flight" normally closed switch setup.

any help would be appreciated. This is the last step I have left on my L1 / L2 project.

thanks in advance,
Jerryb

I use Newton's 3rd Rocketry Arming switch (www.newtons3rdrocketry.com). It is a screw type switch. I line mine up with one of my ports for the alt. I mount mine on the opposite side of the alt. since you have to put a small screwdriver in the hole. I will try to post some pics later tonight.

jerryb said:

Ok, I know there are build threads of circuit boards for Altimeter bays, but the search stuff isn't bringing anything useful up.

Click to expand...

A lot of interesting things turned up from a web search on 'altimeter bay rocketry'

can folks please post how they are mounting thier altimeter switches in the AVA bays? I am looking for either an access hole for a pushbutton switch, or the "remove before flight" normally closed switch setup. any help would be appreciated. This is the last step I have left on my L1 / L2 project.

thanks in advance,
Jerryb

Click to expand...

I like external mounted switches similar to the BinderDesign Alt Bay. Although key'd switches are a good way to not fly. Gwiz has an on board shunt and that access doubles for the baro hole.

What size airframe is this rocket you're building...? On airframes larger than 4 inches, I cut access hatches and use regular slide or DIP switches that are mounted on small circuit boards.

Sorry, should have posted that... its a 3" airframe... not much space in there.

later
Jerryb

LFLekx said:

What size airframe is this rocket you're building...? On airframes larger than 4 inches, I cut access hatches and use regular slide or DIP switches that are mounted on small circuit boards.

Click to expand...

krsconstruction said:

I use Newton's 3rd Rocketry Arming switch (www.newtons3rdrocketry.com). It is a screw type switch. I line mine up with one of my ports for the alt. I mount mine on the opposite side of the alt. since you have to put a small screwdriver in the hole. I will try to post some pics later tonight.

Click to expand...

Ditto. My switch is mounted just above the top of my altimeter for use in one ebay and another is mounted sideways below the altimeter on the sled for another rocket ebay. The key is to make it easy to get to with a screwdriver through the vent hole.

jerryb said:

can folks please post how they are mounting thier altimeter switches in the AVA bays?

I am looking for either an access hole for a pushbutton switch, or the "remove before flight" normally closed switch setup.

Click to expand...

I use a "screw in" not a "remove screw" setup. I don't like the idea of a spring inside of a switch holding the contacts "on" under the force of several Gs.

Here are two pictures of my most recent altimiter bay. It's a lot different than others I've seen, as it's attached to the top of the tube coupler so the body tube is what covers the electronics. This makes everything easily accessable for working on. I've flown it twice and plan to make future electronic bays this way.

The altimiter is a MissileWorks RRC2, and the blue board has a pair of high-current MOSFETs for firing Estes igniters. It also allows me to use a separate battery for powering the ejection charges, so I avoid all the low-voltage issues that single-battery altimiters have.

The two switches are both DPDT. One is for power (i.e. uses as DPST). The other switch, when open, interrupts power to the ejection charges, and shorts the igniter leads together. This is a copy of the wiring Ted Cochran uses on his electronic deployment rockets.

Glen Overby

I already ordered a screw switch from Newton's 3rd, but love the setup you did on the switches... see why photos are so great! I already had that type of switch here and could have saved the 5 bucks I just spent. not sure which way I'll rig it now, but have two alternatives.

I might use the one I have as the shunt for the charges, and the screw one for power.

thanks for the great idea.

Jerryb

overby said:

I use a "screw in" not a "remove screw" setup. I don't like the idea of a spring inside of a switch holding the contacts "on" under the force of several Gs.

Here are two pictures of my most recent altimiter bay. It's a lot different than others I've seen, as it's attached to the top of the tube coupler so the body tube is what covers the electronics. This makes everything easily accessable for working on. I've flown it twice and plan to make future electronic bays this way.

The altimiter is a MissileWorks RRC2, and the blue board has a pair of high-current MOSFETs for firing Estes igniters. It also allows me to use a separate battery for powering the ejection charges, so I avoid all the low-voltage issues that single-battery altimiters have.

The two switches are both DPDT. One is for power (i.e. uses as DPST). The other switch, when open, interrupts power to the ejection charges, and shorts the igniter leads together. This is a copy of the wiring Ted Cochran uses on his electronic deployment rockets.

Glen Overby

Click to expand...

jerryb said:

I might use the one I have as the shunt for the charges, and the screw one for power.

Click to expand...

Please don't use a shunt. Or at least talk about this as a shunt. A shunt implies that you are leaving the igniter/ematch/etc connected to the device that will activate it. Many of these devices (particularly ematches) have a VERY low resistance -- about as low as the shunt. What that means is current will still flow down the path to the ematch, firing it.

The safe design is to disconnect the power. What I did was find which connector on my altimeter is power and which is ground, and interrupt the power side. The common of the DPDT goes to the igniter, the NC side connects to the other igniter wire, and the NO connects to the altimeter. I leave the ground side connected to the altimeter.

Glen Overby

overby said:

I use a "screw in" not a "remove screw" setup. I don't like the idea of a spring inside of a switch holding the contacts "on" under the force of several Gs.

Click to expand...

Ditto.

overby said:

Here are two pictures of my most recent altimiter bay. It's a lot different than others I've seen, as it's attached to the top of the tube coupler so the body tube is what covers the electronics. This makes everything easily accessable for working on. I've flown it twice and plan to make future electronic bays this way.

Click to expand...

How do you ensure a good seal? I assume that the ejection charges are both above and below the altimeter. As the body tube swells and shrinks the bulkhead or whatever you have to the left in the pics has to fit more or less loosely - any leak will kill the altimeter.

overby said:

The altimiter is a MissileWorks RRC2, and the blue board has a pair of high-current MOSFETs for firing Estes igniters. It also allows me to use a separate battery for powering the ejection charges, so I avoid all the low-voltage issues that single-battery altimiters have.

Click to expand...

What does the white wire connect to? I like this idea. Can you post the parts required?

Also what is the white tissue looking thing on the altimeter under the wire near the barometric sensor?

overby said:

The two switches are both DPDT. One is for power (i.e. uses as DPST). The other switch, when open, interrupts power to the ejection charges, and shorts the igniter leads together. This is a copy of the wiring Ted Cochran uses on his electronic deployment rockets.

Click to expand...

Do you have the wiring diagram?

uncle_vanya said:

Ditto.
How do you ensure a good seal? I assume that the ejection charges are both above and below the altimeter. As the body tube swells and shrinks the bulkhead or whatever you have to the left in the pics has to fit more or less loosely - any leak will kill the altimeter.

Click to expand...

The tube coupler end is glued. The top bulkhead is a tight fit in the tube and hasn't been a problem. A short length of tube coupler glued to the upper bulkhead should address any concerns there, I think.

What does the white wire connect to? I like this idea. Can you post the parts required?

Click to expand...

The white wire is a common ground to the altimeter. The RRC2 uses an N-Channel mosfet, so the mosfet is on the "ground" side of the igniter circuit. When the mosfet turns on, it completes the ground side of the circuit.

I hate to admit this, but I continued this mistake by using N-Channel mosfets on the high-current board. On my homebrew altimeter, I use P-Channel mosfets so the ejection charge 'device' (ematch, etc) doesn't have power to it all the time.

Also what is the white tissue looking thing on the altimeter under the wire near the barometric sensor?

Click to expand...

Tape over the buzzer!

Do you have the wiring diagram?

Click to expand...

For the high current board or the power / ejection switches?

Yeah, but it's scribbled on a piece of paper I can put it into xcircuit and post a .ps or .gif of it ... sometime.

Glen Overby

overby said:

The tube coupler end is glued. The top bulkhead is a tight fit in the tube and hasn't been a problem. A short length of tube coupler glued to the upper bulkhead should address any concerns there, I think.

Click to expand...

I'm still a little nervous about this one myself. I would consider some type of o-ring or other seal that has more tolerance for tube expansion and contraction if you are not covering the entire thing in a sealed tube that is isolated from the airframe.

uncle_vanya said:

What does the white wire connect to? I like this idea. Can you post the parts required?

Click to expand...

Do you have the wiring diagram?

Click to expand...

I'm not entirely sure what schematics you are interested in, but I thought there might be general interest in both. So, I wrote up quick schematics. The first is the high current control board. The input to the 2N2222 is connected to the altimeter port that is controled by the altimeter. In the case of the MissileWorks RRC2 and PerfectFlite Alt4600, this is the "ground" side.

The second schematic is the wiring of my altimeter bay. The "Ground" side of the altimeter output is connected through to the igniter/ematch, while the "Power" side is connected through the switch. If I was more of a purist, I'd use a DPDT switch for each output, and also disconnect the ground. Note: this is not a "shunt"!

Glen Overby

overby said:

Please don't use a shunt. Or at least talk about this as a shunt. A shunt implies that you are leaving the igniter/ematch/etc connected to the device that will activate it. Many of these devices (particularly ematches) have a VERY low resistance -- about as low as the shunt. What that means is current will still flow down the path to the ematch, firing it.

Click to expand...

Glen is absolutely correct.

John Lyngdal is doing a series of shunt tests for the Safety Committee using a sensitive recording oscilloscope. We intend to publish the results, but basically, they're not pretty.

If you keep the shunting leads very short, and you solder all the connections perfectly, and you use a high-quality switch with great contacts and a high current rating, and you do all that religiously each and every time, a shunt might work. Interrupting the current path--which is the safety code requirement for high power rockets anyway--is much more effective. Both is OK, too, but don't rely solely on a shunt!

Here's my version for one of the altimeter bays in Quantum Leap (The one for the Olsen, which has a little LCD screen that I look at through a window on the side of the rocket).

A machine screw goes through the side of the rocket, through the side of the coupler, and through a t-nut epoxied in a slot in the underside of the bulkhead. The first switch the screw closes is for power. Once the altimeter powers up, and stabilizes, I drive the screw the rest of the way and de-shunt and connect two ematches. It ends up going into the other t-nut, holding everything firmly in place.

The only trick to doing this is to epoxy the t-nuts with the bolt in place, so the thread spacing is perfect. OK, there may be another trick--reference marks so that the coupler, when installed in the rocket, lines up with the arming bolt holes and alitmeter viewing window.

View attachment 4-7-07a_20070913_0048.JPG

OK, symantics... wrong term, end of the day, there would be a disconnect switch going from the altimeter through one leg of the ejection charges, probably the hot feed to each.

later
Jerryb

overby said:

Please don't use a shunt. Or at least talk about this as a shunt. A shunt implies that you are leaving the igniter/ematch/etc connected to the device that will activate it. Many of these devices (particularly ematches) have a VERY low resistance -- about as low as the shunt. What that means is current will still flow down the path to the ematch, firing it.

The safe design is to disconnect the power. What I did was find which connector on my altimeter is power and which is ground, and interrupt the power side. The common of the DPDT goes to the igniter, the NC side connects to the other igniter wire, and the NO connects to the altimeter. I leave the ground side connected to the altimeter.

Glen Overby

Click to expand...