Request for a simple deployment device

[AlexBruccoleri]

This is a request to all the electronics companies out there. I would like a simple timer or altimeter that an e-match can be hooked up to that can handle the ejection charge heat/pressure. Imagine something of the form factor of a Jolly Logic except it has a single output for one e-match. Also if it could be magnetically armed that would be ideal. I am thinking of a device that can be put in a simple motor deploy rocket as back up. It could be simply tied to the shock cord and placed in the chamber with the chute.

A timer would likely be easier, activated with g-forces. A baro altimeter would be subject to the ejection pressure and could get damaged. Anyway this is just an open request. I am not sure of the feasibility or the market, but I would love this.

 

[rharshberger]

This is a request to all the electronics companies out there. I would like a simple timer or altimeter that an e-match can be hooked up to that can handle the ejection charge heat/pressure. Imagine something of the form factor of a Jolly Logic except it has a single output for one e-match. Also if it could be magnetically armed that would be ideal. I am thinking of a device that can be put in a simple motor deploy rocket as back up. It could be simply tied to the shock cord and placed in the chamber with the chute.

A timer would likely be easier, activated with g-forces. A baro altimeter would be subject to the ejection pressure and could get damaged. Anyway this is just an open request. I am not sure of the feasibility or the market, but I would love this.

People have done just that, for example A Eggtimer Quark with battery ematch and chargewell all in a 3D printed BT50 sized case, electrical taped and lanyard to the shock cord, it does require sampling ports.
As for timers and g activation both are susceptible to "detection errors" or in the case of timers not having an accurate enough flight sim to set said timer and more than a second or two before or after apogee may well end up a damaged/destroyed rocket. Baro really is about the best method for what we do, but you can also magnetic field sensing aka Zeptomag or the old Flux Capacitor to try the same thing.

 

[fyrwrxz]

Alex, As a witness to the birth of Eggtimer Rocketry, Cris has the Apogee deploy unit. His initial question was, "What do you guys need or want? Maybe I can help." Well, shazaam! He comes back next launch with a prototype in a cigar bax and just knocks it out if the park. I couldn't believe how good it was and how well he integrated considerations we had into his design. I don't see a problem using conformal coating on a completed board, the baro sensor would still be exposed if used raw. Reach out to Cris. Explain what you think you need. I could do it for you, may may get it wrong. He's deadly smart, but easy to talk to. Maybe the next iteration would be SM and Lab Rat could supply the capsule you request. I know Frank is back with the new generation of Tiltometer 'cuz components are available again. It's a thru put design and I could see a piggy back, but you can only get things so small at a price point. Reminds me I should swing by and grab one or two from him on the way home from work. Hope this helps.
,

 

[AlexBruccoleri]

I am looking for something less DIY than what is out there. I can certainly rig something together, and this post is a request for manufacturers. The Jolly Logic's have a nice slick form factor. Something like that would be great if it could do deployment.

 

[cerving]

That was actually the initial concept for the Apogee, however the issue is how to arm it when it's inside the rocket. Magnetic requires that the sensor is close to the magnet, or you have a REALLY strong magnet. WiFi (which we already use) is nice, but it does require a fair bit of power so that's a size limiter. Bluetooth requires an app to be written for each device. In the end, we chickened out and used a screw switch... it works well when mounted in the nose cone, and you can't beat the cost. I was a bit concered about having something pyro bouncing around loose in the rocket anyway... I could envision some kickback from the BP charge firing causing some damage to the rocket.

 

[AlexBruccoleri]

That was actually the initial concept for the Apogee, however the issue is how to arm it when it's inside the rocket. Magnetic requires that the sensor is close to the magnet, or you have a REALLY strong magnet. WiFi (which we already use) is nice, but it does require a fair bit of power so that's a size limiter. Bluetooth requires an app to be written for each device. In the end, we chickened out and used a screw switch... it works well when mounted in the nose cone, and you can't beat the cost. I was a bit concered about having something pyro bouncing around loose in the rocket anyway... I could envision some kickback from the BP charge firing causing some damage to the rocket.

Thanks for the response! I have zero experience with magnetic switches. Is 6 inches of range possible?

Also I would not put a charge well on this. My thought is just a terminal to an e-match. The ejection could then be fairly isotropic and wrapped in wadding/nomex.

 

[rharshberger]

Thanks for the response! I have zero experience with magnetic switches. Is 6 inches of range possible?

Also I would not put a charge well on this. My thought is just a terminal to an e-match. The ejection could then be fairly isotropic and wrapped in wadding/nomex.

unless flying fiberglass rockets not having a charge well to direct the gas expansion can lead to holes blown in cardboard airframes especially lightweight Estes airframes.

 

[cerving]

And that's the problem with any "universal" deployment configuration... they aren't universal. What works with one rocket may not work with another. That's part of the process of learning electronic deployments.

 

[AlexBruccoleri]

unless flying fiberglass rockets not having a charge well to direct the gas expansion can lead to holes blown in cardboard airframes especially lightweight Estes airframes.

I have flown numerous electronics in light-weight Estes thin wall paper tubes and not had an issue with ejection. I do not believe a charge well is important and if anything, it adds some danger.

 

[AlexBruccoleri]

And that's the problem with any "universal" deployment configuration... they aren't universal. What works with one rocket may not work with another. That's part of the process of learning electronic deployments.

Nothing is a 100%. Still I think this would be useful. It would bridge a lot of the gap between simple motor ejection and full on electronics bays.

 

[Titan II]

unless flying fiberglass rockets not having a charge well to direct the gas expansion can lead to holes blown in cardboard airframes especially lightweight Estes airframes.

Hundreds of flights with cardboard airframes and no charge wells...not one hole.

 

[waltr]

Yep, here also, use taped paper tube to hold BP in smaller DD rockets. Works well without issues to airframe.

As to using a Apogee eggtimer, I would try it in a coupler tube with end caps taped on. Then inside a screw switch to turn it on. Once rocket is on the pad, pull off the nose and pull up the Altimeter tube enough to turn on the switch, listen for ready chirps and put back in and nose on.

A small hole in one end cap for the Ematch and BP charge.
The hole for the screw switch should be large enough to vent but also need a vent hole (or three) in the BT so the altimeter can sense external air pressure.

I would still have motor delay and ejection as a back-up to ensure chute is deployed.

 

[cerving]

I think there's some trial and error involved in determining how much BP to use with cardboard. I've had plenty of "errors"... hint, it's less than what you'd probably use with fiberglass.

 

[waltr]

Yes it is. For my BT55 rockets I use 0.4 gram. For BT60 0.6gram.

Since the OP does not give the size of rocket, except it seems a BT50 tube will fit inside. He would need to ground test.

 

[AlexBruccoleri]

I say the smaller the better. The goal of this is to have a back up to motor ejection for rockets without "ebays". It would be really great for staged rockets too incase the second stage fails to light.

 

[rharshberger]

Hundreds of flights with cardboard airframes and no charge wells...not one hole.

Its happened once to me, and I have seen similar damage on other rockets with Estes weight airframes, is it common? No, I dont think so, but its still easy to prevent so why not. The heavier LOC airframes I have not seen it in, heard about but never seen.

 

[AlexBruccoleri]

I think the hardest part of this is the switch. Does anyone know the real world range of the magnetic switches?

 

[rharshberger]

I think the hardest part of this is the switch. Does anyone know the real world range of the magnetic switches?

The only one available to rocketry currently afaik is the Featherweight Magnetic Switch and its activation range is 1" (according to Featherweight website), it also needs to be rigidly mounted to maintain proper orientation.

 

[AlexBruccoleri]

The only one available to rocketry currently afaik is the Featherweight Magnetic Switch and its activation range is 1" (according to Featherweight website), it also needs to be rigidly mounted to maintain proper orientation.

That is tough to make work for a "throw in" deployment device. It would need around 6 inches to be viable.

 

[rharshberger]

That is tough to make work for a "throw in" deployment device. It would need around 6 inches to be viable.

and you would need to know its orientation

 

[shockie]

I'd like to see a Jolly Roger that fits in a bt-20.

 

[AlexBruccoleri]

I'd like to see a Jolly Roger that fits in a bt-20.

That would be cool too.

I should be clear on the nature of my post to avoid seeming like a "complainer". The current selection of rocketry electronics is very good. In fact it is amazing. That being said I can think of things I would buy if available.

 

[Tractionengines]

Eggtimmer apogee connected to the wifi mini switch. Use the ez mount with a "stretched" tube. Tether it to shock cord.

With small batteries, TEST AND KNOW THE TIME LIMIT of battery life. Most small local launches time from power up to launch is only a few minutes, so it works. At a larger launch where your wait times get longer...you need larger batteries, or carefully watching time.

 

[AlexBruccoleri]

I suppose my thread was about having the current manufacturers make a "slick" device for single deployment. I can certainly hack a solution together and often do for a lot of my rockets. It would be nice to have a Jolly Logic style device that you just buy, charge and hook an e-match to it, then toss it in. Also I noticed that Featherweight sells a strong magnet with 2 inches of range. That is probably enough for this to work. This would be most useful for small rockets were building a standard e-bay is not often done.

Anyway it is something to think about. If a company build this, I will at least come

 

[Tractionengines]

I say the smaller the better. The goal of this is to have a back up to motor ejection for rockets without "ebays". It would be really great for staged rockets too incase the second stage fails to light.

This is much better the other way around ... THIS is primary, and motor is backup. Then you always pick a longer than needed motor delay.

In your example of failed staging.. the electronics will fire your charge at apogee...

 

[Tractionengines]

Also I noticed that Featherweight sells a strong magnet with 2 inches of range. That is probably enough for this to work.

You said a "device" attached to the shock-cord. As has been noted: to use a magnetic switch you need to know it's exact position and orientation. Even with the "strong magnet", it would be a guessing game to get it turned on/off.

There was also mention of a screw switch. The process said to Lift Nosecone, Arm it, Then re-attach nosecone. The BIG problem with this is if you have a failed/aborted launch; to dis-arm the electronics via the screw switch, you need to lift the nosecone again. This will drop the pressure inside the body tube. And could look like a launch, so (worst case) the charge blows in your hands.... even with a weak g-switch bumping it around could trigger launch detect. (A stronger g-switch then it may not trigger on an actual launch with LP Rockets.)

I think you would be much better with Wi-Fi like Cris said.

 

[Tractionengines]

So.... all the above posts noted ... what are your "requirements" and "wishlist"? It's always a tradeoff, so all of these are inter-related.

Must fit in body tube size:
Would like to fit in body tube size:

Max allowable length:
Would like length to be less than:

Max allowable weight:
Would like it to weigh less than:

Minimum battery life / # of flights:
Would like to get time & # of flights:

Anything else you "require"...

 

[K'Tesh]

 

[OzHybrid]

The only one available to rocketry currently afaik is the Featherweight Magnetic Switch and its activation range is 1" (according to Featherweight website), it also needs to be rigidly mounted to maintain proper orientation.

And when you connect the battery, it's on........ This is still undocumented by Ardian......
An UNSAFE undocumented FEATURE...... From the webpage today. Been known about for years and still not resolved OR documented.......https://www.featherweightaltimeters.com/store/p4/Magnetic_Switch.html

 

[AlexBruccoleri]

So.... all the above posts noted ... what are your "requirements" and "wishlist"? It's always a tradeoff, so all of these are inter-related.

Must fit in body tube size:
Would like to fit in body tube size:

Max allowable length:
Would like length to be less than:

Max allowable weight:
Would like it to weigh less than:

Minimum battery life / # of flights:
Would like to get time & # of flights:

Anything else you "require"...

As someone who flies a lot of rockets, I am speaking in generality and hoping others who fly a lot would "know what I mean". I am looking for a device to add redundancy to motor ejection without the need for a proper e-bay. Simple as that. (The Jolly Logic gives dual deployment functionality in most of my old rockets which is really cool and I was hoping to find something for apogee deployment.) I was also hoping some of the manufacturers would discuss the challenges or maybe suggest its easy. Cris made some good comments and I am grateful for that.

Anyway you are right that this device would be the primary and motor back up. I do not have any "musts" for size except that it function simply and safely. Clearly the smaller the better, but that is harder. If it was the size of a Jolly Logic, that would cover a lot of rockets. If it was accelerometer based, that would likely be better for ejection pressure, but I am not that familiar with the limitations of these sensors. I think the arming situation is the hardest. I have never used the magnetic switch, and maybe someone with experience can chime in. I imaging waving it around close to the spot in the air frame would work if you can hear it harm, but if there is a lot of lag then that would be annoying.

Also good call on a nose cone baro-based system. Taking off the nose cone could fool the system. When I hacked e-bays into nose cones, I went with timers.