Ejection Charge vs Jolly Logic Chute Release

[rose113]

Hello All,

I'm a 4th year mechanical materials engineering student in Canada. My team and I are competing in the ESRA IREC 2017 competition this June. This is the first time we will be competing. This will also count for our final "capstone" project.

I am the lead in avionics and am working to choose the best flight computer for dual deployment. Right now, we are deciding between using the conventional ejection charge method, and the Jolly Logic Chute Release.

In posting here, I'm hoping to pick the minds of all of you who have more experience in this than myself and my team.

We're looking for the following:

• What are the failure rates of the ejection charge method vs the Chute Release?
• Is there a way to make the Chute Release fully redundant? (ie, if one fails, is it possible to implement a backup?)
• Is it more cost effective to use the ejection charges? (we will be using this rocket once, maybe twice)
• If you've used both, which one did you find was easier to use?

If you can help us with any of these questions, we would be eternally grateful. Thanks!

 

[neil_w]

You can implement redundant Chute Releases, by daisy chaining the rubber bands.

Two Chute Releases is $258, but after one or two uses you should be able to sell them for not *too* much less than what you paid, so take that into account.

 

[tim cubbedge]

I have used both. Altimeters are cheaper than the chute release. You can buy 2 of most altimeters for the price of 1 chute release. More importantly though, if you are not using motor eject with the chute release, you will need a deployment altimeter so that defeats the purpose of the chute release.

Failure rates of altimeters is pretty low these days and most failures are due to human error. Have also seen the chute release fail (again human error) as it wasn't turned back on after initial ground test. Have also seen chutes released at apogee due to improper packing of chute within the chute release.

Those are my experiences and I am sure others will chime in!

 

[Nytrunner]

I competed in IREC before graduating.
If they're again offering the bonus prize for non-pyro recovery, you could use the CR's in series for the main, and would just have to figure out a way to do the apogee deployment.
Could do an altimeter rigged to an arduino/microcontroller, so when it "fires" its apogee leads the controller can then actuate a compressed air or springloaded system. Just have to make sure you can lock that system down as per the competition safety requirements.

The judges will look more favorably on you for student ingenuity (as long as your solution is safe of course).
Good luck!

 

[Nathan]

I had originally intended to use dual Jolly Logic Chute Releases on my Upscale Onyx. The apogee event is redundant, with an apogee deployment charge fired by a RRC3 altimeter in the nose cone and motor ejection for backup. But I also wanted redundancy on the JLCRs so the plan was to use two JLCRs "daisy chained" together using two rubber bands. Then the parachute should open as long as either one of them released. But ground testing showed that it would not work reliably. If both JLCRs release then it will probably be okay. But the problem is that both of the JLCRs must be tethered, and from my testing it appears that if only one of the JLCRs releases then there is a good chance that the parachute will get tangled in the two JLCRs, which are both tethered and are also still connected to each other by one of the rubber bands, making a big loop for the parachute to get caught in.

The first flight of the rocket will probably be next month and I now plan to use only one JLCR. In my opinion, the risk of a single JLCR failure is lower that the risk of parachute entanglement if two of them are used.

 

[woferry]

More importantly though, if you are not using motor eject with the chute release, you will need a deployment altimeter so that defeats the purpose of the chute release.

I disagree. The CR does still enable single-opening dual-deployment, so you can use the deployment altimeter to do the apogee separation, but use the CR to keep the main bundled until a lower altitude. I've done this with my 4" Madcow Nike Smoke with an Eggtimer TRS in the nose for tracking and drogue deployment, works great. I'll be flying motors that don't offer motor eject, so an altimeter is a must (though I'm looking forward to seeing what Jolly Logic has up their sleeves for the future). I had initially tried to use the TRS as a hot-wire zip-tie-cutter for the main deployment (in a different rocket, also single-opening, later crashed), but could never get a successful ground test, and once the Chute Release came along I gave up on that idea and just used it.

 

[rocket_troy]

I competed in IREC before graduating.
If they're again offering the bonus prize for non-pyro recovery, you could use the CR's in series for the main, and would just have to figure out a way to do the apogee deployment.

...and that's the trick isn't it.

I've been told that there's a similar event hosted in Europe (France I think) where all (recovery) pyros are prohibited

Troy

 

[boatgeek]

Hello All,

I'm a 4th year mechanical materials engineering student in Canada. My team and I are competing in the ESRA IREC 2017 competition this June. This is the first time we will be competing. This will also count for our final "capstone" project.

I am the lead in avionics and am working to choose the best flight computer for dual deployment. Right now, we are deciding between using the conventional ejection charge method, and the Jolly Logic Chute Release.

In posting here, I'm hoping to pick the minds of all of you who have more experience in this than myself and my team.

We're looking for the following:

• What are the failure rates of the ejection charge method vs the Chute Release?
• Is there a way to make the Chute Release fully redundant? (ie, if one fails, is it possible to implement a backup?)
• Is it more cost effective to use the ejection charges? (we will be using this rocket once, maybe twice)
• If you've used both, which one did you find was easier to use?

If you can help us with any of these questions, we would be eternally grateful. Thanks!

I have had relatively few successful JLCR flights, but that was due to human error (not turning on, packed too tight). You do need to be careful about packing the chute so that it can slide easily. I plan for some fabric (chute or fire blanket) between the JLCR and the body tube. This seems to help a lot with sliding friction.

On the cost effectiveness side, it depends a lot on what you already have on hand, what you're planning on using in the future, and probably how the cost is scored with the competition. If you were only going to make these two flights, the cheapest way to go is to buy two cheap altimeters, some e-matches, and a small amount of black powder. If you're going to fly a lot in the future, it might be worth buying JLCRs to have on hand. If the competition assumes that your cost is the new cost for all electronics used in the project, then it may not be worth using the JLCR either. Also, consider the cost of the drogue. With a JLCR, you might be able to fly drogueless and save that cost.

As far as ease of use, the JLCR is substantially easier IMHO. Making ejection charges takes several minutes, whereas the JLCR doesn't add much time to your normal prep time, just puff testing to make sure the chute will come out.

 

[John Beans]

One of my future goals is to make all deployments completely electronic (i.e. no explosive charges at all, and just use rechargeable batteries as the power source). Want to begin testing that this year. But right now, you'll need at least one charge at the top (motor and/or altimeter-triggered).