Spring and Solenoid Ejection

[benjaminjw]

Has anyone had experience springs or other gadgets to push apart body sections of medium power rockets to deploy a parachute?

I am interested in using an altimeter, microcontroller, and linear servos to push apart a rocket at apogee. I know this can be accomplished with motor ejection or black powder charges (less interesting). I know this can be accomplish with cold or hot gas deployment schemes (too heavy, I want to stick with mid power rockets). For my experimentation, I'm considering a Super Big Bertha or a 2.6" LOC Patriot.

My proposal is to use a strong compression spring to push off the nose cone. The compression spring would be secured to a bulk head in the body toward the top of the rocket with the free end of the spring facing upward. When in compression, the coils would push upward against a circular plate that is free to move in the body (like a bulkhead but not attached to the body tube). The circular plate would have a retention strap mounted and bent at a right angle (i.e. the strap is longitudinal with the body of the rocket) The strap would have an appropriate size hole inside to allow a holding pin to slip inside. The spring would be put into compression during assembly and held in place with the pin of a solenoid (items are typically meant for electric locks for cabinets). The solenoid that would retract on command from the microcontroller; the spring would push the plate against the packed parachute which would push against the nose cone. I think I can find a spring with sufficient force to push it all apart. The combined weight could be as low as 3oz.

Has anyone seen this kind of approach? Any bets if it will work?

 

[OzHybrid]

The advantage of a gas or ejection charge is that a small amount of pressure can generate a large amount of force when multiplied by your cross sectional area. With a gas or ejection charge you can have a backup larger gas or charge. It's kind of difficult to get that kind of redundancy with this method. Your spring would have to provide all of the force required and would be loaded for the entire time against your retaining pins.
But the main issue would be a lack of redundancy.
Norm

 

[cbrarick]

weight and reliability would be my concerns.
build it with rail buttons. I wouldn't want it on the near racks at my club launch.

I like your thinking outside the box, however this seems like a enormously complicated solution to a problem we already have a simple solution.

I'd use the loc rocket as ti's more stout then the super big bertha. the spring may do bad things to a estes airframe or mmt.

 

[Scott_650]

John Beans of Jolly Logic fame has mentioned developing an alternative method for recovery deployment using servos and fairing hatches - IIRC he talked about it during his first interview on The Rocketry Show podcast - and I think there was an article in the NAR magazine a few years ago along those lines. Interesting idea! Post some pictures and updates as you go with your experiment…

 

[WillMarchant]

There was an article in SpRocketry a while ago. And Goddard did this.

 

[rocket_troy]

This has been discussed previously. I think the "spring" part is definitely a workable idea, although I'm not convinced about solenoid retention - solenoids generate piss-all-to-nothing force per unit mass and volume unless you really over-drive them, which... can be doable.

I once provided some info on springs for this application here:
https://www.rocketryforum.com/threads/non-pyro-system.149903/#post-1842143
and regarding retention, you might get some ideas from my latching device here:
http://www.propulsionlabs.com.au/Pyroless_Release/page3.html
TP

 

[aerostadt]

There is a non-pyro ejection system article written in Sport Rocketry a long time ago that used a spring to eject the parachute. The mechanism used a special circuit board to activate an R/C servo triggered by an altimeter, which released the spring. The article is found in the May/June '98 issue of Sport Rocketry on page 6-12 is entitled "Building a Non-Pyrotechnic Ejection System", by Doug Steinfeld. There is a small correction to the circuit board shown on page 3 of the July/August '98 issue.

 

[Voyager1]

You could adapt a method similar to that used with water rockets which employs a side hatch arrangement that is released by a servo to deploy a chute. I have used this method successfully with water rockets, but it would require upgrading for MPR. The technique is described very well here.

 

[aerostadt]

You can find the article here:

https://www.dropbox.com/s/vinjd8lhre3mweu/Sport Rocketry 3.1998.pdf?dl=0
and small correction here:
https://www.dropbox.com/s/oxjd9gh8ry4uyb0/Sport Rocketry 4.1998.pdf?dl=0
The idea of the special circuit board was to activate an R/C servo to turn a locking nut, thus avoiding using a solenoid.

 

[Handeman]

I don't see why it wouldn't work. You might want to research trigger mechanisms for a good catch and release method for your spring. Maximum spring tension with minimum effort to release, but with a safe way to keep it from going off during motor thrust and vibration.

 

[AllDigital]

I am working on an alternative deployment method on an 8” rocket using springs and 12v motorized latches for HED (two out the nose). There have been a dozen different challenges, ranging from spring force in all orientations, flyback interference, and lots of risk around a “soft eject” vs pyros that forcefully eject and separate the vehicle. On our test rocket the nose has about 15 pounds of spring force to eject it, comparing that to the “backup chute” on the other end of the rocket that uses radio controlled pyros, we get 280 pounds of separation force with just four grams of BP. Without a forceful ejection there is risk that the two pieces fall together and the laundry doesn’t come out. There is also risk of too much drag force on the airframe if deployment happens late. None of that should discourage you Benjamin — I love the thinking, but there are more challenges to solve beyond just separating.

 

[benjaminjw]

You all are amazing! Thank you so much for the detailed feedback (weight, redundancy, forceful ejection) and references! The sport rocket articles are exactly the kind of information I was looking to find!

 

[cerving]

I've seen systems like this, there are a few issues to overcome. First, they tend not to be very amenable to redundancy... you need to design it so that there are multiple release points. Second, you need to make sure that the pin or whatever mechanism is used to release the spring can't bind up in flight. I know of at least a couple of pretty spectacular lawn darts that occurred due to that happening.