Ejection delay options & equipment

[Redrocketman]

Hi all, I have been making wonderfull r candy rockets for some time ( nothing like the sound of a space shuttle booster launch!! ), concentrating on very large motors. ( 400 - 500mm X 45mm - 12mm core )

 

My question is what are spolettes? I was told these could be used as a delay, but with the time & effort I am putting into this rocket, I want reliable chute ejection at or just after apogee. I think I will use electronic timers etc, but just wanted thoughts on whether there is a way of incorporating it all in the motor casing?

 

Will most likely run a "I" or "J class motor in it, so it WILL be essential that it all ' pops ' correctly.

 

I can give all the dimensions if that would help, tho I'm now downloading the correct software so I can insert all dimensions to determine apogee with given thrusts and payload weight, I'll let the computer do the maths as I'm still learning, so I really think electronics is the option.

 

Any ideas?

[dagabu]

A spollette is just a thick walled tube, 5/16" - 3/8" ID in many cases, that has black powder rammed into it to create a fuse or timer. Some of the more practiced fireworkers are said to be able to make dozens of them in an hours time.

[Redrocketman]

I am a tad busy for a little while then would like to do through some things. I was told you came up with a simple timer based around a ball bearing closing the circuit, and opening the circuit, thus initiating the ejection charge at apogee???

 

I'll be back!!

[Redrocketman]

Hey Dave,

 

I'm fairly new to the forum, absolutely brilliant

 

Does the idea of a ball bearing activated charge circuit seem logical? Of course, we want our rockets to pop the chute at or just after apogee

My thinking which I believe you might have tried would be to have a small PVC tube, closed at the bottom with a close fitting ball bearing inside. On the top of the tube would be a cap with two contacts to the igniter. With the circuit open ( not closed as I was previously thinking, too much going on at once!! ) at launch the ball would stay seated at the bottom of the tube due to the force applied by the rockets thrust. When it reaches apogee & tilts over the ball will ( hopefully!! ) fall down the tube seating on the contacts, closing the circuit & therefore igniting the recovery charge.

 

Does this seem like a logical approach.

 

Cheers, Luke

[dagabu]

One will discover that in a close fitting tube, the ball bearing travel will be dampened significantly by air pressure, this can be a good thing for the first few millimeters as the ignition can 'bump' the bearing up a bit. The bearing has to be able to travel freely the rest of the distance, and unimpeded by air or the walls so that it can move up with ease when the rocket body drag creates the weightless environment the bearing needs to travel to the switch.

 

There are many downsides to this method, a delay is needed or the chute pops and it zippers the tube wall. This delay can be made by using a timer, many do this and it works well. The ball bearing must not be hindered by dust, dirt, desert sand etc. Usually, a tube with three or four ridges that run the inside length are used for this kind of switch to allow the air to blow by freely.

 

Altimeters are also used and may be mandatory by the rules in certain organizations. Drag switches to wind up timers and simple timers are also used regularly.

 

From zoomcat: "Back in the day amateur rocket types used a simple tilt detector switch to fire a flash bulb when the rocket started to tilt over. You might do the same to trigger the servo using simple servo button code. The tilt detector was a piece of metal ball chain hanging thru a metal ring. When the rocket started tilting over, the ball chain would touch the metal ring making the electrical switch circuit flashing the bulb."

 

Arduino parachute deployment is also available and is taking over many of the complicate tasks that the above methods struggle with, such as apogee deployment etc.

 

Good luck,

[Redrocketman]

Thanks heaps, in relation to tube location and air impedance, the ball tube would be sealed inside the payload bay and would be a completely sealed unit separate to main body tube, centrally located. Will change in atmospheric pressure or is there other forces that could act on this system that I could be missing? I have flown rocket kits and simple r candy beasts ( more like space shuttle boosters!! ) for quite some time, but this is my 1st scratch build so bringing all of these factors together is new to me, tho I am now ( according to my wife!!) totally hooked. Once closed it would activate the delay timer ( which I forgot to mention, big day & had just finished making a batch of BP!! ) which in turn would fire the chute at the designated delay time. An altimeter will be fitted for my own knowledge, but where I live there are no clubs, no formal rules on where, when you can fly, so I just have to use proper common sense. I'll look into the Arduino system, but I'm trying to build this on a deliberate limited budget to see if it's all possible to be made reliable using commonly found electronics or materials. A personal challenge!!!

 

Again thank you, & ill kept u posted on how it's going.

[dagabu]

That plan sounds good but the ball has to be free to move and not be dampened by air.

[Redrocketman]

I'll build it all, fit in a piece of test body tube, & put it throughly its paces thoroughly before fitting to the real thing. I believe this all relies on my rocket flying true, being balanced correctly and all should go as planned. Like I said, this has been completely build from materials found at home, not a $ xxxxxx carbon rocket, so it is not a financial loss if it doesn't go as planned, it's a learning curve before I do spend big time on the " real deal ". Though I am thoroughly impressed by the build quality & finish to date!! This will go!!

 

Dimensions:

 

Body tube length : 700mm ( less nose cone )

Body dia : 45mm

Body wall thickness : 4.5mm ( hand rolled!! )

Fin root edge 200mm

Fin leading edge: 225mm

Fin trailing edge: 50mm

 

I'm having a little trouble finding the link I was given for a software program to help in design, drag coefficient, etc. ideas?

 

Cheers, Luke

[Redrocketman]

I found it. Open rocket software. Sound right?, if so I should be able to put my dimensions in and go from there I hope

[kramrocket]

That plan sounds good but the ball has to be free to move and not be dampened by air.

 

I find it interesting you say that dagabu, many years ago, I made a device using a 5mm ID 100mm long glass tube and close fitting ball, clean and sealed.

It had a four pronged contact point at the upper end (for reliability) and when contact was made, it energised a carefully broken light bulb via a battery to ignite the ejection charge etc.

The idea was to deliberately dampen the ball movement so that any jitter or variation in acceleration, would not cause a premature ejection.

The theory was the ball would never reach the top contacts unless the rocket was beginning to become nose down (after reaching its highest point) and then the ball would gracefully roll down to the contacts.

The tests of this theory was only done on the ground though, many sudden vertical movements were made and never was there an ignition, only when the device was nose down did the charge ignite.

BUT as I go through this method of theory as I write, i'm thinking that the ball, (even with air dampening affects) may WELL slowly travel to the contacts as soon as coasting has commenced... the reasons being, air is now slowing the rocket more than the enclosed ball !!!

 

Love to hear your thoughts...

[Redrocketman]

You would have to figure out the rate of deceleration, and whether that would be sufficient to overcome the weight of the ball, which would still be enhanced due to the forward motion of the rocket during the coasting stage. A very shorted explanation, make sense??

[dagabu]

Perfect sense to me, Kram?

 

There are so many variables to consider that I would not hazard any guesses as to an answer. Add to the formula, the length of the tube, vibration of the rocket, inertia of both the ball and the rocket, tilt, free fall etc...

 

My mind goes back to one particular scenario: Imagine that the motor is done firing, the coast phase begins, the ball is dampened but starts its ascent, inertia becomes *zero at apogee, the ball sits still, the rocket noses over, the ball starts moving, the rocket picks up speed, the ball hits the trigger, pops the chute and the case gets zippered because of the speed of travel in downward flight.

 

Personally, I love drag switches and mercury switches for deployment. If for nothing else than backup.

[kramrocket]

Yep, that's the conclusion I came to as well... too many variables to rely on that method. Thank hell I never actually used it !!!

Thanks for taking the time to respond and clarify that Dave.

[Redrocketman]

Cheers guys. It was just a simple theory. It is impossible to copy the same forces applied in flight, on the ground using a test set up.

I kind of enjoy looking around the house & shed & seeing if the same Job could be done with materials I could find around home. Though way too much time, $$ & effort has gone into this for a failed deployment!! I'll stick with proven methods!

[dagabu]

I would say to pursue it, just keep in mind the limitations. Our club demanded a manual backup to any electronic trigger. I think that you would be fine in testing your theory as long as you have a backup.

[kramrocket]

I would say to pursue it, just keep in mind the limitations. Our club demanded a manual backup to any electronic trigger. I think that you would be fine in testing your theory as long as you have a backup.

 

I love the idea of a manual backup when using an electronic trigger.

 

But it is an interesting challenge to design a reliable mechanical/electrical method to trigger the ejection charge though, rather than electronic means.

 

So getting back to the close fitting metal ball in tube method described above, I have a couple of refined ideas that could work ...

 

Both ideas are putting the tube/ball device in the nose cone, the tube is open at both ends, but not enough to let the ball fall out. the electrical contacts are at the top as before...

 

(1) A loose fitting ball in a tube.

 

The upper end of the tube is close to the TIP of the nose which is hollow by an appropriate amount to let forward motion air pressure keep the ball down. The ball rolls to the electrical contacts after peak height and nose down begins to occur.

 

 

(2) A loose fitting ball in a tube.

 

Several holes are made near the BASE of the nose (and tube) to cause a venturi/vacuum affect as the air rushes by thereby keeping the ball down until the air flow reduces... then the ball rolls to the electrical contacts after peak height and nose down begins to occur.

 

Love to hear any comments,

 

Thanks,

Mark

[stix]

 

. . . (2) A loose fitting ball in a tube.

 

Several holes are made near the BASE of the nose (and tube) to cause a venturi/vacuum affect as the air rushes by thereby keeping the ball down until the air flow reduces... then the ball rolls to the electrical contacts after peak height and nose down begins to occur . . .

 

Have to say I like the idea with that one. A "drag switch" of a sort I guess. It would certainly be simpler to have a completely mechanical method than to have employ an electronic timer as well. Or even an electronic timer only, based on theoretical altitude - a resounding failure as you have witnessed. With large high powered rockets it would be handy or even a requirement to have built in redundancy.

 

Dave, can you expand on: "Our club demanded a manual backup to any electronic trigger" what exactly do you mean by "manual"?

[MrB]

Please don't look at me as if i'm stupid, but... Whats wrong with just using an off the shelf accelerometer, and a micro-controller? (I suppose you could just use a 555 timer, and some cheap logic as well, but i'm not good enough with electronics to design something like that.

A button to "arm" it, at which point the accelerometer is key. It set's the system in "deploy parachute" once it reads over "X" G's. Once it passes below "Z" G's, it triggers the timer, and deploys the chute after a set time.

 

Isn't this the way they do it already?

B!

[dagabu]

 

Have to say I like the idea with that one. A "drag switch" of a sort I guess. It would certainly be simpler to have a completely mechanical method than to have employ an electronic timer as well. Or even an electronic timer only, based on theoretical altitude - a resounding failure as you have witnessed. With large high powered rockets it would be handy or even a requirement to have built in redundancy.

 

Dave, can you expand on: "Our club demanded a manual backup to any electronic trigger" what exactly do you mean by "manual"?

 

I misspoke, it should say "mechanical" not manual. I guess I see it as an independent switch, not controlled by altitude or position. It's funny, I was making drag switches decades ago on water rockets after fixing a sail switch inside a furnace duct used for triggering the humidifier.

 

I ended up using a similar one like the one below to operate a simple servo on my water bottle rockets and then on HP rockets since they were very affordable.

http://media.qcsupply.com/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/2/0/20164_1.jpg

 

Please don't look at me as if i'm stupid, but... Whats wrong with just using an off the shelf accelerometer, and a micro-controller? (I suppose you could just use a 555 timer, and some cheap logic as well, but i'm not good enough with electronics to design something like that.

A button to "arm" it, at which point the accelerometer is key. It set's the system in "deploy parachute" once it reads over "X" G's. Once it passes below "Z" G's, it triggers the timer, and deploys the chute after a set time.

 

Isn't this the way they do it already?

B!

 

Yes! That is the 'standard' way to deploy a chute and it works well. The OP was asking about a ball bearing simple timer, that is why we are still here.

[stix]

 

I misspoke, it should say "mechanical" not manual. I guess I see it as an independent switch, not controlled by altitude or position. It's funny, I was making drag switches decades ago on water rockets after fixing a sail switch inside a furnace duct used for triggering the humidifier.

 

I ended up using a similar one like the one below to operate a simple servo on my water bottle rockets and then on HP rockets since they were very affordable.

http://media.qcsupply.com/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/2/0/20164_1.jpg

.

 

Ah, thanks Dave, that makes more sense. btw. I like the old school drag micro switch thingo.

 

There are various methods to deploy the parachute. Using an electronic altimeter, some devices use the earths magnetosphere to decide apogee and probably the best method these days would use gps.

 

I don't care for those methods. Not because they are not effective, but somewhere in my the back of my tiny mind there still lingers a suggestion of a mechanical solution - perhaps not doable? but you never know - just for the fun of it.

 

I've got my own "crackpot solution" which involves the usual "floating ball" but in a slightly different configuration. Perhaps I'll post some diagrams.

[dagabu]

That would be cool!

[Redrocketman]

where I live there is no clubs. I'm on my own. Therefore I have to figure it all myself. Thanks for the feedback

[sitas]

Hey guys, why not take the older wall mounted furnace thermostat and rob the mercury switch out of it. It will fire a powder chg. or flip a servo with a small lipo battery.

[NeighborJ]

Sitas, the mercury switch concept works but they stopped making them because of the inevitable mercury contamination to the environment. If launched enough, at some point the rocket will have a Cato, unopened chute or any number of mishaps which will cause the glass tube to rupture. The other disadvantage it has is the fluid nature of the mercury, it can bounce around in the tube during ignition or at the end of the thrust phase possibly causing premature ejection of the recovery system. Not all systems are perfect, I've had a rocket fitted with a drag switch end up with a parabolic trajectory so it never slowed down enough for the switch to close. Edited November 24, 2016 by NeighborJ

[sitas]

Yup, I follow you. The wind don't help either. I use an old radio and a servo. It's old stuff, single channel and light as a feather. I use 2 of the tiny 3.7 lipos in the rocket. Coup[le of years now ,pretty sound hookup. I started with the mercury switch though. I don't monkey with any contest flying so, A little extra weight , so what.

Edited November 24, 2016 by sitas