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A water rocket is a type of model rocket using water as its reaction mass. The pressure vessel (the engine of the rocket) is constructed from thin plastic or other non metallic materials (usually a used plastic soft drink bottle) weighing 1,500 grams or less. The water is forced out by compressed air. It is an example of Newton's third law of motion.

suggestions for cheap deployment trigger please?

Discussion about deployment systems including altimeters, timers, air speed flaps, servo systems, and chemical reactions.
GrahamM
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suggestions for cheap deployment trigger please?

Post by GrahamM » Sat Sep 15, 2018 1:55 am

Hi all,

New guy here just getting into water rocketry. I have constructed a 2 litre rocket which lawn darted on its first flight and damaged the nosecone so I am in the process of building a parachute recovery system for it now.

Originally I was going to use a tomy timer, but can't find one anywhere, even ordered some 'hopping frog' toys on ebay from China, but when they arrived it is not an appropriate tomy timer because it unwinds at extremely high speed rather than slowly. :(

So now I am considering something using a servo to release elastic bands holding the nosecone on, but don't want to spend a fortune on it. Looked at the Eggtimer Quantum which is a very nice piece of kit but it seems a bit expensive, around $80 Australian including freight for the Quantum, plus the servo and battery/batteries.

Ideally I would like a simple build yourself project that only needs to activate the servo after a programmable time delay. I assume that it could be started with a cord attached to the launch pad, then activate the servo after the chosen time delay, somewhere around 2 to 5 seconds after launch?

I have been looking around on the net but nothing has caught my eye yet. If anyone has any suggestions or circuit examples etc then it would be very greatly appreciated.
Thanks for your time. TH:


Graham
Melbourne, Australia

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anachronist
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Re: suggestions for cheap deployment trigger please?

Post by anachronist » Sat Sep 15, 2018 2:58 am

Look for small wind-up toys at a party supply store. You'll get a tomy timer out of it.

Ebay has actual classic wind-up toys by Tomy. Here for example: https://www.ebay.com/itm/Lot-Of-15-Wind ... Sw~p1bg~8f



GrahamM
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Re: suggestions for cheap deployment trigger please?

Post by GrahamM » Sat Sep 15, 2018 8:41 am

anachronist wrote:
Sat Sep 15, 2018 2:58 am
Look for small wind-up toys at a party supply store. You'll get a tomy timer out of it.

Ebay has actual classic wind-up toys by Tomy. Here for example: https://www.ebay.com/itm/Lot-Of-15-Wind ... Sw~p1bg~8f
Thanks for that.
The trouble is that US$10.99 for some timers becomes expensive when you add US$24.46 in shipping, then convert it to $AUD.


Graham
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Re: suggestions for cheap deployment trigger please?

Post by anachronist » Sat Sep 15, 2018 10:00 am

Well, I see lots of these little plastic wind up toys (like a monkey that does backflips and varioius walking animals) at a local party supply store.

You could also try an air speed flap. This will release a parachute when the rocket slows down enough.
https://www.thingiverse.com/thing:294758



GrahamM
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Re: suggestions for cheap deployment trigger please?

Post by GrahamM » Sat Sep 15, 2018 10:14 am

anachronist wrote:
Sat Sep 15, 2018 10:00 am
Well, I see lots of these little plastic wind up toys (like a monkey that does backflips and varioius walking animals) at a local party supply store.

You could also try an air speed flap. This will release a parachute when the rocket slows down enough.
https://www.thingiverse.com/thing:294758
Thanks for the links, yes an air flap may be another solution if I can't find a suitable tomy timer or electronic timer. TH:


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addstogether2
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Re: suggestions for cheap deployment trigger please?

Post by addstogether2 » Sun Sep 16, 2018 6:57 am

Hi graham,

re getting some tommy timmers go down to bay st port melbourne.

either Port Melb Discounts 237 bay st
or Shopaholic 80 bay st.

I got mine at one of these two stores, I think it was port melb disccounts

Regards

Al


Life is like riding a bicycle. To keep your balance you must keep moving.
"Albert Einstein"

GrahamM
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Re: suggestions for cheap deployment trigger please?

Post by GrahamM » Sun Sep 16, 2018 7:27 am

addstogether2 wrote:
Sun Sep 16, 2018 6:57 am
Hi graham,

re getting some tommy timmers go down to bay st port melbourne.

either Port Melb Discounts 237 bay st
or Shopaholic 80 bay st.

I got mine at one of these two stores, I think it was port melb disccounts

Regards

Al
Thanks very much Al, I have also sent you an email before I saw this post with the shop details :)


Graham
Melbourne, Australia

GrahamM
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Re: suggestions for cheap deployment trigger please?

Post by GrahamM » Mon Sep 17, 2018 12:36 am

Ok I have an airflap system up and running, just waiting for suitable weather to test it out, forecast says the winds should be suitable in about 3 or 4 days time. Thanks for reminding me about airflaps anachronist http://www.wra2.org/forum/memberlist.ph ... ile&u=3788

Airflap armed and ready
http://www.wra2.org/forum/download/file ... ew&id=3190

Click link here for Short video of deployment
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Re: suggestions for cheap deployment trigger please?

Post by anachronist » Mon Sep 17, 2018 2:24 am

Please let us know how it works out.

I had designed a mechanical gravity-sensing deployment device for 3D printing, but never got around to building it. Basically it would sense the 4 stages of acceleration and deploy on the last stage:
  1. During thrust, objects experience a force toward the back of the rocket
  2. While coasting, objects experience a force toward the front (for a 2L bottle rocket, this forward force can be as much as 5G due to air resistance)
  3. At apogee, the force is zero and objects in the rocket are weightless
  4. While descending nose-first, objects in the rocket experience a force toward the front as the rocket approaches terminal velocity
My device trips a release during the fourth stage.
My problem is that while I've designed the device to sense the stages, I can't figure out a good release or trigger mechanism that's internal, activated by the light forces of my mechanism, and easily settable while preparing for launch.



GrahamM
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Re: suggestions for cheap deployment trigger please?

Post by GrahamM » Mon Sep 17, 2018 3:14 am

My concerns with those sort of deployment devices (and airflaps for that matter) is what happens if you don't get a near vertical flight?
If the flight ends up somewhat parabolic then there is no apogee as such and the system may fail to deploy.


Graham
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addstogether2
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Re: suggestions for cheap deployment trigger please?

Post by addstogether2 » Mon Sep 17, 2018 4:14 am

Hi Graham,

let us know how it goes.

Also from Eggtimer is the Eggtimer Quark at us$20 plus postage
http://www.eggtimerrocketry.com/page43.php

Al


Life is like riding a bicycle. To keep your balance you must keep moving.
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Re: suggestions for cheap deployment trigger please?

Post by anachronist » Mon Sep 17, 2018 10:43 am

Al -- the Eggtimer Quark is OK for pyro rockets but I wouldn't recommend it for water rockets. The minimum deployment altitude on it is 300 feet (about 91 m). A 2L rocket can go that high but often not when you're trying experiments.
The Quantum (which I have) can be set to deploy at 100 feet, which has worked well for me. However, Graham is in Australia, and it seems he has to pay about double the price to get the Quantum or the Quark shipped there.

It's a big investment. If you're doing experiments that can get stuck in a tree, Tomy timers or air speed flaps minimize your financial losses! I'm terrified to fly my Quantum because around where I live, it's hard to find a large enough area that is clear of trees or man-made structures that the rocket can get caught on.



GrahamM
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Re: suggestions for cheap deployment trigger please?

Post by GrahamM » Mon Sep 17, 2018 6:33 pm

Good point about the Quark limitations, thanks for pointing that out.


Graham
Melbourne, Australia

GrahamM
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Re: suggestions for cheap deployment trigger please?

Post by GrahamM » Wed Sep 19, 2018 1:28 am

addstogether2 wrote:
Sun Sep 16, 2018 6:57 am
Hi graham,

re getting some tommy timmers go down to bay st port melbourne.
either Port Melb Discounts 237 bay st
or Shopaholic 80 bay st.
Went down to PM Discounts today and they had the perfect thing, swimming fish toys for a paltry $2.50
Purchased one and just finished pulling it apart and testing, when fully wound it takes about 9 seconds to unwind so that will be ideal for apogees around the 4 second mark. :D
Thanks again for letting me know about the shop, I will go back in the next day or so and pick up a couple of extra toys just to have some spare timers. TH:


Graham
Melbourne, Australia

GrahamM
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Re: suggestions for cheap deployment trigger please?

Post by GrahamM » Thu Sep 20, 2018 3:47 am

Next stage in the development.
Flew the airflap recovery system today with mixed success.
Setting up for the first launch
First flight went well, the nosecone deployed as expected but the parachute failed to open because I forgot to remove a rubber band that I had around it while preparing. :oops:
Here is a slo-mo of the launch, interesting to notice how the launcher moves when the string is pulled. I thought that it was heavy enough but it will need to be pegged down.
Slo-mo launch
While pumping pressure for the second flight I had a nozzle failure. The Gardena tap connector separated from the bottle top that was glued into it with araldite. In the second video you can see the green connector remains on the launcher when the rocket prematurely departs. Either I didn't prepare the surfaces of the two items properly, or araldite isn't the right thing to use for this circumstance.
Nozzle failure


Graham
Melbourne, Australia

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