Launch of our first multi bottle rocket

[MB water-rockets]

On November 1st we had lift off of Antare Ia.

The video can be found here:
[youtube][/youtube]

Technical Data:

Capacity - 3.1 L
Dry weight - 430 g
Diameter - 94 mm
Lenght - 925 mm
Nozzle - 9 mm (Gardena)

General description:

Launch detection is done with a reed switch and a magnet attached to the launcher
Parachute deployment is done with a timer using a NE556 (2 x NE555) and a servo

Unfortunatley the first launch failed. The bottom of the first bottle was blown off well below the test pressure. But the broken parts could be fixed for a second and third launch.

Due to safety reasons (there were too many people around) we had to limit the launch pressure to 8 bar. So the expected height was about 70 m. The flight went well and we were quite happy that all systems worked this time.

The third launch was somewhat unstable. When we compared the setup of launch #2 and #3 we discovered two major changes. We had replaced the standard nozzle with a heavier one. This shifted the center of gravity backwards. In addition we produced a lot of foam when filling the water into the bottles. We suppose that the foam produced less thrust and thus the rocket was slower on the first few metres.
Both measures could have caused the instability.

Comments and ideas are welcome!

Cheers,
Roman (MB-water-rockets)

[rockets-in-brighton]

On November 1st we had lift off of Antare Ia.

Lovely, thanks for sharing your video. (I liked the sock puppet water rocketeer)

From your description it sounds like your bottles were joined with some kind of robinson-coupling, is that right? What sort did you use - base-to-base or base-to-spout - and what materials?

On your third launch, yes you probably made the rocket unstable by making the tail heavier. You were already using a guide rod so I'm guessing that you had more water/foam than could be ejected though the internal diameter of the nozzle. If the rocket was still significantly back-heavy after clearing the guide rod, a light gust of wind could easily send it spinning.

[The Sky Dart]

Thank you for sharing the video with us.

Two suggestions if I may:

1) Replace the reed switch with g-switch. Different designs can be found on the net. The one we use is very simple and reliable. You can find it on our website. There is plenty of space on the control board in your rocket.
2) By using the g-switch you can reuse the rod with a magnet as a guide rod. It'll increase stability.

What altimeter do you use?

[rockets-in-brighton]

Thank you for sharing the video with us.

Two suggestions if I may:

1) Replace the reed switch with g-switch. Different designs can be found on the net. The one we use is very simple and reliable. You can find it on our website. There is plenty of space on the control board in your rocket.
2) By using the g-switch you can reuse the rod with a magnet as a guide rod. It'll increase stability.

Ah, mistook that support post for a guide rail. That woule be the proble, then.

What altimeter do you use?

[/quote]

Says Unilog at the start of the video, but I don't recognise the brand.

[MB water-rockets]

Thanks for the feedback and the questions!

Our chief engineer wasn't amused that you called him a "sock puppet". But one day I think he has to face the truth.

Here are some answers to your questions:

We used two bottles with a robinson coupling base-to-spout. The bottles are heavy and solid (I haven't seen them outside Germany). They hold 14 bar easily (except the one we used for launch #1 ). The coupling itself is made of a threaded rod with an inner diameter of approx 8 mm.

Until now we didn't use a guide rod. We have seen several videos where big rockets were launched successfully without guide rails. So we didn't consider it yet. But it is now on our list and we'll try how this works on our next flight day.
Do you always use guide rods when launching big rockets?

The altimeter is from a webshop which sells lots of stuff for model airplanes. Unfortunately it's all in German: http://www.sm-modellbau.de/shop/
I liked the size (22 x 37 mm) and the weight of 6 grams. The data can be evaluated with Excel which gives you a lot of freedom in scaling the curves etc.

Cheers,
Roman

[rockets-in-brighton]

Ah yes, those lovely German thick-walled bottles (that can be returned for a refund of the deposit? Are they actually reused, like glass bottles used to be, or just recycled?)

I don't use a guide rod myself because I use open necks (22mm spouts) rather than gardena nozzles, which results in a faster launch, which improves stability. Lower speed restricted nozzle launches can be assisted by a guide rod until they are going fast enough to be stable.

Downside of open nozzle is faster launch = more drag = reduced altitude.

[The Sky Dart]

Until now we didn't use a guide rod. We have seen several videos where big rockets were launched successfully without guide rails. So we didn't consider it yet. But it is now on our list and we'll try how this works on our next flight day.

I've checked the site, but I don't get whether an external altimeter has to be connected to the Unilog or it's already build in. Could you please list all part numbers for the altimeter set up including cables if any are needed?

If a long launch tube is used there is no need for a guide rail unless extra stability is needed.

[MB water-rockets]

Ah yes, those lovely German thick-walled bottles (that can be returned for a refund of the deposit? Are they actually reused, like glass bottles used to be, or just recycled?)

They're reused. Sometimes you can find bottles with lots of tiny cracks around the base which indicates aging due to reuse.

I don't use a guide rod myself because I use open necks (22mm spouts) rather than gardena nozzles, which results in a faster launch, which improves stability. Lower speed restricted nozzle launches can be assisted by a guide rod until they are going fast enough to be stable.

We decided some time ago to go for the Gardena solution but didn't consider stability issues. I totally forgot this point. Probably we have to discuss the nozzle design again.

I've checked the site, but I don't get whether an external altimeter has to be connected to the Unilog or it's already build in. Could you please list all part numbers for the altimeter set up including cables if any are needed?

The altimeter is already built in. If you order just the Unilog "UniLog mit USB-Interface Kabel, Art.Nr.: 2500" You'll get the Datalogger (with on board pressure sensor), a power cable, a USB-cable and an Excel-Makro for reading the data, setting the Unilog etc. ready to use. There is no need for extra sensors/ parts.

For better access (we don't want to disassemble the whole rocket each time) we ordered an extension cable "COM-Anschluss Verlängerungskabel für UniLog und InfoSwitch, Art.Nr.: 2522"

A nice feature: It logs also the supply voltage. In our case it is very easy to identify servo action due to voltage drop. So we can check if the timer worked correct.

Let me know if I can help with more info or some pics/ screenshots.

[The Sky Dart]

Could you please post a schematics of your servo control and the timer?
I use 555s as well for both, but not really satisfied with how the timer works.

[MB water-rockets]

Could you please post a schematics of your servo control and the timer?
I use 555s as well for both, but not really satisfied with how the timer works.

Right now I don't have a suitable format for the schematic to post here. I planned to draw it with EAGLE during the weekend. Once it has been completed I'll put the file on our (just recently created) website. Currently you can't find anything but a picture. But within a week or so some details should be available.
http://www.mb-water-rockets.bplaced.de/

Cheers,
Roman

[MB water-rockets]

...at least the schematic is online now.

Cheers,
-roman

[fallens10]

nice video

[MB water-rockets]

nice video

thanks

Shooting and cutting the movie was real fun. Unfortunately the quality of the flight video is poor. It looks like we need to get a camcorder for the next launches.