Advices for rocket flight measurements trough the use of PICs and other sweet stuff

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SPow 16 years ago

Hi,

I am to design and realize electronic cards for a school project. A rocket (7 kilos) will be launched in June, and we need to record its flight since we introduce a new kind of airbreaks that we would like to test.

Principle is pretty simple : at max altitude, the rocket deploys its parachute slowing its descent to 15m/s. After a short moment, airbreaks are deployed. They actually are parts of the rocket's fuselage itself that will open and create enough drag to slow it down hopefully to 8 m/s.

For the means of opening, we thought of a mechanical system with a spring and an electro-sucker (i'm not sure about the translation, sorry) so that we don't have to use heavy/expensive servos. The problem we now face is that we are to choose between the components we'll use and the correct way to place them on a circuit. And we don't know much about that.

We need a PIC so that we can control the opening of the suckers. But the suckers we found need a command in current, which is -i heard- much more difficult to operate than a command in voltage. Also, the one we found needs DC 24V, and that's an incredible amount of energy compared to what we currently board in the rocket. I think we can use a Push Pull to double appearing voltage, but i'm not sure this is DC-compatible. Should the PIC and the suckers be under different alimentation circuits ? Or should we use resistances to 'protect' the PIC/accelerometer ? (that will cause tremendous loss in energy i think)

To detect max altitude and record data, we have to use a 3-axes accelerometer, but the amount of data to be stored will exceed the capacity of the PIC EPROM. I think we need to connect it to an SD card, but i was told this was a very difficult job.

The subject is very vague, and we do not have a tutor yet because the school can't find one. We still have much time for the project, but i hate to do things at the last minute. You can see we need a lot of directions :)

Since this is my first post on usenet and that english isn't my primary language, please apologize me for any mistake i made. Thanks for having read.

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pimpom 16 years ago

I think you should describe the "electro-sucker" in more detail - how it works, how it's constructed. If you have a datasheet or can point to a website that has information about it, perhaps some of us will be in a better position to offer help.

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Martin Brown 16 years ago

I'd hazard a guess that electrosucker translates as solenoid or electromagnet. There might be other more cunning ways to do it with lower mass and power for a one time shot. Some variant of a mousetrap mechanism that is primed when the first parachute opens for instance. Or a fusable link/thermoset glue holding a spring.

As for the log the OP is probably better off with something simple and hardwired like a serial EEPROM 32kbytes .

Regards, Martin Brown

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Royston Vasey 16 years ago

Model rocketry guys use "electric matches" with small charges to deploy parachutes etc. Electric matches are a loop of nichrome (?) with a bit of pyro material on it. There are off the shelf and build your own plans for the hardware to drive all this stuff.

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TheM 16 years ago

works, how it's constructed. If you have a datasheet or

will be in a better position to offer help.

electromagnet. There might be other more cunning ways to do it

mechanism that is primed when the first parachute

hardwired like a serial EEPROM 32kbytes .

parachutes etc. Electric matches are a loop of nichrome

own plans for the hardware to drive all this stuff.

Yep, and this match can cut through a string holding a spring.

M

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Tim Wescott 16 years ago

I'm pretty sure your "electro-sucker" is a solenoid. If so, there are lots of reasons to avoid it's use, some of which you're describing.

Solenoids don't really use a "current command" as much as they need a voltage _drive_ that needs to deliver a lot of current. Search on transistor drive circuits. Using a logic-level FET you can have something as simple as:

|-----o to solenoid from PIC o------|| |---. | === gnd

This works when the other end of your solenoid is connected to +24V (it also burns up without a back EMF diode, but I'm being lazy -- do some web searches for solenoid drive circuits).

Normally when you have high-voltage, high-power devices in the same assembly with lower power devices you either use two sets of batteries or you use a switching power supply to efficiently generate the one from the other.

I'd avoid that solenoid like the plague. At the cost of some speed you can get a much more reliable pull from an RC servo. Or you can use the "electric matches" that have been talked about. Either way you should be able to make your system work on much less power, and strictly off of a

5V supply. You may find that your overall system expense and weight is less with a "heavy and expensive" RC servo than with a solenoid and all the support hardware it needs.

www.wescottdesign.com

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Jim Yanik 16 years ago

Tim Wescott wrote in news:qfednaxla8OPsunWnZ2dnUVZ snipped-for-privacy@web-ster.com:

you can BUY recording instruments for "model" rockets,complete with accelerometer and triggering for the parachute's ejection charge. check the rocketry section of Ebay,or Google "rocketry altimeters". or

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BTW,7 kilos launch weight is in the High Power Rocketry(HPR) realm,and is regulated(in the US). The FAA needs to be notified,and you need to be certified by one of the HPR orgs to buy the rocket motors. You also need a large enough launch field,NOT near any school or resedential neighborhood.

Jim Yanik jyanik at localnet dot com

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Jim Yanik 16 years ago

Tim Wescott wrote in news:qfednaxla8OPsunWnZ2dnUVZ snipped-for-privacy@web-ster.com:

what altitude do you expect to reach,and what motor(s) are you intending to use?

commercial rocket motors,I hope....no "basement bomber" homemade stuff.

Most folks use a pyrotechnic ejection charge(black powder) to push out the chute,some can fire two separate charges to deploy a drogue then the main chute.

the commercial altimeters normally have the ability to trigger ejection charges.(and only use one or two 9v batteries.) They're very lightweight,too.

Jim Yanik jyanik at localnet dot com

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Jim Yanik 16 years ago

"Royston Vasey" wrote in news:ws-dnTJNOsu2kunWnZ2dnUVZ snipped-for-privacy@westnet.com.au:

there's a lot of online resources and info about non-commercial rocketry,and the OP needs to do some research before launching anything so heavy as 7 kilos. He may be unaware of flight regulations and laws concerning hobbyist or amateur rocket launches.

anything over 454 grams(1 LB) is regulated in some respect. (Large Model Rockets and High Power Rocketry)

There's also construction materials to be considered; most hobbyist rockets may not contain "substantial" amounts of metal.

Jim Yanik jyanik at localnet dot com

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Falk Willberg 16 years ago

Am 11.02.2010 13:38, schrieb SPow:

...

I don't think so. I used to record megabytes of data to SD-Cards with a standard AVR microcontroller. Anyhow I did not use any filesystem, but wrote raw text. Fields were delimited by blanks, records by newlines. Makes things much easier.

I used "dd" on Linux to transfer data to the PC.

formatting link

Falk

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SPow 16 years ago

snipped-for-privacy@web-ster.com:

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Hi,

I'm not sure how usenet should be used to respond (either i have to respond individually to everyone or respond in a large post, really don't know), so i'll respond just like on forums, in one big post :)

First, i'm not a tourist looking to build a crazy rocket. This is a very serious project me and friends are completing, though it was not an 'official' subject from our school. We are aware of safety regulations, risks ... Our motors are delivered by a state-regulated provider (i don't live in the US) and we've (our association) been launching 2 meters high rockets over the last 15 years or so, topping 2000 meters in altitude if i remember correctly. We mostly deal with aerodynamics in our school, but the projects given this semester were too crappy so we decided to expand our work area.

I'll look for a proper translation for 'electro-sucker' (i thought solenoides were the L component in electronics...), but i really like the idea of a fuse controlling the opening of airbreaks, which would spare us the trouble of an alternate power circuit.

Here is a picture of what I believe an 'electro-sucker' is :

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Thank you Falk for the PIC to SD link, it might prove very useful. Also, thanks to everyone for the numerous replies.

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pimpom 16 years ago

Common practice is to respond individually to a post that contains points that may merit further discussion. A single blanket reply is OK if no such points were raised.

One thing though: You're posting through Google Groups which many regulars here have blocked because GG is the biggest single source of spam on Usenet. Many of those who replied to your question would not have seen your post at all if I had not replied.

If you want to keep participating in newsgroups, use a proper newsreader program and post via dedicated newsservers.

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Advices for rocket flight measurements trough the use of PICs and other sweet stuff

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