microcontroller for rocket.

[Salik Syed]

My team is building a rocket for a rocketry contest.
We want to use some kind of micro controller that can eject the parachute at a set height etc..
the requirements:
it should be able to control two servos
it should be able to get input from an analog sensor
it should be programmable in C or Pbasic


What should we use? Which is easiest to hook up and program. What model do you recommend basically?

[JBotAlan]

I haven't worked with any microcontroller...ever besides the one FIRST provides...

So I really have no direction to point you in. Sorry.

Why not just build a traditional rocket? Ejecting the parachute is done by the last section of the engine exploding.

That's the only suggestion I've got, only because I haven't ever used a microcontroller (maybe soon though).

Just my take on it,
JBotAlan

[Rickertsen2]

well if you are asking this question, you probably don't have much microcontroller experience. A good beginner choice would be one that can be programmed in pBASIC such as the STAMP microcontrollers from parallax. http://parallax.com . All you need is a demo board, and a STAMP.

Alternatively, you can use a PIC. To program it in C you will need a compiler such as C18. The version that comes in the FIRST kit will only work on the specific PIC that is used inside the robot controller. If you download the demo version off the microchip website, it will work on all PICs but expires after some amount of months. If you use a PIC, you will need a PIC programmer, and some sort of circuit to house the thing. It will need at the very least a battery, a voltage regulator, and and oscillator of some kind to provide the clock signal. PICs are far more powerful but have a steeper learning curve.

If i were you, i would use a STAMP. A kit like http://www.parallax.com/detail.asp?product_id=27206 would have everything you need to get started and learn the how to use stamps. The manual that comes with it even has examples of how to control servos. Its kinda pricey but worth it.

[Joe Ross]

This article may give you some ideas: http://www.circuitcellar.com/library...e181/index.htm

[Salik Syed]

Thanks guys.

Why not build a traditional rocket?
well part of the contest is to get the rocket to EXACTLY 800 ft, this requires onboard monitoring to eject the nose cone at an exact time.

second part is that we need to have a flight time of exactly 45 seconds, so we will deploy/jettison the chute ate very specific times.

[ChuckDickerson]

You might be interested in the R-DAS unit made by AED: http://home.iae.nl/users/aed/rdas/

It is a Rocket Data Acquisition System (R-DAS) that can measure and store data like altitude, etc. and can set off a parachute deployment charge. If you Google a bit you can find where to get them in the U.S.

[Tom Saxton]

You might consider an AVR processor. They are competitive with PIC, but have cross-platform GCC support (i.e., free, awesome C/C++ compiler). The programmer required for programming them can be made from $5 worth of Radio Shack parts if you have a parallel port, or there's a $25 gizmo that does the trick if you only have serial.

If you don't want to do the whole thing from scratch, I'd recommend the ARC board from www.barello.net or one of the Orangutans from www.pololu.com. These boards will do everything you want, and a lot more.

[Al Skierkiewicz]

I think the Basic Stamp listed in an earlier post will be your best bet on weight/size and ease of use. You may need to add a couple of high current drivers to feed the servos but there is a product that is designed with a 9 volt battery clip and a little proto typing circuit area on board. Check out the Parallax website for all their products. Digikey is an outlet for this line and a variety of sensors. If you think you can get away with just an accurae timer, there is a program for that purpose already written for the Basic Stamp.

[Gdeaver]

The control algorithm for firing an ejection charge at a specific altitude is a very complicated thing. If you go down this path you may spend all your development time on the electronics and get nowhere. I would suggest you get a copy of a rocketry design program called ROCSIM and work on the rocket design - engine choice - simulation to build a rocket that by design reaches your goal altitude. Once you get the rocket built you can dial in the altitude by weight. If there is still time and you wanted to add electronics I would suggest a simple timer. There are devices called G-switches that can Trip the start of the timing. An ejection charge is the best way of popping the parachute. This involves the use of 4f black powder or pyrodex. You must be 21 to purchase and use these. A low current e-match is usually used to initiate the ejection charge. You need a low explosive licence for these. I would suggest that you try and track down a NAR or Tripoli rocket club member in your area to mentor you on these parts. I think you will find most members very willing to help. You may also want to visit a high power rocket launch. Just being there and watching is impressive. Remember unlike first robotics, rocketry is more critical engineering. If you make a little mistake you usually end up with expensive confetti

[KenWittlief]

you can probabally get a microcontroller the size of your pinky fingernail, power it with a watch battery

and have more computer processing power on your model rocket than the Apollo 11 Eagle had when it landed on the moon.

sounds like a great project.

[Doug G]

Just to help clarify Salik's post...

Team America Rocketry Challenge is the contest we've registered for, which requires a rocket, no more than 1.5 kg, to loft one egg to 800 ft and return it safely in a total elapsed time of 45 seconds.

Yes, many teams simply design their rocket around a certain size and motor and then ballast it to get it to the right altitude. We do have RockSim as well as a computer model done by scratch using Excel, engine thrust data, and our physical rocket characteristics (mass, drag coefficient, etc..).

But in an attempt to be a little more "high-tech", the students wish to add on-board controller to monitor altitude (barometric pressure) and then activate a servo to release a "spring loaded" nose cone and a parachute as well. In this case the engine would not include the ejection charge or delay - an option they have because they're using a reloadable motor system (Aerotech)

There are commercial altimeters available for model rockets - but they're meant to trigger (relay?) a black powder charge to "blow-out" the nose cone and/or drone chute. The rules of the contest do not allow for separate ejection charges. Which is why they are trying to design their own "altimeter" and non-pryotechnic ejection system.

I suspect if they cannot get their "altimeter" to work, they will just use a standard engine with a normal ejection charge as a fall back approach.

Unfortunately I have very limited knowledge of circuits and programming, but Salik is very familiar with programming the FIRST/IFI/Microchip Robot Controller.

The best type of controller (and possibly programmer) to use is what our team needs help with. We appreciate the help and welcome more ideas or comments.

[Matt Krass]

Do you have any idea what sensor you'll be using and what type of output it will be using?

[Mike]

Originally Posted by Doug G

Just to help clarify Salik's post...

Team America Rocketry Challenge is the contest we've registered for, which requires a rocket, no more than 1.5 kg, to loft one egg to 800 ft and return it safely in a total elapsed time of 45 seconds.

Yes, many teams simply design their rocket around a certain size and motor and then ballast it to get it to the right altitude. We do have RockSim as well as a computer model done by scratch using Excel, engine thrust data, and our physical rocket characteristics (mass, drag coefficient, etc..).

But in an attempt to be a little more "high-tech", the students wish to add on-board controller to monitor altitude (barometric pressure) and then activate a servo to release a "spring loaded" nose cone and a parachute as well. In this case the engine would not include the ejection charge or delay - an option they have because they're using a reloadable motor system (Aerotech)

There are commercial altimeters available for model rockets - but they're meant to trigger (relay?) a black powder charge to "blow-out" the nose cone and/or drone chute. The rules of the contest do not allow for separate ejection charges. Which is why they are trying to design their own "altimeter" and non-pryotechnic ejection system.

I suspect if they cannot get their "altimeter" to work, they will just use a standard engine with a normal ejection charge as a fall back approach.

Unfortunately I have very limited knowledge of circuits and programming, but Salik is very familiar with programming the FIRST/IFI/Microchip Robot Controller.

The best type of controller (and possibly programmer) to use is what our team needs help with. We appreciate the help and welcome more ideas or comments.

Hmm, so it looks to me you don't really need to ever use the altitude, you just want to eject at altitude X. I would look for a sensor that can be set to either allow current to flow, or current to not flow, at a preset height. That would make it much simpler and cheaper. KISS.

But, yeah, I don't know if those types of sensors exist.

[6600gt]

PicMicrochips are cheap and easy to work with but you first have to decide what type of sensor do you want to use to tell you your altitude? And what type of value does it output?

High-g shock accelerometers might work

Here is a cheap programmer that works with a lot of pics:
http://www.picbasic.co.uk/forum/arch...php/t-703.html

It uses the IC-Prog software. http://www.ic-prog.com

You could order a sample pack form the Microchip website(might want to buy 1 or 2 for faster shipping). The 28 pin 18F2580 should be more than enough to do the job. It has the software processing capability of the FRC controllers(at 40 Mhz). It just doesn't have as many hardware features. 18F4520 and 18F2480 are just as capable. 18f4520 is the easier to work with but but it is bigger with 40 pins.

This sensor might work: Motorola MPX4115A(pressure sensor)

http://geocities.com/SiliconValley/O...33/MPX4115.pdf
http://www.geocities.com/SiliconVall...altimeter.html

Try to figure out the voltage to pressure ratio.

[Gdeaver]

Integrating an accelerometer to determine altitude will probably not give good results. For years high power rocket altimeters have used a digital pressure sensor for altitude measurement. The Freescale mpx4115a has been a standard device. There are some newer versions that would work too. On the pressure sensor data sheet you will notice a resistor and capacitor on the output of the sensor to microcontroller ADC pin. You need these. Don't leave them out. You'll use the pressure sensor to watch the drop in pressure. When the pressure measured equals the desired altitude pressure pop the chute. You need to Google "Standard Atmosphere" . This will allow you to determine what pressure you'll be looking for. When the altimeter is powered sample and find the voltage equivalent of the AGL pressure. Subtract the voltage equivalent to your desired altitude this will give voltage the microcontroller will activate the deployment at. Here is the Freescale data sheet. MPX4115A You'll need at least 10 bit resolution. Also you'll need to experiment on the altitude to trigger the deployment to allow for a little coast. Search the rocket forums and NAR about the holes you need to put in the electronics bay. There size and placement is important. You really should go to a high power launch to see someone prep rocket electronics. International Rectifier corporation makes 10 amp logic level FETS that are small and can be driven by the microcontroller directly to power the ejection device. A non pyrotechnic deployment system is hard. I've used a piece of spectra thread wrapped with nichrome wire to hold a compressed spring. Then the FET applies power to the wire it melts the thread releasing the spring. The other easier deployment strategy is to fire you ejection device based strictly on time. Use a pull pin to detect launch and start timing.
Use a long ejection delay on the Aerotech as a backup.

DO NOT underestimate the complexity of the electronics and deployment. Time is running out. Your main focus should be on the physical design of a rocket that reliably flies to that altitude and a parachute for total time. Hint - an overly stable rocket may be a good thing.