Raspberry Pi

So, I finally have one. Freshly delivered, today. One of the first orders of business will be to get an OS going on it.

That said...this thing is just begging for a rocketry application. The question is....what? Perfect form factor to fly!

Thoughts?

-Kevin

Ya think it 'll survive a rocket flight?

Neat. Why did you pick that over Arduino? Arduino has a lot of rebuilt circuits & sensors to use.

kruland said:

Neat. Why did you pick that over Arduino? Arduino has a lot of rebuilt circuits & sensors to use.

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Easy -- the Pi run Linux. Even if I never stick it in a rocket, I can use it for computer-type stuff. For example, it'd be easy to mount this and an LCD panel into a picture frame and make a large photo frame. Much easier to do with this than with Arduino.

-Kevin

What is a raspberry pi?

Agree Kevin. I have been eyeing them since they were first announced. One thing is for sure, you will need to get one of these for the rocket it is housed in:

How about IP/ham and serve video from the rocket over RTP or HTTP?

troj said:

Easy -- the Pi run Linux. Even if I never stick it in a rocket, I can use it for computer-type stuff. For example, it'd be easy to mount this and an LCD panel into a picture frame and make a large photo frame. Much easier to do with this than with Arduino.

-Kevin

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The Raspberry Pi is a cool board, but it is overkill for amateur/hobby rocketry applications. There is very little that cannot be done with an 8-bit MCU far cheaper using less power.

Sweet! I got mine about 2 months ago. I have had a lot of fun with it, and have made most of a graphing program for it.

rockets4kids said:

The Raspberry Pi is a cool board, but it is overkill for amateur/hobby rocketry applications. There is very little that cannot be done with an 8-bit MCU far cheaper using less power.

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Yep, and our hobby isn't necessary, either.

But we do it because A) we can, and B) it makes us happy.



-Kevin

What kind of discrete I/O does it have?

rstaff3 said:

What kind of discrete I/O does it have?

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I'm not a hardware guy; best I can do is point you to www.raspberrypi.org

-Kevin

rockets4kids said:

The Raspberry Pi is a cool board, but it is overkill for amateur/hobby rocketry applications. There is very little that cannot be done with an 8-bit MCU far cheaper using less power.

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That's the kicker--it's about the same price.

I use a lot of Atmel MCUs in my work (the kind that's in an Arduino) and I like them for many applications. But saying that an ARM is overkill is like saying that using a computer for text editing is overkill when you have typewriters :=)

Ari.

troj said:

So, I finally have one. Freshly delivered, today. One of the first orders of business will be to get an OS going on it.

That said...this thing is just begging for a rocketry application. The question is....what? Perfect form factor to fly!

Thoughts?

-Kevin

Click to expand...

How about displaying subliminal messages on the airframe during flight with an LED array?

[video=vimeo;46172052]https://vimeo.com/46172052[/video]

If you could make it compute its speed, you could make it blink out equal distance lines as it flies (night rocket). If it is going faster, it blinks faster. Then you launch it on a fast burning motor and take a time lapse photo of it and count the altitude as it ascends from the number of tick marks.

I had the exact same ideas for when I get one...

I see this having more of a "smart rocket" system, as in one that monitors it's stability in flight, and can adjust accordingly. Also, one that can look with a camera while under decent and steer itself away from trees....

With this kind of computing power, the possibilities are endless. Overkill for "normal" applications, but who wants to be normal?

iter said:

That's the kicker--it's about the same price.

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Not really. The Pi is $35. And that is *if* you can get one. You can get MSP430 dev boards for $4.30 (shipped) and the STM F0 Discovery board for $8.

But the real advantage of the simpler MCUs is that they require far less support hardware, and you can build a running system for about two bucks on a protoboard. So, basically, you can build 17 flight computers for the price of 1 Pi.

troj said:

Yep, and our hobby isn't necessary, either.

But we do it because A) we can, and B) it makes us happy.

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That is only of you treat rocketry as a hobby and not a science.

It you treat amateur rocketry as a science where everything is optimized, you will choose the platform that is the smallest, most lightweight, has the lowest power requirements, and has the fewest components to reduce likelihood of failure.

The Pi is bigger, heavier, requires more power, and is far more complex without providing any benefit in return. Furthermore, you don't have brownout or watchdog control, so even if you can recover from a failure, you still need to wait several seconds while you re-boot Linux, whereas a simpler MCU will be back in a matter of microseconds.

And finally, it is entirely possible for the hobbyist to understand the operation of an 8/16 bit MCU solution end-to-end and actually construct the board from scratch.

I am not saying you cannot use the Pi, just that it is a very poor solution no matter how you look at it.

rockets4kids said:

That is only of you treat rocketry as a hobby and not a science.

It you treat amateur rocketry as a science where everything is optimized, you will choose the platform that is the smallest, most lightweight, has the lowest power requirements, and has the fewest components to reduce likelihood of failure.

The Pi is bigger, heavier, requires more power, and is far more complex without providing any benefit in return. Furthermore, you don't have brownout or watchdog control, so even if you can recover from a failure, you still need to wait several seconds while you re-boot Linux, whereas a simpler MCU will be back in a matter of microseconds.

And finally, it is entirely possible for the hobbyist to understand the operation of an 8/16 bit MCU solution end-to-end and actually construct the board from scratch.

I am not saying you cannot use the Pi, just that it is a very poor solution no matter how you look at it.

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Knowing all that, it seems that a couple of safety issues could arise from using this. First, the length of time it takes to boot, coupled with the lack of brownout control, IMO makes it a bad candidate for any safety sensitive application. Second, how big of a battery would it need? I don't like the idea of a rocket with a large battery catching fire on the pad. As an aside, i'd imagine that most clubs do not have clean agent fire extinguishers available. I could see much weeping and gnashing of teeth if a rocket equipped with a pi caght fire...

RadManCF said:

Knowing all that, it seems that a couple of safety issues could arise from using this. First, the length of time it takes to boot, coupled with the lack of brownout control, IMO makes it a bad candidate for any safety sensitive application. Second, how big of a battery would it need? I don't like the idea of a rocket with a large battery catching fire on the pad. As an aside, i'd imagine that most clubs do not have clean agent fire extinguishers available. I could see much weeping and gnashing of teeth if a rocket equipped with a pi caght fire...

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As far as I know, it runs on 5v at 700mA. (or thereabouts.) LiPos only explode spectacularly skin-bubblingly when overcharged/volted, and that's the most dangerous type. (And let's be honest: Everyone likes spectacle.) However, the Raspberry pi is very probably *terrible* at timing critical applications, since it has no RTC and is multithreaded. Where it really shines is processing a lot of data- say you've got that 8-bit MCU recording things like pressure, temp, acceleration, etc. If you have it process that real-time, it would be quite slow, and even storing that raw data will take a while. Feeding it to the RPi over Serial would fit the bill better.

troj said:

Yep, and our hobby isn't necessary, either.

But we do it because A) we can, and B) it makes us happy.


-Kevin

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Damm , Kev- tough room! Enjoy your whatever it is. I just added more ram to my abacus. I really like the red beads...

Dr. Quigley said:

As far as I know, it runs on 5v at 700mA. (or thereabouts.)

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By way of comparison, my board only takes a few mA and I haven't bothered to optimize it yet. Pushing 10 mA to light an LED indicator dwarfs all other current consumption.

Dr. Quigley said:

LiPos only explode spectacularly skin-bubblingly when overcharged/volted, and that's the most dangerous type.

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They are also quite susceptible to physical damage. This is why R/C batteries (and those in EV autos) should be inspected thoroughly after a crash.

-p.

Dr. Quigley said:

As far as I know, it runs on 5v at 700mA. (or thereabouts.) LiPos only explode spectacularly skin-bubblingly when overcharged/volted, and that's the most dangerous type. (And let's be honest: Everyone likes spectacle.) However, the Raspberry pi is very probably *terrible* at timing critical applications, since it has no RTC and is multithreaded. Where it really shines is processing a lot of data- say you've got that 8-bit MCU recording things like pressure, temp, acceleration, etc. If you have it process that real-time, it would be quite slow, and even storing that raw data will take a while. Feeding it to the RPi over Serial would fit the bill better.

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So how much could the use of periphrials add to the current requirements? One of my greatest fears regarding electronics is a student team with little background in hobby rocketry reinventing the wheel and ending up with somthing powered by a deep cycle battery. I don't remember the competition they were in, but some college classmates of mine came up with a concept combining HPR motors and model airplane motors in an airframe based on that of the SR 71 Blackbird. The objective of their design was to collect video footage from 3000 feet. They also mentioned that in a previous competition, they had looked into using arduino as the basis for a deployment system, apparently without any thought of looking into commercially available altimeters. I think they ended up using an R/C system for deployment. Long story short, somebody might get it in their head to make a Rube Goldburg Rocket that would be unreliable and present unusual hazards in the event of a failure.

rockets4kids said:

That is only of you treat rocketry as a hobby and not a science.

It you treat amateur rocketry as a science where everything is optimized, you will choose the platform that is the smallest, most lightweight, has the lowest power requirements, and has the fewest components to reduce likelihood of failure.

The Pi is bigger, heavier, requires more power, and is far more complex without providing any benefit in return. Furthermore, you don't have brownout or watchdog control, so even if you can recover from a failure, you still need to wait several seconds while you re-boot Linux, whereas a simpler MCU will be back in a matter of microseconds.

And finally, it is entirely possible for the hobbyist to understand the operation of an 8/16 bit MCU solution end-to-end and actually construct the board from scratch.

I am not saying you cannot use the Pi, just that it is a very poor solution no matter how you look at it.

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This is a pretty narrow view of science, not to mention the hobby. There are innumerable scientific questions and approaches applied to amateur rocketry, and building parsimoniously to maximize altitude/thrust ratio is but one.

Trying to figure out how to safely launch and recover a rocket that changes color depending on velocity or altitude, or one that displays a message, or one that carries a functioning web server and WiFi hotspot, or one that plays DOOM, are pretty difficult problems to solve even without "optimizing" the design.

Most of my rockets are built with the goal of maximizing the smile on my kids' and my faces. There is some science to that, but it doesn't have much do to with finding the smallest, most lightweight, etc. components: it has to do with building a rocket that we like, within reach of our skills and available tools and budget, an learning how to fly it safely. Minimum diameter 3FNC designs are cool, but they aren't any more inherently useful or successful than an overstable Big Bertha with googly-eye stickers on it. We all make performance trade-offs to achieve other goals with our projects, and one beauty of rocketry as a hobby is that there is room for all of us and we can all help and learn from each other.

Now let me step down from my soapbox and suggest some friendly competition between the arduino and raspberry pi crowds: Let's come up with some ideas for suitable projects and see what we can accomplish with these cool systems that obviously have tons of untapped potential. Show us your most practical, your coolest, your most original, your most frivolous but compelling ideas. And maybe even build some of them!

In the end, we all treat rocketry as a hobby...except for the few actual rocket scientists. And when thy do sport rocketry, that's a hobby too.

rockets4kids said:

That is only of you treat rocketry as a hobby and not a science.

It you treat amateur rocketry as a science where everything is optimized, you will choose the platform that is the smallest, most lightweight, has the lowest power requirements, and has the fewest components to reduce likelihood of failure.

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"Small, lightweight, low power requirements, and fewer components" is completely unrelated to "likelihood of failure".

rstaff3 said:

In the end, we all treat rocketry as a hobby...except for the few actual rocket scientists. And when thy do sport rocketry, that's a hobby too.

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It is entirely possible to construct small scale rockets (from scratch) as a scientific exercise. "small scale" and "not for profit" are in no way an implicit exclusion of rocket science.

rockets4kids said:

It is entirely possible to construct small scale rockets (from scratch) as a scientific exercise. "small scale" and "not for profit" are in no way an implicit exclusion of rocket science.

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You read my post incorrectly. I listed four reasons for optimization, not three. The fourth of those is that the use of fewer components will, as a general rule, reduce the likelihood of failure.

And while I am here again, I will add two more reasons why the Pi is a poor choice:

1. The program code for the Pi is stored on an SD card with friction fit connectors. These are known to fail even in relatively low-G situations. My trail GPS stores its map data on an SD card, and it regularly loses connection. This happens just bouncing around in my backpack, and it it a serious problem when I mount it on my mountain bike. The GPS unit does not check for this condition, so I need to manually power cycle the unit to recover. Occasionally it will hang to hard that I need to remove the batteries in order to reset it.

2. The Pi only include basic digital GPIO, so you are going to need to add an offboard analog to digital converter in just about every application. Dedicated ADCs are typically *more* expensive than MCUs which contain on-board ADCs.

Again, I cannot think of a *single* advantage to using a Pi on a rocket other than to brag about how your rocket runs Linux. As a huge fan of Linux, I do find this seriously cool.

And just to be clear, I have absolutely nothing against the Pi. The Pi is a killer piece of hardware, and as soon as they become regularly available I plan to purchase several of them. And I *do* plan to use them for rocketry applications, just not as a flight computer.

rockets4kids said:

It is entirely possible to construct small scale rockets (from scratch) as a scientific exercise. "small scale" and "not for profit" are in no way an implicit exclusion of rocket science.

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I concede this is true. I guess I was reacting to your previous statements. I also agree an Arduino or Pic or probably any number of other microcontrollers are easier/better choices for avionics. However, that doesn't diminish Troj's interest in the Pi. He has the skills and the interest and that's all that's needed for a hobby. I also am anxious to see what he comes up with.

Nerull said:

"Small, lightweight, low power requirements, and fewer components" is completely unrelated to "likelihood of failure".

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Why? It seems like a rather logical argument to me. This is an excellent example of the KISS principle. To me, using the Pi for any typical rocketry applications would be like replacing the plastic flap governer on a two stroke Briggs and Stratton with a PLC setup.