best autopilot for rocket

[bearcreek]

I recently finished converting my model rocket to radio control. Now I want to add an autopilot, so that it will automatically steer to a desired location. Are there any GPS's that are fast enough for this, or would I need a gyroscope and a faster update system like a radio homing beacon receiver or light wave receiver for direction finding?

[Tuner]

The Paparazzi autopilot is designed to work with anything.
All you have to do is reconfigure the Airborne code to suite your vehicle ,its the simplest piece of code to modify. I have heard stories of guys who are already familiar with the system setup a PPZ autopilot to drive a boat....

Scott

[tekrunner]

hey bearcreak,
Would you please care to elaborate on how you did this? A radio control rocket sounds really interesting. What's your setup?

Thanks,
tekrunner

[dmgoedde]

Hmmmm - I can't quote the laws or sources... but I think it is illegal to have ANY guidance system on a rocket like this. I am sure people will speak up on both sides.

[Mick Molloy]

Do you want to guide it whilst in the boost stage or after apogee, what rocket are you using?

[bearcreek]

I am running an Estes Big Bertha with an H motor. Capable of 7000 feet. Futaba 6EX radio and want to control it during boost (not apogee). Of course rockets are so fast they are difficult to control, but what if we use a fast servo and a fast autopilot?

[dmgoedde]

I am running an Estes Big Bertha with an H motor. Capable of 7000 feet. Futaba 6EX radio and want to control it during boost (not apogee). Of course rockets are so fast they are difficult to control, but what if we use a fast servo and a fast autopilot?I think it is not about having a fast autopilot (well, I am sure it is a requirement), but rather you need to not over control. My Atto system scales back attitude gains based on airspeed. In a rocket you have an extreme example of this! Possible legal issues aside, I have thought about this much in the past, and came to the conclusion that control throws would have to be very small and would become very small at high speeds.

[bearcreek]

True, I agree the control throw would need to be small. If the rocket travels at say 300 feet per second, then would say a 10hz gps have the accuracy and speed to adjust the trajectory accurately to within a few feet?

[Tuner]

The Paparazzi control loop can be run rather fast, greater than 250 cycles/second.

You can get gyros with a high Roll Rate 900deg/sec and accelerometers to handle high G levels.

The key is to calculate the range of G/forces and roll rates and ensure your sensors can handle it. Then you need an autopilot with control loop that can run fast enough.

You wont use the GPS as much as you would use the gyros and accelerometers. The GPS would just ensure it stays to the trajectory so it can be a slower 4hz update GPS.

I have seen other rockets use an Autopilot and some Balloons. FYI people get really funny when you mention you have an autopilot in an airplane, I would assume they would be a little freaked out you are putting one in a rocket. I sure hope you are involved with a club or some sort of institution so you dont look like a crazy guy.

Scott

[fnev]

I have to jump in here and… most probably get shot down.

I understand the technical challenges and the great excitement from tackling such a project.

I don’t think it wise to speak about it and/or exchange ideas in this particular matter on the Net. ANYBODY has access to this forum: please think twice.

On top of it if you are so smart to develop something of this magnitude, going public about doing something illegal is NOT.

[McLuvin]

Cool, please tell us more about how you did this. What on-board electonics are you using and how much does it weigh? Maybe we should change the name of this thread to "near-supersonic aircraft stabilizer" just to satisfy everyone during this era of political fear mongering.

[dag214]

I have to jump in here and… most probably get shot down.

I understand the technical challenges and the great excitement from tackling such a project.

I don’t think it wise to speak about it and/or exchange ideas in this particular matter on the Net. ANYBODY has access to this forum: please think twice.

On top of it if you are so smart to develop something of this magnitude, going public about doing something illegal is NOT.

Agreed,
This is not a topic for this kind of forum, and it is illegal (under the FAA guidelines with the AMA) to do this.

DAG

[airmcn_3]

You may want to try here. http://www.scalerockets.com/forum.html

[smh20502]

Regarding the law...7000'? You may need to get FAA approval above 2000', but I'd have to go back and look at the actual language.

Regarding a controlled rocket...you can't. It is against the law to launch a guided missile. A rocket is considered a missile in this case.

Now, if you simply had a guided gymble nose cone via two axis gyro..to keep the rocket strait in launch you might get away with it if caught. Now controlling a parachute for controlled decent...may be ok. Once a chute is deployed the divide may not be considered a rocket or missile.

But please don't do this on anywhere other than private property. A problem that with a guided rocked that becomes public can ruin the UAV regulations for the rest of us

[radiohound]

I agree we should not be posting instructions on how to make guided missiles ....

But I hate to see an aspiring rocket scientists' ingenuity stomped out of him. Besides Nasa and Grumman can't have all the fun.

So, just to stir things up a bit .....

There are some legal rockets that are guided, and built by civilians.

http://www.cnn.com/2004/TECH/space/06/21/suborbital.test/index.html

Not sure how much paperwork they had to file though. Also pretty sure they had a few smaller test flights that were also permitted by the FAA.

It would be pretty hard for them to not be guided. And I don't think they called it a missile.....

[uscimo]

Let me start by saying its not possible. The quality of sensors needed to control a solid-fuel powered craft are not available at that size nor, I assume, within your budget. Aside from legal requirements you must abide by, there are some significant technical challenges to overcome.

Don’t waste your time trying to control a solid-fuel powered craft during ascent, the control laws are far too complex:
http://www.mathworks.com/access/helpdesk/help/toolbox/aeroblks/f4-49446.html

I would start with developing a control mechanism for a parachute, then try controlling the descent to steer your craft to a desired location.

[radiohound]

Let me start by saying its not possible. The quality of sensors needed to control a solid-fuel powered craft are not available at that size nor, I assume, within your budget.

Yes, but he is talking about a 200 mph rocket. It is basically a really fast airplane, though not as fast as some rc jets, right? Only, he is trying to fly straight up. There is plenty for him to worry about, but he is really correcting on a 2 axis, not 3 dimensional. So a lot of that stuff on Matlab he can ignore.

I would say it's a difficult project, but doable.

[uscimo]

It all depends on how you define "desired location" if you are trying to get within 1m you are going to need some fast control laws. If your goal is within 50m then the task becomes much easier.