I could use just a little guidance

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Now that I see the size of those controlling fins, I'd be worried that if they are ever used when they are not the farthest aft fins, you might get control reversal. I think Armadillo Aerospace ran into that problem when they tried canards?

Basically, you may have to disable them until the stage behind them has separated.

In that vein, I'd imagine that they'd be best behind the second stage, so that they can right the stack before the second stage really gets it going.

I've been made aware of that problem. It would surprise me that the action could take place over the full length of the booster, but that may represent one more reason to disable the canards on the boost (and until after separation).

The current stack simulation (up to the point where the 2nd stage would light), suggests the velocity would fall below transonic at about 7 seconds into the flight. Might be good to let that happen too. I typically let the speed drop to around 750 ft/s before lighting the next motor. With guidance, perhaps 500 ft/s? Looks like this would be around 17 seconds. So, the profile could be a 7 second delay with 10 seconds of guided coast.

Jim

Sim of Stack.png
 
I haven't posted much just recently, but I have been making a lot of progress. One thing I've done is roll a new airframe section. Part of this will be the container for the stabilization unit in the "lower" position (i.e., when used below the second stage on my three-stager). This is what I actually hope to fly at Balls.

I also got in the fiberglass for my test rocket. The fins are currently large, since I'm not sure where the Cp/Cg will fall when everything is done. I'll reduce the semi-span at some point. The fins will get a layer or two of carbon.

Progress is also being made on my behalf on the UDB5/OpenLog boards that will be used in the short term for data acquisition. The graph is an example file of acquired PWM signals. The system will acquire the Guardian PWM signals, the gyro and accelerometer data and calculated xyz position data. This can all be analyzed to determine if the Guardian is doing what it is supposed to be doing during the flight.

Jim

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PWM Pic.jpg

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A two-stage sustainer might glide for quite a while in the attached configuration.

Jim

Glide? I once saw a single stage DD rocket with large aft fins "glide" down after apogee deployment. The rocket glided down aft end first with the trailing upper bay on the end of the shockcord in a very large, wide flat spiral. It would pick up speed descending and then climb a bit, slowing down but never stalling out. It would just begin to dip the tail and start the wide spiral descent again. The main chute was in perfect position as it blew out from a trailing slot when it hit the main chute deployment altitude. The whole assembly then just swung down like a pendulum in a very "non-stressed" fashion. Darnedest recovery I've ever seen outside of the chute hanging, Hail Mary, last minute deployment-just-before-she-hits routines. Kurt
 
Another on the "TO DO" list, make "steering" canards to bring it back "home"

Now THAT would be cool!

steering.png

Scott
 
Great project Jim!! 1st time looking at this thread!! You don't mess around!!
I envision pulsating jets instead of canards for the end project!!
Please, keep documenting!!
Terry
 
The approval process should go well this year. Hey Mark, it's the three-stager again. I know, drive until the flight line becomes an elevated mirage and then set up the pad. But this year, no apogee events - all the parts are just gonna glide home using pulsating jets!

I suspect Mark would apply just a little guidance.

Jim
 
The approval process should go well this year. Hey Mark, it's the three-stager again. I know, drive until the flight line becomes an elevated mirage and then set up the pad. But this year, no apogee events - all the parts are just gonna glide home using pulsating jets!

I suspect Mark would apply just a little guidance.

Jim

I saw a video a while back where a guy was attempting to to use 4 valves and some type of compressed air instead of canards for active stabilization. One of the 4 valves around the diameter of the rocket would open and pulsate thrust off the side of the rocket to push it back vertical, if it went too far another valve would open and push it back. Pretty much the same concept as yours only 4 little valves and a tank instead of servos. And no little canards hanging off the side of the rocket. One of many problems with this would be av-bay space for a tank. Cant find the video now, Oh well
 
I saw a video a while back where a guy was attempting to to use 4 valves and some type of compressed air instead of canards for active stabilization. One of the 4 valves around the diameter of the rocket would open and pulsate thrust off the side of the rocket to push it back vertical, if it went too far another valve would open and push it back. Pretty much the same concept as yours only 4 little valves and a tank instead of servos. And no little canards hanging off the side of the rocket. One of many problems with this would be av-bay space for a tank. Cant find the video now, Oh well
Lurker here, By any chance was it this [https://hackaday.com/2011/01/18/attitude-control-for-a-really-big-rocket/]
 
Fins don't run out of compressed air, unless you go really high...

On a serious note, have you considered a way to deactivate the mechanism after it's done its job? There will be a lot of unnecessary fin waggling during recovery; much of it would be full deflection too.

N
 
Fins don't run out of compressed air, unless you go really high...

On a serious note, have you considered a way to deactivate the mechanism after it's done its job? There will be a lot of unnecessary fin waggling during recovery; much of it would be full deflection too.

N

I can turn on and off using the associated Raven. Anything that can be programmed with the Raven can be done. I think the strategy won't be known until I get actual data on how the Guardian performs. As it stands, the stabilization part would recover upside down, so full deflection during the recovery. But, full deflection is likely less than 10 degrees.

Jim
 

Yes, thats it. Thanks, The link didn't bring me directly to the picture. I searched "big rocket" in the Hackaday site and it popped right up.

Fins don't run out of compressed air, unless you go really high...

On a serious note, have you considered a way to deactivate the mechanism after it's done its job? There will be a lot of unnecessary fin waggling during recovery; much of it would be full deflection too.

N
https://hackaday.com/2011/01/18/attitude-control-for-a-really-big-rocket/#more-33091 is the direct link.

Cold gas thrusters are horribly inefficient and heavy. https://www.catalinacylinders.com/wp-content/uploads/2015/02/ScubaSpec.8-30-12color.pdf lists 3000 psi cylinders and the S6 tank is close to the size in the photo. The empty tank weights about 1.2 kg and would contain ~0.21 kg of N2. With a 70 psia regulated supply pressure, the specific impulse at sea level would be ~50 seconds and in vacuum ~100 seconds in a perfect isentropic nozzle expansion. Using a simple valve as shown in the video would probably provide not more than 50% of the theoretical value. If the gas delivery system could supply 28 grams per second of flow the thrust would most likely be 0.028 kg/s x 50 seconds x 9.81 m/s/s ~ 14 N at altitude and about half of that at sea level. You would have about 7.5 seconds of burn time and a total impulse of ~100 Ns, and it would be hard to build this system using less than 3 kg of mass in an e-bay compartment that is 18" long. Fast responding valve to minimize gas flow run about $200 per valve and you need 4. The gas cylinder is ~$150 and a small regulator would be ~$150.

Contrast that to a canard system with 4 servos, a Guardian, batteries and fins. A crude servo system would weigh less than 1 kg, and could probably weight as little as 0.5 kg with COTS RC parts if CF over foam fins were employed. This could fit in a 4:-6" e-bay depending on how much effort you want to allocate for packaging. And you don't have to worry about fuel consumption.....

Bob
 
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Progress is being made on the test rocket. I have now completed the application of the tip-to-tip carbon. Nothing fancy here (no bagging for example), as I'm just trying to produce a functioning rocket and not a high performance one. The initial test rocket configuration will be with forward canards. Later on, I'll try the rear canard approach. With luck, I will try the initial flight testing in 2 weeks at our March AARG launch.

Sometime next week, I will receive the UDB5/OpenLog boards. The boards, along with some custom programming, are being provided by the developer, Bill Premerlani. Anyone familiar with the UDB board (aka, the UAV Development board), or do-it-yourself autopilots or Direction Cosine Matrix IMU will know all about Bill. I am very fortunate.

I'm not quite sure what I'm going to get from Bill yet, but I suspect it will perform the same guidance function as the Guardian but will avoid a few pitfalls. I plan to fly the Guardian to collect some comparative data, but it would not surprise me if my use of it is short-lived. I am really looking forward to learning how this board works and making more use of it's capabilities.

Jim

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Sometime next week, I will receive the UDB5/OpenLog boards. The boards, along with some custom programming, are being provided by the developer, Bill Premerlani. Anyone familiar with the UDB board (aka, the UAV Development board), or do-it-yourself autopilots or Direction Cosine Matrix IMU will know all about Bill. I am very fortunate.

Interesting. I did not know of him or those particular boards (only in the generic sense).

I have recently been checking out another kind of R/C autopilot. The NAZE 32 boards, developed from MultiWii, which uses "Baseflight" firmware. The NAZE 32 is more oriented towards multicopters, but has options for controlling servos for airplane type aerodynamic surfaces. So it should work at least as well for vertical rocket guidance as well as the Guardian does, once set up.

What you are doing is probably better for your needs, and you have a "guru" working with you, which is a HUGE plus. The NAZE 32 has a couple of things going for it for some special projects I want to try out. Not sure if it can do what I want but worth trying.

I still think think the Guardian is best in general for hobby rocket vertical guidance, due to simple off the shelf "Plug and Play". But for specialized projects like yours, and what I am looking for in a different way, these more complex boards offer some more capability if they can be figured out and set up right.

By the time I get done I will be highly tempted to use a spare NAZE 32 board to make up my own R/C multicopter to fly for fun. :)

- George Gassaway
 
What you are doing is probably better for your needs, and you have a "guru" working with you, which is a HUGE plus.

Likely bigger than just huge.

The obvious advantage of the UDB5 approach is that you can program it to do whatever you want (assuming you know how). Bill worked with Frank Hermes to develop the tiltometer (Frank is contributing to the project as well), and one of the things they did was to turn off the accelerometers at launch. The gyros drift but don't get spoofed. The Guardian can't be modified in this way.

With respect to off-the-shelf, I would expect that whatever gets developed through our collaboration will be available in some manner to anyone who wants it. And, the developer will answer your questions whereas EagleTree won't.

Jim
 
Progress is being made on the test rocket. I have now completed the application of the tip-to-tip carbon. Nothing fancy here (no bagging for example), as I'm just trying to produce a functioning rocket and not a high performance one.

Jim

Tip-to-tip carbon for a "functional rocket", I'm pretty sure your on a whole different playing field than most of us :)
 
Tip-to-tip carbon for a "functional rocket", I'm pretty sure your on a whole different playing field than most of us :)

Well, I need to take the rocket to around Mach 1. With the large fins, I needed to do something to keep them attached and to prevent flutter. The tip-to-tip carbon solves both problems.

There are several fliers in my home club that have taken this approach (it's possible I may have influenced them). I would suggest this as the optimum approach for many rockets, but I left my soap box over on another thread.

Jim
 
I have recently been checking out another kind of R/C autopilot. The NAZE 32 boards, developed from MultiWii, which uses "Baseflight" firmware.
- George Gassaway

George, that looks like an interesting system. Great software and very flexible, best as I can tell.

Meanwhile, the test rocket construction is mostly done. Just needs shear pins and the recovery system installed, and final work on the stabilization system. The rocket came in at a bit under 20 pounds, and with weights known, I got the rocket modeled in RockSim and then trimmed the fins. It's still quite over-stable.

On the stabilization system, I still need to get my UDB5 board and get it installed. It's hung up in Dallas at the moment due to the weather, but the cold weather there should end after today. If I get it early next week, I should be able to do the initial test flight next weekend. I also need to trim the canards a bit, based on feedback I'm getting from others that have tried this.

First flight will be a CTI K-780 to around 5K. The main objectives are to collect comparative data for the two IMU systems (the guardian and the UDB5) along with gps for the flight path, and to check out the mechanical aspects of the canards. I probably won't be able to resist turning on the canards at least towards the end of the flight.

Jim

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George, that looks like an interesting system. Great software and very flexible, best as I can tell.

Meanwhile, the test rocket construction is mostly done. Just needs shear pins and the recovery system installed, and final work on the stabilization system. The rocket came in at a bit under 20 pounds, and with weights known, I got the rocket modeled in RockSim and then trimmed the fins. It's still quite over-stable.

On the stabilization system, I still need to get my UDB5 board and get it installed. It's hung up in Dallas at the moment due to the weather, but the cold weather there should end after today. If I get it early next week, I should be able to do the initial test flight next weekend. I also need to trim the canards a bit, based on feedback I'm getting from others that have tried this.

First flight will be a CTI K-780 to around 5K. The main objectives are to collect comparative data for the two IMU systems (the guardian and the UDB5) along with gps for the flight path, and to check out the mechanical aspects of the canards. I probably won't be able to resist turning on the canards at least towards the end of the flight.

Jim

Jim, is that table covered with glass for protection? If I photographed a rocket on a nice wood table "without protection" my wife would probably kick me out of the bedroom. Its what I get for marrying a "Mrs. Clean".:tongue: Kurt
 
Jim, is that table covered with glass for protection? If I photographed a rocket on a nice wood table "without protection" my wife would probably kick me out of the bedroom. Its what I get for marrying a "Mrs. Clean".:tongue: Kurt

It's glass, but if I scratch it, my wife will kick me out of the kitchen!

Jim
 
I was able to do a first test of the vertically stabilized rocket today. I didn't get all of the data I was hoping for, but it's a start. I turned on the stabilization system about 5 seconds into the flight, and from the gps path, you can see where this happened (in both the trajectory and the gps ground path). The rocket went very straight after that, but was not quite vertical (the angle averaged about 8 degrees). Still looking at the data.

I decided to let the UDB5 do the guidance and didn't include the Guardian on the flight. The UDB5 will soon be programmed (as a next step) to provide proportional control on both tilt axes and rate control (not orientation control) on roll using all four canards. The Guardian can't do this, and I think it's out of the picture going forward. The good news is that whatever is developed from this should be far better than the Guardian and will be available to anyone ($80 for the board, and you don't need an RC radio).

This flight was on a K780 and the next try will be an L1000 (one of the Aerotech single-use motors).

Jim

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The data looks great! It looks like the system did exactly what it is programmed to do.

Unless you use more feedback than just accelerometers and gyros the system only has enough data to keep the rocket at some angle with reference to gravity. This is not enough feedback information to correct the flight path to make it straight up, unless of course it is a zero wind condition, which is not going to happen. To make a straight up flight path in non zero wind the system would need to fly at some non zero AOA.


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The data looks great! It looks like the system did exactly what it is programmed to do.

Unless you use more feedback than just accelerometers and gyros the system only has enough data to keep the rocket at some angle with reference to gravity. This is not enough feedback information to correct the flight path to make it straight up, unless of course it is a zero wind condition, which is not going to happen. To make a straight up flight path in non zero wind the system would need to fly at some non zero AOA.


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I'm a bit confused? If the rocket is vertical with some wind, is there not an AOA in that condition (along with a horizontal component to the flight path)? A vertical flight path would be a higher AOA?

Your question got me thinking about my three-stage strategy of putting stabilization under the second stage motor. I had thought that having the stabilization would allow a lower speed at second stage ignition. But, when stabilization stops and the motor lights, the rocket will weathercock into whatever wind there is, depending on the relative velocities, defeating the purpose of stabilization. I don't think I can let it slow down all that much.

Jim
 
Your question got me thinking about my three-stage strategy of putting stabilization under the second stage motor. I had thought that having the stabilization would allow a lower speed at second stage ignition. But, when stabilization stops and the motor lights, the rocket will weathercock into whatever wind there is, depending on the relative velocities, defeating the purpose of stabilization. I don't think I can let it slow down all that much.

Just because the rocket is pointed straight up does not mean that its velocity is in that direction.

In any case, vertical might not be the direction you want to go. Based on preflight simulations using the measured wind profile you would set a launcher azimuth and elevation to achieve the desired landing location. The guidance system would then maintain the angle set on the launcher.
 
I'm a bit confused? If the rocket is vertical with some wind, is there not an AOA in that condition (along with a horizontal component to the flight path)? A vertical flight path would be a higher AOA?

Your question got me thinking about my three-stage strategy of putting stabilization under the second stage motor. I had thought that having the stabilization would allow a lower speed at second stage ignition. But, when stabilization stops and the motor lights, the rocket will weathercock into whatever wind there is, depending on the relative velocities, defeating the purpose of stabilization. I don't think I can let it slow down all that much.

Jim

The fact that your absolutely vertical at second stage ignition is worth a lot. The question will be the wind conditions at which all of this takes place. Trying to stay straight up in some wind via a stabilization system will burn some vertical energy as will traveling with some large horizontal component. Regardless your second stage insertion point is vertical which is the best case scenario for that transition, although you have moved down range a bit. At what altitude do you think second stage ignition will occur and what is the expected wind profile up to your final stage insertion point and apogee? Seems like proper timing of your current stabilization system will easily add altitude to your apogee. Not to mention if your other stages weathercock it will be going the opposite direction down range as your initial drift direction under stabilization control.


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The fact that your absolutely vertical at second stage ignition is worth a lot. The question will be the wind conditions at which all of this takes place. Trying to stay straight up in some wind via a stabilization system will burn some vertical energy as will traveling with some large horizontal component. Regardless your second stage insertion point is vertical which is the best case scenario for that transition, although you have moved down range a bit. At what altitude do you think second stage ignition will occur and what is the expected wind profile up to your final stage insertion point and apogee? Seems like proper timing of your current stabilization system will easily add altitude to your apogee. Not to mention if your other stages weathercock it will be going the opposite direction down range as your initial drift direction under stabilization control.


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The second stage should light somewhere around 12K and the third stage around 50K. Assuming I don't slow down too much before lighting the second stage, any weathercocking at 12K feet should not be more than a few degrees (say, 40 ft/s cross wind and 600-700 ft/s ignition velocity). That would be OK. The horizontal movement up to that point would be rather small.

Jim
 
The second stage should light somewhere around 12K and the third stage around 50K. Assuming I don't slow down too much before lighting the second stage, any weathercocking at 12K feet should not be more than a few degrees (say, 40 ft/s cross wind and 600-700 ft/s ignition velocity). That would be OK. The horizontal movement up to that point would be rather small.

Jim

I agree with all of the above, I think it will work well. What will be your delay between dropping the first stage(with stabalization) and igniting the second stage?


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