I could use just a little guidance

[kjhambrick]

Steve --

While I am sure Jim is too humble to toot his own horn, but check out these flights with programmed flight profiles:

Flight of the Infinity Squared

The Python Rocket Flight ( this is not the one I wanted to find but ... )

These are pretty amazing and they were performed with an older version of the VOS.

I may have the temporal order of the YouTube Videos reversed but reading and watching Jim's online stuff gives a great feel of how much work has gone into the VOS and how it has evolved ( as you well know from your experience with your VTS ).

-- kjh

p.s. Steve: I recall one of your flights either at Boulder Dry Lake or Lucerne ( those launches from the 1990's have long ago run together ) but I DO recall how impressive your system was / is !

 

[VTS SkunkWorks]

I would agree that your system adds to the safety of the hobby. It is good to see your system even used by others! Please keep the posts up to date as you progress!

 

[VTS SkunkWorks]

KJH
You have a good memory! Yes the infinity squared flight demonstrates the VOS capabilities very well.

 

[JimJarvis50]

I was able to do a VOS flight at AirFest this past weekend. The primary objectives were to test out some of the new system capabilities and to explore roll control gains. The flight wasn't all that aesthetic, but it does contain a ton of data. A link to the video is below.

The flight consisted of a Gorilla M-745 moonburner to a little over 11K. Not many of those motors around anymore!

One objective was to determine the time required to go vertical using smaller canards that I have used in prior flights. The rocket turned to a 12° angle, and then went to vertical from that point. The main result from that portion of the flight was that the correction took a little longer than I expected. I think it takes a bit more time to turn upward, against gravity, then it does to turn downward. This difference might be a little more evident with the smaller canards.

The second objective was to look at several aspects associated with roll control. We have the capability with the system now to change the roll angle setpoint as a function of time. We can also change any of the system gains. So, for this flight, there were six 60° changes in the roll angle. These were done with varying control gains so that we could look at the response times and compare with our models. With appropriate gain settings, the system can be operated at significantly higher roll gains than what I've used in the past.

Over the next few months, we will be doing some actual control modeling, perhaps trying some things that are much different from what we do now (e.g., a high-gain model). This will be quite interesting I think.

Jim

 

[waltr]

Nice video and a great flight.

 

[Hamid 'Smith' Salehi]

Nice video and a great flight.

Hey,
Which software did you use to tune the pid parameters? I want to do the same thing (canard-based active stabilizing) for a high power model rocket. but I have problem setting the pid parameters, what method or software do you suggest for this? (it travels supersonic so the software must consider and calculate parameters at supersonic speed)
I also asked my question here :
Here
I'm electronic Engineer and amateur Programmer too so I'm familiar with some principles to program it but still working on the issue that i mentioned

 

[JimJarvis50]

Back in Post 894 (February), I mentioned that I had distributed a second set of VOS units (making a total of 12 units at that point). Well, I have been able to sleigh the supply chain dragon one more time, and I have a third batch of units that are coming available in December. I'm able to make 7 units and a few of them are not yet spoken for. If you're an experienced rocketeer with an interest in canard-based orientation control, you can contact me for more information. In the meantime, a flyer is attached with information on the system.

Development has continued with the beta group and we should have several flights over the next few months. I mentioned this before, but the system now allows full gain scheduling for the gains used for yaw/pitch and roll control, as well as full orientation scheduling for tilt angle, bearing and roll angle through the flight. We're still trying to figure out how to best use these capabilities.

Otherwise, I have officially retired my VOS1 system (the system that was used on all of my early flights). VOS1, RIP. I have salvaged the servos and I plan to use them to produce a VOS unit capable of high altitude flight. For high altitude flights, it is helpful to be vertical for staging (since the allowable tilt is pretty low), and it is helpful to avoid roll that leads to coning (such as Kip has experienced on several of his flights). I have some titanium canardlets for it and it won't be too hard to assemble. Hard to say if it will every fly, but it's about the Journey.

Here's a link to the flyer:

Jim

 

[JimJarvis50]

I have almost finished building this year's batch of 7 VOS2 systems. Four are spoken for and three remain. If you have an interest in one of them, contact me.

Otherwise, Gordon Bain did his first VOS flight at our Hutto launch a few weeks ago. The purpose of the flight, with fixed fins, was to start a process to investigate how far the controls can be pushed before experiencing control reversal. The flight went quite well (video link below).

We had quite a launch. Based on a snap from Gordon's flight, I counted 70 cars, and I know more showed up after that. We had Cub Scouts, HS stem students, SLI and Spaceport teams, a TARC team, and even a few people who aren't students. One of our largest launches in quite a while.

Jim

Video link

 

[Rschub]

Jim, once you progress to the point of working on "idiot proofing" the VOS2 I would like to volunteer my services. My qualifications are impeccable.

 

[JimJarvis50]

Jim, once you progress to the point of working on "idiot proofing" the VOS2 I would like to volunteer my services. My qualifications are impeccable.

One of my flights. Unfortunately, idiot proofing is not possible.

Jim

 

[JimJarvis50]

I did another flight on the Test Rocket back on December 30. It went well, except that the main tangled (first time in a long time), and the hard landing caused the gps to reset. The purpose of the flight was to fly at an elevated tilt value (18°) at a higher speed (reaching Mach 1). The reason for flying at that tilt is so that you can land at a "safe" location, rather than leaving the landing location up to the rocket.

One of the more interesting aspects of the flight (for me, anyway) is that the rocket flew at a 45° roll angle instead of the intended 0° roll angle. The reason that this is interesting is that the rocket is programmed to fly in an "x" configuration for the canards. However, it appears that the rocket wants to instead fly in a "+" orienatation, even though the control system is trying to get things back to the "x" shape. So, the control system is fighting against the more stable rocket orientation, and the more stable orientation wins out. The flight video, linked below, shows some instability during the portion of the flight where the speed was the highest. It's possible that this was introduced by simply flying fast at an 18° tilt, but it's also possible that the rocket wasn't as stable as it might have been, and this contributed to the instability.

Brett Bachman flew his VOS system last week and had a similar result. In his flight, the rocket adopted a 4° tilt due to strong crosswinds. As it turned out, the direction of the wind caused his rocket to also be controled in the "x" configuration. His rocket also turned 45° to the "+" configuration, and exihibited a small amount of instability. So, I think an interesting test will be to orient our rockets so that they will fly in the "+" orientation (due to either intended tilt or wind angle of attack), and then see if we get better control at the 0° roll angle with less instability.

As long as I'm posting, there are still a few VOS2 systems available for experienced rocketeers. Contact me if you'd like more information. Also, we are working on VOS designs that would be applicable to 6 - 10" rockets. That should be fun!

Jim

 

[JimJarvis50]

Looks like it's been a couple of months since I last posted. I can only say that there's been a lot going on during that time. One thing I did was to conduct another flight. This was just a fun flight to see how close I could get to a predicted apogee location and then a predicted landing location. The flight was conducted at a 10° tilt using a CTI L1350. The flight went close to 10K and just above Mach 1. One thing I did during this flight was to reduce the yaw/pitch gain a little during the highest speed portion of the flight. That seemed to eliminate the instability observed during the previous flight. There a video of the flight below.

I'm currently prepping for another two stage flight, along the lines of the Infinity and Python flights. This one will be an AT K1275 to a CTI L395. I'm not sure about the flight profile yet, but it is just a matter of how exciting I want things to get. I might fly it this coming weekend, but the wind doesn't look very good. Sigh....

I've also spent time working with Tom Fetter on understanding roll control, and more recently, yaw/pitch control. If I really focus and study, I'm able to understand about 5% of what he says. But that 5% is really interesting. If you have a chance to view his NARCON presentations from this year, they are quite interesting. In our analysis of flight data, one objective is to try and understand how the rocket behaves with both a spin can versus fixed fins. In one flight that we are looking at, where the canards and fixed fins were aligned, the results suggest that the effective gain of the canards is reduced by almost an order of magnitude. The rocket doesn't go into control reversal, but it is strongly affected.

In other news, this year's batch of VOS units has been distributed. It's possible that another batch might appear later this year. We'll see ...

Jim

 

[robopup]

One thing I did during this flight was to reduce the yaw/pitch gain a little during the highest speed portion of the flight. That seemed to eliminate the instability observed during the previous flight.

Great flight! I've been noodling on my own system. One item I want to look into if I get something up and running is to apply control inputs on the canards using a calculated force rather than a gains directly on angle errors. Something along the lines of:

• before flight:
  • rough calc of moment of inertia
  • decide on a reasonable response time (ie I want to pass through vertical again, starting at a 7deg angle in 1s, or whatever)
  • rough approximation of my canard cl-alpha curve. Probably just a single slope
• during flight, in each loop:
  • use above, along with current rocket velocity, orientation, to determine angle I need to apply on each canard to achieve some desired output canard force

Apologies if you already talked about something like this - I've skimmed the whole thread but haven't carefully read every post yet.

Thanks for all the awesome material!

 

[JimJarvis50]

Great flight! I've been noodling on my own system. One item I want to look into if I get something up and running is to apply control inputs on the canards using a calculated force rather than a gains directly on angle errors. Something along the lines of:

• before flight:
  • rough calc of moment of inertia
  • decide on a reasonable response time (ie I want to pass through vertical again, starting at a 7deg angle in 1s, or whatever)
  • rough approximation of my canard cl-alpha curve. Probably just a single slope
• during flight, in each loop:
  • use above, along with current rocket velocity, orientation, to determine angle I need to apply on each canard to achieve some desired output canard force

Apologies if you already talked about something like this - I've skimmed the whole thread but haven't carefully read every post yet.

Thanks for all the awesome material!

Robopup,

I'm not exactly sure about how to implement your concept, but a couple of comments.

Although you can calculate the lift for the canards, that is only one of several components that determine how fast a rocket will turn. I think you would find that basing a control strategy only on the lift from the canards would result in changes in orientation that don't match your predictions. You would likely need some empirical adjustments.

Although the control logic that I use is based on an angle error, the gain of the response can be adjusted. This is along the lines of what you are proposing (to calculate the force needed for the response that you want and adjust to what is appropriate).

I think there is enough forgiveness in the yaw/pitch response to allow a variety of approaches. That is, things change rather slowly, so you don't have to be perfect. The idea is just not to go too far with your corrections.

Jim

 

[JimJarvis50]

As I mentioned above, I've been working with Tom Fetter to model the flights of the Test Rocket. There is both a roll control model and a pitch control model. Both include a complete aerodynamic model of the fins and canards, along with a model that mimics the actual control scheme used in the rocket, including the servos. What Tom has done with these models is remarkable in my opinion. My job is just to get flight data that is good enough so that the data can be compared to the model.

With respect to the roll control model, the primary result to date is that we can detect the interference between the canards and the fixed fins. Sometimes a rocket with fixed fins will experience roll control reversal, but even if that doesn't happen, we can see that the effectiveness of the canards for roll control is significantly reduced relative to what it should be (or relative to what it is with a spin can). It's hard to know that this is happening unless there is a model to compare against.

The roll control model is relatively simple. The pitch control model is not. We have some comparisons between modeled and actual flight data that are interesting. I'll include data from a couple of flights here, but we have a few more. The data from the first flight includes a comparison of the change in the pitch (tilt) and the lateral acceleration. The flight included a tilt to nominally 15° followed by a turn to vertical, followed by a turn to 10°. The last turn was to position the rocket for a closer return to the pad. I think the agreement between the model and the flight data is amazing. I think it's also important to say that the model isn't being "tweeked" to fit the data, other than to match the simulated velocity profile through the flight. That is, no contants are being adjusted so that the model fits the data - it either fits or it doesn't.

Jim

 

[JimJarvis50]

Here's another comparison between flight data and Tom's model. This flight consisted of a 20° tilt in one direction followed by a 40° turn to a 20° tilt in the opposite direction. The rocket didn't quite get to the predicted 20° tilt in the opposite direction, probably because the actual velocity was slower than predicted (due to drag induced by the turns), but the agreement is still pretty good.

The model inputs are basically just the typical inputs you would use for a simulation. Things like weight of the rocket, size of the fins/canards, stability margin, etc. This means that any rocket can be simulated in this manner, not just the Test Rocket. That means systems for rockets that aren't the test rocket can be based on actual information and not just a "best guess".

Jim

 

[JimJarvis50]

I did another VOS flight at the Texas Shootout over the weekend. Great weather (sort of a relative thing in Texas). This was just a fun flight - L1720 to K270 - to around 11K feet. The flight profile consisted of turning the rocket to a 15° tilt after staging, and then changing the bearing of the rocket by 120° while at the 15° tilt (this change in bearing is "the curl"). One objective of the flight was to make a nice smooth turn. There are various strategies for doing this, but for this flight, I decided to make a large number of small changes in the orientation schedule. There are a total of 60 changes in either tilt, bearing or control gains, many at 0.1-second intervals. I think it worked quite well.

Jim

 

[Finicky]

I did another VOS flight at the Texas Shootout over the weekend. Great weather (sort of a relative thing in Texas). This was just a fun flight - L1720 to K270 - to around 11K feet. The flight profile consisted of turning the rocket to a 15° tilt after staging, and then changing the bearing of the rocket by 120° while at the 15° tilt (this change in bearing is "the curl"). One objective of the flight was to make a nice smooth turn. There are various strategies for doing this, but for this flight, I decided to make a large number of small changes in the orientation schedule. There are a total of 60 changes in either tilt, bearing or control gains, many at 0.1-second intervals. I think it worked quite well.

Jim

Awesome !!! You win the sky artist award !

 

[FredA]

BRILLIANT

 

[kjhambrick]

I did another VOS flight at the Texas Shootout over the weekend. Great weather (sort of a relative thing in Texas). This was just a fun flight - L1720 to K270 - to around 11K feet. The flight profile consisted of turning the rocket to a 15° tilt after staging, and then changing the bearing of the rocket by 120° while at the 15° tilt (this change in bearing is "the curl"). One objective of the flight was to make a nice smooth turn. There are various strategies for doing this, but for this flight, I decided to make a large number of small changes in the orientation schedule. There are a total of 60 changes in either tilt, bearing or control gains, many at 0.1-second intervals. I think it worked quite well.

Beautiful, Jim !

I was taking a long cross-country hike when you launched your VOS. I believe I heard your L1720 -to- K270 motors, but I never saw it from my PoV.

Thanks for the video and thanks for the bird's eye view of "my" mesquite tree and the lake I drifted over near the intersection of FM 2395 and CR 445

-- kjh

 

[JimJarvis50]

Beautiful, Jim !

I was taking a long cross-country hike when you launched your VOS. I believe I heard your L1720 -to- K270 motors, but I never saw it from my PoV.

Thanks for the video and thanks for the bird's eye view of "my" mesquite tree and the lake I drifted over near the intersection of FM 2395 and CR 445

-- kjh

Thanks guys.

Konrad, I'm happy to provide flyover data of trees and ponds; I just don't want to land in them. Speaking of which, my recovery prediction is attached. This is a little after-the-fact, but using the wind data estimates from the night before the launch. Looks like I missed by about 500 feet, mainly because I missed the apogee location by about that much. The wind predictions on Sunday were very accurate. I figured I would land reasonably close to a point where I had driven to previously.

Jim