I could use just a little guidance

[BryRocket]

Last September, I tried the "Python" two-stage flight at Airfest. It didn't go well, with the motor finally coming up to pressure just after all of the chutes blew. It was not a good flight, but I repaired everything and finally got a chance to repeat the flight over the weekend. It went pretty well, except that part of the flight was not visible due to a cloud, and I also didn't get all of the planned video. Still trying to figure out what happened there. Anyway, copied below are two YouTube video links. One is of the entire flight and the other is a zoomed-in version where it's a bit easier to see what the rocket was doing.

I posted some data in the first video showing how the rocket generally followed the flight plan with respect to tilt and bearing. Not perfect, but not too bad.

One thing you can see in the videos is that the rocket motion wasn't all that smooth, particularly when the rocket was turning upward against gravity. I think part of the reason for that is that I allowed more time for those turns due to uncertainty in the turning rate when turning upward. I think I allowed too much time. Since each turn is a discrete step, having too long of a step makes the turn look less "continuous". The other thing that I noticed in the data was that the canards never reached the limit of their travel range. I have them set up to turn proportionally up to 7.5° for angle errors up to 7.5°. The steps in the flight program were at 4° increments, and the canard angles never exceeded 4°. That means that the rocket never "fell behind" the flight program. I was concerned that it might fall behind in the upward turns, but that didn't happen (and in fact, the opposite happened).

I managed to break a fin on the spin can again - crap. I suspect I will fix it at some point, but it may be a while before that happens. In the meantime, there should be some beta group flights coming up over the next few months!

Jim

Fantastic.

 

[JimJarvis50]

It's been a while since I posted information on the vertical orientation system beta testing. Recall that back in April, I produced six control systems (with spin cans), and six beta testers started their adventure in vertical orientation system rocketry. A few weeks ago, Paul Snow did a nice flight with his system, flying on an L1050 to 7,100 feet. Unfortunately, he didn't get on-board video, but the flight data from the system (and from an RTOM3 also on board) showed that the flight was very nearly vertical (see the graph below). In addition to the flight, Paul has really helped to improve the system documentation.

I am expecting that most of the other beta testers will do their first flights either later this year or early next year. I was hoping that this process would go a little faster, but the group has opted to build new rockets around the system rather than incorporating the system into an existing rocket. It just takes more time to do this.

I had anticpiated producing additional systems over the summer but just didn't have the time to do it. Now that my peak flying season is over, I have been busy producing six additional VOS2 systems. Given the number of flights so far, I guess it is fair to say that what I want to do is to expand the number of beta testers. There are a few of these systems that haven't been spoken for yet, so if you're interested in participating, just let me know. The system is intended for experienced L2 and L3 flyers, but there is plenty of support available from the group.

Jim

 

[JimJarvis50]

I found a video of Paul's flight. Actually, flights. My first view of the rocket and the flight!

Jim

 

[James Duffy]

Cool video!

BTW, "The Jim Jarvis Canards" would be a terrible band name.

James

 

[Joshua Smith]

Cool video!

BTW, "The Jim Jarvis Canards" would be a terrible band name.

James

Surely it would be "The Janards" LOL

 

[JimJarvis50]

Cool video!

BTW, "The Jim Jarvis Canards" would be a terrible band name.

James

Should have been JJ and the Canards.

But the last month for me has been about spin cans. On the "Python" flight, I managed to knock off a fin. So, I had to remove the tip to tip carbon on either side of that fin, reattach the fin and then redo the tip to tip. I also replaced the fin tips to add 1" of span in preparation for my next flight. Hopefully, that will be in January.

In addition, I made four new spin cans for the next round of control systems (6 control systems and 4 spin cans). The spin cans have billions of fiberglass tube sections, some of which need to be exactly square. I also roll a nice stiff 7-wrap carbon fiber tube that the fins actually get attached to. Then, everything gets glued together and populated with ball bearings. This batch works quite well.

Jim

 

[reddrock]

To be clear, I programmed one servo incorrectly in the first flight, which is why it had so many wobbles and turns. That was not a fair test of the VOS2 system. I also had an error in my RockSim stability model, which I corrected for the second flight. The second flight included some nose weight and the canards are about 75% the area of the canards in the first flight. That one went much straighter. The servo gains were the same in both flights.

Kudos to Derek Honkawa for the videos at FAR.

I can attest to the high quality of Jim's 7 wrap CF tubes. The secret is revealed in the photo. In the foreground you can see the CF fabric attached to a motor case, which applies tension evenly to the fabric while rolling the tube.

 

[JimJarvis50]

To be clear, I programmed one servo incorrectly in the first flight, which is why it had so many wobbles and turns. That was not a fair test of the VOS2 system. I also had an error in my RockSim stability model, which I corrected for the second flight. The second flight included some nose weight and the canards are about 75% the area of the canards in the first flight. That one went much straighter. The servo gains were the same in both flights.

Kudos to Derek Honkawa for the videos at FAR.

I can attest to the high quality of Jim's 7 wrap CF tubes. The secret is revealed in the photo. In the foreground you can see the CF fabric attached to a motor case, which applies tension evenly to the fabric while rolling the tube.

Paul,

Very glad to see a good flight. I can't wait for the next one!

Yes, applying a little tension really improves the quality of the tubes. I actually had another J motor inside that motor tube. But too much weight doesn't help. I got a little carried away on a tube once, and the cloth "un-sprung" when the tension was removed. Not so good. I get about 40% epoxy with this approach. I think that's pretty good for a hand layup, but others might know better.

Jim

 

[TheAviator]

Paul,

Very glad to see a good flight. I can't wait for the next one!

Yes, applying a little tension really improves the quality of the tubes. I actually had another J motor inside that motor tube. But too much weight doesn't help. I got a little carried away on a tube once, and the cloth "un-sprung" when the tension was removed. Not so good. I get about 40% epoxy with this approach. I think that's pretty good for a hand layup, but others might know better.

Jim

40% is incredible. I shoot for 50% and am happy with anything better than that.

 

[JimJarvis50]

40% is incredible. I shoot for 50% and am happy with anything better than that.

I haven't found a technique that works any better than this for multi-wrap tubes.

Now that the spin cans are done, it's time to turn the table full of parts into 6 vertical orientation systems. I have already completed two of the three required wiring harnesses, along with the airframe sections, so once the third harness is complete, it will just be a matter of assembling the systems from the bottom up.

Back in April, I made a video showing how to assemble the system. That way, the users would have a way of getting things back together again in the event that they needed to take their system apart. When we put together BryRocket's system over the summer, the video made the process a lot easier. I suspect I'll be watching that video again shortly!

Jim

 

[JimJarvis50]

Well, it took a month, but that pile of parts and pieces above has been converted into six vertical orientation systems. The third from the left is mine, but a few of the remainder are available to experienced rocketeers. Assuming there is interest, I plan to make a third set of units sometime next year, but that will be it.

Jim

 

[FredA]

IMPRESSIVE!
What do you think the mach limit is on one of these units?
I could use one if they can withstand M4.
What is the presumption on altitude as I assume that changes the gain. Or does that get accounted for somewhere?

 

[JimJarvis50]

IMPRESSIVE!
What do you think the mach limit is on one of these units?
I could use one if they can withstand M4.
What is the presumption on altitude as I assume that changes the gain. Or does that get accounted for somewhere?

Hi Fred,

Yes, I think this could be used at Mach 4, but some changes would be needed. The attached picture can help illustrate how this might work.

In the design, the 1" servo hub is located inside of a bearing mounted on the control unit (Picture 1). The bearing is what protects the servo from lateral forces. Then, a hub spacer is inserted and also sits within the bearing (Picture 2), and then the canard G10 base plate is attached with screws through the hub spacer into the servo hub (Picture 3). The hub spacer has to be long enough so that there is a gap between the canard base and the air frame.

The stock canards have a root cord of nominally 2" are suitable for speeds up to around 750 ft/s, plus or minus. At higher speeds, the canard size is reduced to achieve the correct control authority. At some point, the root cord can be reduced to 1" or less. At that point, the hub spacer length can be reduced such that the canard base (now a 1" disk) is flush with the air frame and only a postage-stamp-sized canard sticks out into the air flow. This would be much more aerodynamic than what is possible with larger canards, and this is one of the things that would make the use of the system at high speeds possible. My guess is that a 1" root cord, with a variable span length, could be used above around Mach 1.5. In theory, this approach could be continued to Mach 4, where the canard might look like a flat screwdriver tip extending perhaps a half inch into the air flow. I suspect that G10 wouldn't work at that speed, so it might be necessary to fabricate a piece from metal that is the combination of the hub spacer and the small canard. I believe all of this would work mechanically, but I don't really have much feel for how this would work aerodynamically. I would just comment that for vertical flight, mild control actions are fine (versus my pattern flights with much more aggressive control action). Mild control actions with small canards is how you would avoid things getting too twichy at high speed, and that's all you need for vertical flight.

I think for Mach 4 that it would also be necessary to replace the fiberglass tube with a carbon or metal tube. I could roll one if all else failed. One thing that I can't really comment on is the effect of really high acceleration on gyro drift. I haven't observed obvious drift at accelerations of 20G's, but I haven't gone near Mach 4 either.

Regarding changes in gain, this is something I've always thought about doing. However, I have come to believe that the best strategy is to design around a moderate servo deflection and then size the canards for the maximum speed. I use a deflection of 7.5° when the tilt reaches 7.5° and above. This is enough of an angle change so that the servos operate with good resolution, but not so much that would make the canards stall. With this approach, there is no point reducing the gain because the sizing was done at the maximum speed. In most of my flights, once the rocket is vertical, it stays that way to apogee even though the control authority of the canards is dropping to zero. Most of my flights backslide.

Fred, as an original beta tester, I know you're interested in this topic. Get in touch if you'd like to pursue this.

Jim

 

[JimJarvis50]

For those interested, I did a TRATech presentation at LDRS back in June. The topic was the development of the vertical orientation system in this thread, and I talked about some of the more interesting flights and how the capabilities of the system improved over time. I managed to come down with a case of laryngitis on the day of the presentation. So, this won't be the best presentation I've ever given, but I managed to get through it. Sort of an interesting journey I think.

Jim

 

[TheAviator]

What servos are you using?

 

[Adrian A]

For those interested, I did a TRATech presentation at LDRS back in June. The topic was the development of the vertical orientation system in this thread, and I talked about some of the more interesting flights and how the capabilities of the system improved over time. I managed to come down with a case of laryngitis on the day of the presentation. So, this won't be the best presentation I've ever given, but I managed to get through it. Sort of an interesting journey I think.

Jim

Thanks for sharing and making this available to more in the hobby!

 

[JimJarvis50]

What servos are you using?

I"m using Hitec 7245. They are reasonable quick with reasonable torque, and they can be programmed, which is the most important feature.

Jim

 

[JimJarvis50]

Thanks for sharing and making this available to more in the hobby!

Thanks Adrian. I enjoy talking about this topic because it has always been such fun to do. You have something to look forward too!

Jim

 

[JimJarvis50]

One of the things we've been working on is to make the VOS canards more aerodynamic. This is mainly for the benefit of higher-speed flights (some of the beta testers are getting a little more ambitious). Bryrocket has been working his magic to develop a canard hub that is strong and doesn't protrude into the air stream. A few pics are below. I should be able to test these in a few weeks.

Jim

 

[OverTheTop]

The shape of those looks remarkably similar to my canards. It is a good example of form following function. Hub is curved and stays in line with the outer airframe radius. I also have mechanical endstops built into the back of the hub.






You may want to consider doing some post-printing treatment of the FDM prints to strengthen them in the z-axis. Exposure to acetone vapour works for ABS. Not sure what you would use, as I assume you have PLA prints? Google search should turn something up.

 

[JimJarvis50]

The shape of those looks remarkably similar to my canards. It is a good example of form following function. Hub is curved and stays in line with the outer airframe radius. I also have mechanical endstops built into the back of the hub.
View attachment 557904

View attachment 557903

View attachment 557902

You may want to consider doing some post-printing treatment of the FDM prints to strengthen them in the z-axis. Exposure to acetone vapour works for ABS. Not sure what you would use, as I assume you have PLA prints? Google search should turn something up.

Bryan prints with carbon fiber polycarbonate, 100% density. There is a socket screw that holds the G10 canard in the slot. The whole assembly is very strong, although we're really targeting the technique for higher speed flight with smaller canards than shown in the pic.

Jim

 

[OverTheTop]

Bryan prints with carbon fiber polycarbonate, 100% density. There is a socket screw that holds the G10 canard in the slot. The whole assembly is very strong, although we're really targeting the technique for higher speed flight with smaller canards than shown in the pic.

Jim

Sounds good Jim. That CF polycarb should be stronger than the regular PLA . You will probably find the largest forces on the fins are when they land. The way the fiberglass sits in the slot is likely to put one side of the slot in tension if any significant side force is applied (landing typically).

As a data point for you, the resin prints I used could take 40kg side load without failure. I haven't had one break on landing yet.

 

[reddrock]

My third VOS2 Beta test flight was on 12/17/2022 at Friends of Amateur Rocketry (FAR) on a CTI L1050BS P75-3G motor. Electronics included the VOS2 UDB in the Control Module; G-WIZ LCX, Rocket Electronics Tiltometer 3 (RTOM3), and Raven 4 in the ebay to control the recovery system; a CSI tracker transmitter attached to the apogee shock cord; and two outboard Mini F9 DVR Sport DV cameras (one pointed up and one pointed down, both mounted at the ebay on the payload section). Since this was a single stage rocket, the RTOM3 did not control anything. It was just to record tilt and compare to the UDB tilt. Canard fins were ~75% the area of the kit canards (2.125” root, 1.125” tip, 1.5” semi-span) mounted on a 15/16” x 2-7/16” oval base. The UDB was programmed for vertical orientation mode with gain of 36.

It was a no/low wind day in the low 50s with a high thin overcast. All electronics worked as planned. The LCX beeped out an apogee altitude of 7125’.

Here’s video from the cameras (edited and produced by Jim Jarvis) with plots of tilt superimposed.


The control system did a decent job of controlling tilt. No backsliding was observed, possibly due to early sensing of apogee. However, there was quite a bit of roll, probably due to the outboard cameras or fin misalignment. This needs to be investigated.

I’ve been lucky so far to land on “soft” desert sand. The spin can and control module need to be cleaned of any dirt from landing before the next flight.

 

[JimJarvis50]

I did a VOS2 flight Saturday at San Angelo. It's a pretty new field that is really nice. West Texas doesn't have a lot of trees.

The purpose of the flight was to start investigating the use of the system for roll control only. When controlling yaw/pitch, the main objective is just to keep the rocket from spinning rapidly and from exceeding the gyro range. For roll-only, the objective would be for video. Since I haven't previously done roll control only, I decided to start with lower gains than we typically use, knowing that these will need to increase to actually hold at the desired bearing through the flight. So, I would say the flight was reasonably successful and there is potential for significant improvement. There is a video of the flight linked below with some data at the end of the video.

Speaking of the VOS2 systems, the second batch of six systems has been claimed. I'm not sure if it will be possible to make more - I hope so - but there is uncertainty just now. Our group should be able to do quite a few flights this year, so I'm looking forward to that.

Jim

 

[boatgeek]

I did a VOS2 flight Saturday at San Angelo. It's a pretty new field that is really nice. West Texas doesn't have a lot of trees.

The purpose of the flight was to start investigating the use of the system for roll control only. When controlling yaw/pitch, the main objective is just to keep the rocket from spinning rapidly and from exceeding the gyro range. For roll-only, the objective would be for video. Since I haven't previously done roll control only, I decided to start with lower gains than we typically use, knowing that these will need to increase to actually hold at the desired bearing through the flight. So, I would say the flight was reasonably successful and there is potential for significant improvement. There is a video of the flight linked below with some data at the end of the video.

Speaking of the VOS2 systems, the second batch of six systems has been claimed. I'm not sure if it will be possible to make more - I hope so - but there is uncertainty just now. Our group should be able to do quite a few flights this year, so I'm looking forward to that.

Jim

It's wild to watch the spin can fins turning and the ground below holding steady.

 

[OverTheTop]

A little oscillatory. Maybe gain is still a little to high. The moment of inertia in the roll axis is surprising small and it makes it easy to have too much gain.

 

[JimJarvis50]

A little oscillatory. Maybe gain is still a little to high. The moment of inertia in the roll axis is surprising small and it makes it easy to have too much gain.

Not sure I agree that the gains are too high. The heading hold gain, which is what keeps the roll angle constant, is very low. Just not enough control authority to keep the rocket centered. The movements of the canards are proportional to roll angle going from 0 to 360° or-360°. I think the control range needs to be over a much lower angle range. But to your point, it's possible that this flight mode may work better with fixed fins, giving some damping, if control reversal can be avoided.

Jim