Blackbird Project -- Arduino-controlled high-power carbon fiber rocket

Hello, Rocketry Forum. As you can see, this is my post #1, which is coincidentally the same as the number of rockets I have ever built and launched. I am far from an expert in this field, but I have been lurking here for a little while, and I think I have found the experts. I am hoping to get some help on a project I am currently developing. (I have not started to build yet, it is still in the design phase. I would like to finalize the design before buying all the materials.)

This is a website I built to quickly present the whole thing. https://therootword.com/blackbird
It includes the .ork file, full written specifications, pictures, and some details on the project itself, as well as some other things.

The short version:
-High-powered rocket
-Carbon fiber construction
-6'7" / 202 cm length
-3.72 kg / 8.20 lb mass
-1210 N*s J140 motor
-Simulates to 1.02 mi / 1.65 km

The interesting part:
-Autonomous active stabilization, powered by Arduino with gyro, accelerometer, and pressure sensor, with four servos and control fins
-Altitude cut-off
-On-board video
-Post-landing GPS tracking

I have tried to be thorough with this, and while there are pages of calculations and notes that have not been uploaded, the website covers most of the important points. That being said, I am sure there are naive errors and omissions, so I look forward to all of you ripping it apart.

Thank you in advance for your criticism and feedback.

Welcome to the Forum Noah.

You have picked an ambitious project. Have to ask if you are high power certified by NAR or TRA, and what local rocketry club you belong to since a project like this will be a lot easier if you launch with an organized group?

0.) I think your time frame is very optimistic unless you can work full time on the project. Level 2 high power certification will be required for you to purchase a J motor and launch the rocket.

1.) With a J140, the best velocity you can expect to obtain is Mach 0.5. To go supersonic you need a K motor for 5.5" od rocket at a minimum.

Also a J140 has a maximum acceleration of ~5G which is quite slow for a rocket in anything more than a light breeze. Your guidance should help, but if the guidance system fails, the rocket could become unstable.

2.) Putting movable control surfaces on the aft end of the fins is not likely to work. You will have all kinds of stability issues. The supersonic solkution would be to have 4 forward canards at the forward end of the rocket where the IMU should be located. The entire canard would rotate to avoid supersonic flow separation. All military missiles use this method of directional control.

3.) This also removes a lot of weigh from the aft end of the rocket. The CG needs to be 2 body diameters forward of the CP for stability in a supersonic rocket.

4.) Using a balanced canard, the torque required is greatly reduced and will minimize the size and weight of the servos.

5.) Carbon composites are radio opaque so the GPS must be located in the nose of the rocket, or the airframe should be made from fiberboard or fiberglass.

6.) If you are going through with this project, a $29 hazmat fee per motor shipment is not a big cost perturbation. If you purchase the motors from a local motor dealer there is not hazmat fee.

7.) Every thing you want to put into the rockets should fit easily in a 4" OD airframe, and in a 3" airframe if you are good designer.

8.) Commercial GPS receivers loose lock between 4G-6G on ascent. They takes several seconds or longer to regain lock.

Sounds like an interesting project. I look forward to your responses.

You also might want to read this thread. https://www.rocketryforum.com/showthread.php?122042-I-could-use-just-a-little-guidance

Bob

Very cool project!
A J180 in an 8lb rocket....better have absolutely no wind, I know you have active stabilization

Thank you for your response.

I am not high power certified yet. I suppose I will have to get around to that at some point. Does it cost money, or do I just have to buy the NAR membership? As for a club, I am not in one. I was hoping to attend an organized launch, though--URRF was one I had in mind.

0) The time frame is optimistic, but I am spending a large percentage of my time on this. It is my single largest commitment at the moment.

1) Yes, I did not really expect to go supersonic on the J140. I would like to fly it again after the project is over, on a larger motor that is capable of getting it to that speed. I am worried about the low average thrust and speed on the J140, and I am not 100% set on that motor.

2) I was trying to avoid canards, primarily because it adds a lot of surface area to the top of the rocket, and brings the center of pressure too far up. It also seems like it would increase drag quite a bit, as opposed to having the stabilizer fins in line with the existing main fin set. After all, the adjustments made by the stabilizer fins would be very small and brief, more like twitches over a maximum range of +/-30 degrees and for a fraction of a second each. Are those premises incorrect?

3) At the moment, OpenRocket has the stability with motor as a little over 1 cal, and without motor (but with casing) as a little over 2 cal. Is this insufficient? If I put the four servos, all the electronics, and the stabilizer fins up front, make the stabilizer fins smaller, and enlarge the main fins, the stability with motor is down to 0 cal. The instability is what worried me about canards, but I expected the opposite from what you are saying.

4) Presumably this is because the aerodynamic drag force will be acting equally on both sides of the canard if it is mounted to the servo at about half the average chord of the fin. I should have done this before instead of attaching the servos to the top line of the stabilizer fins. I feel kind of stupid now.

5) I did not know that. Hm. I really do not want to change the build material, so it looks like a little reconfiguration will be necessary. Off the top of my head, I am not sure how I will do that, because of the location of the Arduino (unless I stop using an Arduino module for GPS and just use a separate receiver/transmitter, and put it in the nose).

6) For me it is. Half-broke college student here, which is why I was planning to go with a local purchase.

7) The reason for the large diameter is because at the base of the rocket, I have a 56 mm motor mount surrounded by 40 mm servos on four sides.

8) I am only interested in having GPS tracking post-landing, for recovery purposes, so I am not worried about losing lock due to acceleration.

I will look through the thread you linked when I have a little more time.

gerbs4me said:

Very cool project!
A J180 in an 8lb rocket....better have absolutely no wind, I know you have active stabilization

Click to expand...

Yes, I am a little concerned about that. If I do wind up going with that motor, it will definitely be a good test of the stabilization system, but it will have to work perfectly.

Well URRF is definitely the place to be to learn. Obtaining certain level 1 is very easy, build a rocket, join NAR or TRA , purchase H or I motor, ask for certify witnesses , fly rocket on H or I motor , recover rocket in good condition, witnesses sign paperwork, mail to organization.

There are many URRFers here .
Bob Krech is one of them

I'm in for this one. It will be fun to watch you grow in the hobby and get this one off the ground.

NoahTurner said:

I am not high power certified yet. I suppose I will have to get around to that at some point. Does it cost money, or do I just have to buy the NAR membership? As for a club, I am not in one. I was hoping to attend an organized launch, though--URRF was one I had in mind.

Click to expand...

Large launches like URRF are a good place to learn fast. If you'd like to join URRG, we fly that field monthly and a level one cert is easy enough to get out of the way. (also will need NAR or TRA membership). Even if you're not ready to fly, you're welcome to come out to a launch and chat/check out some rockets/watch some flights.

Building a few smaller/passively guided rockets to get a better handle on the effects of things may be a good idea.

Another area of interest is the altitude cutoff. What's the purpose of this? Bad things happen when you open up at speed

NoahTurner said:

Thank you for your response.

I am not high power certified yet. I suppose I will have to get around to that at some point. Does it cost money, or do I just have to buy the NAR membership? As for a club, I am not in one. I was hoping to attend an organized launch, though--URRF was one I had in mind.

Click to expand...

You will have to join NAR or TRA and get your L1 and L2 High Power certification before you can launch your rocket at any NAR/TRA or independent hobby rocket launch. This needs to be your first priority.

0) The time frame is optimistic, but I am spending a large percentage of my time on this. It is my single largest commitment at the moment.

Click to expand...

You need to build a L1/L2 rocket first. This is your first priority. You should get a 4" airframe rocket with a 54 mm motor mount. This will allow you to use a 54 mm motor for your L1 and L2 flights. A LOC EZI-65 is a good rocket for this. If AMW Pro-X still has certification specials you can save a lot of money on Pro54 3G and 6G casings and purchase 2 spacers and have the capability of launching any 1G to 6G Pro54 reloads.

1) Yes, I did not really expect to go supersonic on the J140. I would like to fly it again after the project is over, on a larger motor that is capable of getting it to that speed. I am worried about the low average thrust and speed on the J140, and I am not 100% set on that motor.

Click to expand...

That flight is some time in the future.

2) I was trying to avoid canards, primarily because it adds a lot of surface area to the top of the rocket, and brings the center of pressure too far up. It also seems like it would increase drag quite a bit, as opposed to having the stabilizer fins in line with the existing main fin set. After all, the adjustments made by the stabilizer fins would be very small and brief, more like twitches over a maximum range of +/-30 degrees and for a fraction of a second each. Are those premises incorrect?

Click to expand...

The drag of canards is not high at a 0-degree angle of attack, and they don't have to be very large because they are far forward of the rocket CG. It is a leverage problem: The ratio of CP/CG of the aft fins and the forward canards basically gives you a relative fin area for initial design purposes. Look at the photo below for an example of canards on rockets.



Properly designed fins have a L/D > 1, and behave like a wing, not a drag device.


Note the position of the canards and the servos. For a hobby rocket stabilization system they are reversed, the entire package can be mounted in a forward payload compartment easily moved to other rockets with the same diameter airframe.

3) At the moment, OpenRocket has the stability with motor as a little over 1 cal, and without motor (but with casing) as a little over 2 cal. Is this insufficient? If I put the four servos, all the electronics, and the stabilizer fins up front, make the stabilizer fins smaller, and enlarge the main fins, the stability with motor is down to 0 cal. The instability is what worried me about canards, but I expected the opposite from what you are saying.

Click to expand...

You need to learn a bit more before you build, and spend a lot of money.

4) Presumably this is because the aerodynamic drag force will be acting equally on both sides of the canard if it is mounted to the servo at about half the average chord of the fin. I should have done this before instead of attaching the servos to the top line of the stabilizer fins. I feel kind of stupid now.

Click to expand...

You need to read Jim Jarvis's thread now.

5) I did not know that. Hm. I really do not want to change the build material, so it looks like a little reconfiguration will be necessary. Off the top of my head, I am not sure how I will do that, because of the location of the Arduino (unless I stop using an Arduino module for GPS and just use a separate receiver/transmitter, and put it in the nose).

Click to expand...

Look at the posts on TRF that discuss this.

6) For me it is. Half-broke college student here, which is why I was planning to go with a local purchase.

Click to expand...

Again, no one is going to sell you a J motor before you have your L1 certification. You can purchase 1 H or I L1 motor to get your L1 certification, and then once you have the L1, you have to take the L2 written test and can purchase 1 J, K or L L2 motor for certification.

7) The reason for the large diameter is because at the base of the rocket, I have a 56 mm motor mount surrounded by 40 mm servos on four sides.

Click to expand...

That's way too much weight aft. Using canards, you can use much smaller servos and mount the fins directly on the shafts.

8) I am only interested in having GPS tracking post-landing, for recovery purposes, so I am not worried about losing lock due to acceleration.

Click to expand...

Ok.

I will look through the thread you linked when I have a little more time.

Click to expand...

You need to stop what you are doing and read it now.......

Yes, I am a little concerned about that. If I do wind up going with that motor, it will definitely be a good test of the stabilization system, but it will have to work perfectly.

Click to expand...

Please look at the video below. Alyssa Stenberg presented an award winning report on electronic stabilization of a rocket at the R&D session of NARAM 55. It is directly applicable to your project. She used an off the shelf Eagle Tree Guardian RC stabilizer with RC servos to stabilize 3 different rocket designs.
[video=youtube;A4M9Uso9EsY]https://www.youtube.com/watch?v=A4M9Uso9EsY[/video]

Bob

That video is incredible! Thanks for posting it, Bob.