Questions about BPS Space System

[Richard Dierking]

I have some questions regarding the BPS Space system and perhaps others that are developing similar systems. I hope this helps others too.
What's the status of usable motors for the BPS Space system? I've seen that Joe Barnard is testing the new system he is working on using the G8. Please correct me if I'm wrong, but the AT G8 is not currently a certified motor and not available for purchase. How's that going with the heat generated by this motor?
Has anyone used a CTI G33 (about a 4 second burn)?
Has anyone tried a TVC mount made from ABS or Nylon (with CF) instead of PLA?
How about upgrades for the servos? I have similar servos that are provided with the BPS Space kit, but they have metal gears. Has anyone reinforced the servo connection points?

I'm considering making my first rocket with this system to have fins and marginal aerodynamic stability. Launching using a 8' long mini-rail (20mm rail with 5 mm slot), vertical but slightly bent approx 5 degrees toward the top of the rail. So, the rocket would go off the rail a little "wonky." Would you expect the system to correct for this?

I've seen the videos where Joe seems to "arm" the system immediately before launch. Does the system drift a lot while on the pad? (i.e. What's the rate of drift?)

I know that BPS Space's current business model is launching model rockets at relatively low velocity, no fins and realistic powered flight. What's the possibility of expanding this to a stability/guidance system that would go to apogee? So, expanding the time the system is active and a more flexible output from the system.

Or, perhaps others are working on something like this?

 

[jderimig]

The system as I understand it uses thrust vectoring only for directional correction. No thrust, no more stablilization. Others correct me if I am in error.

 

[Richard Dierking]

Sprite (using Signal R2) and the new system Sprint shut down at burnout using acceleration data. You can see this in recent on-board camera videos taken within the airframe looking down at the TVC mount. I believe the new reaction wheel also shuts down. I wonder if the rocket started to spin up (>1 Hz) right before thrust shut down and continued into coast if this would help stability and gain altitude. But, could also create deployment issues.
Glad you are a part of this conversation John.

 

[BDB]

I have a rocket with the BPS system that is ready to fly. I just need to find the time to do it. I am planning to use an Apogee F10 motor (7.8 sec). Joe also told me that Estes F15s work well, so long as you plug them with some epoxy (3.5 sec).

Since the rocket is thrust vectoring, you don't need to worry about a 5:1 thrust to weight ratio. Presumably, a 1.1:1 thrust to weight ratio would be ok.

 

[Richard Dierking]

Will you be using a launch rail or rod? Please post results after your flight. Are you using Rocksim or another sim program? Just wondering about the actual CP-CG relationship and what the sim altitude would be if the rocket had fins with an aerodynamic margin of stability of say 1.0.

 

[mikec]

What's the possibility of expanding this to a stability/guidance system that would go to apogee?

If you're only using thrust vectoring then obviously you have no control left after burnout. I'm not that sure what the point of the reaction wheel is, just to add roll control as a degree of freedom I guess. BPS doesn't seem to be doing anything with control of aerodynamic surfaces. Clearly Jim Jarvis has done much more work on a larger scale on that problem.

All depends on what your goal is. If you want to maximize altitude then using high thrust but not too high and using aero control to stay vertical seems to be what Jim is trying to do. BPS at this point is more interested in just the cool factor (which is fine.) Commercial sounding rockets just spin to limit dispersion and spend more effort on spin balancing that amateurs ever have AFAIK.

 

[Richard Dierking]

Thank you for the responses.

I think BPS Space (can I just say Joe?) has begun actively controlling roll because not doing it first makes TVC on single motor rockets very difficult. As you have seen from his previous flights, he has done it, but spin will always be an issue uncontrolled. And, yes, definitely, balancing for spin takes a lot of work. I created a spin table with rotation up to 5 Hz to try to balance electronics bays and reduce coning. Now, I just try and create rockets that don't spin; Particularly 2 stage projects. Jim Jarvis is interested in maximizing altitude, but also reducing recovery distance. I really appreciate that. Going high alt and still staying in the cylinder during recovery is a great accomplishment. We should all try things to safely reduce recovery distance. But, I'm not a fan of movable canards on rockets.
I also appreciate what Joe has done. I'm more interested in how he is doing it rather than why he is doing it. Just wished he expanded his business model. But, understand it's his business.

Still hope to receive some replies on my first questions.

 

[afadeev]

What's the status of usable motors for the BPS Space system? I've seen that Joe Barnard is testing the new system he is working on using the G8. Please correct me if I'm wrong, but the AT G8 is not currently a certified motor and not available for purchase.

G8 has been de-certified. Which is a shame.

I am planning to use an Apogee F10 motor (7.8 sec). Joe also told me that Estes F15s work well, so long as you plug them with some epoxy (3.5 sec).

The above is correct.
I've test-flown my TVC rocket a few times (with various degrees of success, or lack thereof) on F15, and once on the over-priced Apogee F10.
F15's burn time of 3.5 seconds is way too short.
F10's is more suitable, but is a re-labelled AT motor that is priced at $28/per + HazMat shipping.

Both are marginally under-powered for all but the lightest of the TVC airframes.

I'm considering making my first rocket with this system to have fins and marginal aerodynamic stability. Launching using a 8' long mini-rail (20mm rail with 5 mm slot), vertical but slightly bent approx 5 degrees toward the top of the rail. So, the rocket would go off the rail a little "wonky." Would you expect the system to correct for this?

Aerodynamic stability, fins size and shape, launch rod length, rod angle - all concepts that are 100% irrelevant when you fly a TVC rocket.

I've seen the videos where Joe seems to "arm" the system immediately before launch. Does the system drift a lot while on the pad? (i.e. What's the rate of drift?)

No, but it is a good safety practice to arm electronic ejection system right before flight (with the nose cone aimed away from the humans).
TVC rockets fly with electronic, and never motor, ejection.

What's the possibility of expanding this to a stability/guidance system that would go to apogee? So, expanding the time the system is active and a more flexible output from the system.

If you're only using thrust vectoring then obviously you have no control left after burnout.

Exactly.
But since the TVC mount is fairly heavy, and both F10 and F15 and marginally under-powered, your apogee will be not much higher than the motor burn-out altitude, anyway.

I think BPS Space (can I just say Joe?) has begun actively controlling roll because not doing it first makes TVC on single motor rockets very difficult. As you have seen from his previous flights, he has done it, but spin will always be an issue uncontrolled.

No, not really.
Spinning is not much of a problem.

Now, I just try and create rockets that don't spin; Particularly 2 stage projects.

Why?
Spin helps with stabilization!

Still hope to receive some replies on my first questions.

Hope this helped.

a

 

[Richard Dierking]

Thank you afadeev and others for your responses. It does help. Particularly since you have experience using the BPS system.
I still have questions. So, afadeev has used the F10 and F15 and I'm looking at those motor thrust curves. The F15 burns for 3.5 seconds and according to afadeev as well as Joe B is marginal for power. Also, I'm seeing that it does not seem to quickly come up to pressure. Although they are both F-impulse, the F10 is 76 total Ns vs 50 for the F15. So, going back to one of my original questions, how about the CTI G33? It's about a 4.5 second burn, pretty flat for about 3 seconds and the average on this flat part really isn't that much higher than the peak of the F10 and F15. Would the G33 be too much?

How about using Nylon or ABS for the TVC assembly print?

How about an upgrade on the servos?

I understand why probably most of the TVC users would consider fins useless, but for what I wish to do it's relevant. I would like some aerodynamic stability with the capability to ground launch.

Spin would be a subject in itself, and has been on other threads. Balanced spin can be good. For me, if there is spin (I test all rockets as single stages first) I like for the booster and sustainer to spin in the same direction and approximately the same rate.

Lastly, here's my wish, and frankly it's not having a realistic launch of my Saturn V, Falcon 9, etc. So, maybe appropriate to this thread, and maybe not. However, it wouldn't decrease the ability to do this. The present BPS Space system is cool and impressive. There's no doubt about that. I will learn a lot from using it. Just wish that it was more flexible. Like, being able to set shut off at apogee vs at burn out. The system obviously has outputs to servos that are adjusted to present conditions; I bet most people are amazed when they see this for the first time - I was. But, how about being able to control aerodynamic surfaces with these outputs? Including roll as a separate output. How about it being able to control a sustainer? You would have not only a new type of flight computer, you would have the ultimate flight computer.

Dependable recovery and tracking electronics revolutionized our hobby. Stability control electronics would do the same thing. Am I wrong? Would other people be interested in using something like this?

 

[afadeev]

Would the G33 be too much?
How about using Nylon or ABS for the TVC assembly print?
How about an upgrade on the servos?

How about you do all of the above, and report?

I understand why probably most of the TVC users would consider fins useless, but for what I wish to do it's relevant. I would like some aerodynamic stability with the capability to ground launch.

You don't need the former to do the latter.
At all.

For me, if there is spin (I test all rockets as single stages first) I like for the booster and sustainer to spin in the same direction and approximately the same rate.

Any other outcome would be highly unlikely, unless you stack the two stages on a swivel, for some unknown and weird reason?!

The present BPS Space system is cool and impressive. There's no doubt about that. I will learn a lot from using it. Just wish that it was more flexible.

You can always build a better mouse trap!

Like, being able to set shut off at apogee vs at burn out.

It doesn't really shut-off at burn-out. It still wiggles until you cut the power.
It's just that post burn-out, it doesn't effect the airframe orientation in any material way, since there is no thrust left to vector....

But, how about being able to control aerodynamic surfaces with these outputs? Including roll as a separate output.

Why?
Also, that would no longer be a thrust vectoring control (TVC) anymore, and all the fragile thrust vectoring hardware would become a liability, a ballast that keeps you from flying higher-thrust motors.
If you want to develop airframe orientation controls by adjusting fins - go for it. Plenty of articles have been written about that. Just google.

How about it being able to control a sustainer? You would have not only a new type of flight computer, you would have the ultimate flight computer.

Or an identical copy of the same gizmo you used for the 1 stage, also installed on the 2nd stage.

Would other people be interested in using something like this?

If you build it, debug it, prove that it works, and price it attractively, someone will buy it.
Keep us posted on your progress!

 

[Richard Dierking]

Yeah, that's pretty much how I thought the G33 question would go down. I'll try it with the TVC assembly and post the results, good/bad, happy or sad. And, there's still hope for the G8. We'll see.
Anyway, to clarify, I have ground launched rockets, including a two stage that worked OK, but I think it would have worked better with TVC on the booster. The booster arched immediately after launch. The motors were I to G impulse with booster to 500' and sustainer to 1800'. The usually configured booster also came in "hot" with a retro rocket before the main parachutes deployed which was amusing. The sustainer landed about a mile away.
I got the book Exploring Arduino by Jeremy Blum and hopefully that will aid in my projects.

If I come up with anything interesting or useful I would post it and offer any code I develop, although as pointed out previously, I don't think I'll ever develop the skill set for significant development. Btw, I would never try and make any money with anything I developed for amateur rocketry. Best way to screw up your hobby is trying to make money in it.

As for present info on Arduino-type programs for active aerodynamic stability, there really isn't much. For one reason or another people don't wish to open their coding and it takes a lot of patience going through all the Youtube videos to pick out stuff that's useful. People can be very creative developing Arduino applications for all kinds of stuff. And, there's lots of old material. Sometimes I just sit there amazed that the person got Vista to work on their computer.

Anyway, if someone finds something particularly useful outside of the BPS Space info, please post on perhaps a new thread.