Thrust Vector Controlled "Hopper" Vehicle

The Rocketry Forum

Help Support The Rocketry Forum:

[email protected] Rocket Tech

Student, Drone and Rockets, Aspiring Engineer
Joined
Jun 21, 2019
Messages
576
Reaction score
181
Location
Georgia, USA

Hi everyone! Between my busy school schedule, I have manged to finish my hopper before the end of 2020. This will be used to test TVC hardware and software. It's a carbon fiber frame with simple body panels, fully expandable, and modular.

So this was based off of Masten Space System's
Xombie vehicle

Due to the low Mass moment of Inetia, this will be a pain to control, yet a torture test of the GNC system. Hope you like it, and does anyone have experience with a lander type of vehicle like this? Would like to know
 

georgegassaway

Lifetime Supporter
TRF Lifetime Supporter
Joined
Jan 18, 2009
Messages
4,835
Reaction score
767
Pretty nice design.

What is the mass, ready to fly but without motor? Wondering if 24mm D7/E6 reloads might be practical for it, if not too heavy. Otherwise, 29mm F10's or 32mm F13/G12 reloads.

Due to the low inertia, perhaps you'll need to reduce the travel angle of the engine mount. Or, for first flights, you could perhaps add a long carbon boom on top, with some ballast at the top end, to make it have a larger moment of inertia, to reduce the initial control problems so you can dial it in better. Then make that boom shorter and adjust the control parameters accordingly.

Although you call this a "hopper", you are going to use a parachute for recovery, right? If not, do you plan to somehow control thrust?
 

[email protected] Rocket Tech

Student, Drone and Rockets, Aspiring Engineer
Joined
Jun 21, 2019
Messages
576
Reaction score
181
Location
Georgia, USA
Pretty nice design.

What is the mass, ready to fly but without motor? Wondering if 24mm D7/E6 reloads might be practical for it, if not too heavy. Otherwise, 29mm F10's or 32mm F13/G12 reloads.

Due to the low inertia, perhaps you'll need to reduce the travel angle of the engine mount. Or, for first flights, you could perhaps add a long carbon boom on top, with some ballast at the top end, to make it have a larger moment of inertia, to reduce the initial control problems so you can dial it in better. Then make that boom shorter and adjust the control parameters accordingly.

Although you call this a "hopper", you are going to use a parachute for recovery, right? If not, do you plan to somehow control thrust?
Thank you! So far it's 390 grams but will be heavier when I add more things. The body panels can be removed to make it even lighter. Yes I want to use some D-F motors for this. I call it a hopper because it'll mostly hover through tethers, but later on I do want to control the thrust. I don't mind it being heavy and might even add weight to make it heavy because it won't fly high. There's some ways I am working on at this small scale with some friends ; )

The current version is not meant to go high or might never free flight. I think this one will mostly be tethered so I can get the PID software right. But once I do I wish to expand the vehicle and add parachutes. Yes and your totally right. The Mass Moment of Inertia is super low, so free flight version will probably be expanded up with maybe 2-3 body panel units up or else this thing might be the king of flips.

Anyway this is the plan based on what I know, it'll be modified as I do testing and see how the vehicle reacts. Thank you for the comment though
 

georgegassaway

Lifetime Supporter
TRF Lifetime Supporter
Joined
Jan 18, 2009
Messages
4,835
Reaction score
767
Well, at 390 grams plus motor it might be OK for a C6 for tethering. Otherwise your next step up in thrust level would be a D12, for first tests. And that "D12" level of thrust is in the ballpark for the thrust of F10 (8 second burn), F13 94.5 to 5 second burn), and G12's (8 second burn),

Here's an interesting video of a tethered TVC project from 4 years ago. The guy (Joe Lang) got it to work, flew a nice model, then "poof", gone after 4 videos. Anyway, this video has a progression from overcontrol in test 1 to really nailing it by test 6. And using a nice tethering method. Looks like his test model moment of inertia problem was worse than yours, yours has the outer legs and feet adding to the inertia moment.

 
Last edited:

[email protected] Rocket Tech

Student, Drone and Rockets, Aspiring Engineer
Joined
Jun 21, 2019
Messages
576
Reaction score
181
Location
Georgia, USA
Well, at 390 grams plus motor it might be OK for a C6 for tethering. Otherwise your next step up in thrust level would be a D12, for first tests. And that "D12" level of thrust is in the ballpark for the thrust of F10 (8 second burn), F13 94.5 to 5 second burn), and G12's (8 second burn),

Here's an interesting video of a tethered TVC project from 4 years ago. The guy (Joe Lang) got it to work, flew a nice model, then "poof", gone after 4 videos. Anyway, this video has a progression from overcontrol in test 1 to really nailing it by test 6. And using a nice tethering method. Looks like his test model moment of inertia problem was worse than yours, yours has the outer legs and feet adding to the inertia moment.

Thank you! Yes I will say this is on the list of videos that inspired me to do this! Yes I am planning a similar setup and testing method. Also thank you for the motor suggestions. Thankfully the vehicle isn't too heavy and I have a wide variety. I will do the math, and see what i want to slap on to it! Can't wait!
 

georgegassaway

Lifetime Supporter
TRF Lifetime Supporter
Joined
Jan 18, 2009
Messages
4,835
Reaction score
767
If your tether tests will work on a C6, then you have the potential to later fly it on an E6 (either the expendable or the reload). A few years ago, I took my old 1989 gimbaled engine model, that usually flew on an F10, and flew it on an E6 (8 second burn), using an Eagle Tree Guardian for vertical guidance (In place of the original Sunguidance). It worked, and IIRC the liftoff mass was around 14-16 ounces.

It was unusual though, as the thrust spike got it moving upwards, then dropped to the sustainer burn which was roughly equal to the mass of the model, so it lost a bit of velocity due to drag. And then since the nozzle throat erodes a bit, the thrust drops a bit, so the model reached apogee then stated to descend tail-first for a second or two before it burned out. Then I used R/C to eject the chute. It had reached maybe 100 feet and ejected at about 50.

So, anyway, if you can keep this under 12 ounces liftoff mass with an E6, it would likely fly very impressively slowly to about 150-200 feet.

To me, that's the beauty of gimbaled models, long burn slow boosts, that keep themselves under control. Also, the faster a gimbaled hobby rocket goes, the more trouble it will have with aerodynamic forces, one way or another. Fast guided rockets are best done with aerodynamic controls, not gimbaling.
 
Last edited:

[email protected] Rocket Tech

Student, Drone and Rockets, Aspiring Engineer
Joined
Jun 21, 2019
Messages
576
Reaction score
181
Location
Georgia, USA
If your tether tests will work on a C6, then you have the potential to later fly it on an E6 (either the expendable or the reload). A few years ago, I took my old 1989 gimbaled engine model, that usually flew on an F10, and flew it on an E6 (8 second burn), using an Eagle Tree Guardian for vertical guidance (In place of the original Sunguidance). It worked, and IIRC the liftoff mass was around 14-16 ounces.

It was unusual though, as the thrust spike got it moving upwards, then dropped to the sustainer burn which was roughly equal to the mass of the model, so it lost a bit of velocity due to drag. And then since the nozzle throat erodes a bit, the thrust drops a bit, so the model reached apogee then stated to descend tail-first for a second or two before it burned out. Then I used R/C to eject the chute. It had reached maybe 100 feet and ejected at about 50.

So, anyway, if you can keep this under 12 ounces liftoff mass with an E6, it would likely fly very impressively slowly to about 150-200 feet.

To me, that's the beauty of gimbaled models, long burn slow boosts, that keep themselves under control. Also, the faster a gimbaled hobby rocket goes, the more trouble it will have with aerodynamic forces, one way or another. Fast guided rockets are best done with aerodynamic controls, not gimbaling.
Yes I totally agree with you Sir! Also I have seen the video of your Sun Guidance rocket, and I find it mind blowingly impressive you did that back in the 80s! You launched that when my parents were my age!
 
Top