Gimbaled rocket motor works pretty well on model rockets

Gimbaled rocket motor assembly!

Who would have thunk it? Lol. The question truly is... Can I do it.

I just saw this video on Youtube of a R&D project on electronic rocket stabilization.

Pretty cool stuff. I think I'll use the gimbal rocket motor contraption if I ever decide to build a multi-staged Saturn V model rocket. That way I could fly the upper stage with no fins. My idea before I saw this video was to have fins on the upper stage that would move into place at the moment of staging. I think the gimbal motor mount would probably weigh less in the long run. I dunno. I'll have to study it up a little more.

Cool video though. Definitely food for thought.

David

Very impressive!

I agree, it opens up some real possibilities for different rockets.

Great project. I do have a question... Although I fully understand what was done in the context of a research area, but in general, would adding this to our high-power designs be considered "active control" which I thought was verbotten? Yes/no? Or is active control only when you add another feedback loop (or 5) to home in on a target?

I don't know the answer to that question about high power and active control. Someone from the NAR/Tripoli probably should chime in on that one. I view it as nothing more than active stabilization. Like fins on steroids. Or, in the case of the Gimbaled rocket motor mount, fin replacement technology. Nothing nefarious about that is there? I view as something as benign as dual deploy electronic altimeters and/or timers.

Maybe someone with a little more knowledge should chime in on this one. I don't want to make claims that I'm clear as mud on.

David

One thing to keep in mind is that unlike fins, thrust vectoring only stabilizes a rocket when there is thrust.

Gerald

Similar thread here, with a reference to the cited YouTube at post #90 ...

https://www.rocketryforum.com/showthread.php?51513-Fly-Straight-Up

Greg

If you watch the NARAM R&D video you will see that servo actuated fins are far better than gimbaled motors for providing active stabilization. Servo actuated fins will provide trajectory corrections provided the air speed exceed 20-30 mph or within 2 seconds of apogee. Gimballed motors only provide corrections while the motor is providing thrust which is a very short fraction of the flight. After the motor burns out there no further correction possible.

Bob

dixontj93060 said:

Great project. I do have a question... Although I fully understand what was done in the context of a research area, but in general, would adding this to our high-power designs be considered "active control" which I thought was verbotten? Yes/no? Or is active control only when you add another feedback loop (or 5) to home in on a target?

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Oh don't go there! It has been my Impression that Active Control is widely Accepted, but it just is'nt discussed openly on Forums.
I tried barking up that Tree once.

Is interested...

bobkrech said:

If you watch the NARAM R&D video you will see that servo actuated fins are far better than gimbaled motors for providing active stabilization. Servo actuated fins will provide trajectory corrections provided the air speed exceed 20-30 mph or within 2 seconds of apogee. Gimballed motors only provide corrections while the motor is providing thrust which is a very short fraction of the flight. After the motor burns out there no further correction possible.

Bob

Click to expand...

I agree, the gimbal is not a solution, because the main part of our problem happen at coast and at apogee when the rocket has less trust and more prone to be influenced by the wind.
Also in the video the fins have too much travel, less travel and better response is the thing I'm working on now. Eagle Tree is nice but it?s not the solution, the computer need more power to be able to compute not only the direction to correct, but also the force need to correct it too to avoid projecting the rocket in the opposite direction and correct again in the opposite direction making a wave. We need just enough correction to get the rocket back on a vertical fly.

TopRamen said:

Oh don't go there! It has been my Impression that Active Control is widely Accepted, but it just is'nt discussed openly on Forums.
I tried barking up that Tree once.

Click to expand...

It's not active control like if we will use heat sink or targeting avionic, it's Active stabilisation. I have will to make a rocket fly strait and recover it near, but I have no desire to see peoples work on something that can be used as a weapon by the wrong persons.


They are no problem to make a rocket fly strait and be more secure. Actually it should be the goal no ?

I finally watched Alyssa's talk all the way through. This is a terrific project. Is there some way to get a written copy of the presentation and/or the research?

Area66 said:

....Also in the video the fins have too much travel, less travel and better response is the thing I'm working on now. Eagle Tree is nice but it?s not the solution, the computer need more power to be able to compute not only the direction to correct, but also the force need to correct it too to avoid projecting the rocket in the opposite direction and correct again in the opposite direction making a wave. We need just enough correction to get the rocket back on a vertical fly...

Click to expand...

That's correct, but I don't believe that has anything to do with the EagleTree Guardian, but rather how the fins are pivoted and adjusted.

• The pivot axle point of the fins need to be at the aerodynamic point or slightly forward.
  • Balancing the forward and aft aerodynamic forces maximizes response speed and aerodynamic force delivered to the airflow.
  • The nominal balance point is where 50% of the aerodynamic area is forward and 50% aft of the pivot axle point.
  • In practice it probably is better with 40%-45% forward area bias to insure that the free air flow will keep the fin as 0 degree angle of attack if the linkage breaks.
• The angular movement of the fins probably needs to be limited to not more the +/-15 degrees to insure they do not aerodynamically stall or act as drag breaks.
  • With a +/-60 degree servo you would use a 4:1 linkage or gear ratio to reduce the fin throw to +/-15 degrees.
  • The advantage of the ratio method is that the servo torque is multiplied by the ratio so the applied torque is multiplied by the reduction ratio.
  • It also speeds up the system aerodynamic response time without increasing drag.
• The Eagle Tree manual https://www.eagletreesystems.com/Manuals/Guardian 2D-3D.pdf describes the control system in detail.
  • The gain on each axis is readily adjustable to control the sensitivity.
  • With the fin motion mechanically limited, the sensitivity can be increased to improve response time without worrying about stalling the fins.
• I believe that the EagleTree Guardian can provide more than adequate response time and force multiplication with my recommended fin balancing and angular swing reduction noted above, and proper adjustment of the axis sensitivities.

Bob

bobkrech said:

[/LIST]

[*]I believe that the EagleTree Guardian can provide more than adequate response time and force multiplication with my recommended fin balancing and angular swing reduction noted above, and proper adjustment of the axis sensitivities.
[/LIST]

Bob

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I wll give the guardian a try, anyway I'm stock in the snow for the next 5 months, lot of time to prepare something.

This really irks me... Back in the day I was daydreaming of building a stabilized rocket using less advanced yet very similar ideas but was poo-pooed by the local club and online legal "experts" saying it was against the code of the national orgs and the law.

Now there are a bunch of folks experimenting with it.

Turd said:

This really irks me... Back in the day I was daydreaming of building a stabilized rocket using less advanced yet very similar ideas but was poo-pooed by the local club and online legal "experts" saying it was against the code of the national orgs and the law.

Now there are a bunch of folks experimenting with it.

Click to expand...

With a name like Turd you can't really be surprised they poo-pooed you can you?:grin:

I have worked with a lot of this gear on RC airplanes.

Just a few thoughts:

>gosh! the camera guy's mouth-breathing was very distracting! ...For a minute, I thought she had darth vader in the crowd.

>Very nice examples of adapting existing technology for new uses!

>I would NOT trust those little tower-pro (5g or 9g) servos on a MPR! I use them all the time on little foamie elec airplanes and they are not very robust.

>I would like to see what type of servos she used on the gymbal contros. I don't think the small tower-pro units have enough torque and rigidity to contain those forces.

>As far as passive stability vs active controls: You must have a RC transmitter/receiver functioning to use these flight stability modules, and that creates an active control situation. The Eagle tree unit takes over when you have your hands off the controls, but the controls still work. Don't really understand why people are so uptight about this. Anyone with nefarious intent could get a a lot more functionality using other delivery methods (vs rockets). Have you looked at the FPV, electric aircraft being built? Granted, you cant get the speed/alt like you get with rockets, but delivering a payload to a specific target would be easy as pie.

>As far as the reaction rates on the control sufaces: Most newer RC systems now offer exponential control rates. This might come in vary handy for rocket controls/flight path correction. This would only work for the 'active' controls. I am not aware of any of the flight stabilization products that offer exponential correction, but it would not surprise me if it was out there.

Props to this kid for working out this kind of project, and being able to stand up and present to a group of adults!!

Turd said:

This really irks me... Back in the day I was daydreaming of building a stabilized rocket using less advanced yet very similar ideas but was poo-pooed by the local club and online legal "experts" saying it was against the code of the national orgs and the law.

Now there are a bunch of folks experimenting with it.

Click to expand...

Don't feel bad! I got poo-pooed on the straight up thread for suggesting the use of multicopter/FPV electronics similar to the Gardian. Some :cyclops: people just over think the problems rather than solutions.


Richard

Turd said:

This really irks me... Back in the day I was daydreaming of building a stabilized rocket using less advanced yet very similar ideas but was poo-pooed by the local club and online legal "experts" saying it was against the code of the national orgs and the law.

Now there are a bunch of folks experimenting with it.

Click to expand...

Half the battle is knowing who to listen to and not listen to...

Later! OL JR

Finally had a chance to watch this. I could see using this to build accurate scale models of some rockets. Otherwise fins work pretty good for what they cost.

Turd said:

This really irks me... Back in the day I was daydreaming of building a stabilized rocket using less advanced yet very similar ideas but was poo-pooed by the local club and online legal "experts" saying it was against the code of the national orgs and the law.

Now there are a bunch of folks experimenting with it.

Click to expand...

You may have missed your chance to be the first person to try it, or even the second, but you can still be the Turd.

hball55 said:

With a name like Turd you can't really be surprised they poo-pooed you can you?:grin:

Click to expand...

You make an excellent point.

Anti-roll or anti-weathercocking fins seems to me to be much more useful across the wider range of motors and rocket configurations.

Vectoring WOULD be cool, though... not very effective, but cool.



Later!

--Coop

Area66 said:

Eagle Tree is nice but it?s not the solution, the computer need more power to be able to compute not only the direction to correct, but also the force need to correct it too to avoid projecting the rocket in the opposite direction and correct again in the opposite direction making a wave. We need just enough correction to get the rocket back on a vertical fly.

Click to expand...

The great thing about simple linear proportional controller implementation is that both your % overshoot (i.e. the rocket correcting past vertical as the controller worked what we decided is "too aggressively" for the angular error) and the feedback / input lag introduced by what may be a "slow" (in this case, Eagle Tree) computer are both solved by decreasing the gain!

I have no experience with this specific eagle tree product demonstrated, but doing advanced things like switching to a microcontroller which implements cascaded controllers or state control by factoring in a rocket's precomputed mathematical model (even a linearized one), taking in expensive inputs like real-time airspeed to exponentially scale your calculated servo angles, differential pressure sensors for crosswind speed, etc. is without a doubt too computationally expensive for the hobby prices and size constraints we have. Basically, with the simple proportional controller here, any competitor to the eagle tree product used, even if it had a higher data rate and more accurate accelerometers, would minimally improve the response time for the rocket to achieve vertical flight versus simply adjusting controller gain(s).

Aside, a PWM controller for a couple hobby servos is very small / cheap, and takes ADC voltage inputs that could be appropriately scaled and output from a little arduino-type single-board computer whose only inputs are 2 axes of acceleration (and time). A third axis could integrate thrust axis acceleration to cheaply approximate airspeed for proportioning control surface angle to airspeed without slowing the angular error calculation. I'm rambling, but my point is that the eagle tree telemetry products seem to be ready-made for RC purposes, and if you cut out the relays and other RC receiver crap, you're talking about much less cost and fewer question about whether or not we're talking about active control.