Stopping Spin on a Video Camera Rocket

Try rollerons?

Or more simply, keep fins small, present a symmetric drag profile by mirroring protuberance such as launch lugs, optical windows, etc.

Most importantly, build fins straight and keep their airfoiling simple to minimize chances of inducing a roll moment.

Try rollerons?

Or more simply, keep fins small, present a symmetric drag profile by mirroring protuberance such as launch lugs, optical windows, etc.

Most importantly, build fins straight and keep their airfoiling simple to minimize chances of inducing a roll moment.

I seem to remember a guy who made a gyroscopic platform for his camera to sit on. The rocket would still roll, but the camera base would not.

Mike Fisher

Assuming you've got a camera or mirror sticking out on one side, try putting something of similar shape on the other side. It seemed to work for me.

Bill Spadafora

or or NARTS snipped-for-privacy@comcast.net snipped-for-privacy@billsplumbing.com

I've heard the term before, but had forgotten it. To be honest, I'm not sure how they work - the descriptions on the net aren't clicking for some reason. Anyone got a URL?

Has anyone actually used them on a rocket?

Already have that.

Built the fins as straight as I could, but there still seems to be a bit of misalignment. The airfoil is real simple. There is none. It's high power and getting to altitude is not exactly a problem with this

3 in. diameter rocket.

Thanks.

Zooty

Neat trick - I'm not sure I could get it to work with this design.

Zooty

The rocket I'm using has a slight spin to it. I was wondering if there was an easy way to knock down the rate of spin.

Ah darn, we all know I want to build a bigger rocket, anyway - hybrid ready (or maybe hybrid only).

Zooty

It's a pretty simple concept - each fin is hinged or pivoted (along a roughly radial axis relative to the airframe) so that it can twist and thereby act like the aileron of an airplane and apply a roll torque.

In the tip of the fin is mounted a small wheel, with its outer edge exposed to the airstream so that it is kept spinning by the dynamic pressure. If the rocket is performing a roll motion, the gyroscopic precession of the spinning wheels will twist the fins in a direction that will tend to counteract the roll motion.

The ASCII art graphic below may help clarify the concept: the trapezoidal shape represents the outline of a fin, and the vertical line to the left of it is the edge of the airframe at the tail of the rocket. The O and the line of dashes indicate the positions of the spinning wheel and the pivot hinge.

| | | ||\ || \ || \ || \ || | || | |--- O || | || | || / || / || / ||/

-dave w

I've had good luck with just being very careful and putting the fins on very straight. I've got one video where the rocket only rotates once in getting to 2000 feet.

Hap Griffin

Zoot, a few things in addition to the aforementioned stuff.

Try to ensure that the mass distribution is also axially centered, in other words, so that you don't have a significant mass (like a camera body) creating an unbalanced condition, when viewed straight down the long axis of the rocket. Try laying out the camera components on a flat disk equal to the diameter of the rocket, to determine the right position for good balance. You may have to counterbalance the camera with some lead (or whatever) if the camera position can't be modified.

Also, if the camera is in the nose section, you could try building a couple of different booster sections to test either different designs, or just multiple copies of one design while trying to get the fins "just right".

Finally, remember if you sand a bevel into one side of a fin's trailing edge, it will act as an airfoil to "pull" the rotation of the rocket in the direction of the bevel. This might be an easier approach to final "fine tuning" of the roll rate, than messing with trim tabs.

Make sure fins and mirror shroud are a straight as possible. Whenever I've had problems with too much spin, it's been due to misaligned fins or (less frequently) a mirror shroud.

Speed is another factor though. A rocket that exhibits very little spin on an J125 might have significantly more spin when flown on a J450.

You can CA a small dowel to the trailing edge of one or two fins as a "spin tab" in the reverse direction of the spin. Cut it shorter for less spin braking, replace it with a larger one for more spin braking. You don't need much. 1/8" x 3" to start.

Jerry

now there's an idea

I can imagine the camera payload body a clear cylinder (polycarbonate?), a mirrored disk with a center cut for the tube to fit through, capped with a shroud for aerodynamics

the camera, positioned on a gyroscopic platform that remains fixed relative to the horizon while ascending, with the camera facing at an angle up and out to the mirror

the camera will always see through the polycarbonate tube to the mirror and down regardless of the roll, and although it would be seeing through different areas of the polycarbonate at different roll attitudes, it would always be oriented the same relative to the horizon

a single axis gyro could provide the signal to a servo which rotates the platform on which the camera sits.

The Robot Marketplace

- iz

That should have been obvious. Didn't think about that. I wonder what the chances are of me getting at least two motors of the same kind at a launch?

If I can go to hybrid, that won't be as much of a problem.

Zooty

from

=== From: snipped-for-privacy@nutation.phys.columbia.edu (Steven K. Kasow) Newsgroups: sci.space.tech Subject: Re: Rolleron Ques. Date: 13 May 1997 22:14:37 GMT

In article , Cb61 wrote: >I recently saw a drawing of a device called a rolleron. It mounts >to the fin of a missile and looks like a circular saw blade. What >is its purpose and principle of operation? I've seen them on >Sidewinders but never knew what they were. >Thanks

I have also seen them - on a Sidewinder mockup. The fins on the rear of the Sidewinder had metal disks resembling your description peeking out of the edge of the fin, with the 'teeth' pointed forward, as if the disks were intended to be spun up by the air stream.

There was one other thing I observed as well- the part of the fin the rolleron was in was subdivided from the rest of the fin and on a pivot: let me try and depict my (probably incorrect) recollection with some ascii graphics.

______________________________________________

body of Sidewinder

______________________________________________ | / | / | / |------- / | /physics student and not an aerospace engineer and am speculating about >the actual purpose of the thing without much hard evidence. I know >there are more experienced and knowledgeable folks out there- am I at >all close here?

Spot on. The Sidewinder's IR seeker head controls pitch and yaw, pointing the missile toward the target. It can cope with a *slow* roll (rotation around the long axis) because it just tries to point the missile toward the target, regardless of which way that is. But if the missile is rolling too rapidly, the controls won't be able to keep up with the changing apparent direction of the target, and the missile will become confused. The rollerons are spun up by the slipstream and gyroscopically deflect the fins, just as Steve speculated, to keep the roll rate down. An elegant low-tech solution to a problem that others solved with much more complex hardware at much greater cost.

-- Committees do harm merely by existing. | Henry Spencer -- Freeman Dyson | snipped-for-privacy@zoo.toronto.edu ===

- iz

Try adjusting the fin airfoil to compensate.

If you want to solve your problem go here:

deltavrocketry.com

Brittian has some interesting hardware.

I'd just use adjustable spin tabs. However, since you are going big and heavy, you could also go active and use a heading hold gyro system to keep the roll angle constant.

Alan

I don't understand how this will help ?

Hy-brids really can't be the same launch to launch. the fill factor is really too random.