WBR GYRO System?

[Going For Time]

I've started a new project. I am working on a gyro system for a Water Bottle Rocket (WBR). I'm using a disc made of delron sheet which I turned down to a 4" disc. I'm using 1/4" delron rod with tappered ends and non-metalic circuit card spacers to hold the rod ends. I have the end pieces made out of the same delron sheet but sized bigger to fit the inside of a 2 litter bottle. The pictures are just a proof of concept without a way to spin the gyro. I hope to get that operational before Friday COB. So far the device is heavy. I plan to lighten the unit by drilling holes in the end pieces. If you have ever seen something like this please let me know if it is worth the time of experimenting. I'm going for a complete non-metalic system.

Going For Time - Prototype Lab

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[SaskAlex]

Well, the idea isn't new, but you might be the first one to actually try it. I remember seeing someone who tried to spin the whole rocket via multiple angled nozzles, but it didn't really work. I think you are going need to get that gyro spinning insanely fast to make it work. It will be really cool if you do get it working, though. Good luck.

Alex

[air.command]

Hi GFT, interesting project. What do you hope to achieve with the gyro setup? Are you trying to get the rocket to fly straight? Or do you wish to use it to sense apogee? Just going off the photo, I'm guessing you are trying to get the rocket to fly straight (the gyro's spin axis appears fixed). If that's the case you'll probably find that it doesn't quite work the way you intend. This is because a gyro's input axis is at 90 degrees to its output axis. So a disturbance on the rocket say coming from the north will cause the rocket to veer east. If you are trying to stabilise your rocket using a gyro you may want to consider putting it in a free moving gimball and then cross link the output to control flaps on your fins at 90 degrees. This way the rocket will react in the right direction. I have seen several attempts of people using gyros on water rockets. The biggest problem I've seen is in the sensitivity of the systems to damage from launch and landings. Make sure you build yours strong enough to withstand these. Good luck with the build.

- George

[SaskAlex]

Hi GFT, interesting project. What do you hope to achieve with the gyro setup? Are you trying to get the rocket to fly straight? Or do you wish to use it to sense apogee? Just going off the photo, I'm guessing you are trying to get the rocket to fly straight (the gyro's spin axis appears fixed). If that's the case you'll probably find that it doesn't quite work the way you intend. This is because a gyro's input axis is at 90 degrees to its output axis. So a disturbance on the rocket say coming from the north will cause the rocket to veer east. If you are trying to stabilise your rocket using a gyro you may want to consider putting it in a free moving gimball and then cross link the output to control flaps on your fins at 90 degrees. This way the rocket will react in the right direction. I have seen several attempts of people using gyros on water rockets. The biggest problem I've seen is in the sensitivity of the systems to damage from launch and landings. Make sure you build yours strong enough to withstand these. Good luck with the build.

- George

George, I've heard this argument before, but I'm not sure if it's quite complete. I'm just taking this material in a mechanics class right now, and I haven't looked at this particular problem in detail, but here's how I understand it. The gyro in the rocket will act just like a top spinning on a table. If the rocket is naturally unstable then a small deviation from being vertical will result in a torque which tends to amplify that deviation. Now, the gyro doesn't simply create an opposite torque as some people might think, but it causes the rocket to precess about the vertical axis, rather than simply rotate about the axis of the torque. Ie, the rocket won't tend to line up perfectly with the vertical, but the axis of the rocket will likely make some small angle with the vertical and it will precess about the vertical. Similar to a spinning top which isn't spinning perfectly. It's not quite how most people think it works, but I think it could theoretically keep the rocket "straight enough".

I might be wrong, but I've never seen any actual analysis of what would happen with a gyro in a rocket, and just thought people might actually be over simplifying it.

Alex

[SaskAlex]

George- My last post didn't do you justice. I didn't look at side winds, as you mentioned, which would exert a torque on the rocket in a constant direction. I agree that a wind from the North would cause the rocket to start to point either East or West (ie. rotate about a horizontal N-S line). However, we can (theoretically) make this rotation as slow as we want by making the angular momentum of the gyro greater.

In the end, the effectiveness of the fixed gyro for either side winds or unstability due to CP being ahead of center of gravity all comes down to the angular momentum you can achieve. I doubt it would ever be enough to "keep the rocket straight" (I don't want to say stable), but I don't see why it's not possible in theory.

[air.command]

In the end, the effectiveness of the fixed gyro for either side winds or unstability due to CP being ahead of center of gravity all comes down to the angular momentum you can achieve. I doubt it would ever be enough to "keep the rocket straight" (I don't want to say stable), but I don't see why it's not possible in theory.

Hi Alex, interesting point, I hadn't thought about using a gyro to keep an otherwise unstable rocket stable. I was thinking that a gyro would have been used to attempt to correct the flight path of an otherwise passively stable rocket. I tend to agree that in practical terms you would need to have a fairly heavy/large or fast enough gyro to be able to directly maintain the rockets attitude.

[thampson]

Hi Guys,

been offline for a while, but hoping to be back into it this summer. Just as an addition this this conversation, we did some work with rc servos for our water rocket car for steering which was working pretty well. These servos are light-ish and small, so you could use a solution like this with 2 servos on 2 sets of fins to possibly control the direction of a water rocket.

look at this video on a plane as an example


-todd-

[marksmandcs]

George is correct. Before i got my engineering degree and was able to mathimatically confirm this(which i did), i attempted this sort of guidence with a model rocket(using the estes black powder engines). The applied torque to the rocket from "wind cocking" resulted in a torque along the axis 90 degrees to the wind cocking torque and the gyro axis. The result was a rocket in the garbage can. Here is what someone else said in another forum:

"It might be useful to consider the effects of a gyroscope as mimicking the effect of an increase in mass, but the dynamics are quite completely different. For example, if a torque is present about a horizontal axis making the gyroscope rotate from vertical, this will induce a rotation about a third axis - also horizontal but perpendicular to the first. This is called precession and will make the rocket execute a gyroscopic wiggle about the vertical axis. The greater the force, the faster the precession with only a small increase in amplitude."

[marksmandcs]

A gyro makes itself useful in rocketry as a reference device for guidence systems. This is because it tends to keep its orientation when NO TORQUE IS APPLIED TO IT. The ideal system will be able to read the gyro's rotation relative to the rockets reference frame and make adjustsments to the rockets flight dynamics in order to correct the flight path. A method that may be a bit simpler than electronically reading the gyro position would be to have the gyro(that is free to rotate in all axes) provide a mechanical link to a steering fin setup. The gyro would be exerting a torque due to mechanical forces needed to operate the fin and therefore precession will happen. So, this mechanical force should be minimized by gearing or other means. This very system was used in Robert Goddards early guided rockets. If you watch the videos, he does get some guidence but there is obviously some precession present in the flight.

[U.S. Water Rockets1]

A gyro makes itself useful in rocketry as a reference device for guidence systems. This is because it tends to keep its orientation when NO TORQUE IS APPLIED TO IT. The ideal system will be able to read the gyro's rotation relative to the rockets reference frame and make adjustsments to the rockets flight dynamics in order to correct the flight path. A method that may be a bit simpler than electronically reading the gyro position would be to have the gyro(that is free to rotate in all axes) provide a mechanical link to a steering fin setup. The gyro would be exerting a torque due to mechanical forces needed to operate the fin and therefore precession will happen. So, this mechanical force should be minimized by gearing or other means. This very system was used in Robert Goddards early guided rockets. If you watch the videos, he does get some guidence but there is obviously some precession present in the flight.

Have you considered an electronic gyro system that controls servo motors? We've done some experiments with such a system to stabilize our rockets and cancel spinning. As long as you don't exceed to maximum angular speed of the servo, it does a good job, and you can use a microcontroller to scale or filter the input signals in ways a purely mechanical system cannot easily do.

[Going For Time]

All of these posts have been great. Thank you for the guidance on how the Gyro should be used and what the effects would be if used in a WBR in the way I had intended. My primary goal is a WBR without any metal parts, which includes no circuitry for electronics. My intentions for the gyro being used in the nose of the WBR was for stability and straight vertical flights. With the information given in the posts above I'm lead to believe a force acted upon the rocket from a direction would result in a correction in a direction 90° from the opposing force. I can see this causeing a spiraling effect unless countered by a guidance system using servos that would direct the fins to counter this effect. So, in conclusion I will forgo the gyro until a later date when I move from non-metalic to some circuitry with very little metal moving parts.

[U.S. Water Rockets1]

All of these posts have been great. Thank you for the guidance on how the Gyro should be used and what the effects would be if used in a WBR in the way I had intended. My primary goal is a WBR without any metal parts, which includes no circuitry for electronics. My intentions for the gyro being used in the nose of the WBR was for stability and straight vertical flights. With the information given in the posts above I'm lead to believe a force acted upon the rocket from a direction would result in a correction in a direction 90° from the opposing force. I can see this causeing a spiraling effect unless countered by a guidance system using servos that would direct the fins to counter this effect. So, in conclusion I will forgo the gyro until a later date when I move from non-metalic to some circuitry with very little metal moving parts.

It's fabulous that you have come up with an original goal and are paving your own way with your own research and sticking to your plan. That's the sign of a true innovator! You get a big thumbs up for thinking outside the box and setting a lofty but achievable goal! Please post updates as you progress and everyone can follow along and offer suggestions if you get stuck.