Corona688

NOT A BUG: Reaction wheels don't care where they're mounted

102 posts in this topic

31 minutes ago, String Witch said:

This may be unrelated, but, what makes a long thin spacecraft take longer to build up rotational speed? Or does it just seem that way because all my long spacecraft are generally much heavier than my short ones?

Even if the long an the short ones were the same mass it would take much longer for the long ones to start spinning coz some of their mass is much further out than on te short ones. As we all know, pulling a long lever requires much less force if we pull on the end that is farthest from the joint. But the closer to the joint u get, the harder it is to pull the lever. On ur long ships that means the further out u place ur RCS relative to the CoM the faster the ship is gonna react. But reaction wheels are just spinning mass so with those only their torque in relation to the ship's mass and shape is relevant. Their position still doesn't matter.

Let's look at the well known ice dancers doing their pirouettes again: When they spread their arms during spinning they slow down coz the same mass moving at the same speed is moved further away from the center of rotation and has to travel further to achieve the same angle of rotation. Likewise, if they pull their arms in they'll spin faster again.

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4 hours ago, Snark said:

Actually, turns out there are zero spinning thingies inside those cylinders we add to our craft, because they're just polygon models that exude magical torque from nowhere.  I'm not being pedantic, here-- it's very relevant, because KSP reaction wheels are very unrealistic, in one very important way:  they violate the heck out of conservation of angular momentum, even though they obey conservation of linear momentum.  :wink:

That particular unrealistic aspect of their operation, however, is irrelevant to this thread.  They're unrealistic in that they create torque from nowhere.  Other than that (which I realize is kind of like saying "other than that, Mrs. Lincoln, how did you like the play?", but please bear with me, here), they're modeled realistically, in every way that is germane to the discussion in this thread.  Whether they conserve angular momentum or not has nothing to do with "does placement matter?"  Placement doesn't matter, whether they work like IRL reaction wheels or whether they magically create torque from nowhere.  Torque is torque.  Once you've got the torque, it behaves in certain ways, which is why placement doesn't matter.

 

Well apparently the position of the spinning thingies inside the "reaction wheel" assembly does matter, even if the position of the assembly itself in the spacecraft doesn't matter.

I suspect this is what all the confusion relates to: the cylinder model we place in a spacecraft in the game is not meant to represent a single "wheel spinning." It represents at least three if not four wheels spinning (inside of it) arranged in geometry that allows their combined spinning at various revolutions to exert torque in any direction. No?

 

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27 minutes ago, Diche Bach said:

Well apparently the position of the spinning thingies inside the "reaction wheel" assembly does matter

Citation please?

The orientation of the spinning thingies (specifically, the orientation of their axes) matters.  If you have three of them, they should be arranged with their axes at 90 degrees relative to each other.  If you have four of them, they should be arranged with their axes pointing the same way that tetrahedron vertices point.  But that's orientation.  The position doesn't matter at all.

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Pedantic much? :sticktongue:

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3 minutes ago, Diche Bach said:

Pedantic much? :sticktongue:

No, literally addressing the topic of this thread.

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It seems to me the point is: the relative positions of the spinning wheels do matter (if their orientations are all that matter then they wouldn't even need to be on the space craft now would they?). The prevailing confusion on the topic comes from the misconception that a "reaction wheel" in game is meant to represent ONE wheel, when in fact it must be representing a module with multiple wheels in it, three, four, whatever.

It is the combined spinning of these electric motors which can produce torque in any direction, thus the position of the "reaction wheel" (really more accurately the "reaction wheel assembly") on the spacecraft doesn't matter, as long as it is affixed to the spacecraft with sufficient adhesion, the computer that runs it knows where it is (and thus how exactly to spin it's innards so as to achieve any particular torque), and the specs of the assembly itself are sufficient for the craft in question (how much electricity does it require, how much heat does it generate, how big is the asembly, etc., etc.).

Obviously, in order to function as an assembly, the wheels need to be within a certain proximity to one another, and mounted on a common frame and with the correct spacing relative to the orientation of their axes and the range of velocities at which they will spin. I'm going to go out on a limb here and guess that smaller wheels can manage the same effect as bigger wheels but they have to be spun faster and/or spaced farther apart?

ADDIT: little daydreamy thought I just had . . . Nano Reaction wheels! 

Edited by Diche Bach
idear

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12 minutes ago, Diche Bach said:

It seems to me the point is: the relative positions of the spinning wheels do matter (if their orientations are all that matter then they wouldn't even need to be on the space craft now would they?).

That's just being silly now. The point is that they don't matter, actually, as was said already. They have to be in the craft because they transfer torque by being mechanically attached to it, not because of relative position. If you want to affix it at the opposite end of a kilometer-long pole attached to the rocket, sure, go ahead. The torque will be the same. The rocket's moment of inertia, on the other hand, will skyrocket (heh), and the same torque won't be nearly enough anymore.

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Well correct me if I'm wrong, but the positions of the wheel_s_ DO matter. It is the position of the assembly of wheels that does not matter.

The assembly torques itself by virtue of a set of wheels inside it. It thus torques anything it is attached to, and it doesn't matter where it is attached to it. But for any given set of wheels, they must require a particular positioning relative to one another (spacing, orientation, the whole nine yards) inside the assembly of wheels.

It is okay if we don't understand this stuff and can just muddle through it as fellow gamers, eh? It is after all not a conference on rocket science at which any of us are posing themselves as professionals.

ADDIT: here is what a "real" one looks like. Pretty much what I expected.

 

Edited by Diche Bach

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26 minutes ago, Diche Bach said:

It seems to me the point is: the relative positions of the spinning wheels do matter (if their orientations are all that matter then they wouldn't even need to be on the space craft now would they?)

 

26 minutes ago, Diche Bach said:

the wheels need to be within a certain proximity to one another

No, position doesn't matter and they don't need to be within a given proximity, as long as they are correctly oriented and fixed to a rigid frame, and the computer that controls them knows how they are oriented, balanced and spaced. Torque performance will be affected by spacing and rotation speed etc, but the torque-magnitude and direction-of-torque of each individual flywheel are based only on the mass distribution, rotation speed and orientation of that wheel. Complex interactions between tetrahedrally distributed wheels are more complicated when the distribution and balancing aren't uniform, but they're still possible because they can be balanced dynamically by a computer through rotation speed.

It is convenient to build a 'set' of wheels as a functional unit, and size and spacing may be specified for practical reasons, but the theory of how the system works does not require this.

Edited by The_Rocketeer

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23 minutes ago, The_Rocketeer said:

 

No, position doesn't matter and they don't need to be within a given proximity, as long as they are correctly oriented and fixed to a rigid frame, and the computer that controls them knows how they are oriented, balanced and spaced. Torque performance will be affected by spacing and rotation speed etc, but the torque-magnitude and direction-of-torque of each individual flywheel are based only on the mass distribution, rotation speed and orientation of that wheel. Complex interactions between tetrahedrally distributed wheels are more complicated when the distribution and balancing aren't uniform, but they're still possible because they can be balanced dynamically by a computer through rotation speed.

Another way of saying: any positioning is possible as long as it is the "correct" position, in that only positions that allow the wheels to function as intended are possible.

It makes sense that there is a wide range of possible positions that can work, but given the the specs of the wheels and the way they will function it would seem to me that there is one ideal position and that the further the wheels are from that ideal relative positioning the less efficient it will function.

Seems to be some fascinating engineering innovations underway in this area!

 

ADDIT: Hah! I love the top-rated comment on that video:

Quote

 

Bah! My Washing machine does this and more when I put a BRICK in it!

One question that emerges though: I see that several of these have the wheels in a similar arrangement (the 90-degrees relative to axes of spin like Snark said above). But what about the "4-wheel" model (three with a backup) in a tetrahedral arrangement I see referred to in various wiki and youtube sources? What the heck does that look like?

I guess the four wheels are arranged flat and centered on the faces of the tetrahedron?

Tetrahedron.jpg

 

Edited by Diche Bach
humoh

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14 minutes ago, Diche Bach said:

Another way of saying: any positioning is possible as long as it is the "correct" position, in that only positions that allow the wheels to function as intended are possible.

It makes sense that there is a wide range of possible positions that can work, but given the the specs of the wheels and the way they will function it would seem to me that there is one ideal position and that the further the wheels are from that ideal relative position and that the further the wheels are from that ideal relative positioning the less efficient it will function.

If the 'correct' position is the one that the controlling computer program recognises as being where the wheels are, then I guess yes. Otherwise, no.

On a Y-shaped craft 20mx30mx1m in size, you could have one wheel at each of the extremities of the Y-shape that were each completely different sizes and different distances from the true CoM. As long as they faced perpendicular x/y/z axes relative to one another (not the craft) and as long as the controller program was correctly programmed, the craft would be fully controlable. So it truly doesn't matter where the wheels are, or how big the unit is, as long as it is correctly calibrated and controlled. The craft will always rotate around it's CoM wherever any wheel of any size on any rotational axis is physically placed on the vessel, and it will always rotate at a speed that is a function of the wheel's mass distribution and rotation speed. That's all that really matters for the system to work.

The necessary controller program will always have to exist to steer the vessel correctly anyway, so whether the physical parameters of each wheel in the system are wildly different or generally uniform makes very little difference as long as they are accurately entered into the program. Of course uniformity has other engineering benefits, like the cost of replacements for one thing, and having everything in a neat little box is very convenient, especially on a size-shape-and-mass-limited spacecraft, but that has nothing to do with the physics behind how the system actually works.

Edit:

Just to be clear, I have consistently used 'oriented' to mean 'directionally facing' and 'position/distribution' to mean 'relative position from other wheels in the system/on the craft'.

Edited by The_Rocketeer
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Interesting Rocketeer, however, another question: I could almost conclude that what you are suggesting is that: "any position of the three or more wheels can function equally as well as any other position, and for equivalent 'cost' [time, energy, wear-and-tear]." That seems rather counterintuitive, and is probably not what you intend to mean, but as I say, it seems one can go from what you are saying to that extreme.

Let us say we have 100kg spacecraft. We have (I don't know my physics at all . . .) 10 watts of power allocated to our reaction wheel part of the project. The craft needs to be able to achieve 10-degrees in any direction within 30 seconds of receipt of a maneuver command, and with no more than 0.001 degree of error within +/- 1 second (something like that). The unit cannot generate more than 1-degree Centigrade of waste heat, and the unit must function for 10 years minimum. The unit overall cannot weigh more than 2.2kg and it cannot cost more than $50,000 . . . yadda, yadda . . . .

If we have specifications like this that we need to meet in designing one of these, then the theoretical "any position is possible" has to go right out the window eh?

For any given purpose/specifications, there will be ONE or at least a narrow range of configurations for the wheels inside the given reaction wheel assembly that will serve well, no?

But again, the position of the module itself is irrelevant, except for wobble . . .

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8 minutes ago, The_Rocketeer said:

If the 'correct' position is the one that the controlling computer program recognises as being where the wheels are, then I guess yes. Otherwise, no.

On a Y-shaped craft 20mx30mx1m in size, you could have one wheel at each of the extremities of the Y-shape that were each completely different sizes and different distances from the true CoM. As long as they faced perpendicular x/y/z axes relative to one another (not the craft) and as long as the controller program was correctly programmed, the craft would be fully controlable. So it truly doesn't matter where the wheels are, or how big the unit is, as long as it is correctly calibrated and controlled. The craft will always rotate around it's CoM wherever any wheel of any size on any rotational axis is physically placed on the vessel, and it will always rotate at a speed that is a function of the wheel's mass distribution and rotation speed. That's all that really matters for the system to work.

The necessary controller program will always have to exist to steer the vessel correctly anyway, so whether the physical parameters of each wheel in the system are wildly different or generally uniform makes very little difference as long as they are accurately entered into the program. Of course uniformity has other engineering benefits, like the cost of replacements for one thing, and having everything in a neat little box is very convenient, especially on a size-shape-and-mass-limited spacecraft, but that has nothing to do with the physics behind how the system actually works.

Edit:

Just to be clear, I have consistently used 'oriented' to mean 'directionally facing' and 'position/distribution' to mean 'relative position from other wheels in the system/on the craft'.

^ This. /Thread

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The tetrahedral arrangement has faces at 60 degree angles instead of 90 degrees. The wheels are managed by a more sophisticated controller program that adjusts multiple wheel speeds per axis of rotation. The engineering benefit is probably primarily redundancy, as if any one wheel fails there is still limited rotation (but less total torque) on any given axis. I'm not an engineer, however.

7 minutes ago, Diche Bach said:

If we have specifications like this that we need to meet in designing one of these, then the theoretical "any position is possible" has to go right out the window eh?

For any given purpose/specifications, there will be ONE or at least a narrow range of configurations for the wheels inside the given reaction wheel assembly that will serve well, no?

Again, not an engineer, but I believe the 'optimal configuration' is simply going to be the one that fits most neatly into the overall craft design and has sufficient power and mass to deliver the required rotation performance. Such limitations, though, have less to do with the laws of physics than the constraints of the design specification. However, in terms of how well the craft will turn, it would turn just as well if the same wheels where placed 'anywhere' on the craft as it does with them in their neat 'reaction wheel assembly' box. It could theoretically turn just as well with smaller/less massive wheels turning faster, or larger/more massive wheels turning slower (except for the conservation of angular momentum issue, which is another story).

Edit:

Again, for clarity, I am speaking primarily of the physical properties and interactions that allow such a system to work, rather than the practical application of the same to real spacecraft projects. In other words, I am speaking of the physical effect, not the logistics of building something that demonstrates it.

Edited by The_Rocketeer

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1 hour ago, Diche Bach said:

Another way of saying: any positioning is possible as long as it is the "correct" position, in that only positions that allow the wheels to function as intended are possible.

Position doesn't matter, only orientation of the axes. If you relocated one of the wheels to another location but kept orientation the same it would work just as well, and with the same controller.

1 hour ago, Diche Bach said:

One question that emerges though: I see that several of these have the wheels in a similar arrangement (the 90-degrees relative to axes of spin like Snark said above). But what about the "4-wheel" model (three with a backup) in a tetrahedral arrangement I see referred to in various wiki and youtube sources? What the heck does that look like?

I guess the four wheels are arranged flat and centered on the faces of the tetrahedron?

 

They don't have to be centered on the faces, just have their axes perpendicular to them. The tetrahedral face-centered arrangement is useful for compactness and reduced structural mass but being centered on the faces doesn't affect functionality directly. Position does not matter for imparted torque on the craft.

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The relative positioning of individual reaction wheels in the assembly matters only from the structural stress point of view:
When craft rotates around some axis, wheels that are not along this axis (if they are rotating at the moment) will create plenty of torque that they will have to compensate for each other by altering the rotation rates. And here you get a bunch of torque on individual wheels that doesn't go outside of the gyro assembly, because the wheels compensate that. So you want to have them close to each other on a very rigid assembly. Just because its internal stress will be much higher than the stress on attachments to the other other parts of the spacecraft

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23 hours ago, Diche Bach said:

Pedantic much? :sticktongue:

No, just pointing out that what you said was not correct.  I went into technical detail because I wasn't sure whether you said what I thought you might be saying (in which case you'd be flat-out wrong), or else maybe I just misunderstood you.  Turns out it was the first one.  :wink:

23 hours ago, Diche Bach said:

It seems to me the point is: the relative positions of the spinning wheels do matter

No.  They don't.  They really don't.  Essentially you've gone back to "the position of a reaction wheel matters", which was the initial assertion in this thread, and which is simply, flat out incorrect, as has been demonstrated at length in this thread.

23 hours ago, Diche Bach said:

(if their orientations are all that matter then they wouldn't even need to be on the space craft now would they?)

False comparison.  They do need to be rigidly attached to the spacecraft.  But other than that requirement, it doesn't matter where they are, either relative to each other or relative to the rest of the spacecraft.

23 hours ago, Diche Bach said:

the position of the "reaction wheel" (really more accurately the "reaction wheel assembly") on the spacecraft doesn't matter, as long as it is affixed to the spacecraft with sufficient adhesion

You're correct in that, but for the wrong reason, because,

23 hours ago, Diche Bach said:

the computer that runs it knows where it is (and thus how exactly to spin it's innards so as to achieve any particular torque)

...wrong.  The computer doesn't have to know where the reaction wheel is.  Because the placement doesn't matter.  The reason placement doesn't matter is not because there's some smart software that compensates for placement.  It doesn't matter because it really, honestly, truly, physically doesn't matter.

 

23 hours ago, Diche Bach said:

Obviously, in order to function as an assembly, the wheels need to be within a certain proximity to one another

No, not at all.  It may be "obvious" to you, but it's wrong.  Doesn't matter where they are relative to each other.  One wheel could be out at one end of the craft, another could be at the opposite end, etc.  Doesn't matter in the slightest.  If they're packed together in a small assembly, it's only for reasons of engineering convenience.  All that matters is the relative orientation of their axes.  As long as each of the wheels is rigidly attached to the frame of the craft, that's all that matters.

23 hours ago, Diche Bach said:

I'm going to go out on a limb here and guess that smaller wheels can manage the same effect as bigger wheels but they have to be spun faster and/or spaced farther apart?

You're correct that they'd need to be spun faster.  Doesn't matter how they're spaced because placement doesn't matter.

22 hours ago, monstah said:

That's just being silly now. The point is that they don't matter, actually, as was said already. They have to be in the craft because they transfer torque by being mechanically attached to it, not because of relative position. If you want to affix it at the opposite end of a kilometer-long pole attached to the rocket, sure, go ahead. The torque will be the same. The rocket's moment of inertia, on the other hand, will skyrocket (heh), and the same torque won't be nearly enough anymore.

^ Quoted for truthiness.

22 hours ago, Diche Bach said:

Well correct me if I'm wrong, but the positions of the wheel_s_ DO matter.

Okay, you're wrong.  :)  It doesn't matter.  Really.  Go back and read what all the physics majors in this thread are telling you.

22 hours ago, Diche Bach said:

ut for any given set of wheels, they must require a particular positioning relative to one another (spacing, orientation, the whole nine yards) inside the assembly of wheels.

Orientation, yes.  Spacing, nope.

22 hours ago, The_Rocketeer said:

No, position doesn't matter and they don't need to be within a given proximity, as long as they are correctly oriented and fixed to a rigid frame, and the computer that controls them knows how they are oriented, balanced and spaced. Torque performance will be affected by spacing and rotation speed etc, but the torque-magnitude and direction-of-torque of each individual flywheel are based only on the mass distribution, rotation speed and orientation of that wheel. Complex interactions between tetrahedrally distributed wheels are more complicated when the distribution and balancing aren't uniform, but they're still possible because they can be balanced dynamically by a computer through rotation speed.

Mostly correct.  I've taken the liberty of highlighting in red the bits that aren't quite there.  Spacing doesn't matter.  Everything else you mention, does.

22 hours ago, Diche Bach said:

Another way of saying: any positioning is possible as long as it is the "correct" position, in that only positions that allow the wheels to function as intended are possible.

Not quite.  I've taken the liberty of striking out the necessary phrases to make the statement correct.

22 hours ago, Diche Bach said:

there is one ideal position and that the further the wheels are from that ideal relative positioning the less efficient it will function.

Nope.  Because, again, position doesn't matter.  Relative orientations of axes matter.  Location doesn't.

22 hours ago, Diche Bach said:

I guess the four wheels are arranged flat and centered on the faces of the tetrahedron?

Basically yes.  Or you could think of them as pointing in the direction of the vertices.

The reason for having a 4-wheel tetrahedral setup, rather than a 3-wheel XYZ setup, is redundancy.  If you have a 3-wheel XYZ setup, then if any one wheel fails, the craft completely loses the ability to orient itself on that axis.  Whereas with a 4-wheel tetrahedral setup, any set of 3 of the wheels has the ability to do full 3D orientation on any axis.  Therefore, it's fault tolerant-- any one wheel can fail and it still works (albeit at reduced capacity).

21 hours ago, Diche Bach said:

That seems rather counterintuitive, and is probably not what you intend to mean

It may be counterintuitive, but it happens to be correct.  So I assume he does mean precisely that.  :wink:

21 hours ago, Diche Bach said:

Let us say we have <situation>

If we have specifications like this that we need to meet in designing one of these, then the theoretical "any position is possible" has to go right out the window eh?

For any given purpose/specifications, there will be ONE or at least a narrow range of configurations for the wheels inside the given reaction wheel assembly that will serve well, no?

No, it doesn't go out the window, because the positions don't matter.  Really doesn't.  The only reason to put them together in an assembly is if the engineering makes it convenient to do so.

21 hours ago, The_Rocketeer said:

The tetrahedral arrangement has faces at 60 degree angles

Actually, they're at 109 degree angles.

 

21 hours ago, The_Rocketeer said:

Again, not an engineer, but I believe the 'optimal configuration' is simply going to be the one that fits most neatly into the overall craft design and has sufficient power and mass to deliver the required rotation performance. Such limitations, though, have less to do with the laws of physics than the constraints of the design specification. However, in terms of how well the craft will turn, it would turn just as well if the same wheels where placed 'anywhere' on the craft as it does with them in their neat 'reaction wheel assembly' box.

^ This.

20 hours ago, Red Iron Crown said:

Position doesn't matter, only orientation of the axes. If you relocated one of the wheels to another location but kept orientation the same it would work just as well, and with the same controller.

^ And this.

3 hours ago, Alchemist said:

The relative positioning of individual reaction wheels in the assembly matters only from the structural stress point of view:

^ And this.

If you'd like the reasons behind my repeated assertions here that "placement doesn't matter", I'd suggest going back through this thread and carefully reading the posts that give detailed, specific physical examples, often with numbers backing them up.  :wink:

 

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23 hours ago, Diche Bach said:

It seems to me the point is: the relative positions of the spinning wheels do matter

Not really, just the direction they point.  You could break it up into 3 unidirectional reaction wheels, an X, a Y, and a Z, scattered on different points of your craft.  As long as they turn in the right plane of motion they will act the same at any location.

It took me a while to get over this bit:  Lever-effect happens when the center of rotation is forced to be somewhere other than the center of mass.  No fulcrum?  No lever.  No lever?  No lever-effect.  No amplification or reduction of torque.  Every location is equally (in)efficient.

Edited by Corona688

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So in summary, they can be in any permutation of positions which fits two conditions:

1. The positions are all attached to the spacecraft.

2. The orientation of the axes of the wheels is appropriate for the wheels to be able to function as they are intended.

There are many possible permutations of positions for three or four wheels on any given space craft which fit these two conditions. However, the wheels have to be connected to the space craft and the axes of the wheels have to be oriented correctly, so position obviously does matter. Saying "position does not matter" means they can be anywhere, even not on the spacecraft, and that is obviously wrong. Even given they are on the spacecraft, the three wheels cannot be grinding against one another: there needs to be space for each of them to spin freely, and given the orientation of their axes of spin have to be correct, this means that there is inherently a finite number of positions which will allow the wheels to function properly on any given space craft. A very large finite number, but not infinite, which is the required condition for me to accept the assertion that "position does not matter."

But all of that is just theory. In practice, they need to be where it is best suited for the engineering of the craft, and this will generally reduce the viable permutation of positions from the very large "possible" set to a much smaller "viable" set.

Why this is such a contentious topic I cannot fathom.

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@Snark yes you're quite right. I had a feeling something I said wasn't quite on target - the 3rd parameter I meant to highlight was the mass-distribution of each wheel, rather than their spacing from one another. For example, I believe spoked wheels with heavy rims would be more effective than solid discs of equivalent mass.

Edit: actually I just realised where the confusion arises - all I really meant was that (rather obviously) the controlling computer just needs to know which wheel is which so it turns the right one/s for the right axial rotation. I guess I was a bit ambiguous here. :blush:

Edited by The_Rocketeer

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1 minute ago, Diche Bach said:

So in summary, they can be in any permutation of positions which fits two conditions:

1. The positions are all attached to the spacecraft.

2. The orientation of the axes of the wheels is appropriate for the wheels to be able to function as they are intended.

There are many possible permutations of positions for three or four wheels on any given space craft which fit these two conditions. However, the wheels have to be connected to the space craft and the axes of the wheels have to be oriented correctly, so position obviously does matter.

Well, not really.  It can be clipped as far out into space as it will let you and still work.  People have built space bases by clipping things hundreds of meters apart.

I get your point, though.

1 minute ago, Diche Bach said:

But all of that is just theory. In practice, they need to be where it is best suited for the engineering of the craft, and this will generally reduce the viable permutation of positions from the very large "possible" set to a much smaller "viable" set.

Why this is such a contentious topic I cannot fathom.

I misunderstood your post.  I thought you were saying again that they should work better at the center of mass.  I apologize.

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1 hour ago, Snark said:

Actually, they're at 109 degree angles.

Another good point, tho we are talking at slightly cross purposes. Turns out the dihedral angle of the tetrahedron I was using is still not 60 degrees, although the equilateral triangle that describes each face is comprised of them - it's actually 70.528779 degrees. Who knew! (Well, Snark obviously... and probably others...)

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Just now, Corona688 said:

Well, not really.  It can be clipped as far out into space as it will let you and still work.  People have built space bases by clipping things hundreds of meters apart.

I get your point, though.

I misunderstood your post.  I thought you were saying again that they should work better at the center of mass.  I apologize.

No harm done! Before reading the lengthy explanations, I'm not sure how well I understood how these things work, but I don't think I was ever in the "it needs to be far from the center of Mass" group :sticktongue:

I still think that the primary source of confusion is that the game leads players to think that the model they are placing in their space ship is ONE wheel, when in fact, what it models in real life would be: a cylindrical container with three or four wheels inside it, each positioned inside the container so that their orientations are appropriate (either the 90 or 109 degree angles Snark refers to) and so that they axles are all attached to the space craft and can thus impart their torque (and receive their instructions for when to spin and how fast, etc.).

If you think about it, it doesn't make sense that you can take A WHEEL and place it ANYWHERE attached to the spacecraft and have it impart torque in any direction, and I think this is really the source of confusion for most. However, when one considers three or more wheels spinning in an orchestrated manner it is probably much less counterintuitive.

Am I right or what?

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8 minutes ago, Diche Bach said:

If you think about it, it doesn't make sense that you can take A WHEEL and place it ANYWHERE attached to the spacecraft and have it impart torque in any direction, and I think this is really the source of confusion for most.

They're completely separate questions, though.  Even if it was one single fixed wheel, its torque would be the same no matter where it was mounted, it'd just be limited to exerting it in one axis.

Whatever mental model helps you see it best though.

Quote

However, when one considers three or more wheels spinning in an orchestrated manner it is probably much less counterintuitive.

Am I right or what?

It's not that intuitive, period.  :sealed:  It's not the sort of thing you can easily demonstrate with ramps and wheels.  KSP taught me something college-level physics hadn't.

Edited by Corona688

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Using assemblies of rapidly spinning electric wheels to orient space ships, and make self-assembling robots . . . We've come along way from cracking rocks into jagged chunks and hacking wildly at carcasses to cleave off something tasty . . . but most of us probably still operate at about that level :wink:  

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