Reactionless drive using reversers [Dawnshard]

[Chiberty]

Normally, when you want to make something accelerate, a force must be applied from some external source. With Newton's 3rd law of motion, the same force will also be applied in the opposite direction on that source. Because of this limitation, any sort of vehicle we build must be pushing or shooting something backwards. With land vehicles, the ground is pushed backwards; in rockets, stuff is shot out the bottom. However, using fabrials, we can get around this.

This topic would be possible without RoW and DS spoilers, but the information we get about fabrial mechanics in both of those is too relevant to leave out.

The main fabrial mechanic that my design uses is the ability of a pair of reversers to remain completely immobile in the perceived reference frame. If you already know about what I'm referring to, skip to the next section, otherwise, I explain that mechanic here:

Spoiler

Look at Navani's archer towers:

Spoiler

In the sequence of images shown on the left, picture where the center point between the two platforms is. In each of the four images, the center point is at the same location. Because of how reversers operate, when active, the center point of the two halves will not move. Now, as we see in Dawnshard, what counts as "moving" is influenced by perception. The reversers were affected by the perceived frame of reference, and anything moving with the boat was treated as stationary. Of course, that is still true on the larger scale, as one fabrial half doesn't shoot off the planet as the other is carried around the sun by Roshar. This ability of reversers to keep the same center point in a perceived reference frame can be manipulated for odd effects. Picture now on the 4th step shown in Navani's sketch, the archer tower being above the other platform. When the other platform is released, what will happen? The heavy archer tower will fall down towards the platform, but the platform would also rise up to meet to archer tower. When they do meet, they will remain floating in the air. They will not fall towards the ground, as the center point must remain in the same place.

This can be used to make a device that, when activated, will remain immobile relative to the perceived reference frame. If the two halves are held together, they can't move apart, but as we see with the archer towers, the center point won't move, so both halves will just remain at that point. (Yes, I know I said "perceived reference frame" a lot)

The design:

Spoiler

The most important components of the design are two pairs of reverser fabrials. Attach the matching halves, or place them in the same box, so they will remain immobile when activated. Now, we didn't learn exactly how conjoiners are activated/deactivated in RoW, but spanreeds show that that is possible. I am assuming that there is some mechanical means by which to activate/deactivate them, perhaps by using logicspren clocks to activate and deactivate them in a pattern. 

In addition to the reversers, this design uses a fabrial that can be switched from attractor to a repeller using iron and steel wires controlled by a fabrial clock, along with the solid that is affected by that fabrial. This solid the fabrial is made to affect would preferably be as unique as possible, so the fabrial would not try to push and pull on objects that are not part of them machine. These components are not strictly necessary, as all you need is a device that can push and pull, or expand and contract. Really, this component is just a way of converting Stormlight energy to mechanical energy. A electricity-powered linear actuator would also work.

To assemble this, attach the attractor/repeller fabrial to the top of one of the reverser boxes, and attach the corresponding affected object to the bottom of the other reverser box. Attach the box with the object on the bottom to the top of the other box using rails that will allow the two boxes to slide up and down, but not to the sides, forcing the boxes to stay arranged vertically. Next, the timing fabrials must be made to activate in the following sequence: First, activate the reversers in the bottom box, immobilizing it. Then, activate the fabrial affixed to its top in repeller mode. The other box should be pushed up by the repeller. Next, activate the reversers in the top box, immobilizing it. Then, switch the repeller fabrial into attractor mode and  deactivate the reversers in the bottom box. The bottom box should be pulled up to meet the top one. Repeat this process, and the contraption will rise into the air, and the only work done on pieces of the contraption will have been internal to the system, impossible under normal physical laws.

(Note that either the extension length of the rails must be limited, or the attractor must be run at a higher power than the repeller in order to make sure the attractor force is greater than that of gravity.)

Above is an image illustrating the process. The ovals represent fabrials, and purple indicates reversers. Active fabrials are glowing blue.

 

Edited December 14, 2020 by Chiberty

[Gderu]

So far we have not seen any repellers/attractors that have been able to apply as much force as is required in your schematic. The best they seem to be able to do is push or pull on liquids to attract them. I seriously doubt they'd be able to apply enough force to counteract gravity in this design.

[Blackwarder]

I had a similar idea while reading part one and than onward into the book.

One thing to remember is that conjoined gems when one is begged than the other will result in corresponding change in movement.

I need to sit down and see if I’m right but I’m pretty sure than we can build a piston like engine that can at least propel an aircraft forward. 
 

 

[Chiberty]

4 hours ago, Gderu said:

So far we have not seen any repellers/attractors that have been able to apply as much force as is required in your schematic. The best they seem to be able to do is push or pull on liquids to attract them. I seriously doubt they'd be able to apply enough force to counteract gravity in this design.

I disagree, as in Dawshard, they are used them to move weights in the ship to stabilize it, which would be uphill, and they are also used in fabrial pumps, which requires them to pull water uphill.

The repelled/attractor is not very important though. Anything that can push and pull could be used.

[PeterElricPines he/him]

Ooh, I really like this! Thing is, it'd still be able to shift around laterally. This design lets you control your movement in one dimension, but it would be unstable in other directions, and you'd have no control over it. And I dunno about you, but if I'm gonna go on a spaceship to another solar system, I'd prefer to drive something that can turn. And something impractically expensive. So what you could do is just make three of these monsters and stick 'em together with Flex Tape so they're all perpendicular to each other. Then you can just lock two of them in, and voila, you're only moving along one axis. Full three dimensional control of your motion.

Now, this may seem unrelated at first, (because it kinda is) but I promise I'll come back to sticking giant Minecraft pistons together. As technology advances, conjoiner fabrials will become more and more valuable. There must be a way to put very small conjoiners in computers for something similar to super fast internet. Computers built with these would be bigger than ours for a while, but I'm thinking deep future. In theory, you could expand into nanotechnology to use the space efficiently enough to build computers that would be small by our standards. I know nothing about computers, but hold your booing until the end. So, now we have tiny computers that can communicate instantaneously, as well as Connections to Honor and Cultivation. One to advance, and one to bring people together. Now, what better way to do both those things at once than to stick computers in your brains and make a hive mind!

So this just seems like a really cool way for Roshar to advance in the future, so they'd end up being a hive mind of cyborgs that fly through space in giant cubes-

Spoiler

... Huh.

That green there could be Lifelight.

 

[Chiberty]

On 12/19/2020 at 11:51 PM, PeterElricPines said:

Ooh, I really like this! Thing is, it'd still be able to shift around laterally. This design lets you control your movement in one dimension, but it would be unstable in other directions, and you'd have no control over it. And I dunno about you, but if I'm gonna go on a spaceship to another solar system, I'd prefer to drive something that can turn. And something impractically expensive. So what you could do is just make three of these monsters and stick 'em together with Flex Tape so they're all perpendicular to each other. Then you can just lock two of them in, and voila, you're only moving along one axis. Full three dimensional control of your motion.

Welcome to the Shard! (Well, to the forum version at least, since you were already on the discord)

I really like the idea of sticking three perpendicular ones together for 3D movement. In regards to the instability in certain directions, I had some thoughts about a way you could use regular conjoiners to fix that. Since moving a conjoiner half in a direction causes the other to move in the same direction, I think they might be able to be used to resist rotation. If you had one half attached to one side of a wheel, and the other half attached to the other side, when you try to spin the wheel, it will try to push one of the halves up and the other half down. But, since the conjoiners will try to move the same direction, there will just be a stress on the gems, and it won't spin. Using this in a similar way that my design above uses reversers, you could control a rotational degree of freedom. Combine three of these rotational control devices with the three lateral ones, like you suggested, and you'd have control over all 6 degrees of freedom, without needing any sort of reaction mass for any of it.

 

Edited May 9, 2021 by Chiberty

[impec1995]

Pretty sure this wouldn't work due to the fact that when you pull or push, an equal and opposite force is applied on the object that is pushing or pulling (We can see this very clearly in allomatic steelpushing and ironpulling). So for example when the machine would be pushing the other part upwards, it will fall down around the same height. Meaning that the center point between the two conjoiner fabrials will stay equal at all times when they push or pull each other without any support or external force.

The machine would only fly as long as something is keeping it from applying the force that occurs when pushing or pulling on the bottom part, like the ground. This should generally be the case with all methods of pushing or pulling due to the newton's 3rd law. I'm not exactly sure if this would actually work then.

[Chiberty]

5 hours ago, artifabrian longshadow said:

Pretty sure this wouldn't work due to the fact that when you pull or push, an equal and opposite force is applied on the object that is pushing or pulling (We can see this very clearly in allomatic steelpushing and ironpulling). So for example when the machine would be pushing the other part upwards, it will fall down around the same height. Meaning that the center point between the two conjoiner fabrials will stay equal at all times when they push or pull each other without any support or external force.

The machine would only fly as long as something is keeping it from applying the force that occurs when pushing or pulling on the bottom part, like the ground. This should generally be the case with all methods of pushing or pulling due to the newton's 3rd law. I'm not exactly sure if this would actually work then.

You are correct that Newton's 3rd law should prevent this from being possible, due to conservation of momentum. That is the reason why reaconless drives cannot exist in real life. In real life, to move, you must move something else the opposite direction. 

However, reverser fabrials do not follow conservation of momentum. Consider two halves of a reverser. When one moves one direction, the other moves the opposite direction. Since they are the same size, this means the total momentum of the two halves always adds up to zero, as momentum is a vector, and if two vectors of equal magnitude - but facing opposite directions - are added together, the total will be zero. What happens when something runs in to one half of a reverser? Well, we know that the added momentum of the two reversers can't be increased, so if we try to follow conservation of momentum, the object that hit it should continue moving at the same speed. But that doesn't make sense. If the moving object doesn't change speed, that means that no force was imparted on it, but what would that mean about the fabrial it just hit? In order to not impart any force on the object, the fabrial either would have zero mass, or it would have had to pass through the object. As you can see, this situation does not make any sense. Of course the object wouldn't keep moving at the same speed; it would slow down during the collision. But what does that mean about the momentum? If the speed of the moving object decreases, but the only other two objects (the two halves of the reverser) in the system are moving at equal speeds in opposite directions, that means the momentum of the system changed. Momentum was added to the system - momentum in the opposite direction from the object's movement. The design I showed above takes advantage of this way the reversers can add momentum, only it adds momentum in the direction I want to move.

On a different note, I recently thought of a possible limitation to this system. If the device is put on a sufficiently large ship, the perceived frame of reference may shift to include the movement of the ship, as we see on the ship in Dawnshard. If that happened, this device would then only be rising relative to the surface of the ship, even if the ship is falling, so it wouldn't be able to pick it up. This device should still work fine on the small scale, but due to that limitation, it may not be possible to use this on a large ship with percieving beings on board.

[PeterElricPines he/him]

15 hours ago, Chiberty said:

Welcome to the Shard! (Well, to the forum version at least, since you were already on the discord)

I really like the idea of sticking three perpendicular ones together for 3D movement. In regards the the instability in certain directions, I had some thoughts about a way you could use regular conjoiners to fix that. Since moving a conjoiner half in a direction causes the other to move in the same direction, I think they might be able to be used to resist rotation. If you had one half attached to one side of a wheel, and the other half attached to the other side, when you try to spin the wheel, it will try to push one of the halves up and the other half down. But, since the conjoiners will try to move the same direction, there will just be a stress on the gems on the gems, and it won't spin. Using this in a similar way that my design above uses reversers, you could control a rotational degree of freedom. Combine three of these rotational control devices with the three lateral ones, like you suggested, and you'd have control over all 6 degrees of freedom, without needing any sort of reaction mass for any of it.

Ooh, that's a good idea. So this would end up looking like a cube with three rings around it. But then how exactly do you start rotation? I guess you could use attractor/repeller fabrials placed at regular intervals along the ring itself? Like... six rings total, two for each direction, one of them the conjoiners are always active, and the other they're switched on and off. Then on the stationary ring, you place attractors (or repellers, or both) at regular intervals, and then you can sorta pull it along? For that to work, then, you'd need to have more reverser pairs on each ring to make sure they don't go where you don't want them to. The stationary ring would have to remain unattached to the main body, and then use conjoiners to make sure it's effectively attached. Or, actually. It might be much simpler and easier to just attach attractors to the corners of the cube, and then have all three rings be stationary.

That might not make any sense.

3 hours ago, Chiberty said:

On a different note, I recently thought of a possible limitation to this system. If the device is put on a sufficiently large ship, the perceived frame of reference may shift to include the movement of the ship, as we see on the ship in Dawnshard. If that happened, this device would then only be rising relative to the surface of the ship, even if the ship is falling, so it wouldn't be able to pick it up. This device should still work fine on the small scale, but due to that limitation, it may not be possible to use this on a large ship with percieving beings on board.

Ooh, that's a good point. This could potentially be mitigated by the fact that you only really need to engage any fabrials when you want to accelerate or decelerate. I'm no physicist, but if you disengaged the reversers while the ship was in the phase of pulling the pieces together, wouldn't the aft pair bump into the fore pair (I am using boat terms that I had to look up because I want to sound smart) and cause acceleration still? So in theory, a big ship would only be able to accelerate when near something for the passengers to root their frame of reference to, but... well, yeah, that'd be an awful ship, you'd lose the steering wheel I worked so hard to build in. But I think it would still work, and it should still be entirely functional for small one man fighters.

So a death star is possible and the trench run is possible. Beggar's Canyon can be in the Shattered Plains.

"Perceiving beings" makes me wonder how our friend Bringle Singledon will handle computers and AI. What would they look like in the cognitive realm? Would they be marbles in Shadesmar? Would it depend on whether other sapient beings see them as sapient? Would they be able to use magic? But that's probably a discussion for another thread.