Space Engineers

Space Engineers

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Grav Drive made simple
By Dom452
The easiest way to figure out how much gravity drive your ship needs for how fast you want it to accelerate.
Nothing could be easier.
   
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Gravity Drive Basics
Gravity drives are super simple to make and even easier to understand. But in order to get that super massive star destroyer to maneauvre like the Millenium Falcon, the whole system has to be perfect.

A Gravity Drive is made by pairing an artifical mass block with gravity.
The force is generated by the gravity acting on the mass of the artificial mass.

Here's how to build a super simple gravity drive.

Place one artifical mass block.
Put a Gravity Generator on the side of it.
The configuration will move (by default) in the same direction as the gravity - by default that is the DOWN orientation of the gravity generator. i.e. towards the base of the generator.
Give it power, watch it zoom away.
How the math works
The math behind a gravity drive is so simple that 8 year olds can understand it.

Not kidding, I taught this to an 8 year old.

You have to understand THREE things before we start.

FIRST:
Acceleration is loosely defined as the amount of velocity that is added to something every second.
So an accelaration of 3 metres per second would increase the velocity of the object by 3 metres per second, every second.
at 0 seconds = 0m/s velocity
at 1 seconds = 3m/s velocity
at 2 seconds = 6m/s velocity
at 3 seconds = 9m/s velocity
at 4 seconds = 12m/s velocity
And the pattern continues for an acceleration of 3.
Now the important thing - ONE g (like a gravity generator makes) is 9.8 metres per second per second of acceleration.

Second:
FORCE = MASS x ACCELERATION
aka
f=m*a

Third:
Force is measured in NEWTONS
One NEWTON (one 'N') is the amount of force it takes to ACCELERATE 1kg by 1 metre per second, per second.
THEREFORE applying a force of ONE NEWTON to a ONE KILOGRAM object would give it an acceleration of 1 metre per second per second.


So from all of that we can say that
N (newton) = 1kilogram x 1m/s/s
OR, assuming we're working off the gravity drives
9.8N = 1kg x 1g



That's all the basic info.

The math is easy.
One gravity generator working on one artificial mass block makes force like this...
N = m * a
N = 50,000 kg * 1g
N = 50,000kg * 9.8(acceleration of gravity)
N = 490,000

What's the point of all that?
It means that one gravity generator, and one mass block, can accelerate 490,000kg at 1m/s/s
But it increases in a special way.

TWO gravity generators working on TWO mass blocks is this... (I've used brackets for visualisation)
N = (m*a) * 2
N = 2m * 2a
N = (2 * 50,000kg) * (2*1g)
N = (100,000kg) * (2*9.8)
N = 100,000kg * 19.6
N = 1,960,000

That means that TWO gravs working on TWO masses can move 1.9 million kilos at 1m/s/s

If you factor in the mass of your ship, it's easy to see that you want the N to be working that well on EVERY KILO

Therefore you MULTIPLY the N by the TOTAL MASS OF THE SHIP to give you the desired NEWTONS

Now, the working backwards part.
Applying the Formula
If our desired acceleration is 20m/s

Then for a 13,000,000 kilo ship (yep, she's a big un)
we need 13,000,000 * 20 Newtons.
Or 290,000,000 N

To make that much force we need
290,000,000 / 490,000 Artifical mass blocks and one grav generator

Or

591.8 mass blocks one gravity generator.

But that's a lot of mass blocks and not much gravity. Let's even it out.

So we make more grav generators instead and try and cut down mass blocks.

So lets DOUBLE the grav gens, then we only need HALF the mass blocks. Assuming the grav field covers them all.

Then it's 592/2 mass blocks and 2gs
or 296 mass blocks.

Still too many.
Lets double the grav again.

296/2 and 4gs = 148 mass blocks
and again
148/2 and 8gs = 74 mass blocks
and again
37 and 16gs
getting closers , lets not double it, just increase by 50%

37/1.5 and 16*1.5 = 24.666 mass blocks and 24 g

Just round it up, cos it's fun to go faster.
25 mass blocks, 25 grav generators for a 13,000,000 kilo ship to accelerate at (a tiny bit faster) than 20m/s, which should get us to top speed in 5 seconds.
Optimal placement
So you know how many you need of both gravity generators and mass blocks.
But you gotta put them somewhere.

This is the part some people miss - you MUST put the MASS BLOCKS in the CENTRE OF GRAVITY on your ship.
AND
They must be evenly space around the FORWARD DIRECTION OF TRAVEL

Basically, start from the exact centre of gravity (or the multiple blocks that overlap it) and put mass block.
Then work your way toward the front and back of the ship, and expanding around those blocks exactly evenly.

The reason for this is that if the mass blocks aren't perfectly centred, they will apply a twisting action to the ship.

Think of pushing a tissue box along a table by pushing your finger on the corner instead of the exact centre.

Other than that, enjoy your super accelleration and the immediate redundency of forward (and even reverse) thrusters.
69 Comments
Dom452  [author] 13 Dec, 2021 @ 6:20pm 
@Widde
Yeah I wrote this in 2014 :) Probs the thruster values are quite different now
Widde 10 Dec, 2021 @ 3:15pm 
Problem is with some numbers don't match in the game, according to the numbers given in the game you'd need around 20 *large* atmo thrusters to lift the space pod spawn ship, so either the masses or the engine forces are wrong... just a note... :3
Far-Seeker 18 Jul, 2021 @ 9:15am 
@Dom452 I have to disagree with you on this guide being totally unnecessary. After Keen moved scripts into Experimental Mode I'm sure there some players that don't use them because of the warnings for that mode. Furthermore, it's good to have a grasp of the fundamental (in-game) physics when designing your own ships, so as not to be completely dependent upon someone else's scripts being able to handle every edge case you might come up with. ;)
Far-Seeker 18 Jul, 2021 @ 9:09am 
@DARKLORD Of course, but that unnecessarily increases the power draw to use the gravity drive, and a design with multiple gravity generators that can be quite high to begin with.
DARKLORD 17 Jul, 2021 @ 1:46am 
Even if the ship spins because the artificial mass is off centre, you can still use gyroscopes set on override to solve that.
Dom452  [author] 16 Oct, 2020 @ 5:17am 
It's worth noting that this guide was written before programmable blocks came up - and some smart brained people came up with a great solution that automatically solves the amount of force (or gs) a grav gen should exert on any mass blocks regardless of placement on your ship.
AND
They tied it to your thruster outputs so you don't need special controls - just one thruster in each direction.
TL;DR - this guide is fun, but totally unnecessary and has been that way for a while now :)
M200Chan 27 Sep, 2020 @ 7:14am 
Thanks for the guide! I never realised that grav drives applied a turning force like this! I always thought they were like the usual "point and go" style that thrusters have. Hm, time to test this out!
bookworm408 26 Sep, 2020 @ 1:29pm 
thank you so much for explaining this!
Dom452  [author] 2 Jan, 2018 @ 12:20am 
That's true, since you need one for each thrust vector.

As for calculating the weight, the above formula doesnt consider the weight of all the generators. If we did, I'd say that it moves up at a disproportional and decreasing rate to the total desired thrust of the grav drive. That is, at lower weights, the extra 2 grav gens for the 2 extra dimensions would matter a lot, at larger weights, it would matter very little, . That's just my instinct though.

For example, it would increase the total mass of the 13m ton ship above by approximately 500,000kgs - which is only a net 4% increase in weight, and therefore a 4% decrease in acceleration because of it. So you'd be getting about 19m/s^2 instead of 20m/s^2. Not really a significant change.
Unknown Playe72 30 Dec, 2017 @ 7:03pm 
Because F=m*a, the most optimum setup would be to have an equal number of gravity generators to mass blocks. However, to make a balanced ship, you will have three generators for everyone mass block. With Gravity Gen's at 8532 kg and Mss Blocks at 9544 kg, this would make the optimum setup be GG=3* MB in terms of weight on you ship (one grave gen for every 3 mass blocks) since mass block weight is very close to grav gen weight. Despite this, possible configurations factor in and if for evens sake you are worried about it, power can factor in. What are your thoughts on this FullMetal?