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The ARM megathread


KvickFlygarn87

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My information is coming from this "
" with Scott Manley and C7

C7 states "One of the updates to unity 4.3 is subtle. Previously you couldn't control both ends of the joint ...", the joint issue, to me, seems to very clearly be a Unity update issue allowing the physics engine update. I think I linked at around where C7 starts talking, but it's around 10:30.

They are discussing it immediately following bringing up ARM, though. So maybe the joint physics update is coming in 0.23.5 afterall.

As far as I know these are two different things. What they were talking about is that previously the joint was not from attach point of one part to attach point of another part, but to the center of the other part. So for jumbo tank it was the red line:

QOwqd6J.png

What I meant was that different parts have their attach points represented by different sizes of green balls which don't always correspond to the size of the part. And as far as I know the strength of the attachment does correspond to the size of that ball. For instance, the monopropellant unit is notorious for its weak joints.

oUZvF1p.png

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The new grapple device lets vessels grapple other vessels/asteroids that don't have docking ports. Killer.

But.

The nominal purpose of the device is to allow vessels to move asteroids that are large, and the first thing you learn designing rockets is to line up the CoT with the CoM so you can travel in a straight line.

So how are we going to ensure that the axis between the grapple and the engines will be in line with the axis between the asteroid's CoM and the point of docking? I'm really curious to see what the solution is. It may be as simple as a way to target the target's CoM the same way we can currently set docking ports as targets currently.

Has this been addressed? Thoughts?

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Well if the grapple is attached in the back of your ship, like in the middle, then you should be able to tug it around no problem. The mass of the asteroid is evenly distributed despite its shape because its all one part. It won't matter where your grapple attaches to it.

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If the grapple/claw/whatever is flexible, and you're pulling the asteroid, then the asteroid will automatically swing to put its CoM behind the CoT.
Most likely this.

The pictures we've seen clearly show rockets set in the push configuration.

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Indeed, but a flexible claw even in push configuration will allow stabilization. And actually, this statement isn't really true.

http://i.imgur.com/Cf5YcBC.png

Source

Oh, interesting, I hadn't seen those little ones. Rather inefficient though for pulling at that angle though.

I'm not sure I get how a flexible grapple could allow for push stabilization unless its manually controllable, and the same for a pull configuration unless its extremely flexible which is unlikely.

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Yeah I was thinking about this earlier. Take an orange tank for an example guys. If you put a docking port on the end of it and dock with it, The tank will still tip towards the SoM of the orange tank. I'm guessing you can target asteroids like docking ports and lining up the node with the target you can find the SoM. I doubt the grapple will be flexible as it would be much, MUCH less useful for pushing if the thing your using to push it is flexible. Like pushing a wagon backwards by its handle. Again though, I could be wrong :P

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Well if the grapple is attached in the back of your ship, like in the middle, then you should be able to tug it around no problem. The mass of the asteroid is evenly distributed despite its shape because its all one part. It won't matter where your grapple attaches to it.

the location of the connection doesn't matter, the orientation does, which is what I'm talking about.

No idea, but I'm sure the folks on the QA and Experimentals teams have probably brought this up already. :D

Oh yeah, I'm sure they have a solution. When I said "has this been addressed", I meant have they discussed what the solution is/was, at GDC or elsewhere. I think it's obvious that they have a solution, I'm just curious what it is.

Attach enough thrust to anything and CoM doesn't matter as much.

Some thrust oblique to your CoM causes some spin, and tons of thrust oblique to your CoM is going to cause tons of spin. that's just newtonian physics.

The pictures we've seen clearly show rockets set in the push configuration.

Yeah, the grapple is obviously not a flexible connection, its basically just a docking port. But putting the engines in a tractor configuration instead of a push could be interesting.

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Physics.

Even if you're not thrusting against the asteroid's CoM, you're giving it acceleration in the direction of your thrust as long as you avoid the ship turning around common CoM (and thrusting in different direction).

So the answer is torque.

Edited by Kasuha
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Well if the grapple is attached in the back of your ship, like in the middle, then you should be able to tug it around no problem. The mass of the asteroid is evenly distributed despite its shape because its all one part. It won't matter where your grapple attaches to it.

Asteroids are frequently just loose piles of rubble...

And even if they aren't, I highly doubt the material they are made of would have enough tensile strength to allow you to pull the entire asteroid. You would likely end up pulling away from the asteroid with a claw full of gravel.

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