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[WIP] RealChute parachute systems - development thread v0.3.3

stupid_chris

By stupid_chris
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therealcrow999

therealcrow999

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@stupid_chris, with my own personal game I change the deploymentAlt = 800, do I need to change anything else to compensate that adjustment? Like will this make the chutes take even longer to open?

I have always changed the stock deployment height of chutes to 800m. Even though it takes long for then caspule to splash down, I like the height I get, feels more real to me.

V0.2 is on, changelog below

November 23rd 2013
v0.2
-Added a compatibility mode for a second parachute on the same part! Can only be used if the parachute has a a
second set of parachute transform/animation
-Reworked deployment code from the ground up to allow the above feature

I'll now start working on implementing real drag. Parachutes will now be dependant of the area of the chute and use real drag equations. Some brand new parts specifically for the mod should also be available at the same time :)

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stupid_chris

stupid_chris

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@stupid_chris, with my own personal game I change the deploymentAlt = 800, do I need to change anything else to compensate that adjustment? Like will this make the chutes take even longer to open?

I have always changed the stock deployment height of chutes to 800m. Even though it takes long for then caspule to splash down, I like the height I get, feels more real to me.

Yes, parachutes take longer to open. And I've myself bumped deployment height to 700m on all parachutes, so you could leave them like this :)

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therealcrow999

therealcrow999

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Yeah I will leave the 700m alone. That's one of the many things I like about this mod, is the deployment height. The mod works good, the only thing I notice was once in a while on some chutes when they are deployed and coasting down, they jitter a little. I don't notice it on all test tries. I also think someone already brought that to your attention on the main mod thread.

Yes, parachutes take longer to open. And I've myself bumped deployment height to 700m on all parachutes, so you could leave them like this :)
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stupid_chris

stupid_chris

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Yeah I will leave the 700m alone. That's one of the many things I like about this mod, is the deployment height. The mod works good, the only thing I notice was once in a while on some chutes when they are deployed and coasting down, they jitter a little. I don't notice it on all test tries. I also think someone already brought that to your attention on the main mod thread.

Yep, I know, and I fixed it. I'll update later today with a few fixes including this.

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stupid_chris

stupid_chris

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Updated to v0.2.1, cangelog below.

November 24th 2013
v0.2.1
*Hotfix*
-Fixed a bug where single parachutes don't show the right icon colours
-Fixed the weird glitchiness of the parachute's orientation in some occasions
-Fixed parachutes not working if not on the current active vessel

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stupid_chris

stupid_chris

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Alright, time for a dev update on what is coming next.

The next step for RealChute is getting rid of stock drag. Stock computes drag by multiplying a drag factor with the part's mass. That means than a lighter part has less drag. Then, this number is added to every other part's number, and this creates the ship's drag coefficient. Which is kind of not very realistic. For example, if you have a drogue and a main parachute on the same craft, their drag will not add to each other. They will compell each other's. So let's say that when you stage your main chute, the ship's coefficient jumps to 300. Then, if you were to stage a drogue chute, it wouldn't actually raise your drag coefficient, it would lower it, because the drogues coefficient is lower than 300.

In reality this doesn't happen really in the game because some more stuff is involved, but this example was just to give an idea that thing's are kind of wierd with stock drag.

Now this is how real parachutes work:

99a6015b6a230860c9b1517b238e5de9.png

Where:

Fd is the drag force

ÃÂ is atmospheric density

v² is the velocity squared

Cd is the drag coefficient (usually between 0.75 and 1.25 for parachutes)

A is the (cross-sectional) area

This means, the parameter that is of interest to us here is A, the parachute's canopy's area. This is the parameter that will change over time and affect our parachute. To make things simpler and work with more familiar units, we'll be assuming parachutes are round, and we'll be speaking of it's diameter, which is defined this way:

Diameter = √(4 * A / pi)

Now comes the tricky part. This is much less intuitive than stock drag, who works with a simple coefficient, and is kinda hard to calculate. If I asked you what should be the diameter of a parachute to land a 10t craft at a speed lower than 10m/s on Kerbin, you would probably have no idea. And I would not either. For this reason, I create a clever little tool to do this for us and allow everyone to edit their parachutes easily once the new version is out :)

Javascript is disabled. View full album

This is quite easy to use. If dealing with main or drogue chutes, just type in how heavy your craft is, the drag coefficient, which you should really leave to 1 (I'll come back on this in a few instants), how slow you want to land, and how many parachutes you will be using. This will return the diameter of the parachute you will need, and this is the number you will need to plug into the cfg file eventually. Drags need an extra input: the deceleration you want them to apply on your craft on deployment. This tool will be available at the same time as v0.3

Now about that drag coefficient. Usually, this is defined by a few factors, which are a little too complex to delve in too much. However, I have an idea of how I could use this nicely for the game. Eventually, in future updates, the drag coefficient will represent the material in which is made the parachute. Then, I'll try to add those values to be researchable, and allow for a nice career integration where you can research better parachutes over time.

All of this is thoughts and plans for now, but this semester is coming to an end. I'll be very busy for the next three to four weeks, but hopefully during Christmas break I'll have a lot of time to work on this :)

Cheers!

Edited by stupid_chris
typos
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mdosogne

mdosogne

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You mentioned future plans to

Make the parachutes repulse each other.
Just an idea, but what if the chutes were angled outward as a function of their distance from COM, where distance is measured perpendicular to the velocity vector? I'm not interested in modeling air/fluid dynamics to generate repulsion, but a quick and dirty simulation of the end result would be nice. Of course, after fanning out, if you want to have the chutes fail because they're just placed too closely, that's fine by me.

Speaking of packing chutes too closely, I'm looking for something big to replace the 336 stock chutes I've been using to land a fully fueled, 750-tonne beast on Eve. On 16 of the 2.5m stacks sits a conical 1.25 to 2.5m Rockomax adapter with a drogue chute at the top and 20 radial chutes strapped to it, plus struts to keep the thing attached… Please consider making some 2.5m chutes… the sort of thing that would slow a stack of double orange tanks with a mainsail and all :)

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stupid_chris

stupid_chris

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You mentioned future plans to Just an idea, but what if the chutes were angled outward as a function of their distance from COM, where distance is measured perpendicular to the velocity vector? I'm not interested in modeling air/fluid dynamics to generate repulsion, but a quick and dirty simulation of the end result would be nice. Of course, after fanning out, if you want to have the chutes fail because they're just placed too closely, that's fine by me.

The current plan would be to locate each parachute on the ship, and then work some mathematical magic to orient the "random "vibrations" in the chute to go in the opposite direction. I'll see about it then.

Speaking of packing chutes too closely, I'm looking for something big to replace the 336 stock chutes I've been using to land a fully fueled, 750-tonne beast on Eve. On 16 of the 2.5m stacks sits a conical 1.25 to 2.5m Rockomax adapter with a drogue chute at the top and 20 radial chutes strapped to it, plus struts to keep the thing attached… Please consider making some 2.5m chutes… the sort of thing that would slow a stack of double orange tanks with a mainsail and all :)

Most of the stuff will entirely be left to user customization. That tool you can see up there can calculate for you how much parachutes you will need to land a given object at a given speed on a given planet, with a given number of parachutes. Once the new update comes in, say if you want to limit yourself to 5 parachutes, you plug the other values in and it will give you anumber. Then all you need is to modify the part cfg with this number and put the wanted number of chutes on your craft to get the wanted speed on touchdown :)

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mdosogne

mdosogne

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Dropping my ship onto the launch pad to test chutes is getting old… I'm really looking forward to the next update with a chutes calculator!

I've scaled a stock chute model to create a Mk16-XXL (2.5m), but am not so sure about the drag parameters, mass, etc. Would you consider including an estimate of the chute mass and volume based on chute material, size and force?

Keep up the good work!

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stupid_chris

stupid_chris

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Dropping my ship onto the launch pad to test chutes is getting old… I'm really looking forward to the next update with a chutes calculator!

I've scaled a stock chute model to create a Mk16-XXL (2.5m), but am not so sure about the drag parameters, mass, etc. Would you consider including an estimate of the chute mass and volume based on chute material, size and force?

Keep up the good work!

Parachute weight won't matter in the amount of drag created. You just set whatever you feel is right. However, I'm thinking of adding weight to the part depending on how much parachute is in it. Info to come soon.

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stupid_chris

stupid_chris

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This mod is awesome. I love mods that add more realism to the game.

Speaking of which, I correctly added real drag today and tried the ifrst implementation of parachute mass depending on how much area it has. More info to come soon.

P.S. stupid_chris your new avatar creeps the crap out of me! xD

I'm not even sorry.

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sumghai

sumghai

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Guest Contributor's Progress Report, 2 Dec 2013

I've finished modelling the meshes for the new RealChute parts, and am currently 2/3 of the way in doing the textures for the single-chute parts:

_wip__realchute_case_models___single_chutes_by_sumghai-d6wg8i0.png

Fig 1 - All RealChute parachute case form factors

ksp_realchute_case_models_wip_2_dec_2013_2_by_sumghai-d6wg8m6.png

Fig 2 - Common texture atlas - main parachute (blue) version; similar atlases would be used for drogues (orange) and drag chutes (green)

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S4qFBxkFFg

S4qFBxkFFg

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Excellent! I can see this being especially useful for stage recovery, once that gets to be possible in the game.

(Before I realised falling parts got deleted at the 2.5km limit, I put parachutes on all my lower stages, with the 'chute set to activate immediately on separation. This often had worrying effects at high speeds, so deployment that waits until descent would be nice.)

Once we actually have to pay for MOAR BOOSTERS, recovering them will be imperative - we can look forward to a rain of spent boosters and lower stages gently parachuting into the sea...

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