V6 Physics

Quick Setup Info

If you have mesh components in your build or more than 32 individual prims, you must take additional setup steps. All of your parts except the root will sink into the ground or pass through walls until you specify their prim shape.

ACS will automatically set your prim shape, all prims you have labelled with the solid keyword in the prim name as well as any prims with wheel or tire in the name to solid/convex hull prim shape, required as to not sink into the ground.

If you have 32 prims or less ACS will by default assume you have no mesh and will use the Legacy physics style, which will produce errors in mesh. Simply include the keyword mesh in one of your prim names and ACS will know you are using mesh no matter the prim count. This manual step is required as SL currently has no script level commands to detect mesh in a link set.

After renaming prims with keywords, be sure to reboot the vehicle so it can scan and detect the prims.

More Info

ACS has a built in automated system that will set your prim shapes based on keyword to help manage your physics settings. Some builders prefer to manually set the prim types using their viewer, and the ACS automated system can be disabled.

Second Life's newer physics settings can be confusing at first , so this is an attempt to explain and make it easy to set up.

For the sake of simplicty, there are TWO types of vehicle builds you can have in SL, each can use a different style of physics system:

Legacy style vehicles - vehicles with 32 prims or less, constructed with regular prims or "sculpties", sculpted prims. Until late 2011/early 2012, this was how all vehicles were built. Each link/individual prim is counted as a single land impact, and has a solid physical bounding box. Some builders prefer to continue to use this type of build (all links are set to prim shape PRIM) because the whole vehicle is solid parts, and interacts well with roadways/land. An excellent choice for racing vehicles due to the low asset limit (easier sim crossings, lighter use of sim resources) and the solid physical nature of the parts gives the entire vehicle weight against the physics system as well as prevents getting caught/stuck/sinking etc.

Mesh physics vehicles - the "new" physics style that vehicle can have up to 255 individual links. For any vehicle that has mesh in the linkset, or required for any vehicle with or without mesh that has over 32 prims. Three prim shapes can be set for links these vehicles - Convex Hull, which gives the prim solid physical shape, None, the prim is basically phantom, and the legacy Prim shape. The old 32 prim limit still counts for the total land impact score of any Convex Hull prims in the vehicle, so some additional engineering may be required by clever vehicle builders by strategically selecting prim shapes, using a combination of simplified invisible prims set to Convex Hull to create solid surfaces on the vehicle, and None being used for complex mesh and sculpty prims.

Physics Setup Questions

My vehicle contains 32 prims or less and only uses regular prims and sculpties and does NOT contain mesh

You need not worry about anything. By default, ACS sets all builds 32 prims or less to standard Legacy prim settings, all prim shapes in the link set are set to Prim automatically.

My vehicle uses mesh OR has 32 prims or more (or both)

Add the keyword mesh to the name of one of the links in your vehicle. ACSv6 will turn on mesh physics to the linkset. By default it sets all prim shapes to None except for the root which is solid/Convex Hull, and any other prims you specify via keyword. You will need to specify solid/Convex Hull portions of the vehicle to interact with ground, road prims, etc. This is done by placing the keywords solid, wheel, or tire in the name of the links. The root prim is always solid/Convex Hull in a new physics build, which is one more reason why your root prim should be a simple cube set to transparent. The more complex a part set to solid/Convex Hull, the higher the land impact score will be and there is the SL limit of 32 prims/land score set to solid/Convex Hull. Using a mesh or sculpty prim for the root is not reccommended for this reason. Rezzing your own root prim will show you as the vehicle creator.

I want to set links in a mesh physics build to Prim shape, not just Convex Hull or None

In v6 you can add the prim keyword to any link, and its prim shape will be set to Prim.

I want to manually set up my own prim shapes in the linkset and not use the automated keyword system

Open the Root Settings script, and at the top, line 15, set NewPhysics to 1 and save. Then reboot the vehicle from the > Options, > Advanced menu. After rebooting, any changes you make to the prim shapes will stay the way you set them.

integer         NewPhysics  =      1;

I have been away from SL for a while. What's this about vehicles using more than 32 prims? Is it only for mesh vehicles?

A new style of physics settings/land impact score system has been introduced in SL. This means a little extra set up for vehicles. SL still supports the old style of physics, referred to as Legacy style vehicles on this site, and you can continue to use that system. You can now have more than 32 prims in your vehicle (without using an auto attach system) but you have to define the link shapes. ACS can automate this process for you by your use of keywords in the build. You do not have to use mesh, you can simply add more sculpties to your existing vehicles if you choose.

What's so special about your script? I can set my own link shapes by hand, what is the point?

Originally the automated physics script was written to set prim shapes at the script level, as many (now older) viewers did not have the prim shape commands in them yet, so it was the only way for some users to adjust prim shapes. A version was (and still is) given away free for use in any vehicle running any vehicle script as the KCP Over32 script. Nobody was charged a single $L for that script and anyone is free to use it.

ACS v5+ incorporated it as an optional feature combined in the script set, as the keyword system is convenient to use, especially for new vehicle builders, and in ACS gives you feedback on your physics limits as you link/unlink prims during the building process.

Experienced builders may wish to set prim shapes by hand.

How many prims can I use?

In theory you can use up to 255 individual prims, the limit for a linked object in Second Life. The new method of calculating prim cost equivalent for a physical vehicle depends greatly on the complexity of any mesh parts, and how many prims are set to solid/convex hull mode, and not literally by number of prims. For traditional sculpty-based bikes with some solid parts (tires, frame) you may be able to comfortably fit 60-80 prims. As you link in each new prim, the scripts will announce how much physics allotment is left. If you go over the count, the script will generate errors when you try to operate the vehicle. You can also choose to disable the automatic physics settings in the scripts and set them manually with your newer viewer.

Vehicles 32 prims or less are automatically in "Legacy" prim mode, all parts solid.

Keep in mind that the more parts your vehicle has, the longer it will take to load for anyone else present. Your 255 prim monster truck may look great, but in reality, when you rez it it will be forcing everybody nearby to load every part and texture. Imagine how your favorite vehicle sim would suffer greatly if everyone there was driving 100+ prim vehicles. Those who purchase your vehicles are going to be far less likely to leave them parked on display the more prims they have. You should indeed take advantage of the ability to add more prims than 32, but be reasonable. It's far more realistic now to be able to add extra details like individual turning indicators that previously would have been left out of a build, but going overboard with prims can actually negatively impact the usability of the vehicle even if it technically can support the prim count/cost.