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From HalfLife 2 Knowledge Base

The following tutorial shows how to create a ragdoll model. These models are for more than just characters. The famous mattress model is a ragdoll model. If you want parts of a model to swing or move separately from the rest then you should use a ragdoll model. To use a ragdoll model you use prop_ragdoll instead of prop_static or prop_dynamic.

To create a ragdoll model you must create one with separate bones for each part of the model which will move. Here is an example of a simple ragdoll model in milkshape.

Create a reference smd file from milkshape or your favorite editing tool.

If you were going to just compile this model as a static prop you would use the following .qc file

 $modelname "mymodels/myragdoll.mdl"
 $scale 1.0 
 
 $cd "<path to model directory>" 
 $body "Body" myragdoll.smd 
 $cdmaterials "models\mymodelmaterials"
 $staticprop 
 
 // 1 sequence 
 $sequence idle "myragdoll" fps 5 ACT_IDLE 1
 
 $surfaceprop "wood"
 
 $keyvalues { "prop_data" {"base" "wooden.large" } 
 
 $cdmaterials "models\mymodels"
 
 $collisionmodel "myragdoll.smd" { 
 // Mass in kilograms 
  
   $concave
   $mass 500.0
 }

To change this to a ragdoll model you change the $collisionmodel to $collisionjoints and specify how the joints can rotate with respect to the root joint. An example .qc is as follows

$modelname "mymodels/myragdoll.mdl"
 $scale 1.0 
 
 $cd "<path to model directory>" 
 $body "Body" myragdoll.smd 
 $cdmaterials "models\mymodelmaterials"
 //$staticprop 
 
 // 1 sequence 
 $sequence idle "myragdoll" fps 5 ACT_IDLE 1
 
 $surfaceprop "wood"

 $keyvalues { "prop_data" {"base" "wooden.large" } 

 $cdmaterials "models\mymodels"

 $collisionjoints "myragdoll_ragdoll.smd" { 
 // Mass in kilograms 

   $rootbone "joint1" 
   $concave
 
   $mass 80.0
   $inertia 5.00
   $damping 0.01
   $rotdamping 1.50
 
   $jointconstrain joint1 x limit 0.000000 0.000000 0.000000
   $jointconstrain joint1 y limit 0.000000 0.000000 0.000000
   $jointconstrain joint1 z limit 0.000000 0.000000 0.000000
   $jointconstrain joint2 x limit -90.000000 90.000000 1.000000
   $jointconstrain joint2 y limit -90.000000 90.000000 1.000000
   $jointconstrain joint2 z limit -45.000000 45.000000 1.000000
   $jointconstrain joint3 x limit -90.000000 90.000000 1.000000
   $jointconstrain joint3 y limit -90.000000 90.000000 1.000000
   $jointconstrain joint3 z limit -45.000000 45.000000 1.000000

 }

Each of the jointconstrain commands control the joint rotation in a specific axis. For example the above .qc allows joint2 and joint3 to rotate +/- 90 degrees in the x and y and +/- 45 degrees in the z (up/down) axis.

In the above example I used boxes for each of the joints, so I don't need to create a separate ragdoll collision model. If your model is more complicated, then for the collision model you should create a new .smd with one box assigned to each joint. The box will be used for collisions for that joint and the size will determine the weight of the joint.