Dynamics VFX: Rag Doll Tutorial; Hinge Constraints
The Dynamic sub menu in Maya is not just about creating particles. Within this menu set, you can create basic skeletons for characters using hinge constraints that will be used with fields to generate basic movements without having to set keys on the timeline. These dynamic simulations can, if need be, be baked out and keys added to the time line once you are happy with the over all result of the simulation.
In this tutorial, we will be looking at how to construct a hinge constraint skeleton for the mannequin provided in the UFO scene file for the tractor beam assessment. The aim is to get the mannequin to start off in a standing position, then once the tractor beam has done what it needs to in order to lift the mannequin up, we will use dynamics to lift him into the hatch of the UFO.
To start we need to have a model, in this case our wooden man, free from constraints and that the geometry is separate. Here is the model I will be using for my simulation.
Because our geometry is separated, we will need to attach it to the rest of the mannequin to avoid geometry being left behind when we go to add fields to the finished mannequin. For example;
I found that the best way to attach the ball joint geometry to the rest of the models geometry is to parent constraint selecting the “r_upperArm” and then the “r_shoulder” going to the animation sub menu > constraints > parent option box, reset the settings and making sure maintain offset is turned on.
Hit apply and repeat this for the rest of the ball joints. Your mannequin and out liner should look like this once you have completed this step.
Now that the mannequin is parent constrained, we can start setting up our hinge constraints. Selecting the head of the mannequin then the chest, go to the Dynamic Sub Menu > Soft/Rigid Bodies > Hinge Constraints Option Box. Before we do anything else make sure the settings are reset within the tool, File > Reset Settings; make sure the drop down menu stating which type of constraint it is has hinge selected.
Above is an example of the options I used when applying the hinge constraint to the left ankle. Besides from little adjustments to the translation and rotation of the constraints, I found this way to work. Continue to do this to the rest of the mannequin by following the flow of joints; for example select the chest and then the right upper arm and constrain then move and rotate the constraint into position, replicating how a joint should bend, now the right upper arm then the right lower arm and constrain then move and rotate the constraint into position, the right lower arm and the right hand then constrain then move and rotate the constraint into position.
You will end up with a skeletal structure looking like so;
To test that everything is working, select for example, the hand and apply a gravity field. Depending on which direction you wish for your mannequin to move, change the settings in the gravity field to achieve this. For me I want my mannequin to float upwards so I will change the second attribute in the direction fields to a positive number and bump the magnitude up to a number that will actually cause an effect, for me I chose 100. Make sure you have enough frames on your timeline to create a decent simulation to accurately test that it works.