Thrust gradients and quadrotor dircol example

Good check.  I actually left it like that precisely because it is always zero.  I guess it's probably more robust to call it the way you recommend.
(The problem is that you cannot insert a taylorvar into a double, so the only case this would catch is if some later method tried to do a subassgn into force, but I guess it could happen!)


On Jun 10, 2014, at 1:31 PM, Benoit Landry <notifications@github.com> wrote:

> In systems/plants/RigidBodyThrust.m:
> 
> >        %B_mod maps the input to generalized forces.
> > -      kinsol = doKinematics(manip,q);
> > -      
> > -      [x,J] = forwardKin(manip,kinsol,obj.kinframe,zeros(3,1));
> > -      B_mod = manip.B*0*q(1); %initialize B_mod
> > -      
> > -      axis_world = forwardKin(manip,kinsol,obj.kinframe,obj.axis);
> > -      axis_world = axis_world-x;
> >        
> >        force = sparse(6,getNumBodies(manip));
> I think inline differentiation (taylorvar) will always return zero until you add sparse(...)*q(1). Someone also used that trick in the TimeSteppingRigidBodyManipulator. It's not something your test would catch because your dforce is also always zero, but I guess it's right for the wrong reasons?
> 
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