No this is not specific to Kane's method. You, as the modeler, get to choose whatever coordinates you want to describe a system including redundant coordinates. But for efficiency and simplicity's sake you are better off choosing a unique set of minimal coordinates, i.e. generalized coordinates. You will get much tidier and easy to work with results if you try to choose a good set of generalized coordinates for you system. The KanesMethod object can work with anything, but things will be much cleaner if you make good gc choices. Your pedulum is redundantly described by all of the coordinates you have. I think you pendulum should only have 2 generalized coordinates.
Jason moorepants.info +01 530-601-9791 On Wed, Aug 17, 2016 at 2:28 AM, Nuno <nmi...@gmail.com> wrote: > Jason, thanks again for answering and excuse me for any dumb questions. > > When you are saying that I can't use the position (x,y,z) and euler angles > (roll, pitch, yaw) as my generalized coordinates, is that something > specific to the Kane's Method? > I ask this since that's the first time I hear about that and for example, > when one wants to model a rigid body in space (both its position and > orientation) those are the generalized coordinates used (Think for example > of a quadcopter model). > > Thanks, > Nuno > > > segunda-feira, 15 de Agosto de 2016 às 19:13:25 UTC+1, Jason Moore > escreveu: >> >> Nuno, >> >> You can only select one set of independent generalized coordinates for >> things to work out. You seem to be setting two sets, both the cartesian and >> the angular coordinates. You may need to refer to a dynamics text to see >> how to go about selecting generalized coordinates. >> >> >> >> >> Jason >> moorepants.info >> +01 530-601-9791 >> >> On Thu, Aug 11, 2016 at 4:30 AM, Nuno <nmi...@gmail.com> wrote: >> >>> Right now I'm trying to get the equations of motion of a 3D pendulum >>> system (spherical pendulum) and I want to describe the system using the >>> (x,y,z) coordinates of the mass as well as its attitude (phi, theta, psi), >>> >>> >>> >>> <https://lh3.googleusercontent.com/-1z2YB-NMqyI/V6xeoxDJD8I/AAAAAAAAAOg/mXiuBW11_ZEjKZWSnK56ILAP1XzrXzB1wCLcB/s1600/simple_diag.png> >>> >>> >>> In the jupyter notebook (https://nbviewer.jupyter.org/ >>> github/ndevelop/sympy_3D_pendulum/blob/master/3D%20pendulum.ipynb) I >>> have added 3 reference frames (Inertial, one for the anchor point and other >>> to the mass). >>> >>> The anchor frame is not really necessary since its the same as the >>> inertial frame for this problem, however futher down the line I want to >>> test the system with a mobile anchor point (imagine it as a balloon with a >>> lift force applied in the anchor center of mass). >>> >>> >>> The mass frame is centered on the "Mass" center of mass (this >>> nomenclature is not the best) and it's orientation in relation to the >>> inertial frame is composed by 3 euler angles. >>> >>> >>> Now the twist in the problem is that the mass is "actuated". Besides the >>> gravity force acting on its center of mass (along the inertial frame >>> z-axis), there is also a force F applied on the positive direction of >>> x-axis of the mass reference frame and a torque T about the z-axis of the >>> mass reference frame. >>> >>> >>> Furthermore, I want to "model" the cable connecting the mass to the >>> anchor point, by using a distance constraint: (r_anchor - r_mass) - >>> cable_length = 0 >>> >>> >>> The goal is to obtain the equations of motion for this system. >>> >>> I have set everything as described in this jupyter notebook >>> <https://nbviewer.jupyter.org/github/ndevelop/sympy_3D_pendulum/blob/master/3D%20pendulum.ipynb>, >>> however I'm not sure if the way I'm doing things is correct, since the >>> resulting equations of motion seem to be really large for such a simple >>> problem. Then again, I'm not experienced with this kind of problems. >>> >>> >>> Thanks in advance for all the help, >>> >>> Nuno >>> >>> >>> >>> >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "sympy" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to sympy+un...@googlegroups.com. >>> To post to this group, send email to sy...@googlegroups.com. >>> Visit this group at https://groups.google.com/group/sympy. >>> To view this discussion on the web visit https://groups.google.com/d/ms >>> gid/sympy/41580794-f61d-4106-9425-d2552d71424a%40googlegroups.com >>> <https://groups.google.com/d/msgid/sympy/41580794-f61d-4106-9425-d2552d71424a%40googlegroups.com?utm_medium=email&utm_source=footer> >>> . >>> >>> For more options, visit https://groups.google.com/d/optout. >>> >> >> -- > You received this message because you are subscribed to the Google Groups > "sympy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to sympy+unsubscr...@googlegroups.com. > To post to this group, send email to sympy@googlegroups.com. > Visit this group at https://groups.google.com/group/sympy. > To view this discussion on the web visit https://groups.google.com/d/ > msgid/sympy/4d22f6ec-f826-4a45-98ac-14152edaeac5%40googlegroups.com > <https://groups.google.com/d/msgid/sympy/4d22f6ec-f826-4a45-98ac-14152edaeac5%40googlegroups.com?utm_medium=email&utm_source=footer> > . > > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "sympy" group. 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