Thanks very much Peter.
I hope I'm not making an error but would welcome you finding one if I am.
I'm getting the same error in tutorial examples so suspect it's an error
with a new version of sympy or python, or something specific to my setup.
I'm using python 3.8 and sympy 1.8. I get the same error on 2 different
machines although the same versions of sympy/python.
Code is below. It's when executing the final line that the error comes up
- everything else is fine. Thanks again.
_____________________________________
import sympy as sm
import sympy.physics.mechanics as me
## REFERENCE FRAMES
A = me.ReferenceFrame("A") # earth reference frame
P1 = me.ReferenceFrame("P1") # 1st pendulum arm reference frame
P2 = me.ReferenceFrame("P2") # 2nd pendulum arm reference frame
## ORIENTATION
theta1, theta2 = me.dynamicsymbols("theta1 theta2") # generalised
coordinates
P1.orient(A, "Axis", (theta1, A.z))
P2.orient(P1, "Axis", (theta2, P1.z))
## KINEMATICS
### Points and Locations
m1, m2, L1, L2 = sm.symbols("m1 m2 L1 L2")
O = me.Point("O")
p1 = me.Point("p1")
p2 = me.Point("p2")
p1.set_pos(O, L1 * P1.x)
p2.set_pos(p1, L2 * P2.x)
### Kinematical Differential Equations
omega1, omega2 = me.dynamicsymbols("omega1 omega2")
kinematical_differential_equations = [omega1 - theta1.diff(),
omega2 - theta2.diff()]
### Angular Velocities
P1.set_ang_vel(A, omega1 * A.z)
P2.set_ang_vel(P1, omega1 * P1.z)
### Linear Velocities
O.set_vel(A, 0) # point O has zero velocity
p1.v2pt_theory(O, A, P1)
p2.v2pt_theory(p1, A, P2)
## KINETICS
g = sm.symbols("g")
F_grav_1 = m1 * g * A.x
F_grav_2 = m2 * g * A.x
B1 = me.Particle("B1", p1, m1)
B2 = me.Particle("B2", p2, m2)
## EQUATIONS OF MOTION
coordinates = [theta1, theta2]
speeds = [omega1, omega2]
loads = [F_grav_1, F_grav_2]
bodies = [B1, B2]
### Kane's Method
kane = me.KanesMethod(A, coordinates, speeds,
kinematical_differential_equations)
fr, frstar = kane.kanes_equations(loads, bodies)
_________________________________________
On Monday, 4 April 2022 at 12:12:29 UTC+1 [email protected] wrote:
> I have done all sorts of pendulae, single, double, triple.....
> If you could send your code, maybe I could find a mistake.
> Peter
>
> On Mon 4. Apr 2022 at 13:00, n doherty <[email protected]> wrote:
>
>> Hi,
>> Looking for some help if possible. I was recently trying to get the
>> equations of motion of a double pendulum via SymPy. When I used
>> "kanes_equations" to obtain Fr and Fr* I got the above TypeError message.
>>
>> I have the loads and the bodies contained in lists which are input into
>> the kanes_equation method, which I think is causing the problem here? If I
>> apply the method for a single pendulum with a single body (not contained in
>> a list or array) kanes_equations works fine.
>>
>> I suspect it's a newer version of sympy or python which is causing the
>> issue. If I try to perform the same method on the human standing tutorial
>> I get the same error but for the bodies being RigidBody instead of
>> Particle. I've run this tutorial and numerous other examples in the past
>> without this error occurring.
>>
>> Is there a known workaround to this issue?
>>
>> Thanks,
>> Nick
>>
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>>
> --
> Best regards,
>
> Peter Stahlecker
>
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