Use BodyShape for the 3D bot bodies now that its CoM offset is fixed

JuliaComputing/MultibodyComponents.jl#150 fixed BodyShape placing the
center of mass at twice the requested r_cm offset, so both 3D plants can
use the idiomatic BodyShape instead of the plain-Body workaround. Both
bodies follow the planar bot's convention of a rod extending to twice the
center-of-mass height with the mass in the middle; dynamics are unchanged
(CoM at L and body_height respectively).

Note: this requires a MultibodyComponents build containing the fix; the
compat bound should be raised from "0.2" to the first release that
includes it once one is registered.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: baggepinnen

dyad/segway_3d.dyad

@@ -25,11 +25,8 @@ component DyadBot3D
   rod_right = MultibodyComponents.FixedTranslation(r = [0, 0, -track / 2]) {^rod_right}
   "Small mass at the center of the axle"
   axis_body = MultibodyComponents.Body(m = 0.01, r_cm = [0, 0, 0]) {^axis_body}
-  "Main body extending upward from the axle"
-  # A plain Body with an explicit r_cm is used instead of BodyShape, which
-  # places the center of mass at twice the requested r_cm offset
-  # (JuliaComputing/MultibodyComponents.jl issue 149).
-  body = MultibodyComponents.Body(m = body_mass, r_cm = [0, body_height, 0], I_11 = 0.01 * 0.05 ^ 2, I_22 = 0.01 * 0.03 ^ 2, I_33 = 0.01 * 0.05 ^ 2) {^body}
+  "Main body extending upward from the axle, with its center of mass in the middle"
+  body = MultibodyComponents.BodyShape(m = body_mass, r = [0, 2 * body_height, 0], r_cm = [0, body_height, 0], I_11 = 0.01 * 0.05 ^ 2, I_22 = 0.01 * 0.03 ^ 2, I_33 = 0.01 * 0.05 ^ 2) {^body}
   damper_left = RotationalComponents.Components.Damper(d = d_wheel) {^damper_left}
   damper_right = RotationalComponents.Components.Damper(d = d_wheel) {^damper_right}
   "Use a compliant (elastic) vertical wheel-ground contact instead of a rigid contact constraint"
@@ -221,10 +218,7 @@ component RollingDyadBot3D
   wheels = MultibodyComponents.RollingWheelSet(radius = R, m_wheel = m / 2, I_axis = Iw / 2, I_long = Iw / 4, track = track) {^wheels}
   "Body tilt joint about the axle axis"
   pitch = MultibodyComponents.Revolute(n = [0, 0, 1]) {^pitch}
-  # A plain Body with an explicit r_cm is used instead of BodyShape, which
-  # places the center of mass at twice the requested r_cm offset
-  # (JuliaComputing/MultibodyComponents.jl issue 149).
-  body = MultibodyComponents.Body(color = [0.2, 0.2, 0.2, 0.9], m = M, r_cm = [0, L, 0], I_11 = Ib, I_22 = Ib / 10, I_33 = Ib) {^body}
+  body = MultibodyComponents.BodyShape(color = [0.2, 0.2, 0.2, 0.9], m = M, r = [0, 2 * L, 0], r_cm = [0, L, 0], I_11 = Ib, I_22 = Ib / 10, I_33 = Ib, radius = 0.03) {^body}
   "Splits the motor torque equally between the two wheels"
   gain_half = BlockComponents.Math.Gain(k = 0.5) {^gain_half}
   torque_left = RotationalComponents.Sources.TorqueSource() {^torque_left}

generated/DyadBot3D_definition.jl

@@ -130,9 +130,9 @@ stacks, with both rigid and compliant vertical contact.
   # Subcomponent axis_body of type MultibodyComponents.Body
   axis_body_overrides = __pop_subcomponent_overrides!(__overrides, "axis_body")
   push!(__systems, @named axis_body = MultibodyComponents.Body(; m=0.01, r_cm=[Float64(0), Float64(0), Float64(0)], axis_body_overrides...))
-  # Subcomponent body of type MultibodyComponents.Body
+  # Subcomponent body of type MultibodyComponents.BodyShape
   body_overrides = __pop_subcomponent_overrides!(__overrides, "body")
-  push!(__systems, @named body = MultibodyComponents.Body(; m=body_mass, r_cm=[Float64(0), body_height, Float64(0)], I_11=0.01 * 0.05 ^ 2, I_22=0.01 * 0.03 ^ 2, I_33=0.01 * 0.05 ^ 2, body_overrides...))
+  push!(__systems, @named body = MultibodyComponents.BodyShape(; m=body_mass, r=[Float64(0), 2 * body_height, Float64(0)], r_cm=[Float64(0), body_height, Float64(0)], I_11=0.01 * 0.05 ^ 2, I_22=0.01 * 0.03 ^ 2, I_33=0.01 * 0.05 ^ 2, body_overrides...))
   # Subcomponent damper_left of type RotationalComponents.Components.Damper
   damper_left_overrides = __pop_subcomponent_overrides!(__overrides, "damper_left")
   push!(__systems, @named damper_left = RotationalComponents.Components.Damper(; d=d_wheel, damper_left_overrides...))

generated/RollingDyadBot3D_definition.jl

@@ -136,9 +136,9 @@ the top level of the enclosing model.
   # Subcomponent pitch of type MultibodyComponents.Revolute
   pitch_overrides = __pop_subcomponent_overrides!(__overrides, "pitch")
   push!(__systems, @named pitch = MultibodyComponents.Revolute(; n=[Float64(0), Float64(0), Float64(1)], pitch_overrides...))
-  # Subcomponent body of type MultibodyComponents.Body
+  # Subcomponent body of type MultibodyComponents.BodyShape
   body_overrides = __pop_subcomponent_overrides!(__overrides, "body")
-  push!(__systems, @named body = MultibodyComponents.Body(; color=[0.2, 0.2, 0.2, 0.9], m=M, r_cm=[Float64(0), L, Float64(0)], I_11=Ib, I_22=Ib / 10, I_33=Ib, body_overrides...))
+  push!(__systems, @named body = MultibodyComponents.BodyShape(; color=[0.2, 0.2, 0.2, 0.9], m=M, r=[Float64(0), 2 * L, Float64(0)], r_cm=[Float64(0), L, Float64(0)], I_11=Ib, I_22=Ib / 10, I_33=Ib, radius=0.03, body_overrides...))
   # Subcomponent gain_half of type BlockComponents.Math.Gain
   gain_half_overrides = __pop_subcomponent_overrides!(__overrides, "gain_half")
   push!(__systems, @named gain_half = BlockComponents.Math.Gain(; k=0.5, gain_half_overrides...))