tweak rope and chain appearance

Author: baggepinnen

docs/src/examples/ropes_and_cables.md

@@ -22,7 +22,7 @@ t = Multibody.t
 
 world = Multibody.world
 number_of_links = 6
-@named rope = Rope(l = 1, m = 1, n=number_of_links, c=0, d=0, air_resistance=0, d_joint=1, radius=0.03, color=[0.5, 0.4, 0.4, 1])
+@named rope = Rope(l = 1, m = 1, n=number_of_links, c=0, d=0, air_resistance=0, d_joint=1, radius=0.03, color=[0.5, 0.4, 0.4, 1], dir=[0.05, 1, 0])
 @named body = Body(; m = 1, radius=0.2)
 
 connections = [connect(world.frame_b, rope.frame_a)
@@ -31,11 +31,8 @@ connections = [connect(world.frame_b, rope.frame_a)
 @named stiff_rope = ODESystem(connections, t, systems = [world, body, rope])
 
 ssys = structural_simplify(IRSystem(stiff_rope))
-prob = ODEProblem(ssys, [
-    collect(body.r_0) .=> [1,1,1];
-    collect(body.w_a) .=> [1,1,1]
-], (0, 5))
-sol = solve(prob, Rodas4(autodiff=false); u0 = prob.u0 .+ 0.1);
+prob = ODEProblem(ssys, [], (0, 5))
+sol = solve(prob, Rodas4(autodiff=false))
 @test SciMLBase.successful_retcode(sol)
 
 import CairoMakie
@@ -48,7 +45,7 @@ Next up we model an elastic rope, we do this by setting `c > 0`. We also introdu
 ```@example ropes_and_cables
 world = Multibody.world
 number_of_links = 6
-@named rope = Rope(l = 1, m = 5, n=number_of_links, c=800.0, d=0.01, d_joint=0.1, air_resistance=0.2)
+@named rope = Rope(l = 1, m = 5, n=number_of_links, c=800.0, d=0.01, d_joint=0.1, air_resistance=0.2, dir=[0.2, 1, 0])
 @named body = Body(; m = 300, radius=0.2)
 
 connections = [connect(world.frame_b, rope.frame_a)
@@ -57,12 +54,8 @@ connections = [connect(world.frame_b, rope.frame_a)
 @named flexible_rope = ODESystem(connections, t, systems = [world, body, rope])
 
 ssys = structural_simplify(IRSystem(flexible_rope))
-prob = ODEProblem(ssys, [
-    collect(body.r_0) .=> [1,1,1];
-    collect(body.w_a) .=> [1,1,1];
-    collect(body.v_0) .=> [10,10,10]
-], (0, 8))
-sol = solve(prob, Rodas4(autodiff=false); u0 = prob.u0 .+ 0.5);
+prob = ODEProblem(ssys, [], (0, 8))
+sol = solve(prob, Rodas4(autodiff=false));
 @test SciMLBase.successful_retcode(sol)
 
 Multibody.render(flexible_rope, sol, y = -3, x = -6, z = -6, lookat=[0, -3, 0], filename = "flexible_rope.gif") # May take long time for n>=10
@@ -73,7 +66,7 @@ Multibody.render(flexible_rope, sol, y = -3, x = -6, z = -6, lookat=[0, -3, 0],
 
 
 ## A chain suspended in two points
-When a [`Rope`](@ref) component is used to model a chain that is suspended between two fixed points, a kinematic loop (kinematic chain) is formed. To break this loop, we introduce a spring in one end. 
+When a [`Rope`](@ref) component is used to model a chain that is suspended between two fixed points, a kinematic loop is formed. To break this loop, we introduce a spring in one end. 
 
 ```@example ropes_and_cables
 number_of_links = 8

src/components.jl

@@ -414,8 +414,14 @@ There are three different methods of adding damping to the rope:
 - Damping in the stretching direction of the rope, controlled by the parameter `d`.
 - Damping in flexing of the rope, modeled as viscous friction in the joints between the links, controlled by the parameter `d_joint`.
 - Air resistance to the rope moving through the air, controlled by the parameter `air_resistance`. This damping is quadratic in the velocity (``f_d ~ -||v||v``) of each link relative to the world frame.
+
+## Rendering
+- `color = [255, 219, 120, 255]./255`
+- `radius = 0.05f0`
+- `jointradius=0`
+- `jointcolor=color`
 """
-function Rope(; name, l = 1, dir = [0,-1, 0], n = 10, m = 1, c = 0, d=0, air_resistance=0, d_joint = 0, cutspherical = false, cutprismatic=false, color = [255, 219, 120, 255]./255, radius = 0.05f0, kwargs...)
+function Rope(; name, l = 1, dir = [0,-1, 0], n = 10, m = 1, c = 0, d=0, air_resistance=0, d_joint = 0, cutspherical = false, cutprismatic=false, color = [255, 219, 120, 255]./255, radius = 0.05f0, jointradius=0, jointcolor=color, kwargs...)
 
     @assert n >= 1
     systems = @named begin
@@ -433,6 +439,8 @@ function Rope(; name, l = 1, dir = [0,-1, 0], n = 10, m = 1, c = 0, d=0, air_res
         iscut = cutspherical && i == 1,
         # state=!(cutspherical && i == 1),
         state=true,
+        color=jointcolor,
+        radius=jointradius,
         d = d_joint) for i = 1:n+1]
 
     eqs = [