Skip to main content

graphics - Animating a rotating disk


I have a system with 3 degrees of freedom that I want to know if it is possible to visualise with Mathematica in the two-dimensional $X-Y$ plane. I have a plane circular object rotating at its set speed say $10$ deg/s. This object is not rotating at the $(0, 0)$ origin point but is displaced from the origin $(0, 0)$ coordinates and its motion path is described by


$x=x_0 + a \times \cos(\omega \: t)$ and $y=a \times \sin(\omega \: t)$


Some values: $x_0 = 1$ mm; $a=0.25$ mm, $\omega=10$ deg/s (same as the rotating speed of the circular object). The radius of the circular object can be taken to be a couple of cm say $2$ cm.


The time parameter $t$ in the parametric equations can be discretised in $20$ steps as follows:


$\mathrm{step}= \frac{360 \; \mathrm{deg}}{\omega \times 20} = \frac{360}{10 \times 20}=1.8$ s


so that $\mathrm{step}$ will take values $0$, $1.8$, $3.6$, $\ldots$, $34.2$ s.


Thus the product $\omega \: t$ as the cosine and sine arguments of the parametric path can be written as



$\omega \: t = \omega \times \frac{\mathrm{step \times \pi}}{180}$


which in units gives $\frac{\mathrm{deg}}{\mathrm{seconds}} \times \frac{\mathrm{seconds} \times \mathrm{radians}}{\mathrm{deg}} = \mathrm{radians}$.


Any help will be appreciated to this Mathematica newbie on how to go about to simulate this kind of motion. Desired animation fatures:




  1. Perhaps the circular object can have hatched shading so that its rotating motion can be seen on top of its following the parametric circular path;




  2. The $x-$ and $y-$axes should be visible;





  3. The parametric path given by the parametric equations in $x$ and $y$ should be visible as a circle.





Answer



Lets start with some parameters (note that I've chosen larger values for a and x0 here to actually see the movement of the centre)


radius = 20;
x0 = 10;
a = 5;
om1 = 10 Degree;

om2 = 10 Degree;

The centre of the rotating object at time t is given by


centre[t_] := {x0 + a Cos[om1 t], a Sin[om1 t]};

I'm using RegionPlot to create an image of the disk centred at the origin


circ = RegionPlot[x^2 + y^2 <= radius^2, {x, -radius, radius}, 
{y, -radius, radius},
Mesh -> 20, MeshStyle -> {{Red}, {Blue}}, BoundaryStyle -> Black,
PlotStyle -> None]


Mathematica graphics


Next, we're defining a function for creating the plot at time t. I'm using Rotate and Translate to get the orientation and position of the disk. The path of the centre is plotted using ParametricPlot


plot[t_] := Show[Graphics[
Translate[Rotate[{circ[[1]], Point[{0, 0}]}, om2 t], centre[t]]],
If[Abs[t] <= $MachineEpsilon, {},
ParametricPlot[centre[s], {s, 0, t}, PlotStyle -> {Black}]],
PlotRange -> {{-2 radius, 2 radius}, {-2 radius, 2 radius}},
Axes -> True]


Plugging this function into Animate will create an animation of this function:


Animate[plot[t], {t, 0, 36}]

Mathematica graphics


Comments

Popular posts from this blog

mathematical optimization - Minimizing using indices, error: Part::pkspec1: The expression cannot be used as a part specification

I want to use Minimize where the variables to minimize are indices pointing into an array. Here a MWE that hopefully shows what my problem is. vars = u@# & /@ Range[3]; cons = Flatten@ { Table[(u[j] != #) & /@ vars[[j + 1 ;; -1]], {j, 1, 3 - 1}], 1 vec1 = {1, 2, 3}; vec2 = {1, 2, 3}; Minimize[{Total@((vec1[[#]] - vec2[[u[#]]])^2 & /@ Range[1, 3]), cons}, vars, Integers] The error I get: Part::pkspec1: The expression u[1] cannot be used as a part specification. >> Answer Ok, it seems that one can get around Mathematica trying to evaluate vec2[[u[1]]] too early by using the function Indexed[vec2,u[1]] . The working MWE would then look like the following: vars = u@# & /@ Range[3]; cons = Flatten@{ Table[(u[j] != #) & /@ vars[[j + 1 ;; -1]], {j, 1, 3 - 1}], 1 vec1 = {1, 2, 3}; vec2 = {1, 2, 3}; NMinimize[ {Total@((vec1[[#]] - Indexed[vec2, u[#]])^2 & /@ R...

functions - Get leading series expansion term?

Given a function f[x] , I would like to have a function leadingSeries that returns just the leading term in the series around x=0 . For example: leadingSeries[(1/x + 2)/(4 + 1/x^2 + x)] x and leadingSeries[(1/x + 2 + (1 - 1/x^3)/4)/(4 + x)] -(1/(16 x^3)) Is there such a function in Mathematica? Or maybe one can implement it efficiently? EDIT I finally went with the following implementation, based on Carl Woll 's answer: lds[ex_,x_]:=( (ex/.x->(x+O[x]^2))/.SeriesData[U_,Z_,L_List,Mi_,Ma_,De_]:>SeriesData[U,Z,{L[[1]]},Mi,Mi+1,De]//Quiet//Normal) The advantage is, that this one also properly works with functions whose leading term is a constant: lds[Exp[x],x] 1 Answer Update 1 Updated to eliminate SeriesData and to not return additional terms Perhaps you could use: leadingSeries[expr_, x_] := Normal[expr /. x->(x+O[x]^2) /. a_List :> Take[a, 1]] Then for your examples: leadingSeries[(1/x + 2)/(4 + 1/x^2 + x), x] leadingSeries[Exp[x], x] leadingSeries[(1/x + 2 + (1 - 1/x...

What is and isn't a valid variable specification for Manipulate?

I have an expression whose terms have arguments (representing subscripts), like this: myExpr = A[0] + V[1,T] I would like to put it inside a Manipulate to see its value as I move around the parameters. (The goal is eventually to plot it wrt one of the variables inside.) However, Mathematica complains when I set V[1,T] as a manipulated variable: Manipulate[Evaluate[myExpr], {A[0], 0, 1}, {V[1, T], 0, 1}] (*Manipulate::vsform: Manipulate argument {V[1,T],0,1} does not have the correct form for a variable specification. >> *) As a workaround, if I get rid of the symbol T inside the argument, it works fine: Manipulate[ Evaluate[myExpr /. T -> 15], {A[0], 0, 1}, {V[1, 15], 0, 1}] Why this behavior? Can anyone point me to the documentation that says what counts as a valid variable? And is there a way to get Manpiulate to accept an expression with a symbolic argument as a variable? Investigations I've done so far: I tried using variableQ from this answer , but it says V[1...