% ---------------------------------------------------------------
% Motor CC controlado pela armadura — circuito elétrico + carga
% mecânica (exemplo de modelagem eletromecânica).
% Requer \usetikzlibrary{decorations.pathmorphing} no chunk .qmd.
% ---------------------------------------------------------------
\begin{tikzpicture}[>=Latex, line width=0.9pt]

  % fonte de tensão de armadura
  \draw (0,0) circle (0.35);
  \node at (0,0) {$v_a$};
  \draw (0,0.35) -- (0,1.0) -- (0.9,1.0);
  \draw (0,-0.35) -- (0,-1.0) -- (2.9,-1.0);

  % resistor de armadura Ra (zigzag manual)
  \draw (0.9,1.0) -- (1.1,1.15) -- (1.3,0.85) -- (1.5,1.15) -- (1.7,0.85) -- (1.9,1.0);
  \node[font=\small] at (1.4,1.4) {$R_a$};

  % indutor de armadura La
  \draw[decorate, decoration={coil, aspect=0.5, segment length=4pt, amplitude=3pt}]
    (1.9,1.0) -- (3.3,1.0);
  \node[font=\small] at (2.6,1.4) {$L_a$};

  % motor (rotor)
  \draw[fill=blue!8] (3.3,1.0) -- (3.3,-1.0) arc (180:-180:0.0);
  \draw[fill=blue!8] (3.9,0.0) circle (0.6);
  \node at (3.9,0.0) {$M$};
  \draw (3.3,1.0) -- (3.9,0.6);
  \draw (3.3,-1.0) -- (3.9,-0.6);
  \node[font=\small] at (3.9,-1.4) {f.c.e.m. $e_b = K_b\,\omega$};

  % eixo
  \draw (4.5,0.0) -- (5.6,0.0);
  \node[font=\small] at (5.05,0.3) {eixo};

  % carga mecânica: inércia J e atrito b
  \draw[fill=blue!8] (6.3,0.0) circle (0.7);
  \node at (6.3,0.0) {$J$};
  \draw[->] (6.3,0.7) arc (90:20:0.9);
  \node[font=\small] at (7.1,1.0) {$b$};

  \draw[->] (7.0,0.0) -- (8.2,0.0) node[right, font=\small] {$\omega(t) = \dot\theta(t)$};

  \node[font=\small] at (2.1,-1.4) {$i_a(t)$};
  \draw[->] (2.1,-1.0) -- (2.1,-1.25);

\end{tikzpicture}