Create curved TikZ single arrow

Question

I want to create a curved single arrow inside some circles indicating rotation. Currently I'm doing it using the \draw arc but the result is very ugly, the arrow tip is very weird when I make the arrow thick. Since each of the arrows must have different thickness, I can't just make them thin.

This is what I have right now:

I'd like the arrows to look like the arrow at the bottom but with varying thickness, which is created with the single arrow from the tikzlibrary shapes.arrows.

This is my current code:

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{shapes.arrows}

\begin{document}

\begin{tikzpicture} %[>=latex]

% cross
\draw[gray,line width=3pt,opacity=0.5,line cap=round] (-2,0) -- (2,0);
\draw[gray,line width=3pt,opacity=0.5,line cap=round] (0,-2) -- (0,2);

%rotors
\draw[inner sep=3pt,outer sep=0,fill=blue,fill opacity=0.3,draw=blue] (-2,0) circle     [radius=1cm];
\draw[inner sep=3pt,outer sep=0,fill=blue,fill opacity=0.3,draw=blue] (2,0) circle     [radius=1cm];
\draw[inner sep=3pt,outer sep=0,fill=red,fill opacity=0.3,draw=red] (0,-2) circle [radius=1cm];
\draw[inner sep=3pt,outer sep=0,fill=red,fill opacity=0.3,draw=red] (0,2) circle [radius=1cm];

% rotation direction arrows
\draw [->,line width=5pt] (-2.4,0.3) arc[x radius=0.5cm, y radius =.5cm, start angle=-220, end angle=40];
\draw [->,line width=1pt] (1.6,0.3) arc[x radius=0.5cm, y radius =.5cm, start angle=-220, end angle=40];
\draw [<-,line width=2.5pt] (-0.4,-1.7) arc[x radius=0.5cm, y radius =.5cm, start angle=-220, end angle=40];
\draw [<-,line width=2.5pt] (-0.4,2.3) arc[x radius=0.5cm, y radius =.5cm, start angle=-220, end angle=40];

% rotors asterisk to indicate front and side
\draw plot[mark=asterisk,mark size=5pt,mark options={color=red}] coordinates {(-2,0)};
\draw plot[mark=asterisk,mark size=5pt,mark options={color=green}] coordinates {(2,0)};
\draw plot[mark=asterisk,mark size=5pt,mark options={color=cyan}] coordinates {(0,-2)};
\draw plot[mark=asterisk,mark size=5pt,mark options={color=red}] coordinates {(0,2)};

% translation direction
\node[fill=black,single arrow,minimum height=3cm] (arrow)  at (0,-3.5){};

\end{tikzpicture}
\end{document}

Answer 1

This is due to the large curvature with thick linewidth. TikZ makes some inner calculations before putting the arrow heads such as measuring the finishing angle and going a little backwards to make sure the arrow head joins the lineend nicely etc. I think in this example you can get away with small corrections. I've added tiny extensions in the angle that I want to place the arrow head in the examples.

I really recommend using nodes and coordinates for referring to known points. Also to avoid the repetitions you can create custom styles. ++ syntax is used for adding some coordinate to the last point of the current path. Finally arc (start angle:end angle:xrad and yrad) is sufficient.

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{shapes.arrows}

\begin{document}

\begin{tikzpicture}[
rotor/.style={inner sep=3pt,outer sep=0,fill opacity=0.3,minimum width=2cm,circle},
crossline/.style={gray,line width=3pt,opacity=0.5,line cap=round}
]

% cross
\draw[crossline] (-2,0) -- (2,0);
\draw[crossline] (0,-2) -- (0,2);

%rotors
\node[rotor,fill=blue,draw=blue] (n1) at (-2,0) {};
\node[rotor,fill=blue,draw=blue] (n2) at (2,0)  {};
\node[rotor,fill=red,draw=red]   (n3) at (0,-2) {};
\node[rotor,fill=red,draw=red]   (n4) at (0,2)  {};

% rotation direction arrows
\draw [->,line width=5pt] (n1) ++(140:5mm) arc (-220:40:5mm) --++(110:2mm);
\draw [->,line width=1pt] (n2) ++(140:5mm) arc (-220:40:5mm);
\draw [<-,line width=2.5pt] (n3) ++(138:5mm) --++(60:-1pt) arc (-220:40:5mm) ;
\draw [<-,line width=2.5pt] (n4) ++(138:5mm) --++(60:-1pt) arc (-220:40:5mm);

% rotors asterisk to indicate front and side
\draw plot[mark=asterisk,mark size=5pt,mark options={color=red}] coordinates {(-2,0)};
\draw plot[mark=asterisk,mark size=5pt,mark options={color=green}] coordinates {(2,0)};
\draw plot[mark=asterisk,mark size=5pt,mark options={color=cyan}] coordinates {(0,-2)};
\draw plot[mark=asterisk,mark size=5pt,mark options={color=red}] coordinates {(0,2)};

% translation direction
\node[fill=black,single arrow,minimum height=3cm] (arrow)  at (0,-3.5){};

\end{tikzpicture}
\end{document}