Control text in Tikz picture that is turned a certain degree

Question

I am making a small picture to explain the capacity of a car driving up a slope. I have problem controlling the labels that are next to each arrow. I would like to have them either perpendicular or parallell but they will not turn with the picture.

\documentclass[border=0.2cm]{standalone}
\usepackage{tikz}
\usetikzlibrary{arrows, arrows.meta}
\begin{document}
\newcommand{\ang}{30}
\begin{tikzpicture} [font = \small]
% triangle:
\draw [draw = orange, fill = orange!15] (0,0) coordinate (O) -- (\ang:10)
    coordinate [pos=.35] (M) |- coordinate (B) (O);
% angles:
\draw [draw = orange] (O) ++(.8,0) arc (0:\ang:0.8) 
    node [pos=.4, left] {$\theta$};
\draw [draw = orange] (B) rectangle ++(-0.3,0.3);
\begin{scope} [-latex,rotate=\ang]
% Object (rectangle)
\draw [fill = purple!30,
    draw = purple!50] (M) ++ (0,0.2) rectangle ++ (4,1.5);
% Object (wheel1)
\draw [fill=lightgray] (M) ++ (0.3,0.2) coordinate (w1)  circle (.2cm);
% Object (wheel2)
\draw [fill=lightgray] (M) ++ (3.5,0.2) coordinate (w2)  circle (.2cm);
% Weight and its projections
\draw [dashed] (M) ++ (2,.9) coordinate (MM) -- ++ (0,-1.29)
    node [midway,  right] {$mg\cos{\theta}$};
\draw [dashed] (MM) -- ++ (-0.75,0) 
    node [very near end, left] {$mg\sin{\theta}$};
\draw (MM) -- ++ (-\ang-90:1.5)
    node [very near end,below left ] {$mg$};
% Normal Force 2
\draw (M) ++ (0.3,-1.1) coordinate (N2) -- ++ (0,1.1)
node [very near start, left] {$N_2$};
% Normal Force 1
\draw (M) ++ (3.5,-1.1) coordinate (N1) -- ++ (0,1.1)
node [very near start, right] {$N_1$};
% Speed
\draw (M) ++ (1.5,2.2) coordinate (w2) -- ++ (0.75,0)
    node [above] {$v$};
% Traction force
\draw (M) ++ (-0.8,0) coordinate (TF) -- ++ (1,0)
    node [very near start, above] {$F_t$};
\end{scope}
\begin{scope} [rotate=\ang]
\draw  [blue] (MM) --  ++ (2.7,0)   node [very near end, left] {$ $};
\draw [blue,>=triangle 45, <->] (8,0.9) --  (8,0) node [midway, right] {$h$};;
\draw [blue,>=triangle 45, <->] (3.8,-0.9) --  (5.5,-0.9) node [midway, above] {$b$};;
\draw [blue,>=triangle 45, <->] (MM)++ (0,-1.8) --  (7,-0.9) node [midway, above] {$a$};;
\end{scope}
\end{tikzpicture} 
\end{document}

Image: