Update docs

docs/winch.md

@@ -2,25 +2,25 @@
 
 First, we calculate the acceleration of the tether at the ground station. It can be calculated as
 
-$$a_{t,o} = \frac{1}{I_w} \frac{r}{n} (\tau_g + \tau_d - \tau_f)$$
+$$a_\mathrm{t,o} = \frac{1}{I_w} \frac{r}{n} (\tau_\mathrm{g} + \tau_\mathrm{d} - \tau_\mathrm{f})$$
 
 where $I_w$ is the winch inertia as seen from the generator, $r$ the drum radius $n$ the gearbox ratio, $\tau_g$ the generator torque, $\tau_d$ the torque exerted by the drum on the generator and $\tau_f$ the friction torque.
 
 The torque exerted by the drum depends on the tether force $F$ as follows:
 
-$$ \tau_d = \frac{r}{n}~F$$
+$$ \tau_\mathrm{d} = \frac{r}{n}~F$$
 
 The friction is modelled as the combination of a viscous friction component with the friction coefficient $c_f$ and the static friction $\tau_s$
 
-$$ \tau_f = c_f v_{t,o} + \tau_s~\mathrm{sign}(v_{t,o})$$
+$$ \tau_f = c_\mathrm{f}~v_\mathrm{t,o} + \tau_s~\mathrm{sign}(v_\mathrm{t,o})$$
 
 ### Torque controlled winch
 If the winch uses a generator with Direct Torque Control (DTC) it is possible to calculate $a_{t,o}$ as function of $\tau_g$, $F$ and $v_{t,o}$.
 
 ### Test case
 
 We assume an ideal kite that pulls with the force:
-$$ F=(v_w~\mathrm{cos}~\beta)^2 K$$
+$$ F=(v_\mathrm{w}~\mathrm{cos}~\beta)^2 K$$
 with $K=328~Ns/m$ and the elevation angle $\beta = 26^o$.
 
 Furthermore we assume the following wind speed: