Tp4
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Here,

f = 2
a = 1
l = 7

from which, we get

(1)
\begin{align} \frac {\omega_{7/1}}{\omega_{2/1}}& =\frac {\omega_7-\omega_1}{\omega_2-\omega_1}\\ \end{align}
(2)
\begin{split} \frac {\omega_{7/1}}{\omega_{2/1}}& =\left(\frac {-N_2}{N_3}\right)\left(\frac {N_3}{N_4}\right)\left(\frac {-N_4}{N_5}\right)\left(\frac {N_5}{N_6}\right)\left(\frac {-N_6}{N_7}\right)\\ & =\left(\frac {-N_2N_4N_6}{N_3N_5N_7}\right)\\ \end{split}

Note:

(3)
\begin{equation} N_3/N_4=1 \end{equation}

and

(4)
\begin{equation} N_5/N_6=1 \end{equation}

because they are axial gears

therefore from (1) and the expression above, we get

(5)
\begin{align} \omega_4 & =\left(\frac {-N_2N_4N_6}{N_3N_5N_7}\right)\left(\omega_2 - \omega_1\right) + \omega_1\\ \end{align}

This is the angular velocity of the Ring gear in terms of the angular velocity of the Arm and the angular velocity of the Sun gear for the configuration shown.