Step 1: Differentiate displacement to get velocity.
Given,
\[
S=6t-\frac{t^3}{2}
\]
Velocity is
\[
v=\frac{dS}{dt}
\]
So,
\[
v=\frac{d}{dt}\left(6t-\frac{t^3}{2}\right)
\]
\[
v=6-\frac{3t^2}{2}
\]
Step 2: Find the maximum value of velocity.
The velocity function is
\[
v=6-\frac{3t^2}{2}
\]
Since
\[
\frac{3t^2}{2}\geq 0
\]
for all real values of \(t\), we get
\[
6-\frac{3t^2}{2}\leq 6
\]
Thus, the maximum possible value of velocity is
\[
6
\]
This occurs at
\[
t=0
\]
Step 3: Final conclusion.
Hence, the maximum velocity during the motion is
\[
\boxed{6}
\]