3. The base of the triangular pyramid $S-ABC$ is an equilateral triangle, the side edge $SA=1$, and the projection of $A$ on the side face $SBC$ is the orthocenter $H$ of $\triangle ABC$, then the maximum value of $V_{S-ABC}$ is $\qquad$ .
3. $\frac{1}{6}$ Hint: From the problem, we can prove that the tetrahedron $S-A B C$ is a regular tetrahedron, $V_{S-A B C}=V_{A-S B C} \leqslant \frac{1}{3} \times \frac{1}{2} \times 1 \times 1 \times 1=$ $\frac{1}{6}$, with equality holding if and only if the three lateral edges are pairwise perpendicular.