You could do
\newcommand{\sbigotimes}{%
\mathop{\mathchoice{\textstyle\bigotimes}{\bigotimes}{\bigotimes}{\bigotimes}}%
}
and
\[
\sbigotimes_{i=1}^n A_i\otimes B
\]
would produce

to be compared with the original (with \bigotimes
)

I suggest an “abstract” version:
\documentclass{article}
\usepackage{amsmath}
\makeatletter
\newcommand{\makesmalleroperator}[1]{%
\expandafter\let\csname saved\string#1\endcsname#1% save the old command
\def#1{\mathop{\small@mathchoice#1}}% redefine it
}
\def\small@mathchoice#1{%
\mathchoice{\textstyle\@nameuse{saved\string#1}}%
{\@nameuse{saved\string#1}}%
{\@nameuse{saved\string#1}}%
{\@nameuse{saved\string#1}}%
}
\makeatother
% now we declare what operators should be treated like this
\makesmalleroperator\bigotimes
\begin{document}
\[
\bigotimes_{i=1}^n A_i\otimes B
\]
\end{document}
This will give the same result as above with \sbigotimes
. What are the advantages?
You can do the same for \bigvee
, \bigwedge
and all the operators you need with a single line for each of them.
You can use the normal names; if you change your mind or have to submit the document somewhere, you can simply remove the definitions and the calls to \makesmalleroperator
The same size as in display math will be used for inline usage.