Perhaps you should try some spelling variations:
"stroller based" » "controller based", "stroke based", "speller based"
"trolley base" » "trolley buses", "trolley type"
"trolley bus" » "trolley buses", "_ trolleybus", "trolley lies"

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (("trolley bus") OR ((("trolley base") OR ("stroller based"))))*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"trolley bus\") or (((\"trolley base\") OR (\"stroller based\"))))*".
• Removing quotes may allow a broader search: (( trolley bus ) or ((( trolley base ) OR ( stroller based ))))*.