laravel, substring in groupby()

I would group selected column by orderBy without last 3 character from cars.name.

$objects_collection = $objects_collection
        ->groupBy("cars.name", "parts.part_catalog_id", "parts.colour_id")
        ->select($this->getProperTableName(str_plural($this->getRoute())) . ".*", DB::raw("count(*) as quantity"))
        ->paginate($paginate);

How should I do it ?

via Chebli Mohamed