High torque that can be purchased.

[wireties]

Try pre-loading your design with stretched surgical tubing or something else. We tried the balancers used in commercial window mechanisms this year (since a student's father works for a company that donated a few). We disconnect our arm (from the motor) and let it hang freely then pre-load the mechanism using a passive mechanism (surgical tubing or balancers in our case) so that the arm will just sit in a horizontal position with no help from the motor. Then all the motor has to do is supply a delta force rather than working against gravity etc.

We "went to school" on comments in a blog by one of the Robo-Wrangler #148 mentors. It was veeery helpful! Our arm moves up and down smoothly and easily with a single window motor and I think a smaller motor would work as well.