Please use the standard 57mm Rubik;s cube. Do not use a speed cube, or a cube with rounded-corner plates.
The grippers do need to hug the cube tightly and make full contact.
Our choice of servos was driven by cost-saving considerations, that is why the robot employs two kinds of servos (one cheap and one expensive.)
Please contact us directly via our contact form at www.otvinta.com for further help.