As described in the ALTO’s manual, when ALTO arm rotates you may notice a small hesitation or gap in the movement as the weight of the ALTO/GIOTTO passes through the apex of the movement. This is normal as the weight of the GIOTTO transitions from an upward to a downward movement (or opposite) and the backlash in the drive gear settles. But this backlash has to be small so, if you notice a large backlash (that can be generated if you manually force ALTO’s arm rotation), you can follow this guide in order to minimise backlash.
By using a 2mm Allen key slightly loosen the grub screw that locks the ALTO’s arm to the motor shaft, as you can see in the picture below.
Now rotate the ALTO arm so that the position of the grub screw aligns with the flat side of the motor shaft. Keep in mind that the motor shaft is not visible, so you will need to find the position of the flat side by making small adjustments until you find the best position to tighten the grub screw.
Now tighten the grub screw and test if backlash of ALTO’s arm rotation is now reduced.