No parts of the original Otto need to be modified for it to work. It's plug-and-play! The attached .ino file is the programming for the Nano. 

It uses the ultrasonic sensor to detect a gesture 10 cm away to trigger the actions. Afterwards, taking a few steps towards you and patiently waiting for you to get the amount of tissue you need. It will celebrate with a happy gesture and walk backwards.

Print settings :

1. Wall count — 3 or more;
2. Top and bottom layers — 3;
3. Infill — 20%, grid;
4. Layer height — 0.2 mm.

All parts are printed with a 0.4 mm nozzle.

Assembly :

The arms use M6 bolts and nuts to fix them in place. The bow tie goes in just like how the matrix LED housing is supposed to. Lastly, the tissue box cover are held together with rubber bands and a zip tie to pull them together. 

Please refer to the images below.

To see Otto the Tissue Butler do it's thing, you may visit my Instagram, @printed.hands! 

Have fun!