Reply to Tempo fader encoder design

Hi guys, i'm still working on my project, i've been working mainly in the arduino code which is not that interesting, but i have the base for the code worked up i'll be using 26 rotary encoders 80 buttons &64 leds, split in 2 identical units to sit to each side of the mixer. One particular design obstacle i've seen in most of the DIY controllers is the tempo control, since it varies automatically when you use the "sync" feature so using an analog potentiometer with "soft takeover" seems to be the most popular solution, but trying to correct the tempo "on the fly" with "soft takeover" on leads to disaster. So i got the idea of using an encoder but, i found different problems, rotary encoders for tempo are awful, linear encoders have finite motion (end are expensive as hell!) touch strips give an absolute value (if tempo is in -1 position and you touch +6, it will jump up to +6!) and lack tactile feedback.
So i came with this design, please fell free to make any suggestion and use it for you project.
The rotary encoder would be one without detents and the belt is a geared belt.


pulleys

Pulleys

Belts

Frame