Tennis ball machine DIY - part 2

After several months of hard work ;) I hereby present an update on my home-made machine.
New features:
construction is now stable, has rubber bands so it won't damage the floor
significantly less vibrations
added ball feed tube, now it won't accidentally tear off an arm
electronic adjustment of rotation speed of each wheel (in a closed loop, PID controllers, opto-couplers and slot discs)
electronic adjustment of vertical angle
can be controlled with switches and buttons
can be controlled remotely (currently with cellphone over bluetooth)
music:
"Cold Funk" Kevin MacLeod (incompetech.com)
Licensed under Creative Commons: By Attribution 3.0
creativecommons...
"Repercussions" by JewelBeat.com