flying faders, was [sdiy] keyboard resources

[Tony Allgood]

>This probably isn't that difficult, just rather tedious.

This is not an easy task. The main problem is that you are dealing with
faders that are driven by ordinary motors. These need to be controlled.
You need to have a feedback loop checking the position of the fader for
much of the time. This can be done in software, hardware or preferably
both. The gain of the feedback loop is not constant, it changes with
age, speed of the motor, temperature and the position of the fader.
'Look up tables' need to be made that are dynamic. Too great a gain in
the motor servos and the fader oscilates. Too little and the fader moves
too slowly, or worse not at all and gets stuck.

And what happens when you touch the fader? .. some touch sensor needs to
be made. You don't want the servo battling against you. Flick the faders
on the old Yamaha ProMixes with your fingers and you'll really upset the
faders (and owners). This was a nasty trick used at trade shows by some
people.

And now we come to the slight matter of current. If all motors are
moving at the same time, how much current do you need? For the moving
faders on the 24 channel Soundcraft/Spirit we had a 10A +/-12V switch
mode. Thats only 24 faders... if you can move one fader at a time it
gets better.

The finest flying faders are/were made by Penny and Giles and retro
fitted onto the Neve and bigger Soundcraft consoles. I think they used
linear motors and the bearings were better than the cheaper Alps types.
I think they were 60UKP each back in 1990.

I think the best way now is probably to go the way of the Nord Lead 3
and have rotary encoders with LEDs around them to show the position of
the pointer.

BTW: At Marconi we had a 'just-box' where you had to put 10 pence for
charity everytime you said 'just' in relation to the difficulty to an
engineering problem. :-)

Regards,

Tony Allgood, Penrith, Cumbria, England

Oakley Modular Synth and TB3030:
www.oakleysound.com/projects.htm
My music: www.mp3.com/taklamakan