Anyway, here's the set-up - an Eomono USB MIDI Expression Pedal sending various CC messages to a Moog Theremini, with Lemur allowing me to quickly change the effect of operating the pedal, and also allowing for automated control over the theremini in by modulating various controllers on the theremini to sweep them up and down repeatedly at a rate determined by the pedal, and to send sequences of control codes to transpose the pitch of the instrument, thereby creating arpeggios. There will be methods to switch quickly between user defined fixed arpeggios and also to combine arpeggios of different lengths to give very long sequences, again, speed to be controlled by the pedal. (I only get one pedal to play with because I need the other one to stop me falling over, and both my hands will be busy waving around near the theremini's antennas, with only brief moments to tap on the iPad screen during a performance.
This is how far I have got. I have a fader that can receive and respond to messages from the pedal and direct them to the appropriate controller on the theremini, and I have a couple of knobs that control the speed and friction of the ball-and-spring physics behaviour of the slider. The physics behaviour works fine when I operate the slider directly with my finger, but not when I operate the pedal. With the pedal there is no physics. This is my sticking point. I can't figure out how to fix it.
I have read the manual until my brain melted, and found on page 69 that "It’s important to note that a Variable assigned to a Custom MIDI can output data but will not react to the corresponding incoming message. Custom MIDI messages are not bidirectional." which sounded like it might be the problem. I'm not entirely clear on the ramifications of having bidirectional messages, but searching this forum for people with similar problems turned up a couple of pieces of advice, one being to use a custom MIDI message (I tried, it did not work. I do not know if this is because I did it wrong, or because it is not the right advice for me - it was given in relation to a different setup) and the other advice I found for a similar-ish situation was to use a script. This reportedly worked, but there was no description of the script that did this.
Any help with this will be very gratefully received and a tremendous boon to me in my quest to become a power user in double quick time.
