I've rewound the youtube basic synthesis tutorial 10 times and can't get the sub-patch working.
create voice
view/settings/sub patch mode/ polyphony
save voice.axp in new folder
create new patch and save in same folder
call new object with ./voice
no joy
In case you mean that it's monophonic; how are you playing the patch?
iirc. midi/in/keyboard object must be inside the polyphonic subpatch for polyphony to work.
I ran into that once or twice...
Carefully go thru Sub patching https://sebiik.github.io/community.axoloti.com.backup/t/axoloti-user-guide/50
… it takes perseverance 
Also another way is to use object patch/patcher
click - edit and paste your "creation" here - save your patch
More info @chaosmoon https://sebiik.github.io/community.axoloti.com.backup/t/more-on-sub-patches/55
Not working here either, I also followed the tutorial. In fact, even the factory demos that are polyphonic are failing to compile.
I've found that the demo synth patches with a sub patch need refreshing, probably because I'm running 1.0.8. The procedure is as follows:
- load the synth patch that fails to compile
- open the voice sub patch
- save the voice sub patch (this is the refresh)
- close the synth patch, don't save it
- open the synth patch again and it should compile
I've fixed this in 1.0.9
released today
I think I have done everything right and yet does not find the object voice in new patch! im confused
use patch/patcher aka embedded patch instead... the videos were made before these existed.
(I think all the demos are now using embedded patches, so you can look for examples there)
as for the example.. the issue you have is probably are having is down to the path of the subpatch... be aware you need to save both the main and subpatch before you compile.
apart from that we would need to see the error, and exactly what you have done.
... anyway as i said, use embedded patches , much better 
How do I set the amount of polyphony for the main patch once I have, say, an osc patch inside that patch?
I followed the original instructions and managed to create a working subpatch without isses, but when I play it, it's still monophonic so I assume there's a setting for it, but I can't find it among the other settings.
the main patch settings have nothing to do with polyphony.
you need to edit the setting on the sub patch (aka voice patch), and change is mode to polyphonic,
check the videos/user guide, and tutorials.. these show sub patches/voices so you can see how they are 'constructed'
Thanks Mark, I already did that, but it's still monophonic 
EDIT: Actually no I haven't seen a video, only a written tutorial, I'll check it out.
id need to see your patch if its still not working
I assume your putting your midi/in objects in the sub patch? as per demos etc
Yup, have the midi keyboard object in the subpatch, plus an oscillator going to an outlet, that's all is in it!
Do you have a link to the video about polyphony, I can't find it, just demonstrations of the patches. Then I looked at your channel and ended-up watching a bunch of your Eigenharp videos instead 
Loving my new poly brass patch !