I don’t know about the Atom (I have a Neo), but if you want erg control from within Zwift you can only achieve this by performing a workout. Of course, you are free to create your own custom workout, such as…
10 minute warm-up ramp;
40 minutes at 240W;
10 minute cool down ramp.
Or whatever you like.
Alternatively, disable the controllable trainer pairing in Zwift and then you can use an external device - phone, watch etc. - to set a power target for the trainer.
I sometimes do exactly this, nowadays with my Garmin watch, but in the past with the Tacx app on my phone. The important thing to avoid is more than one device trying to exert control. That’s why you need to turn off the controllable trainer pairing in Zwift.
Thank you both for the very helpful replies. So if I understand correctly there is no way to manually adjust a target wattage during a free ride, except for a) building my own training programme (which takes away the flexibility) or b) effectively adjusting the gradient.
… or of course I could just try to keep my power constant manually!
Hub ERG controls are far superior to Zwifts unfortunately…
You can run both together, Zwift needs to be set up as power source only, Hub controls the wattbike.
Following on from my earlier reply, yesterday i used erg control from my watch to warm up and then ride in a TT on Zwift. I had complete flexibility to adjust target power, but also kept a tight control on my Watts.
The break in the power was during the warm-up, when i stopped pedalling in order to consume a gel. Towards the end I tweaked the power up just a little (+10W), as i had more in the tank.
Here’s how it looked in Zwift (with the warm-up in the pen ignored).
So, very easy to apply erg to any ride in Zwift using external control - presumably this Hub app for the Atom. Although, actually, I guess any app that can exert trainer control would be OK.