Setup:
HE
Lutron Pro Hub
GE ZWave Fan switches
Found a sweet deal for Lutron Pico remotes @ $10 each on Amazon
I checked the online forums and also reached out to Hubitat support asking if there was a way to use the Lutron fan remotes, to control the GE Zwave fan switches the same way Lutron controls their own fan switches. Up button to increase speed from what ever speed it is, to one level up and down button, for speed down. Support said - no can do! The deal on the remotes was not something I wanted to pass up. Bought them, connected to Lutron hub & set them up via the button controller to function as static buttons:
On button - turn fan on
Up button - turn fan on to "High"
Center button - turn fan on to "Medium"
Down button - turn fan on to "Low"
Off button - turn fan off
It's not the smooth/native control like how the Lutron fan remote would work on the Lutron fan switch. It allows me the option to have a fan remote while not having to rip the GE fan switches out and purchase the lutron fan switches
Here is my question - has anyone setup a Lutron Pico remote to work with a GE ZWave fan to work like how the Lutron native integration will work? Up button to increase speed, middle button for favorite speed, down button to decrease speed
I don't see why this wouldn't be possible. What driver are you using? I'll assume "GE Smart Fan Control," but any fan (or even dimmer) driver should work. There isn't a built-in way to go precisely "up" or "down" based on the current speed; the closest you can get there is cycleSpeed, which will step up to the next supported speed and wrap around back to the lowest after it reaches the top. What you'll have to do to work around that if you want to go only up or down is set the level manually using setLevel, just like a dimmer. (Alas, Hubitat doesn't have something like a "next higher speed" or "next lower speed" you can just run, which would make this a lot cleaner.)
I'd recommend trying all the speeds your device supports and watching what the percentage is on the device page, but based on this post, I'll assume it's 25%, 50%, and 75%. Assuming that's correct, an easy way out would be to map the up and down buttons to increase or decrease the speed by 25%. This may cause issues with some edge cases, but I'm not familiar enough with this particular device to know. What I mean is that when on low, decreasing 25% by 25% may take it down to 0%, which usually turns off the device. Increasing 75% by 25% may take it up to 100% (no change since they're both high but would require an extra press to get it back down to 50%/medium), but that's generally not a value supported by most Z-Wave devices, so it may either fail or set you at a 99% cap (neither of which would change anything, and the latter is unlikely to cause any problem except the former).
To get it to to exactly what you want, you could create a rule. How did you set up what you already have? I'd use a "Button Device" trigger capability in Rule Machine, though Button Controller alone (this trigger in RM basically gives you a same interface with a bit more power) should also be able to handle this. In your actions for the up/down buttons, you can check the current level and adjust accordingly if needed (e.g., for the up button, actions that effectively do: if current level >= 33% then set to medium; else if current level >= 66% then set to high). This is a bit more work for only marginal benefit over the basic solution proposed above, but it's certainly possible if you figure out what percent ranges your fan uses. I'd be happy to help you write such a rule if you're unfamiliar.
Thanks
For the fan, it is the GE Smart Fan Control driver
To use the cycle speed button, then I will need only one button on the remote - not all of them. I was attempting to recreate the fan remote functionality that Lutron natively supports!
I'm comfortable with the rules - I was looking to "increase" or "decrease" from the current level, when the up or down buttons are used. Maybe I'm missing something - how would you propose the rule look like?
Are you just wondering what action to use? If so, you want the "Adjust Dimmer Level" action (under "Set Dimmers and Bulbs"). Use an unsigned number to adjust the level up or one prefixed with a minus sign to adjust down (e.g., 25 to increase 25% or -25 to decrease by 25%). If you wanted to go the more complicated route and evaluate the current dimmer level and while manually setting it to one higher/lower, you'll need conditionals. I could certainly show an example if that's what you're after.
PS - You might actually like the remote better the way you have it set up now. Since it's just a Pico, you don't get the level indicator LEDs on the side like you do with the "real" fan switch, and adjusting up or down is sometimes hard (think: struggling with a pull chain wondering what the heck you just changed it to). Having buttons mapped to a specific speed is a quick way to know exactly what you're going to do, although since the labels don't exactly line up it can be non-intuitive for anyone but especially guests.
That did it... I used this option on the button controller for the Pico:
Set Dimmers -> Adjust these dimmers -> Selected the GE Fan switch -> By this amount
For the up switch, I set the amount as 25
For the down switch, I set the amount as -25
Works like a charm
Now I have to decide, do I live with the set speeds which I'd setup earlier, or use this... decisions decisions
Here is my question - has anyone setup a Lutron Pico remote to work with a GE ZWave fan to work like how the Lutron native integration will work? Up button to increase speed, middle button for favorite speed, down button to decrease speed 
