And as for spoolup - I have read a lot about that, and tested a lot.
With "Fixed Wing" in HobbyWing ESC it is not possible to get a smooth spoolup at all, using Spirit as a governor. No matter what you set in Spirit, the initial start is a kick. I read about that and it seems this is normal. It seems getting smooth spoolup at initial phase (from 0 RPM) is complicated, needs varying motor timing and only ESC could do this. Not FBL.
And I believe this is why HobbyWing ESC has "HeliLinearTH" option. This one makes soft spoolup, done by ESC, whenever you start the motor. But after some short time (either something like 2 sec. or maybe crossing some 400 RPM limit - not sure) it starts to work like "Fixed Wing" - that is, whatever power is requested with throttle, it makes it instantly. My belief is, this is what should be used for external governors (I can point to a proper thread on helifreak, but it is long..)
Now, what happens with HeliLinearTH and Spirit governor is - I believe - this:
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As you see, because spoolup is controlled by ESC at the beginning, it makes RPM increase slower than what spirit requests. At some point Spirit maybe wants 200 RPM, but ESC makes 100 only. Then Spirit wants 300 maybe, but ESC makes 150. And at some point, what Spirit requests starts to work, because ESC stops spoolup and starts to react immediately to throttle level. And then we get a kick, because RPM increases wildly.
One way to fix this is to set very slow spoolup in spirit (flattens the blue curve) - but it has to be the slowest one, which is wasting time and batteries - I don't want to spoolup for 25 seconds. And I'm not sure, but I think it still wasn't perfectly smooth (tested that some year ago).
Another way is to increase "Startup power" in Hobbywing, to steepen the red curve. But then it is not smooth anymore.
The "Spoolup rampup" does not help in this case. It will just delay everything. But at some point motor will start - just little later - and then it's RPM will not increase at the rate Spirit is requesting. And we have same problem.
On the other hand, what the HW internal ESC - I believe - is doing, it makes this slow spoolup for 2 seconds (or so), and then it starts a normal spoolup with whatever speed you have selected (I use 15 sec), from whatever RPM it has there. You can see that spoolup speed is not constant - it is changing at the beginning.
Does this makes sense what I'm writing, or am I missing a point somewhere?
Is there any way to make soft spoolup?
I'm testing this another day, so there's a chance I go nuts here..
From the thread on helifreak it seems it is a matter of somehow aligning these curves. So at the point, at which ESC is giving full control to throttle level (stops spoolup), the RPM requested by the FBL and the RPM which we have in reality are close to each other. But I don't see any parameter in Spirit which would make this. It seems Spirit is increasing the throttle slowly, independent of anything. Could it take RPM into account? Or have different spoolup speed for first few seconds? Whatever could work..