Two common problems when adding parameters. First is the enumeration needs to be right. ie:
AP_GROUPINFO("SV2_POS", 2, AP_MotorsHeli_Single, _servo2_pos, AP_MOTORS_HELI_SINGLE_SERVO2_POS),
The 2 is the enumerator, you need to make sure you're using a new number.
Second common problem, is that the total param name string cannot be longer than 16 characters. In this case, the SV2_POS, is 7 characters. But note, that since this is in the heli param family, it has a H_ prefixed to it. So it actually ends up being 9 chars long.
Your PID objects will also have a prefix added, and I imagine that is what is tripping you up.
OK, so your planned approach is to that each rate PID will have a notch filter that should be set at the blade frequency? That doesn't quite make sense as your proposed 6.2Hz would mean you have a rotor speed of 186 RPM?
There's a lot of things going on here that we need to consider before a PR like this could be accepted. I'm certainly very interested in improving our rate control, don't get me wrong, but this is a big change. But we need to make sure we're looking at the big picture. Leonard was actually planning on signficantly revamping the Rate filtering scheme. Be aware that there are already several filters on the heli that could be confusing your testing. Not sure if you've looking at this.
INS_GYRO_FILT defaults to 20Hz, and filters all data coming from the Gyros. So that will affect the rate controllers.
Then be aware that the ATC_ACCEL_P_MAX and R_MAX affect the rate at which the stability loops will try to make the machine move, and correct errors. I wonder if this might not be affecting your measurements. You really need to turn this feature off to be sure that you are "poking" the rate PID's directly.
And then we also have the ATC_RATE_P_FILT_HZ, which filter the P and D terms on heli. Note that this only filters the D term on multirotors.
Now, as I said, Leonard was planning on totally revamping this system. I believe he wants to get unfiltered gyro data from the AHRS. And then get have separate P and D term filter rates in the rate controllers. I think the main idea is to have more obvious control over the P vs. D term filter rates. The D-term normally uses a much slower filter, like 5-10Hz compared to 20-40 for P term on a multirotor.
On Helis, the P-term is being double-filtered at 20Hz.
Also note, that there is a fixed rate filter on changes to the Rate Feedforward. This is set to 10Hz. I had played around with making this a param at some point, but never ended up pushing it.
You say that your new control scheme takes attenuates aeroelastic effects. But what about things like Following Rate, head damper stiffness, etc? Is that all rolled into what you are calling aeroelastic effects?