Jetcat has made an excellent head speed control system for the SPH5, but unfortunately, there is no mention of how to set it up in the manual. Hopefully this will at least get you started until an official manual is released.
First, lets get some basics done and sorted. You need to have the fan fitted properly, inverted with the blades at the bottom, and the small sensor attached and plugged into the AUX input on the ECU. You need to know the gear ratios of your helicopter, both gearbox output shaft to rotor head and rotor head to tail rotor.
The gap between the fan and the sensor is fixed and is quite large. This is OK and a check can be performed to see if the sensor is working. If you look at the fins on the fan you will see a magnet in one of them. Switch the system on and wait for the RUN screen to come up. Wiggle the fan so the magnet passes over the sensor and the display will change at the bottom left and will say FAN and then a number which will change as the speed of the fan varies. OK, now we know the sensor is talking to the ECU, we can start to set it up to control the head speed.
The first thing to do is to enter the gear ratios and this is a hidden menu! Press SELECT MENU and hold it down while pressing the + key. Keep pressing the + key until you get to TURBINE LIMITS. Release both keys
Now press and hold the LIMITS key and press the + key once and this will get you into the hidden menu.
Step through the menu with the + key until you get to TURB->ROT. This is the main gear ratio and on my Cuatro needed to be changed to 9.23. On the 6 blade Skycrane it needs to be changed to 21.43!!! To change it, press and hold the CHANGE VALUE ITEM key and adjust the value with the + and - keys until it is correct
OK, that's the head gear ratio set, so press the + key once and you will see RATIO TAIL_>ROT. Alter this number with the CHANGE VALUE ITEM key and the + and - keys until you put in the correct head to tail gear ratio which on my Cuatro was 4.23
Thats the two gear ratios set up, now to set the head speed. Press and hold the LIMITS key and step through with the + key to TURBINE Limits again and then release the LIMITS key. Step through with the + key to SHAFT HiR1.
Press and hold the CHANGE VALUE key and use the + and - keys to adjust the shaft speed until the ROT value underneath it displays the headspeed you want.
Now you are all set. If you want to change the head speed just change the shaft speed and if you put the turbine in a different model, change the gear ratio accordingly.