If you hold down the "Function +" and "Function -" buttons while turning on a Futaba GV-1 or GY-501, you will have access to many parameters not mentioned in the documentation. I got curious about the 'hidden' parameters, so I made a list of all of the standard setup screens, and a list of all of the 'secret' screens. I've also included the default value for each parameter, plus a few guesses at what the undocumented parameters might be for.

Note that everything that follows is just my GUESS as to what the parameters do. Even the ones that don't end with "?" are just guesses, and are probably wrong, so the ones that do end with "?" are utter and complete guesses and very very likely to be wrong. If you adjust these and crash your helicopter and/or blow up your engine, don't blame me. But do tell me what you changed and what happened first, so I can pass this on to other adventurous souls out there.

If you have experimented with these settings, please let me know what you have found. I'd like to document the undocumented as much as possible.

There are a few things that I hope the undocumented parameters will allow me to change:

I'd like to know how to get the GV-1 to back off on the throttle more than it does by default. My Concept has a slight overspeeding problem, even with the GV-1 installed, and I think it's because the GV-1 never reduces the throttle to less than some fixed percentage. If that's 30% and I can move it down to 10%, my overspeeding might be cured.

I currently have with my GV-1 is installed on my YS 1.20 four-stroker. When spooling up with the governor enabled, it begins to oscillate just as the engine reaches the governor's "active" RPM range. Rather than slowly approaching the set speed, the GV-1 blips the throttle, then backs off greatly, then blips again, and so on, very rapidly. This sucks. The solutions is to lift off with the governor disengaged, then turn it on manually when the rotor is fully up to speed.

With the GY-501, I find that my pirouette rate is not constant when pirouetting in fast flight or during knife-edge descents (fast flight at another angle, basically...). This wasn't a problem with the CSM heading hold gyro, in fact it was one of the things that had me so excited about the CSM initially.

I've also got a problem with the GY-501 during hovering flips. After a half-flip, I always need a stab of left rudder to straighten things out. I have this problem now with my Concept and the GY-501, and I've seen it before with my Futura and the CSM, so I'm less optimistic about fixing this with a parameter things. And yes, I'm pretty sure it's not my thumbs that are causing this. :-)

If I figure out how to solve any of the above problems I'll post my findings here.

Random observation: there are a lot of settings that are defaulted to 0%, as if some feature were turned off. I wonder if the "GY-502" will be the exact same hardware and software with new defaults for the 'hidden' screens?

GV-1 Standard Parameters

rpm	Current RPM Display
Max	Max RPM Display
Sx	Speed Settings (x=1-3, set by radio)
Disp	Speed Display Mode (engine/rotor)
GRt 	Gear Ratio
SWPt	on/off
StSw	Stick-Switched on/off
SWCd	Switch Condition
GvOf	Governor Off "high point" (disable GV-1 at high throttle)
Volt	Voltage Display
MxMD	Mixture Channel Control Mode (governor / Tx?)
MGx	Mixture Channel Output (x=1-9, set by radio)
ATV	Adjust Travel Volume for Throttle Servo (A/B endpoints, set by radio)
Msx 	Mixture Servo Direction (normal/reverse)
MTrm	Mixture Servo Trim
B/FS	Battery Failsafe on/off
B/FD	Battery Failsafe position
Lmt	Limit Setup (Idle / Max / Kill, set by radio)
Tst	Limit Test
Sen	Sensor Signal Strength

GV-1 Sooper Seekrit Parameters

Ver	1.20		software version?
PHis	0.6%		Proportional something?  
IHis	0.8%		Integral somthing?  history?
G	42%/50%		balance can be adjusted 1-for-1 with +/- keys, but
			what does G stand for?
			Maybe it's Proportional vs. Integral gain balance,
			is that what Bob P was needing?
IGa	1.7%		Integral Gain?
GDan	00%
GC8->100%		not adjustable from front panel - tx maybe?
			(I'm wishing I'd had the Tx with me when i was
			documenting the GV-1, I suspect the "8" would
			vary with one of the input channels...)
GCo-	0%
ICo-	50%
LmHV	20%
GLmt	35%		could this be the minimum throttle setting????
LmSt	50%
TAdL	30%		travel adjustment low?  30% coincides with Futaba
			Tx minimum
TAdH	90%		ok, maybe not
Gov	ACT		switches ACT/INH with data keys: Governor Active /
			Inhibited?
Smpl	1Fr		sample N frames (of what?)
AVR.	7t		average over N passes to determine speed?
FLT.	4n
Dlay	3us		Delay (of what?)
OnRv	70%		Governor turns on when actual RPM reaches this
			percentage of desired RPM
Wait	2Fr		skip a couple frames before...   hm?
DlUP	3S		Delay when raising speed - allow N seconds to
			reach new speed
DlDN	5S		Delay when lowering speed - allow N seconds to
			reach new speed
LDl	100 Fr		something-delay, 100 frames?
RAdj	INH		toggles ACT/INH with data keys
RESET	blinking	restore factory defaults, probably

OnRv is the only one of the above that has been confirmed to do what it hints at. It sets the point at which the GV-1 will take over. In stock form, the GV-1 will engage when the rotor speed reaches 70% of the set point.

Michael MacLeod reports that if OnRv is reduced to 50%, the GV-1 will engage much sooner, "it's like flipping into idle-up too soon," causing the heli to thrash a bit. A setting of 60% caused his GV-1 to engage a bit sooner but with no bad side effects.

GY-501 Standard Parameters

You can read all about these in your manual, they are included here just for reference...

(heli)	(current voltage)
G:	Gain Adjust
GDiv	Gyro Direction
ACGx	Rudder Control Gain
	x=(A,B), depending on rudder stick position
CDlx	Control Delay
	x=(A,B), depending on rudder stick position
Trk	Gain Tracking
Frm
Mode
Lmtx	x=(A,B), depending on rudder stick position

GY-501 Sooper Seekrit Parameters

That's all, folks. Happy tinkering, and keep me posted with anything you learn!

Suggestions from Todd Bennett:

Raise ILT from 300 to 780 
Raise ACGA/ACGB to 200 

"That will make starts and stops 
better, also makes it pirouette
more consistently."

As noted above, I tried the ILT change on my own with negligible impact on performance. However, I didn't mess with ACGA/ACGB. When I get a chance to try that, I'll post my experiences here...