Question on Dual Rates and Expo

[Espeefan]

Could someone explain to me how dual rates and expo work? I am working on setting up my new Futaba 12FGH radio and I could use a little help understanding what it is I should be doing.

I was playing around with the dual rate functions and from what I saw, it looked like dual rates can be used to slow down the servo response time to tame a model down in different flight modes. My radio allows me to set different speeds for all of the servos, and at first I thought it would speed them up, but after trying it, it looks like the speed settings only slow them down. Am I right in assuming you would turn off the dual rates to run a wild set-up, servos running full speed, and then in normal for hovering, you could turn on the dual rates and tame the servo speed down?

Also, I understand how Expo works and how it softens the response curve of the servos near center stick. I noticed my radio allows me to set different expo rates for all of the flight modes I want to run (up to 8 different modes). Normally I think everyone runs three modes, or four if you count the throttle hold mode. Normal, Idle up 1, Idle up 2, and throttle hold, correct? I don't really see a need for more modes then that. Now I like running full linerar curves, even in hovering or normal mode, so other then maybe using some expo in normal mode for hovering, do you guys dial in some expo in all flight modes too?

My last question is I can enable dual rates for 8 different functions, or channels and asign them all to a single switch, or different switches. Now I can only think of running dual rates for pitch, aileron, rudder, and elevator. Would there be any benefit to running dual rates on the gyro or maybe gov. as well? If I read correctly, dual rates can change the gyro and governor settings or sensitivity. What would you guys recommend I set up dual rates for? Or what specific functions?

Most of the time, I find myself flying on the sim with dual rates always turned off. I actually like the extra sensitivity and response, even when in normal mode and just hovering around.

[TheBum]

Dual rates are nothing more than adjusting the maximum servo throws on demand. For example, dual rates on elevator and aileron will perform the same function as the elevator and aileron swash mix settings, except that they're adjustable in flight via a switch. The difference between swash mixes and elevator/aileron dual rates is analogous to the difference between subtrims and trims.

Expo just changes the servo response so it's no longer linear. More accurately, it changes the servo movement so that it's no longer a smooth arc; if you have it set just right, it can actually cause whatever linkage is attached to it to respond in a linear manner. Expo can soften the response around mid stick, but it can also sharpen response around mid stick, depending on the sign of the expo percentage. Someone else will have to explain exactly what property the percentage pertains to; all I know is the higher the absolute value of the percentage, the less linear the response curve is.

That said, I don't use dual rates except on the rudder (and only because the G770 gyro instructions included it in the suggested T-Rex 600N settings; that's a whole other deceased equine that has been assaulted in another thread) and I suspect most other people don't either. Whether you use expo depends on the twitchiness of the heli and how much control you have over the heli; I don't run expo either.

[Espeefan]

Thanks Alan. I appreciate the info. Found a little more on the subject after doing a quick search on the net too. I understand things better now.