Important Notice

It has come to my attention that the radio/gyro setup detailed below does not work well when the CSM ICG-360 is used with the 8U's PCM mode. Plugging the gyro gain lead into channel five works much better. I have not yet tested this setup technique with the ICG-360 and FM/PPM mode, so I can't say whether that works or not. It does seem to work will with the Futaba GY-501 and FM/PPM, and with the Arcamax PI Pro/Interface and PCM, so I suspect that it's the specific combination of the ICG-360 and PCM that has trouble.

All I know for certain right now is that when using this setup with the 148DP reciever, the gyro did not work at its best. It was prone to over-rotating at the end of fast pirouettes, and to occasional weathervaning during fast backwards flight. These symptoms went away when I connected the CSM's gain lead to channel 5. Two people have reported similar problems, and that the problems went away when channel 5 was used to control the gyro gain.

It has been suggested to me that the 7th and 8th channels of Futaba PCM receivers are not updated at the same rate as channels 1 through 6, but I have not been able to verify this myself yet. I suspect that the ICG-360 may "expect" the gain pulse to come right after the rudder pulse, and the delay introduced by moving the gain from channel 5 to channel 8 might be just enough to confuse it.

Background

or, what's the big deal?

The CSM gyro is a big step forward in model helicopter technology, but it brings a bit of additional complexity to the setup process. First there's the fact that the gyro has two different modes of operation; then there's the fact that it uses a single auxiliary channel to set the gain and the mode of operation; then there's the fact that in standard mode the CSM gyro requires the same sort of tail rotor compensation mixing as any other high-end piezo gyro while in heading hold mode it works best with all tail rotor mixing turn off completely.

Many people prefer to fly with the CSM in heading hold mode all the time, but I'm not one of them. It seems to me that the CSM acts weird when spooling up in heading hold mode. The heli will yaw before it lifts off, which gives me the creeps, especially on uneven ground. Standard gyro also tend to allow some yaw during spool-up of course, but I've been flying with a standard gyro for some time now and I've learned to compensate with the rudder control so it's no big deal.

For a while I had the CSM's aux channel hooked up to the 8U's gyro channel. This allowed me to switch gyro modes easily. Since tail rotor mixing on the 8U is programmed on a per-flight-mode basis and cannot be turned on and off with a free switch, I wound up having to toggle two switches to switch the revo mixing off and enter heading hold mode on the gyro. This was tedious and error-prone.

The solution I found was to use channel 8 to control the gyro gain and flight mode. The 8U has two built-in 5-point mixes that operate channel 8 as a function of the throttle stick position; one curve is active in normal mode and the other curve is active in both idle-up modes, which turns out to be more than adequate for solving the gyro control problem.

And, for what it's worth, I don't think the built-in mixes are going to be particularly useful for controlling a carburetor mixture as Futaba apparently intended. A proper fuel control circuit would mix from the throttle servo position, not the left stick position. With different throttle curves in idle-up-one and idle-up-two, there's no possible way to get the right mixture control in both modes.

Also note that channel 8 goes to 100% (or 0%, depending on the reverse switch) when you activate throttle hold. Unless you can achieve the proper fuel/air mixture at idle with the mixture servo set to 100% (or 0%), you're going to be "practicing" autorotations with an unhealthy engine. Practice might then become reality in short order, which sort of defeats the purpose of practicing, don't you think?

The idea behind my setup is to get the CSM to act like a standard gyro when the transmitter is set for the normal flight mode, and get the CSM to act like a heading hold gyro when the transmitter is set for the idle-up (stunt) flight modes. Tail rotor mixing for normal mode would be the same as for any other high-end piezo gyro, whereas tail rotor mixing for the idle-up flight modes would be set to zero at all points.

Implementation

or, how do you do that?

First of all, connect the gyro's gain wire to channel eight on the receiver.

Set the the "TH->NDL" curves to 0% at all five points in normal mode, and to 100% at all five points in idle-up. Use the channel 8 ATVs to adjust the actual gain in each mode, just as if you were using a two-position switch to control the gyro gain.

Because of the undocumented channel-8 / throttle-hold behavior described above, you get standard gyro behavior when you activate throttle hold, no matter which position the flight modes switch is in.

If you'd rather have heading-hold gyro action in throttle hold, reverse channel 8, and set the TH->NDL curve to 100% at all five points in normal mode and 0% at all five points in idle-up.

Verify everything on the bench before you fly, of course. This rule holds true for any major setup change. Go into normal mode and make sure that the gyro acts like a standard gyro. Select an idle-up flight mode and macke sure the gyro acts like a heading-hold gyro. Hit throttle hold and make sure the gyro acts like you expect it to. Set the channel 8 ATVs to reasonable values (50% if you're setting the CSM up for the first time, otherwise use the values you had been using for whatever other channel you had the gyro connected to). Make sure you have a reasonable tail rotor mixing curve in normal mode, and make sure you have no tail rotor mixing at all in either of the idle-up flight modes (zero at all five points in both curves).

The Big Picture

or, how does it all fit together?

When I started thinking about setting up the CSM, I would have preferred a way to toggle gyro modes and enable/disable revo mixing with one switch in any flight mode. As far as I can tell, the only way to enable/disable revo mixing on the 8U is through the front-panel programming buttons, which isn't something I want to mess with in the air.

The "solution" I came up with turned out to be less flexible but - my personal preference of course - more convenient. Standard gyro behavior when spooling up the blades (in normal mode) and heading hold gyro behavior for everthing else (idle-ups). One switch, no brains required, I like that. :)

Flight modes on my Futura SE are set up as follows:

Flight mode	Pitch curve	Throttle curve	Gyro mode
idle-up-zero	linear, with half negative pitch at the bottom and full positive pitch at the top. The heli hovers just under 3/4 stick.	The top four points of the throttle curve are set for a constant head speed of 1700 RPM. The bottom point is set for a smooth idle.	standard
idle-up-one	linear, with half negative pitch at the bottom and full positive pitch at the top. The heli hovers just under 3/4 stick.	all five points of the throttle curve are set for a constant head speed of 1700 RPM.	heading hold
idle-up-two	linear, with full negative pitch at the bottom and full positive pitch at the top. The heli hovers at about 3/4 stick upright and 1/4 stick inverted	all five points of the throttle curve are set for a constant head speed of 1700 RPM.	heading hold

I use normal mode (idle-up-zero) for starting the engine, spooling up the blades, and recovering head speed after an auto. With the similar pitch and throttle curves, I can switch into idle-up-one at any time after the blades come up to speed, with no visible effect. Idle-up-one is what I use for hovering stuff and purely upright flight. Idle-up-two is where I spend 90% of time, as it allows all sorts of aerobatic fun.

The bottom line is that I haven't had to change my flying habits with this gyro setup. I still lift off in normal mode, I still fly with the same idle-up modes, and I still have only one switch to think about. That's good, because when the heli is airborne I don't want to have to think about anything else...

Fly and enjoy.