3GX - tolerance to transmitter command

[rudi]

On my Spektrum DX8, the exact point when the red rate-mode light comes on is at +12%. At +12.5% it is in Heading Hold (green light) with minimum gain. At 12.5% the heli flies fine. Obviously the tail is loose, but perfectly flyable and I quite like this for the type of flying I do.

However, when I go to 12% (one click down on the transmitter) all hell breaks loose and the heli spins out of control.

I have 3 gyro positions on my DX8 and I want to set one of them to be "minimum rate heading hold". The sensible thing to do, given no further information, would be to leave some margin and set my transmitter to perhaps 15% or 20%.

Does anybody know, if I did set 12.5% (right on the limit), is there any chance that the 3GX (or the DX8 or the DSM2 protocol) has a margin of error and may be received/interpreted as 12% or 11%? Or am I safe with to assume 12.5% will be a guaranteed 12.5%, and the 3GX's changeover point won't shift?

I don't intend to take any chances but it would be nice to understand the technology, so if anybody can confirm either way, that would be appreciated.

[1chris]

Something is not right here should switch between heading hold and rate on +1, -1 you did set the transmitter to +100,-100 when you initially set the tail up

[coolice]

Hey.

You need to set your gyro gain switch to either a 2 position switch or activate the gyro gain menu in the transmitter and set individual gain values for each of the 3 positions.
It sounds like your 3 position switch is giving you a centre channel pulse in the middle which could lead to problems.

You can visually see gyro gain settings with the 3GX commented to your PC using the software, the second from last tab off the top of my head shows you the various gain values.
.

[rudi]

The DX8 has a 3-way gyro switch, and I can assign a value (-100% to +100%) to each setting. I've checked the servo menu and travel, sub-trim and reverse are all at default.

I've connected the 3GX to my laptop and I'm watching the "Rudder Gain" indicator under the "Setting Display" tab while I change the gain on the transmitter. I'm using v2.1.

Here are the results:
Transmitter=+100%, 3GX=108, LED=Green
Transmitter=+75%, 3GX=80, LED=Green
Transmitter=+50%, 3GX=51, LED=Green
Transmitter=+25%, 3GX=22, LED=Green
Transmitter=+12.5%, 3GX=8, LED=Green
Transmitter=+12%, 3GX=8, LED=Red
Transmitter=0%, 3GX=5, LED=Red
Transmitter=-25%, 3GX=34, LED=Red
Transmitter=-50%, 3GX=62, LED=Red
Transmitter=-75%, 3GX=91, LED=Red
Transmitter=100%, 3GX=120, LED=Red

My limits are about +56% on the transmitter (3GX=58) for heading hold, after that I get tail vibration/very fast wagging.
For rate hold, -52.5% on the transmitter (3GX=65). After that, I get a tail vibration/fast wag when making a slow turn.


I agree I would expect 0% on the transmitter to be the point when the LED changes from Red to Green.

Can anybody else check and confirm what they get on their unit - what transmitter % corresponds to what 3GX reading (on the laptop) and at what point the LED changes colour.

Thanks.

[1chris]

I dont understand what you are trying to achieve, if the tail wags fast in heading hold mode, then the gain is to high, reduce gain until the tail holds without wagging, rate mode is irrelevant (unless you want to fly in it)
Percentages to a certain extent are irrelevant as well, flight is the true test of how well the system is working
I have 2 helicopters with the 3GX, a Trex 500 and a 600LE nitro, both tails fly fine

[coolice]

The DX8 has a 3-way gyro switch, and I can assign a value (-100% to +100%) to each setting. I've checked the servo menu and travel, sub-trim and reverse are all at default.

I've connected the 3GX to my laptop and I'm watching the "Rudder Gain" indicator under the "Setting Display" tab while I change the gain on the transmitter. I'm using v2.1.

Here are the results:
Transmitter=+100%, 3GX=108, LED=Green
Transmitter=+75%, 3GX=80, LED=Green
Transmitter=+50%, 3GX=51, LED=Green
Transmitter=+25%, 3GX=22, LED=Green
Transmitter=+12.5%, 3GX=8, LED=Green
Transmitter=+12%, 3GX=8, LED=Red
Transmitter=0%, 3GX=5, LED=Red
Transmitter=-25%, 3GX=34, LED=Red
Transmitter=-50%, 3GX=62, LED=Red
Transmitter=-75%, 3GX=91, LED=Red
Transmitter=100%, 3GX=120, LED=Red

My limits are about +56% on the transmitter (3GX=58) for heading hold, after that I get tail vibration/very fast wagging.
For rate hold, -52.5% on the transmitter (3GX=65). After that, I get a tail vibration/fast wag when making a slow turn.


I agree I would expect 0% on the transmitter to be the point when the LED changes from Red to Green.

Can anybody else check and confirm what they get on their unit - what transmitter % corresponds to what 3GX reading (on the laptop) and at what point the LED changes colour.

Thanks.

Hey.

I wouldn't worry too much about cross referencing other peoples DX8 & 3GX values to your own, as there will always be differences due to the different calibrations of the DX8's. They should all be within a certain range, but will probably be a little different.

As long as you can switch between each mode, rate & heading hold, then adjust the gain within each mode you are good to go Of course just don't have one of the switch positions set at he cross over point, just in case.
.

[rudi]

I dont understand what you are trying to achieve

Nothing really, my original post was to understand the intricacies of the way the DX8, DSM2 and 3GX interpret signals, and if there was any random variation tolerance. Obviously if an analogue potentiometer or mechanical servo linkage was involved, I would expect there to be variance. But for gyro gain, where there is a switch, a digital signal, and no mechanical parts, I wondered if it was safe to set a gyro gain 1 click from disaster or if I should leave a few clicks for tolerance.

Hey.

I wouldn't worry too much about cross referencing other peoples DX8 & 3GX values to your own, as there will always be differences due to the different calibrations of the DX8's. They should all be within a certain range, but will probably be a little different.

As long as you can switch between each mode, rate & heading hold, then adjust the gain within each mode you are good to go Of course just don't have one of the switch positions set at he cross over point, just in case.
.

That makes sense. 1chris above said the LED should switch at +1, -1 rather than my +12.5, +12, I thought I should post all my settings and get further advice in case there was something wrong.