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Old Sep 30, 2011, 04:37 PM
Tye
Chacotoma, NM
Joined Jan 2004
749 Posts
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I desperately need help programming a Spektrum DX-7

I want to install a gyro on the rudder of a big groundloopy warbird. I am using a Spektrum DX-7, and a AR-7000 combination. I know of course, that the gyro goes between the rudder channel, and the rudder servo, but in what channel do I plug in the gain control lead, that varies the gain, or even turns the gyro off ? Can I use the programmable Aux2 channel ? And if so, what switch do I select, one of the sliders, or the 3 position switch ? Most important is, what are the actual programming steps necessary to turn it on and off, and also vary the adjustable gain of the gyro ?



I am completely lost, please help. Thanking you greatly in advance.



zak
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Old Sep 30, 2011, 05:24 PM
Air, Ground & Water
freechip's Avatar
Canada, ON, Rockland
Joined Aug 2008
24,307 Posts
Generaly Spektrum use the 5th/gear channel for gyro use if equiped with a gyro menu.
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Old Sep 30, 2011, 06:45 PM
60 years of RC flying
Daedalus66's Avatar
Canada, ON, Ottawa
Joined Feb 2006
16,727 Posts
Calm down. No need for desperation. It's a simple issue in terms of programming, but you do need to understand how the gyro response is set. Here are the principles, though the details could vary depending on your gyro.

Normally the gyro sensitivity is controlled by a signal that ranges from 0% at one end (corresponding to full over if a servo were plugged into the channel) to 100% at the other end. The part of the range from 0-50% gives you a rate gyro (one that essentially damps the rudder response, which is what you want for fixed wing). From 50-100% the gyro is in heading hold (HH) mode, which is great for helis but not what you want for normal fixed wing flying. Maximum sensitivity is at the ends of the range -- 0% for rate and 100% for HH. Normally you want to be somewhere in the middle with sensitivity (e.g., 25% or 75%).

So what you want to set for your fixed wing model is two values: 50% will turn the gyro off (zero sensitivity) and something like 25% will give you a fair bit of damping in rate mode, which you can adjust by changing the value.

To do this adjustment, HELI mode programs provide a GYRO option, but nowadays most people ignore it and go to GEAR or AUX2 to set the gyro directly. Anyway, GYRO is not available in ACRO mode. So forget it.

So which channel to use? Stay away from AUX1 because it's often used for flaps or dual aileron. Likewise, GEAR may be needed for (guess what) gear.

So let's assume you decide to use AUX2. On the DX7 you have a menu choice INPUT SELECT on the Setup menu. The first item there allows you to choose what activates AUX2. Choose 2P SW (2-position switch). For this job you don't want three positions.

Now how do we get those two values 25% (gyro on) and 50% (gyro off)? Using Travel Adjust for AUX2, set 0% and -50% (you have to flip the switch to set the two values).

The zero travel value puts the output dead center, which corresponds to 50% on the gyro scale, which means zero sensitivity or Gyro OFF.

The -50% travel value means the control is halfway towards the low end, i.e. at 25% of total throw or 25% on the gyro scale. That's what you want for gyro ON.

To see what's going on, go to the Monitor screen on the DX7 (it's your best friend when trying to figure any of this stuff out. You should see there what I'm talking about. With the switch in one position, you should see the cursor in the middle (50%) while in the other position it should be on the first left mark (which 25%). The next mark to the left is 0% and the last one to the left is off scale.

The confusing thing about this is the two different scales, but once you figure that out it's fairly simple.

If you want more gyro effect, you move away from the middle by setting travel to say -60%, which means (if you draw a diagram) -20% on the gyro scale.

Everything clear now? Give it a good try and if it doesn't make sense come back for more. No one ever said gyros are supposed to be easy.

(Of course, you could simply find a rate gyro that lacks remote sensitivity and uses a pot to adjust it. But then you'd miss the fun.)
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Old Sep 30, 2011, 09:49 PM
Tye
Chacotoma, NM
Joined Jan 2004
749 Posts
" To do this adjustment, HELI mode programs provide a GYRO option, but nowadays most people ignore it and go to GEAR or AUX2 to set the gyro directly. Anyway, GYRO is not available in ACRO mode. So forget it. "

Excellent response from both, thank you very much. It looks like I did the right thing by coming here. Regarding the above statement, does this mean that I will need to fly the warbird using the HELI mode, and AUX 2 ? AUX 2 is available, and what switch should I use ? Yes, GEAR is already taken up. And will I loose all of my good Trim, Expo, and Dual Rate settings by switching to HELI mode ? I am using a JR G 370 A gyro, which is RATE only, for Aircraft only. Will this make anything easier for me ?

Thank you for your patience with this old guy, and please don't go away. I need you.

zak
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Old Sep 30, 2011, 10:16 PM
60 years of RC flying
Daedalus66's Avatar
Canada, ON, Ottawa
Joined Feb 2006
16,727 Posts
Hi Zak:
A lot of what you need to know is right there in the instructions. First, though, you need to understand that "rate mode" has nothing to do with "dual rate". It's all about how the gyro functions. Here's what the instructions say:

Warning: Use of tail lock or heading hold gain in an aircraft can result in the control surface connected to the gyro lock in one direction potentially causing a crash. Use care to ensure the gyro is always in rate mode at all times.

Then they explain with a diagram what I was trying to say about using regular travel adjust to control the gyro sensitivity and turn it on and off:

"When Using Travel Adjust to Change the Gain
Gyro gain control is as shown in the figure below. Positive values are tail lock mode and negative values are rate mode, with zero gain at +/-1% and the maximum gain at both ends (+/-100%). Warning: Do not use a range between -1% and +1% because it is unstable."

I didn't know about not using the very middle of the control range. They go on to explain:

"If using travel adjust to select the gain, the gain should be set to -1% for zero gain. For increased sensitivity, decrease the percentage in the travel adjust function. The lower the value in the travel adjust program the higher the gain will be (with -100% being full gain in rate mode)."

Very important: you MUST NOT use this gyro with an analog servo. I can tell you from personal experience that the life of an analog servo is about 2 seconds if used with a digital-only gyro.

Anyway, there is some very important information about how to mount the gyro. Obviously orientation counts, but so does the type of mounting. You must follow the instructions about using adhesive foam for mounting.

Read everything they say about using the gyro in an airplane, and if you don't understand it, come back here (or PM me if you like).

What is the model?
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Last edited by Daedalus66; Sep 30, 2011 at 10:23 PM.
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Old Oct 01, 2011, 07:57 PM
Tye
Chacotoma, NM
Joined Jan 2004
749 Posts
The model is a Ziroli Stuka, and takeoffs are fine, it's just the rollouts after touchdown that get groundloopy and I drag a wing. I am using a JR G 370 A gyro, which is RATE only, for Aircraft only, so I only need to concern myself with adjusting the rate. Any suggestion on how much rate to begin with, and where in the landing pattern is the best place to turn it on ? ? ?

zak
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