SpartanRC DS760 Gyro Review and Setup Vids

[Angelos]

Do not use subtrim to change the neutral of the servo. The stick position does not drive the servo directly although some correlation may appear due to how the system works. The stick position is a command to the gyro of how fast you want to yaw. The gyro then is in charge of the servo. The mid-point of the stick is memorised each time the gyro is powered so next time you power on the subtrim you added will have no effect as the gyro will learn the new mid-point.

The 90deg angle does not have to be perfect but it helps a bit if it is. With Futaba servo you can use a different arm. They gave small offset between them and one of them will give you the ideal fit. Failing that you can use the ds760 PC software and adjust the servo mid-point trim.

-Angelos

[BruceW]

I was trying to use the Mikado servo horns (single arm) on the servo but will most likely switch over to the supplied servo wheel in the package since it centers properly.

Are you saying the gyro learns the mid-point from the servo and does not use the signal on the RX?

[Finless]

The gyro on power up sees the rudder stick and uses that signal as the rudder neutral or center stick position. If it is sub trimmed after initialization then the next time it is powered up it will see that sub trimmed position as center stick and you would have to sub trim again. If you keep doing this each power up eventually your sub trim would be maxed to one side. Not good! This is why you don't trim or subtrim the rudder stick.

Make sense now?

Bob

[Angelos]

Are you saying the gyro learns the mid-point from the servo and does not use the signal on the RX?

No, the ds760 learns the mid-point from the rudder channel each time it is powered on. If you change the trim etc the ds760 will be affected while you are doing it. But next time you power on it will tread the new rudder signal as mid-point. This is how Futaba gyros work too.

The important thing is to understand the concept that the rudder channel of the radio does not control the tail servo. It only tells the ds760 how fast to yaw. Then ds760 will then decide on how much tail pitch is needed to do the job. If you add trim or sub-trim etc you are not adjusting the servo position, you are only telling the gyro to yaw very slow. On the same principle adjusting transmitter’s rudder endpoints will not affect the tail servo limits, it will only affect the magnitude of the command to the ds760 thus resulting to slower or faster yaw rates when full rudder is applied.

Since the ds760 is in full control of the tail pitch it needs to be aware of how far it can drive the tail servo before mechanical binding occurs. For this purpose it has its own set of endpoints and servo mid-point trim.

-Angelos

[BruceW]

Make sense now?

Bob

No, not really. When I add subtrim while in rate mode to get 90 on the arm, the servo is then in the correct position the next time I re-initialize in HH mode. There is no more subtrimming necessary after the initial setup and all works as expected. I could see yaw rate not being equal for both directions because of the subtrim but if the gyro learned about the new center position (with subtrim) it could presumably apply the offset to yaw rate control.

[xStatiCa]

The gyro on power up sees the rudder stick and uses that signal as the rudder neutral or center stick position. If it is sub trimmed after initialization then the next time it is powered up it will see that sub trimmed position as center stick and you would have to sub trim again. If you keep doing this each power up eventually your sub trim would be maxed to one side. Not good! This is why you don't trim or subtrim the rudder stick.

That makes no sense to me and goes against my experience with other gyros. I only have experience with the gy240, gy401, and G770 3D gyros but I don't see why this gyro would work any different. When the gyro powers on... whatever subtrim/trim is set in my DX7 that is interpreted as 0 input to the gyro. Why would you need to adjust sub-trim a second time? The gyro already initialized and sees the current trim/subtrim as 0 input. The next time I power the gyro off and on again it will see that same subtrim/trim as 0 input again. Once you trim/subtrim the servo to 90 degrees you never have to touch sub-trim or trim again. Does the DS760 work differently? I don't see how it could because as long as the transmitter always gives the same signal when the gyro powers up it should always think that is 0 input.

[xStatiCa]

If you add trim or sub-trim etc you are not adjusting the servo position, you are only telling the gyro to yaw very slow.
This is always done in rate mode on the gy401 to get the servo at 90 degrees if I can't get a servo horn to give me the 90 degrees. Once that is done then the next time the gyro is powered on the gy401 will see that as center position for HH mode. Does the DS760 not have a rate mode?

[BruceW]

This is always done in rate mode on the gy401 to get the servo at 90 degrees if I can't get a servo horn to give me the 90 degrees. Once that is done then the next time the gyro is powered on the gy401 will see that as center position for HH mode. Does the DS760 not have a rate mode?

I adjusted the servo to 90 degrees while in rate mode on the DS760.

[BruceW]

Angelos,

I understand the concept of how gyros use the rudder signal to control yaw rate but from all that I've read in the last few posts it seems that the gyro learns about the new center position of the subtrimmed servo and then works properly. So far it seems that if subtrimming is done once in rate mode, the gyro is re-initialized in HH mode, that it will work the same as an untrimmed servo. I am also assuming that the gyro takes into account the new 0 point and can still perform equal yaw rates in both directions.

So with all that has been said, I'm still not understanding why it is said that subtrimming must be 0 for the gyro to work properly when the gyro learns about the new position.

Bruce

[Angelos]

yes, but you will probably find out that as soon as you get back to HH mode the horn will no longer be at exact 90.

-Angelos

[xStatiCa]

It will in a hover if you setup trim/subtrim so that the servo arm is 90 degrees at hover in rate mode. Which is the whole point of setting up the 90 degrees at the servo. This gives equal arc movement either direction from hover position.

[Finless]

Yes trimming in rate mode works but you must power up in rate mode then go to HH mode. If you power up in HH mode then HH mode will see the trimmed rudder as the NEW center stick position. Most people I know DON'T do it this way and correct me if I am wrong but most gyro need to be powered up in HH mode no?
If so (and I am unsure since I never tried this myself) then all this wonderful trimming you did in rate mode does nothing for HH mode.

Bob

[BruceW]

yes, but you will probably find out that as soon as you get back to HH mode the horn will no longer be at exact 90.

-Angelos

It seems the gyro makes a slight jump in position when switching between rate and HH mode and this was witnessed in both trimmed and non-trimmed configurations. Is the amount of this position change related to the difference in gyro endpoint limits? I guess this means my slider is probably not mechanically centered in the full range. Overall I will probably never come out of HH mode for all practical purposes.

[xStatiCa]

Whatever trim/subtrim you setup in rate mode will also be seen as 0 input signal from the transmitter if you power up in HH mode. You do not have to power up in rate mode with trim/subtrim added. I set all my helis up this way without issue.

The only exception to this rule is if you have not rebound your DX7 transmitter/rx to learn the new center position(with trim/subtrim). If the DX6/7 rx takes time to lock onto the tx signal then it will go to failsafe for the rudder which will be the last bound position. If you have applied subtrim/trim after binding your tx/rx and this happens, The gyro will see the bound position as 0 signal for rudder and then your rx will lock onto the tx and the tx will give the new trim/subtrim signal which is different and you will get drift.

I wonder if this gotcha causes some people trouble and makes them think trim/subtrim is bad.

As long as you rebind the DX6/DX7 tx/rx to the new fail safe tail servo center position after setting up rate mode for 90 degrees you won't have problems with trim/subtrim. Any time you change trim or subtrim though it is best to rebind the DX6/DX7 to program the new center signal(The manual states this too for this reason). As long as the rx/tx sync up before the fail safe position is given by the rx this issue will not reveal itself though.

Receivers that do not output any bound position at power on if the signal does not lock on does not have this problem (before 2.4ghz receivers?). I only have experience with the DX6 and DX7.

[xStatiCa]

It seems the gyro makes a slight jump in position when switching between rate and HH mode and this was witnessed in both trimmed and non-trimmed configurations. Is the amount of this position change related to the difference in gyro endpoint limits? I guess this means my slider is probably not mechanically centered in the full range. Overall I will probably never come out of HH mode for all practical purposes.
The reason it moved could be that in HH mode it is trying to correct for some amount of movement that it thought it saw so I wouldn't worry about it. Rate mode is the only easy way to know for sure if your servo is setup for 90 degrees on the arm at hover because it will auto center. In HH mode you would have to hover and look at the servo position. If you were to look at it in HH mode after landing or at first power on it could be anywhere in the travel trying to correct for some movement that it saw.

The important part for me is making sure at hover the servo is at 90 degrees for equal arc movement.

[BruceW]

I agree, setting it up for 90 in rate mode has worked just fine and once in HH mode, the gyro takes over anyway and locks in the tail. I'll be in HH mode the whole time anyway so this doesn't matter too much.

[Finless]

Yea this gets debated a LOT. I have seen more posts debating this "setup for rate" than I care to shake a stick at!

Believe it or not Pro's that I fly with dont do this!! They set up 90 and center the slider and be done with it!!!! I could name all kinds of well know names that do it this way. I know it's not right (per the manufacturers) but these guys dont ever use rate mode so it works for them and is easy to setup.

FYI other than my 6110T and this DS760 all my other gyros (401 and 611's) are setup 90 and center slider and I dont have a problem either. I did it that way because the Pro's I fly with said to do it that way right or wrong... It works for me.

So there you have it. Go figure aye?

Bob

[BruceW]

The difference here is that I'm not setting up for stable hover in rate mode, I'm only trying to get the servo arm to 90 and have the tail slider in the center mechanical position. What your talking about is different.

[Angelos]

This discussion has gone unnecessarily overcomplicated. The gyro does not care whether it is 90 degrees, 89 or 88. Keep it as close as you can and if you are picky use the the right servo arm or trim it any way you wish. But make sure the gyro is restarted to get the new mid-point for the AVCS mode. At the end of the day the gyro will work out what tail pitch is needed during flight even if the normal mode is a little out. The only reason for the 90deg is for the left and right arcs of the servo arm to be fairly symmetrical.

-Angelos

[Finless]

EXACTLY Angelos!!! That is what I have learned over the years too.... Your setup instructions about getting CLOSE with tail pitch worked perfect and is what I have really experienced on many other gyros too.... You really dont need to slice hairs to get a good working setup!

Bob

[xStatiCa]

Angelos, You just summed it up nicely.

Quick question for you... When setting up the limits does the tx signal at gyro power on determine the center position from where the limits are set? For an extreme case take that you give full subtrim one direction. Does the gyro use that power on signal to skew the center of the limit adjustment that direction? I wonder if this behavior is standardized by all the well known gyros out there.

[BruceW]

Thank you, that simplifies the discussion. The basic thing I wanted to know is whether the calculations being used by the firmware would be affected by trimming the servo to 90 and it sounds like they do not care. I want to stick with my non-90 Mikado servo arms so I will keep it setup the way I have already done with trimming and test fly soon.

[Angelos]

For an extreme case take that you give full subtrim one direction. Does the gyro use that power on signal to skew the center of the limit adjustment that direction?

I guess you mean sub-trim on the radio. Let's ignore the gyro for a moment and assume that a servo is connected directly to the receiver which is a bit easier to understand (I connected my oscilloscope so I can get accurate measurements). On Futaba radios when the ATVs are at 100% and the stick at full travel the servo signal is only reaching 70% of it's potential full travel. Then the mid-point shifts because of trim or sub-trim the end-points also shift by the same amount. So the left and right controls remain symmetrical. However if you max-out the ATVs and then apply trim or sub-trim there will be no room for endpoint to move thus one side will get less travel. So if you are going to use lots of sub-trim and you want to keep both sides symmetrical you should not use max ATV; 5-8% less should be plenty. You should be able to see if it hits the end in the servo monitor screen. Most radios now have it.

-Angelos

[xStatiCa]

That helps a little but the main question I am trying to ask is not being communicated properly I guess. Let me try it another way. It can be difficult to describe things...

If I setup the gyro limits to not bind either direction with no subtrim/trim on the rx and then I go into the tx and give full subtrim and trim to the left will the gyro's idea of limit position change at next power on when the tx gives a new 0 input center signal position?

Now take that example and apply it to rate mode. Will the result be the same?

[Angelos]

No they won't change. The gyro limits as absolute. When the servo hits them it stops. No other setting will affect them either on the radio or the gyro itself. This applies to the ds760 and from observations I believe it applies to Futaba gyros too.

-Angelos