Logitech G940 Reversal Bug - v1.42 Firmware Update - ED Forums
 


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Old 10-14-2018, 11:50 PM   #1
Drakoz
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Default Logitech G940 Reversal Bug - v1.42 Firmware Update

This is a new thread about an old problem for the Logitech G940. Since the links to Logitech's original forum topics have disappeared (because Logitech removed their old forums and didn't archive them in a linkable way), I thought I would summarize and provide new links from archive.org to the Logitech forum topics and the v1.42 firmware that partially solves the reversal bug.

The link to the v1.42 firmware can be found at the bottom of this post. It is not available on Logitech's support site, but still available from their ftp site. It was an unofficial release, only available from the Logitech forums.

New Info June 2019: fred41 has created a patch for the v1.42 firmware that solves the reversal bug for ALL axis now, as well as improves some of the force feedback settings which improves the general feel of the stick. Finally after a decade since it was released, the G940 HOTAS works the way it should. You apply fred41's patch to the v1.42 firmware installer which is linked below. Then just run the v1.42 firmware installer like normal and fred41's patches will be applied to the stick. Thanks fred41!!

Link to fred41's forum topic on the firmware patch: https://forums.eagle.ru/showthread.php?t=240114
Link to the patch: https://github.com/fred41/G940-firmware-fixes


What is the reversal bug?

By design, Logitech added a form of hysteresis to all the analog axis on the G940. Hysteresis is kind of similar to a dead zone, but dead zone is normally added at the stick center (centered by the springs) where hysteresis would look like a dead zone, but occur anywhere you reverse the direction of an axis.

There is benefit to this. Many people like having a dead zone as it resolves the issue of noisy pots, and that is probably why Logitech added this feature in the first place. But they took it a step further and that was a disaster. Hence why we call this a reversal bug instead of a reversal feature.

First, you can't get rid of the hysteresis dead zone. It is added by the G940 firmware and there is no option to get rid of it. Second, it isn't true hysteresis. In fact when you reverse the axis, it causes the axis position to jump after reaching the other side of the hysteresis dead zone. Third, odd effects with FFB would occur due to the reversal bug, most of which have disappeared with the v1.42 update.

What does this mean? Load some software that lets you see the position of an axis in percentage. If you move any G940 axis from say 50% to 80%, then reverse the direction, with simple hysteresis, you would physically move the axis a small amount and the % position in the software would not change. But after a bit of movement (through the dead zone) you would see the axis go from 80% to 79%. That is hysteresis - a dead zone that occurs any time the axis is reversed. On the G940, though, what really happens is the axis moves from 80% to 77% once you move past the dead zone. That is the disaster. Upon reversing direction after moving through the dead zone, the axis always jumps 2-3%, as if the dead zone didn't actually exist.

Both the jump, and the dead zone are problems. Also, for the FFB on the stick, I often got jumps in the motors trying to counteract either my reactions to the reversal bug jumps, or perhaps as part of the way the reversal bug affected the FFB algorithms internally. I never tested completely to understand. All I know is not only did v1.42 fix the reversal bug for the stick, but the FFB got way better. What I thought was just really bad FFB mechanical design, turned out to be mostly software.

The G940 FFB design still isn't as good as the Microsoft FFB2, but the v1.42 software makes it worth using the G940 over the MS FFB2 because the MS FFB2 doesn't have enough hats and buttons to be called a HOTAS setup. Also, the MS FFB2 has a dead zone at the stick center which cannot be removed - which I also consider as a fatal flaw. The hysteresis dead zone on the G940 follows the stick as the FFB holds the stick in different locations, but the MF FFB2's dead zone is always at X/Y center regardless of what the FFB motors are doing. Microsoft made an excellent product in the FFB 2 except for that one issue, and it almost ruins it for some applications.

But back to the G940.....

The dead zone is a problem because on certain aircraft (helicopters especially), having a dead zone gets in the way rather than helping.

The jump is a problem because imagine you are using the G940 Throttle as a helicopter collective. Being able to make a 0.5% adjustment to the collective (or the throttle on any aircraft) is important. But the best you can do is a 2-3% jump every time you reverse the axis. The same is true when using the trim knobs on the joystick, or the separate slider wheels on the throttle to adjust the position or size of a targeting camera or radar reticule, or the size of the targeting circle on a WWII war bird. It is infuriating, and a significant percentage of G940 users either returned their units, or just gave up and put them in the closet because of this.

Search on "G940 reversal bug" and you'll see several links to discussions of the issue. Here is a Youtube video that shows the issue: https://www.youtube.com/watch?v=SZlUWwOJUN0

Here is a discussion of the issue on Logitech's main forums (linked from archive.org):
https://web.archive.org/web/20101222...em/td-p/445318

Several links in the Logitech forum topic are broken (like viewing later pages of the topic, or other linked topics). You may have to use archive.org to hunt them down if you want to read the entire topic.


What is the solution?

CharlesB on Logitech's fourm (a Logitech employee) championed the effort to fix this in late 2010. You can see his original comment about the effort here (which is page 3 of the Logitech forum topic I linked above):
https://web.archive.org/web/20101222.../445318/page/3

He released firmware v1.42 which solves the issue for the joystick axes only. The other axes still have the issue. The reversal bug is still there on the stick too, but instead of jumping like 2-3% when you reverse the joystick axes, it jumps only about 0.3% which is good enough to not notice the issue anymore.

After the release of v1.42, no further effort occurred to fix the other axes. I believe CharlesB tried to get it done, but it wasn't given priority. So the other axes are mostly useless.

You can see his original posting on the v1.42 firmware here:
https://web.archive.org/web/20120119...le/td-p/542496

Installing the v1.42 Update

You can still download the firmware direct from Logitech here:
https://download01.logitech.com/web/...ate_FW0142.zip

If the above link is broken, PM me and I will send you the firmware. Archive.org did not archive the download link.

To install it, note the following:

Notes from CharlesB:
  • This release specifically targets and improves the accuracy of the X/Y on the joystick
  • The firmware updater may hang. Don't panic. Simply close and reopen the updater. The G940's firmware wont be fully written until all blocks of data are transmitted and verified.

Additional notes to consider:
  • You may need to "run as admin" (right click on the installer and run as administrator).
  • The v1.42 updater still worked for me in Windows 10.
  • You may need to install the latest G940 Software which includes the v1.41 firmware update, and apply that firmware update if your G940 has older firmware. I don't know if the v1.42 firmware will update from older versions of the firmware. The latest G940 software is available from Logitech's website (Logitech Gaming Software v5.10.127) and still works under Windows 10 in my experience.
  • You don't need to use the Logitech Gaming Software v5.10.127 to use a G940, but it still works fine under Windows 10, and provides several important features (FFB settings) as well as a profile editor to assign custom key presses to keys and axis.
  • Logitech Gaming Software v5.10.127 is not specific to the G940 - it supports many older (now unsupported) Logitech gaming devices. The latest version of Logitech Gaming Software is completely different than v5.10.127, but in my experience, I am able to run v5.10.127 and the current versions side by side without issue.

Last edited by Drakoz; 08-12-2019 at 07:14 AM.
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Old 10-15-2018, 01:14 PM   #2
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Great post. Just necrod a thread about this topic. Gonna try it again.
Now I cant find the power supply sighhhh..
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Old 10-21-2018, 11:11 PM   #3
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So found the PSU for and finally got it mounted in my pit ect.
However, I'm having trouble with the logitech profiler settings not doing anything.
The only thing that seem to be working is Centering Spring Strength. Also Choosing FFB in options only ****s up trim and doesnt move stick.
Ever had the same problem?
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Old 10-22-2018, 06:08 AM   #4
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What happens when you go to the Windows Control panel for the G940. When you press buttons on the stick, it should exercise the FFB effects. This should happen regardless of whether the profile software is loaded or not.
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Old 10-22-2018, 04:50 PM   #5
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All the effects work in the control panel. I also seems very arbitrary when the settings actually take hold. For example, just now I was playing around with min/max setting to see difference and nothing happened. I applied new settings, activated an effect and then checked resistance force ect. Some of the time not even Centering Spring settings were applied. Other times the (not as often) the new setting isent applied and it just feels like a standard centering force.
Im unsure what the problem is.
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Old 10-22-2018, 10:37 PM   #6
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Small update:

So the arbitrary settings mostly seem to work only just after confirming them and while in the device control panel window (where the ffb effects are activated). If focusing on DCS window or closing control panel, the standard ffb setting takes hold emediatly (felt by stick stiffening).
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Old 10-23-2018, 01:29 AM   #7
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This stick should have been the one to get... a complete HOTAS package, stick, throttle, and rudder pedals with force feedback. It is a shame they found a way to fail with such a great concept and at a decent price, too. With just a few relatively minor hardware and software changes, this package would have dominated its niche.
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Old 10-23-2018, 05:33 AM   #8
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Speedstick, sometimes, something will happen that causes DCS to no longer control the FFB.

For example, I have gotten DirectX game controller resets (the messages in the upper right corner of the screen saying all your controllers disconnected and then reconnected - but that's another conversation). Anyway, when that happens, the stick will default to some config not controlled by DCS (or rather probably controlled by the Logitech software, or random???). In my case, the stick just goes limp. I have spring force turned OFF in the Logitech software and depend on DCS to drive the spring force completely, so the stick goes limp. BTW, that is how you should use a G940 with DCS - turn spring force off in the Logitech software. Anyway, if I then do something that would affect FFB (e.g. tap the magnetic brake button on the cyclic in the Gazelle or do a trim change in most aircraft), then DCS takes over the FFB effects again, and all is determined by the settings in DCS (the stick goes back to normal).

Not sure if that is what you are seeing, but something to consider.

The Logitech Profile software also has the ability to control non-spring effects like friction and hydraulic feel. This would cause the stick to feel sluggish when moving it, but not spring it back to center if you also have the centering spring turned off. But I'm not sure if these effects are active, or if DCS overrides them. I haven't thought about it in a while.

I used to use simFFB with my Microsoft FFB2 stick, to create these effects or to give FFB function to any aircraft that didn't have FFB, or where it was implemented incorrectly. There are some features of simFFB that may help you diagnose the issue here. But otherwise, the Logitech software more or less does the same thing. Search on simFFB and you'll find several forum topics about it and where to get it if you are curious.
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Old 10-23-2018, 06:06 AM   #9
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I had this stick years ago when I first bought the a10c module, but after a few months I sold it due to the deadzones it had, I was extremely frustrated with it. It's a real shame, the setup was really great otherwise

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Old 10-23-2018, 08:24 PM   #10
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Ah yes simFFB. Already have it installed, just forgot about it. And it seems like the only thing that works at the moment.
Would be nice if ffb work like mirage fbw or something, or some more effects.
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Last edited by SpeedStick; 10-24-2018 at 12:09 AM.
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