HOW TO FIX YOUR LOGITECH G940 JOYSTICK

First off, CLICK HERE for a direct link to this webpage[url]

I've been putting off repairing my G940 until the warranty ran out. Well guess what? It's expired now! So the question is.. what's wrong with the G940? Two words: REVERSAL BUG. This is a known 'bug' in the joystick's logic and Logitech is being a huge PITA about fixing it. From what I understand their engineers believe that this is a feature of the stick and NOT a bug. They call it 'hysteresis' and claim that it must exist.

Here's a quick run down:

Lets say you start at 0% throttle. As you slowly increase the throttle you would expect it to do the following:

0% 1% 2% 3% 4% 5% 6% 7% 8% 9% 10% 11% 12%

Easy enough to understand, right? OK lets say at this point you decide to slowly reduce your throttle. You'd expect to see this:

12% 11% 10% 9% 8% 7% 6% 5% 4% 3% 2% 1% 0%

Still with me here? OK Good. Logitech has implemented a 'hysteresis' upon reversal of an axis to help compensate for something called 'pot jitter'. Have you ever slowly turned the volume knob on an old radio only to be scared silly by a loud SCRATCHING noise coming from the speakers? This is due to an extreme amount of jitter called 'spiking'. Joystick potentiometers are very similar and lower quality pots will do this under normal circumstances. Granted it's only a little bit but it can still happen. Logitech decided to use firmware logic to slightly reduce the sensitivity when the direction is reversed. It's actually a brilliant solution and if properly implemented, if you were to slightly reduce your throttle you'd see this as you slowly move the lever:

12% 12% 12% 11% 10% 9% 8% 7% 6% 5% 4% 3% 2% 1% 0%

The problem is that it has NOT been properly implemented, and instead what you get is this:

12% 12% 12% 9% 8% 7% 6% 5% 4% 3% 2% 1% 0%

Do you see the difference? It registered no movement at first but then JUMPED to compensate for the physical travel. This makes fine-tuning things extremely difficult and the amount it jumps varies depending on the axis. It's about 3% for the rudders, 5% for the throttles and 3% to 4% on the trims. It also exists on the toe brake axes, the mini-stick axes and even the PRIMARY X and Y axes of the joystick itself! This is especially confusing considering the primary X and Y axes use hall effect sensors instead of potentiometers!


In December 2010 Logitech released a new firmware which greatly reduced the amount of hysteresis in the primary X and Y axes, reducing it from about 1.2% down to about 0.15%. Yes it's still there but to be fair it's almost impossible to notice while flying – even during precision maneuvers such as formation flying and dogfighting. The problem is that all of the other axes have just as much hysteresis as before! Not a single word has been heard about software/firmware development for the G940 since then and that was SIX MONTHS AGO! Time to take matters into my own hands now.

The whole idea of this modification is to leave the stick itself alone. While it may be possible, rewiring the stick's primary axes would result in loss of Force Feedback and that would defeat the purpose of it all. I could rewire the three trim knobs and the mini-stick on the main stick but I don't see a huge need to as none of those axes require precision.

Instead I rewired the seven axes of the throttle and rudders through a third-party controller board, leaving the buttons intact so that they can still be programmed through the Logitech software. I chose Leo Bodnar's BU0836 controller board as it can handle up to 8 axes and a whole bunch of buttons. Maybe later I'll add some custom controls to the board but for now I'm only worried about the axes. I suppose you can use just about any stick's circuitry but I chose the BU0836 because of its easy to use layout and because I didn't feel like butchering an old stick just for its electronics.

The factory configuration of the G940 requires that the throttle and the rudders connect to the stick using 9 pin (DB9) serial cables. The stick then connects to your computer with a USB cable and a power supply is connected as well. The new configuration has the rudders connecting ONLY to the BU0836 controller board. The throttle is now connected to BOTH the BU0386 and the G940 joystick, and of course the Joystick itself has remained unchanged.


I spent about $10 at monoprice.com on some adapters to make the wiring go easier. Here's a picture of the adapters I bought:



On the left is a CAT5 connector I ended up not using. On the right is a DB9 (serial) to RJ45 (network) adapter of which I bought four of. A couple spares just in case. They were cheap and came in VERY HANDY!


The first thing I did was to remove the base of the throttle. There are eleven screws total so make sure you have a thin phillips-head screwdriver handy as the holes aren't very large:




Once the screws are all out you need to peel back half of the rubber feet – the halves with the holes in them. Be careful not to tear the rubber like I did:




Now you can remove the base but be careful here. You can open it up just far enough to get your hand in and undo the larger four-pin connector. This must be unplugged in order to get the base out of the way:




Once you have the base out of the way you will see this:




Here is a close-up of the circuit board. You will end up rewiring all four wires of the smaller four pin connector as well as four of the pins from the twelve pin connector as marked here:




On the base itself, there was plenty of room to install the RJ45 end of one of the adapters. I ended up cutting a rectangular hole in the base of the G940 throttle. I also ended up cutting off half of the adapter's housing (the part that accommodates the DB9 serial plug) as it's not needed here:




Next you have to extract four of the twelve wires from the twelve pin connector. I suppose you could just cut the wires but I wanted my operation to stay reasonably reversible just in case. You can release the wires by inserting a thin tool (in my case a small sewing needle did the trick). You have to insert it between the wire and the clip holding it in place. Then pry the clip back just enough to release the wire and slide it out. It's almost an operation that required three hands so if you have a friend handy it will go much easier:




Here is a blurry picture of the clips on the backside of the four pin connector. The clips on the twelve pin connector are exactly the same. Be careful not to bend it too much as it might break:




Here's a picture of the twelve pin connector with the wires extracted (and the connecter reattached):




I happened to have an old CD-ROM audio cable laying around and I noticed its small four pin connector was identical to what is used here, so I installed the four wires I extracted into that connector. This step isn't necessary but I thought it would keep things looking clean and relatively professional:




Next I found some solid network cabling and extracted the wires from it. I also extracted the pins from an old VGA cable I had laying around:




Then I soldered the pins to the wires:




Then I inserted the pins into the two four wire connectors and used some shrink wrap to make a harness in order to keep things neat, tight, and free of electrical shorts. I also took the time to install a zip tie to keep the wires that remained on the twelve pin connector from flexing. A hardware issue with these is that as you move the throttle the wires flex at the connector causing buttons to quit working intermittently and causing the trims to do crazy things. You want to keep enough slack on the wiring going up the throttles so that it isn't stretched at full throttle, but you want the wiring at the connector to not move at all while moving the throttle. This is where the zip tie comes in handy:




Here's another look at my harness except this time connected to my network connector. The female pins for the serial adapter worked out great as I was able to slide the stripped ends of the wires into them and crimp them tight. Then I heated it up with a solder iron and the solder flowed right into the slots on the sides of the pins keeping everything nice and secure:




I suppose that if I had planned it better I could have made something work that didn't require so much soldering but it's not a big deal. The biggest problem I have now is that if I take it back apart I have no easy place to simply unplug it but the network plug fits tight enough to not move while plugging in the cable, but loose enough so that I can push it out if I ever have to disassemble it again.

When reinstalling the base don't forget to reconnect the larger vertical four pin connector:




And here's a final shot of the rear of the throttle:



Once you get to this point you can connect the throttle back to the stick with the original serial cable (don't worry about the new connections just yet) and make sure all of the buttons still work. All of the axes will still be present, but will be 'stuck' at 50%.

The rudders themselves are much easier to modify. Since there are no circuit boards or processing chips involved you can simply tap into their 9 pin serial connector. Also the fact that there are no buttons on the Rudders makes things even more simple. No dis-assembly required! There are only five pins you need to access.


OK so you're thinking that this is all fine and dandy and all that, but “how do I know what wire goes to where?” I've created an easy to use chart for you. What type of wire you use and how you do it isn't so important as is making sure the right wire gets to the right connection. The wire colors of the chart are the same factory wire colors used in my G940.

The throttle trims (R1 and R2) use black, white, pink, and light blue wires. The throttles themselves use black, yellow, dark blue, and red wires. Make sure you don't confuse the black wire used for the trims (1) with the black wire used for the throttles (2). In case you haven't figured it out, “W” stands for “white”.

For the rudders, instead of colors I used pin-out numbers. I didn't feel like taking them apart just to get the wire colors:




Here's a picture of the BU0836 controller board. It's VERY tiny and comes with connectors. I found that soldering to the connectors proved to be a pain in the rear and I ended up using a USB motherboard connector and a speaker wire connector to make the rudder connections:




This is the BU0836 fully connected. Yes, it looks rough because I haven't purchased a project box for it just yet but I will soon. Mainly I wanted to get everything connected and make sure it works. You'll notice that my wire colors don't match that of the diagram but that is because the wiring that came with the adapters don't quite match up. What's important is that the proper wire gets to the proper terminal of the BU0836 board:




Here is a run-down of how it shows up in the device manager. This is Windows 7 but I see no reason why it wouldn't run on Vista or XP either. No drivers had to be installed. It's a simple matter of calibrating and you're good to go:




Last but not least here's a final diagram of how everything is now connected to each other after the modifications are complete:



The reversal bug is NOW GONE!

I hope you've enjoyed my write up! Feel free to contact me at thereisnospoon@ympsa.com if you have any questions!

"Time to take matters into my own hands now." .........LOL Sounds like a WD comment.

Woah !!! A home electronics project finally done right. Way to go Master Tec. This will help out many folks who Logitech in actuality, cannot. (their true engineering staff is mostly in Switzerland and Vancouver, CA, and of course is far removed from the actual complaint lines). Your style is pure EE student. I will link this at Lock On files and Mission 4 Today. A did get a chuckle though when the soldering started, bc just as Stephen Hawking's editor mentions that for every extra equation added to the text of one of his books, the readership drops by half, such is likely true in North America for every extra soldering diagram.

S! and great work - WD

Great idea, do not you ever thought about doing so? Not lose any programming options.
Greetings.

Must admit I'm still happy enough with my G940 after a year to not require something like this yet.

However, my Saitek Pro Flight Throttle Quadrant was horrendous due to lousy pots and they are now connected through the BU0836X. That doesn't fix it, of course, but the effects is less bad.

X52 throttle dials are known for this issue, too.

For what we pay for these HOTAS and control systems, you'd expect high quality components, but the only quality these companies seem to be interested in is the marketing and profit margin areas.

FH

There is one company Flash, whose pots have passed thru the trial by fire.... CH Products. Check em out.

I did *NOT* lose any programming options. All of the buttons on the throttle still go through Logitech 's controller board and are still fully programmable through Logitech 's software. Also all of the button inputs on the BU0836 are still unused so if I wanted to add a box with buttons later on I can easily do so.






Keep in mind I did not do this modification because of lousy pots.. I did it because of Logitech 's lousy firmware that they developed to deal with lousy pots. I could have replaced the lousy pots with the best pots in the world and my issue would still be present because the G940 reversal bug is a problem with the programming of the firmware, not a problem with the pots themselves. Yes I did fix a 'spiking' issue with the throttle cabling while I was in there but that was not the primary reason for performing this mod.

If you don't have issues with this on your G940 it's because you don't fly very precisely. To be honest if all I used my G940 for was Flight Simulator then I wouldn't be likely to have a problem with it either, but since I fly combat games that require precision in order to fly in formation and to hit a moving target 200-800 meters in front of me... well its problems stick out like a sore thumb!

HERE IS A VIDEO DEMONSTRATING THE G940 REVERSAL BUG:

http://www.youtube.com/watch?v=SZlUWwOJUN0

Think I'll ignore those remarks and this post and go back to minding my own business.

FH

Ignore what remarks? That wasn't a personal stab at you all I was stating was that under some styles of flying the G940 reversal bug isn't so noticeable, that's all. That's why I posted the video link.. so that you could see exactly what I was talking about.

There are a few people out there that swear that their G940 isn't affected by the reversal bug but that just isn't possible. This isn't due to a manufacturing defect that only affects some units... no this was put there on purpose by Logitech and every (unmodified) G940 suffers from it.

I do not understand

OK I decided to tear back into my throttle to mount the BU0836 controller board into the throttle housing itself. That operation was a success but I suffered from strange glitches in the throttle when all was said and done. The trims would quit working if the throttle was set to less than about 95% and one of the buttons only worked when throttle was at full as well.

I tore it back apart and determined that the wiring going up the right side throttle is simply bad. I had some open circuits when the wiring was flexed a certain way so it was time to replace it.

I took some floppy drive ribbon cable and cut it into two six-wire strips:



Then I took the throttles apart and replaced the wiring with the ribbon cable:

BEFORE:


AFTER:


BACK TOGETHER:


The width of the ribbon cables fit perfectly into the recesses of the throttle arm itself and even with its metal support reinstalled I was able to slide the cable inside the unit to get the correct length at both ends.

Then it was just a matter of soldering the connections to the proper wires (there are 12 of them) on each end and putting the unit back together. I also had to make sure the cable was routed away to the side at the throttle base so it wouldn't rub against things while moving the throttle. I've used it several times now and it's working great!

Once I had it all soldered up I noticed that one of the thin wires at the four-pin connector that I had swapped the pins into had broken so I just eliminated that connector and soldered the wires directly. If it develops wiring issues now it's going to be at the 12 pin connector and if that happens I'm going to locate several old-school CD-ROM audio cables with the small connectors (uses the same pins but with thicker wires - see the image below) and swap those wires into the 12 pin connector at the throttle circuit board.

If Logitech had made those wires just a tiny bit thicker and made that harness just 1/4" longer then there would be no issues with it.. but they didn't.

Hey Master Tec, I had the exact same thing occur after my first rewire.Had to go back in and find the problem wires but just ended up redoing the whole thing again. Great idea with using the floppy drive ribbon. Also applaud your post at the Logitech site concerning these issues, I chimed in as well under a different name.
great job --s

UPDATE: It's been over four months now and it's still WORKING GREAT! I use it at least 5-10 hours a week and I'm still very happy with its performance!

There's just one little glitch I've learned about the BU0836 Bodnar Board: You HAVE to have the rudder plugged in when it powers up otherwise it will not allow those circuits to register. In other words if you turn your computer on (or plug in the board) before you plug in the Rudder pedals then the rudder pedals won't work.

It's not a big deal.. just remember to plug the rudders in first before turning on your computer (or plugging in the USB cablefor the BU0836). If you forget then just go ahead and plug the rudders in and then unplug the USB cable and plug it back in.

Make sense?

I wish I had taken more pictures of me rewiring the throttle.. and mounting the BU0836 inside the throttle but I was in a situation where I just wanted to get it fixed and I simply forgot about doing all that!

I think I got the important stuff out of the way though. If you were to look at the back of my throttle now the network cable is now gone. I did away with that because I was getting intermittent connections with it - I think due to having cheap network sockets. If you look at it now you'll see the USB cable coming out of a hole (that is plugged into the BU0836). Next to that is the 9 pin female serial plug which is screwed in place (where I plug the rudder pedals into) and of course the factory wire that plugs into the joystick is still there as well!

I really couldn't be happier with its performance now. I still wish the reversal bug didn't exist for the three trim knobs under the stick but modifying them requires tearing the stick apart and obtaining another controller board and to be quite honest I don't use them that much anyway. It just doesn't seem worth it to me.

Anyway good luck if you decide to tackle this project! If you want a G940 DO NOT BUY A NEW ONE! Instead buy a broken one dirt cheap with throttle axes and buttons that don't work and fix it yourself! I saw one for sale like this for $50 on craigslist not too long ago! All you need is less than $10 is hardware and the $40 Bodnar board and you're good to go! You might even be able to pick up an old USB joystick with bad pots for a few bucks and wire the G940 axes to its controller board!

If I ever end up needing to tear open my throttle again I'll update things in this thread and take a whole lot of pictures I promise! I've also been considering a project to shorten the length of my stick (har har I know you smirked) by about 1/2 inch or so... obviously I'll document that mod as well if/when I decide to do it.

If anyone wants these mods to be made to their stick and are willing to pay for shipping, parts and a tiny bit of my time feel free to PM me - I'm sure we can work something out!

I think this is due BU0836 feature that automatic disable axis without plugged pot/sensor.
Seem that you can disable this with L.Bodnar configuration software:

http://www.leobodnar.com/products/BU0836/BU0836%20configuration.exe

But, since pot cable involve +5V ad Gnd is good idea plugged the in "cold way".

Sokol1

Master Tec,

Check your PMs.


Monte Sliger

Are the problems with this HOTAS for new buyers still valid and it's not recommended if you don't plan on doing any modding to it?

Hello friends,

I ordered and received the BU0836 controller about a month ago but I was postponing the installation on my G940 because of the amount of work that had to be done...

I mainly fly FSX and for the last months I fly almost exclusively helicopters at maximum realism (using HTR at 100%). If anyone is into helicopters knows how sensitive they are to control inputs, especially while hovering. Here the reversal bug on the throttle and rudder axes was more evident and annoying than in any other situation.

For example, when the hovering heli was slightly yawing to the left and I slightly pressed the right pedal to stabilize, the heli immediately started yawing to the right instead of just stopping the left yawing. I had to press harder on the right pedal (and yaw harder to the right) and then correct pressing slightly left again to find the sweet spot. Exactly the same was happening with the throttle axis. Fine control of the aircraft was very difficult.

Yesterday I made the decision to install the BU0836 controller. The whole process took about 5 straight hours. The difference to to above process was that I installed the BU0836 inside the throttle unit, as in the attached photos. I also mounted a 9-pin female connector on the throttle unit where the pedals now connect. After the installation I did a test flight in some of my favorite helicopters. The difference is amazing! Fine control of the heli is now perfectly achievable. No more need to compensate by overcontrolling and then reversing direction to find the sweet spot!

I think the modification was definitely worth the effort.

Nick

Looking good! That's almost exactly how mine ended up being! I wish I had taken pictures of my BUO836 mounted inside the unit but it's not too different from yours.

I should add that mine is still working great!

Just a note, the pictures are not mine, but my BU0836 is placed in exactly the same spot and the 9-pin connector for the pedals is mounted in exactly the same place on the throttle unit.

My only minor problem is some very slight stickiness of the pedals in very small inputs, noticed only in helicopter fine yaw control. I think that a re-lubrication of the pedals will be enough to make it butter smooth..

Thank you very much for your directions, the G940 now is a real joy to use!

Hello all.

These are my modifications after the idea from MasterTec:









After that I started to resolve the trim axes. I bought 3 rotary encoders with switch on axis depress and some push buttons. like these: http://www.newark.com/alps/ec12e2424407/encoder-incremental-5vdc/dp/74M1068




I've chosed to use only 12 buttons from maximum 32 possible cause it was easier this way and I have enough buttons... for now. So I used this scheme from LeoBodnar site:




And started to build a little box made of raw circuit board.










I made the proper "fast" wiring and testing






All looked great. Started the PC and after a bit of tweaking the wires in pin connector of BU0836 all was ready for final setting with Bu0836_Encoders program from Leo Bodnar site:

http://www.leobodnar.com/shop/index.php?main_page=page&id=12

This worked excelent for me:





The rotaries work like the trim console of P51 Mustang. Top Blue is rudder trim, Left Green (tilted outward for ergonomy) is elevator trim and Back Red tilted is elerons trim. They are digital and this way very precise and I can reset quickly the trim axis to neutral without the need to find a central point by pressing on top of the each rotary.

The three forward lighted push buttons can be used for other functions.


I hope is useful for the rest of people.

Hi,

I would like to attempt the mod that you all did to your G940's, but for some reason, I am unable to see the pictures that MasreTech posted. I am able to see his HOW TO FIX YOUR Logitech G940 JOYSTICK post, but no pictures.

Would it be possible for anyone to send these to me please, and any more useful information that you may have regarding this mod.


Kindest regards,

Ken

Good thing I archived these: http://www.sendspace.com/filegroup/h97j7N37ywP154dptueZ1g

This is what I did http://dangerdogz.com/forums/topic/10450-logi-g940-throttle-mod/

Some time ago I searched for lost images of the original MasterTec's thread. After searching for a long time I found a document created by Tomkin that translated the text of Mastertec into German with the original images. (https://elitedangerous.de/forum/index.php?thread/6448- Logitech -g940-mit-bu0836a-ausr%C3%BCsten-reversal-bug-weg/)

I have created an identical document but using the original text (English) and the images. I share this file as well as the ZIP file with the original images.

regards

https://www.mediafire.com/file/32448ldzjye4g4h/G940_MasterTec_Mod_Images.zip/file

https://www.mediafire.com/file/637pkdjv5wbl23z/G940_MasterTec%B4s_mod.pdf/file