Sunday, November 28, 2010

Logitech Momo Force (red) hardware calibration

Hi dear reader(s)! :)

Today I'm gonna take some time to explain how to manually fix the calibration on the Logitech's Momo red wheel. This wheel has auto-calibration feature, where you turn the wheel completely to the left and then completely to the right and it will calibrate in the middle. Same principle is working for pedals too, pressing the pedals fully would calibrate the maximum position.

Problem: While connected and auto calibrated, my Momo would be centered about 15-20 degrees to the left.

This is easily solvable on Windows operating systems by using Center Adjustment Utility from WingMan team. I tested it and i needed the set +4 for the correct center position.

This however doesn't fix the calibration error if wheel is used on PS3 or any other non-Windows platform. While waiting for GT5 and testing the wheel on GT5: Prologue, I had few days to figure out how to fix this. On PS3 I had no way to set-up calibration and while the wheel was working (I could play Prologue), gaming was very awkward and bad due to the incorrect center position.

Logitech support was no help (they couldn't offer any spare parts or support for manual repair). Google was also not very helpful :) so i needed to do something myself (i figured this would be the case from the start).

After some fiddling with college from work, he proposed I try connecting extra potentiometers to correct the results coming from the main potentiometer responsible for reporting wheel position. And boy did this work beautifully! I tested it and noticed that putting more resistance on the black wire made the wheel center towards right (just what i needed :) ) and vice versa on the red wire. With some clever guessing, i decided 5kOhm potentiometers were gonna be enough to fix calibration errors of about 40%. So I bought two, with mounting possibility, as I'm gonna put them outside for easier manual calibration. While you could use 10kOhm (or more) potentiometer to fix larger calibration errors, you will loose some of the fine tuning possible with "smaller" potentiometer.

Besides 2 5kOhm potentiometers, you're gonna need soldering iron, philips screwdriver, allen key (is that the proper word for it?), electric drill, isolation tape or heat shrink wrap and some time.

I tried to include many pictures for easier understanding buy comment below if you have any questions! Let's go over the steps.


1. Unscrew 6 screws from the bottom of the wheel.

 
2. Unscrew all 6 screws from the wheel front.

3. Take the metal cover off (it should come off pretty easily) and pull out the marked connectors on (it's good to label them first).

4. Now you're all set for dismounting the wheel. Take it off.

4a. Skip this if everything is OK with your potentiometer. Unscrew 3 screws in the "black hole", you'll need this for later.

5. You can take off the top plastic now.

6. I've marked the main potentiometer responsible for reporting the wheel position. Normally, it's connected to the three pins on the board, but I've already taken this cable off (it's visible in the next picture though).

6a. Skip this if everything is OK with your potentiometer. Without lifting up the black plastic wheel shaft, there is no way to remove the potentiometer as it's fixed to the bottom and the side. Lift it up just so you can take the potentiometer off.

6b. There it is, as you can see, mine has small plastic side holder broken. I've put some paste and glue there :)


7. This is the cable connecting the potentiometer with the board. I've already soldered the extension (about 20cm of extra cable on each lead).

8. This is the modified cable in place.

9. New potentiometers I've bought for correcting the calibration (5kOhm). I've already trimmed the handle to the size i wanted.

10. I needed two holes on the wheel cover to fit the new potentiometers. I drilled 1cm holes on each side. Remember, increasing potentiometer on black wire, centers the wheel more towards right and vice versa on red wire. Here is how it looks mounted on the cover connected to the base.

11. At this point, you might want to put the plastic back on, together with the wheel (you don't need to connect two connectors in the wheel) and test the workings. After everything works, you can connect the two connectors, and deal with all the screws you've taken off. Finished product on few pictures below ;)



Perhaps it could have been done more nicely, but I'm quite happy with the results and the end looks. Now I was all set to connect the wheel on PS3, correct the calibration for GT5 and do some gaming!

Hope you will find this helpful, perhaps the basic idea can also be ported on other wheels, do post your findings ;)

Until next time, bye!

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