Logitech Driving Force Pro... 270 or 360?: Pictures Added

[Dmod]

I took my Logitech Driving Force Pro (PS2) wheel apart this week and found that the wheel is connected to an optical encoder rather than a pot.  There are two different mechanical stops for limiting the range of motion to either 200 or 900 degrees of motion.  The default mode is 200 degrees.

I'm using this wheel with MAME on my PC. 

Does anyone know how this steering wheel gets interpreted by the PC?  It shows up as a gamepad device, and it seems that the logitech driver and encoder board map absolute wheel position to a location (similar to a paddle).

So I'm thinking that even though this is an optical wheel, to MAME it behaves as a paddle rather than a dial.  Is this accurate?

[NoOne=NBA=]

The software interprets it as an analog joystick axis.
The length of travel can actually be set in the middle of the 900 degrees as well.
There is a setting in the PC drivers that allow you to put in your own value.

[Dmod]

So as far as MAME is concerned, is this equivalent to a potentiometer-based wheel?  As far as game behavior, is there any advantage to using a true pot-based 270-wheel over the Logitech?

[NoOne=NBA=]

Yes. It sees it as a pot based wheel/pedal set.
For MAME games there's no big difference one way or the other.
The big difference comes when you shove in a PC game that supports Logitech's force feedback.

[u_rebelscum]

FWIW:

It doesn't matter how the information is gathered (POT vs opto-mechcanical vs optical vs Hall Effect vs ect), but how the device reports the info to the computer / PCB.  "Absolute analog joystick" or "relative analog mouse" or "absolute analog lightgun".  (Mame doesn't even care if it's an analog joystick or wheel.)

In directX PC's, what matters the most is the type the device and its driver say it is.  For example, the driver says "I'm an wheel with a dozen buttons" and sends the computer that information in the standard way the windows expects said information to be sent.  The device and its driver are responsible for translating any info into what the computer expects.  It doesn't matter that the info is gathered with an opti-mechanical encoder wheel and two sensors (mouse like) or POT or Hall Effect, as long as the device & its driver translate it into whatever it told the computer to expect.  There are other analog joysticks that use opto-mechanical or hall effect instead of POTs (nintendo 64 controller & dreamcast controller, respectively for example) and it doesn't mater, as long as you have the right driver and (if needed) adapter.

The opposite is true too.  If the computer/PCB expects the info to be reported one way, but the device sends it in another, it won't work, even if the device collects the info the same way as a device that does work.  The widest seen example is with spinners; most arcade PCBs (and optipac & optiwiz & mouse hacks) expect the info to be sent one way (quadrature signal on two wires), but some expect direction and speed on the same two wires and use spinners that send the info this way instead of the other.  That's why some arcade spinners won't work on PCs or other PCBs (without hacking).


So, technically, mame see it as an absolute analog joystick, and treats it the same as, say, a PS dual analog gamepad.  Not a wheel at all.

It's you that can tell the difference, and from what I hear, it does make a difference in favor of the logitech wheel being better than most other wheels, POT based or not.

[Dmod]

Great information guys.  Thanks very much.   

[Popcorrin]

The logitech driving force pro used to use a pot, I wonder when they switched to an encoder wheel.  I know that they have been using an encoder wheel on the momo for awhile.

I am specifically looking for a driving force pro with a pot, so this might make it more difficult to track one down.

[Dmod]

I took a bunch of pictures when I opened it.  Let me know if you need to see anything.

[u_rebelscum]

I am specifically looking for a driving force pro with a pot, so this might make it more difficult to track one down.

Any reason why you're looking for the POT one?  Planning to hack it?  Something else we should know?

I took a bunch of pictures when I opened it.  Let me know if you need to see anything.

I'd like to see pics of the encoder wheel and sensor, if you have them.  Just for fun, no real need. Thanks

[2600]

I'd like to see how they switch it from 200 to 900 as well.

[Dmod]

I'd like to see how they switch it from 200 to 900 as well.

I'll put some pics up tonight but basically, there's a plastic stop that mechanically shifts in when you're in 200 degree mode.  A fitting on the wheel rotates into the stop, and stops the motion.

For 900 degree mode, the stop comes back to allow full rotation of the wheel.  The shaft of the wheel is geared and fits into a geared plastic slider that travels in a track along the bottom of the chassis.  When the slider hits the end of the track on either end, the motion of the wheel stops.

It's a pretty clever design, which makes it challenging to decase the wheel and put it into a custom control panel.  I think it's a lot easier if you're willing to give up the 900 degree mode of operation.

[Dmod]

The first pic shows the top of the chassis removed.  The force feedback motor is the metal cylinder.  It's attached to the wheel through a series of gears inside the narrow black chassis between the wheel and the cylinder.

At the bottom of the cylinder is the optical encoder wheel.  The second pic shows a close up of the encoder wheel.  It spins between two photodiodes which are wired back to the main interface board.

Beneath the large metal clip in the center you can see part of the white geared
slider, and to the right of the motor, you can see part of the track it slides in.   As you turn the wheel, the white part slides until it hits the end of the track.

To the far left is the socket where the gear shifter sits.  There are two black push switches on either side of the gear shift box which are pushed when the gear shift knob is tilted forward and backward.

[Dmod]

Here's a picture with the large metal clip removed.  Here you can clearly see the mechanical parts of the wheel that control 200 and 900 degree mode.

The small brass gear in the middle slides the small white block in the center in and out.  When it's in, it makes contact with a black switch labelled SW1.  Notice that the large black hub on the steering wheel has a shape that makes contact with the block when the wheel is fully rotated.

The small gear at the end of the hub fits into the teeth on the white slider, causing it to slide back and forth as the wheel is turned.  When the white block is out, the wheel will turn the full 900 degrees by pushing the slider to the ends of the track.

There's  black wire that travels through the center of the gear into the main part of the wheel and ties into the interface board, presumably for the gamepad buttons on the face of the wheel.

Power for the force feedback motor is provided by a separate power cable.

[u_rebelscum]

Thanks for the pics!   Makes me almost want to get one just to look at the insides, but I already have too many wheels in different states of repair, and shouldn't spend the $$$ just for the wheel to get very little use.

At the bottom of the cylinder is the optical encoder wheel.  The second pic shows a close up of the encoder wheel.  It spins between two photodiodes which are wired back to the main interface board.

With five wires attached to the board.  Hmm... makes me think there's three sensors (vs the normal two) and one of the three could be "index".  The index sensor, marking once per revolution, is very common in high(er) end optical encoder wheels used in areas such as such as astronomy and industry.   The only game I've seen an index in arcade games is the 720 controller, and not in any mouse/trackball, either PC or arcade.
It's hard to tell, but it don't look like the sensors are reading the gear teeth but something closer to the axle, correct?  Any more pics of the holes (or whatever) the photodiodes detect, and a closer pic of the photodiodes themselves?  If not, no worries.

Here's a picture with the large metal clip removed.  Here you can clearly see the mechanical parts of the wheel that control 200 and 900 degree mode....

Do the stops feel any different?  I only tested in the store awhile ago, and I think they felt the same solidness, but I wasn't really thinking about the mechanics behind the two settings so I wasn't looking at it at the time.  Pretty simple but effective way of doing it.

[2600]

With five wires attached to the board.  Hmm... makes me think there's three sensors (vs the normal two) and one of the three could be "index".  The index sensor, marking once per revolution, is very common in high(er) end optical encoder wheels used in areas such as such as astronomy and industry.   The only game I've seen an index in arcade games is the 720 controller, and not in any mouse/trackball, either PC or arcade.
It's hard to tell, but it don't look like the sensors are reading the gear teeth but something closer to the axle, correct?  Any more pics of the holes (or whatever) the photodiodes detect, and a closer pic of the photodiodes themselves?  If not, no worries.

Remember, There has to be and index channel.  Otherwise, they wouldn't be able to center.
Personally, I'd probably hack it so that it is a wheel and a mouse.

[u_rebelscum]

With five wires attached to the board.  Hmm... makes me think there's three sensors (vs the normal two) and one of the three could be "index".  The index sensor, marking once per revolution, is very common in high(er) end optical encoder wheels used in areas such as such as astronomy and industry.   The only game I've seen an index in arcade games is the 720 controller, and not in any mouse/trackball, either PC or arcade.
It's hard to tell, but it don't look like the sensors are reading the gear teeth but something closer to the axle, correct?  Any more pics of the holes (or whatever) the photodiodes detect, and a closer pic of the photodiodes themselves?  If not, no worries.

Remember, There has to be and index channel.  Otherwise, they wouldn't be able to center.
Personally, I'd probably hack it so that it is a wheel and a mouse.

The index will definitely help centering, but technically it's not needed for centering: 
a) The Nintendo64 gamepad centers fine without an index channel even though it uses encoder wheel IIRC. 
b) The encoder wheel probably turns a lot more than once per wheel turn.  (Dmod, could you shine some light on number rotations of encoder wheel vs rotations of steering wheel?)  This would make the index not always signal the center, but other places too.
c) The motor looks like it is what centers the wheel.  If so, "center" is wherever the device thinks it is.  It would be a pain if you could only turn 50 degrees right and 150 left (in 200 degree mode), but it would still "center".

That said, the index channel probably really helps keep it calibrated over time.  Vs, say, using driver software to manually set the center when it gets off center, which can work but is not automatic like the index channel.

Maybe I'm arguing semantics, though.

[Dmod]

Do the stops feel any different?  I only tested in the store awhile ago, and I think they felt the same solidness, but I wasn't really thinking about the mechanics behind the two settings so I wasn't looking at it at the time.  Pretty simple but effective way of doing it.

The wheel feels the same in both modes.  Whether the center stop is slid in place or not, the wheel travels on the geared slider.  The stop doesn't really make contact with the slider and just prevents wheel motion when the fitting on the wheel makes contact with the stop.

The only thing that really seems to change feel is the resistance of the force feedback motor.   I played with a few games using the Project64 emulator, and they seem to vary the amount of resistance the wheel gives toward turning.

[Dmod]

It's hard to tell, but it don't look like the sensors are reading the gear teeth but something closer to the axle, correct?  Any more pics of the holes (or whatever) the photodiodes detect, and a closer pic of the photodiodes themselves? 

This is the only other picture I have of the encoder wheel.  You're right, it doesn't read the teeth.  There are little holes in the wheel closer to the axle.  You can just barely make them out in this picture.  If I open it up again, I'll try to get a closeup of the electronics in this area.

[Dmod]

I thought this was interesting...

The correct name for the part I've been referring to as a 'slider' is a 'rack', and the mechanical term for the combination of the wheel gear and the rack is 'rack and pinion'.  I've heard this expression a lot before with regard to 'rack and pinion steering' but never really understood what that meant.

Here's a pic of the gear in action from Wikipedia.

[Popcorrin]

I am specifically looking for a driving force pro with a pot, so this might make it more difficult to track one down.

Any reason why you're looking for the POT one?  Planning to hack it?  Something else we should know?

That's correct.  I was planning to hack it.  I want to use an actual arcade wheel and interface it to the pc by using the guts of the driving force pro.