Logitech G27 Service Manual

A long-term investigation into the Logitech G27 racing wheel with the goal of publishing a freely available in-depth service manual.

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The idea is to document everything I can about the Logitech G27. It's a popular wheel (though not as popular as the DFGT, but I don't own one of those) so I figured it would be useful to the sim racing community to essentially know it inside and out, though Logitech's customer support and the device's reliability are so good that hacks to keep these things running are rarely actually required. That said, I feel that a product as popular as this should have an in-depth service manual, so I intend to write it. Right now the outcome is expected to be similar to a MCU's datasheet but who knows, maybe there'll be some videos, CAD models for 3D printing, etc.

This project started much earlier this year, maybe in April, May... Maybe even last year, I honestly can't remember. It started out as a sort of modularisation project - I wanted to upgrade the size of the wheel rim on my G27 (mainly so I could add a quick release mechanism), but that meant I'd need to upgrade the motors to retain the stock torque, but that meant I'd have to do away with the gear drive mechanism because it's far too loud even with the weedy stock motors and of course I'd need to upgrade the similarly weedy MOSFETs (I mean, they fit two in one heatsinkless SOIC package in a case with no active cooling!). So I set about investigating the wheel to figure out how to convert it to belt drive. I got as far as buying all the mechanical components but then I moved in with my girlfriend almost immediately afterwards and I haven't had enough spare cash to spend on laser cutting the enclosure for it. In fact I haven't even moved my G27 back in yet!

Anyway, so now the idea is that since I've already done some research, possibly more than I've found anywhere on the internet after many hours of searching, I might as well compile it into a sort of master document of everything anyone might want to know about the wheel.

  • Progress so far

    neema_tas12/01/2015 at 12:09 0 comments

    To date - this project is a good six to nine months old - I've found datasheets for the DC motors (those are 3.175mm shafts, by the way), MOSFETs and MCU used in the wheel but I can't post them because I'm at work right now. I've found that the two motors have 11-tooth helical pinion gears machined out of brass, the steering wheel shaft has a 180-tooth plastic helical gear. The helical gear shape is obviously to prevent the noise backlash makes, and to that end they do work, but the bigger problem is the axial thrust effect; when the motors change direction there's an audible clicking noise as the motor cores shift along their axis (because of the helical gear shape), in some situations in some sims the direction changes rapidly which results in a very irritating rattling sound that never used to happen with the Driving Force Pro's straight gears.

    Anyway, this information is useful to people who may wish to build a belt drive conversion since the key thing they need to know is the gear ratio - Unsurprisingly, I'm one of those people (which is how this project started), and if you're planning on using off-the-shelf pulleys you'll need four; 60, 22 and two 10-teeth pulleys. One 10T on the motor shaft (p.s. the cheapest solution is to join the motors together with a shaft coupler, since they're both dual shaft) that drives the 22T as an idler, then a 10T on the same shaft as the 22T that drives the 60T on the steering wheel shaft. That way you'll get the same torque and RPM as stock but much quieter operation. You can adjust the ratios but you'll be trading RPM, torque and also altering your steering lock since the MCU can only count so many encoder pulses before it gives up.

    The next step, as far as I'm concerned, is to get my hands on another G27 so I can dissect the PCB. This will take months because I'm still buying things like a bed, dresser and such for my room, so this project is effectively on hold until then. There's only so much I can do by simply looking at the one I've got, after all, and besides I'm hardly going to dissect it because I still use it. Maybe I'll attempt to replicate just the PWM, H-bridge and DC motor part of the circuit, though, and see if I can do something with that.

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