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Thread: NA Miata Electric Power Steering

  1. #1
    High Speed Low Drag aMaff's Avatar
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    NA Miata Electric Power Steering

    I posted this in drips and drabs over in the "What have you done to your Miata today" thread, but figured I should post it somewhere on its own in case anyone's interested in doing this themselves.

    If I have one complaint about the race car it's that the steering wheel is fairly brutal on the driver. With aero and 9" slicks going through a Manual rack there's a ton of feedback. Too much feedback. And because of how heavy it is even with the Manual rack (again, 9" slicks), I haven't even wanted to run a depowered PS rack.

    Of course, power steering would fix this, but it's heavy, often messy when they boil over, and saps power from the engine. I already don't have nearly enough power, so that's out.

    However, I found out recently about a GM electric steering column that's been seeing heavy use in Rally and other offroad racing disciplines, along with a company that sells a controller that spoofs the CanBus signal, and allows you to adjust the amount of steering assist. I've been toying with the idea for a while now, but an autox buddy had one installed in his Ecotec powered Lotus 7 clone and frigging loves it. With some direct experience and some research in the bag, the time has come to start building.


    So here's the plan:
    -Snag a steering column & controller
    -Fabricate mounts and an intermediate "adapter" to go between the end of the GM rack and the input of the Miata's intermediate shaft.
    -Fix the bump-steer because hella low (not really, but the geometry is pretty d**ked right now)
    -DePower and refurb the PS rack I've had sitting on the shelf for ages now waiting for its moment to shine.
    -Add steering rack travel limiters to prevent the 15x10s rubbing on the sway-bar in paddock / grid / during big spins.


    The column in question is out of the Saturn Vue & Chevy Equinox, and is a little over 3" shorter than the stock NA steering column. I went to Pull A Part North and snagged one out of the yard, along with the full wiring harness. The nice thing about that is that they're built for far heavier cars than what I'm putting it into, so it should be plenty.




    I spent some time this weekend rotating the motor and gearbox housing on the assembly to get it above and out of the footwell. I'm not sure I'm going to be able to keep the tilting functionality, but I definitely want to keep the full, collapsible column for safety reasons. It's available, no reason not to run it. Also the mounts are within an inch or so of where the Miata's mounts are. I'm not sure if I'll try and weld brand new mounts in or make a set that bolt to the factory mounts and then bolt to the GM mounts yet, it'll depend on where everything sits once it's in the car.



    ~Andrew
    Atlanta Region SCCA
    114 DP

  2. #2
    High Speed Low Drag aMaff's Avatar
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    After taking those measurements, I disassembled the Miata steering column to see what made it tick. That's when I discovered something that will make my life MUCH easier:

    The column is based on a 3/4" shaft (or, at least, the output shaft is). If you've ever messed with steering systems in race cars, 3/4" stuff is absolutely ubiquitous.



    The splines are much smaller, but the fact that the shaft size is 3/4" is massive because epowersteering sells a splined bolt-on coupler for the GM column to a 3/4" shaft. I'll be able to cut off however much of the miata's shaft I need to make a bolt-on extension that will future proof this thing in the event of the EPS unit taking a **** and needing to be replaced for any reason. I won't know for sure how much needs to be cut until taking much more careful measurements, and getting the coupler in hand to see how deep the 3/4" pocket is. See the "ISH" on the shaft. That's a full 3-1/4", but I'll likely need less than that.

    http://www.epowersteering.com/purcha...mooth-coupler/
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  3. #3
    High Speed Low Drag aMaff's Avatar
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    While I wait for parts to ship, I wanted to get started on depowering the PS rack. So that I can add power steering back in...

    Look, it makes sense to me, mmkay? :lol:

    When the rack's out of the car, you need to break out some big tools to break the tie-rod hardware loose. Sledge hammer and pipe wrench were the order of the day (using soft jaws in the vise so I didn't actually gall up the inner tie-rods, as they're in good shape).




    This thing is FILTHY. I mean, I guess just about all of them are. The only one I've ever seen is clean is the on in my car because it's a race car and I cleaned it before I installed it last, but even then, this thing is guh-ross.




    I spent some time with the parts washer and ultrasonic cleaner (for the hydraulic fittings). Massive improvement:



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  4. #4
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    Took the steering rack down to the proverbial pins & screws, and gave everything a bath in the parts washer, then the ultrasonic bath.

    All the tutorials I'd read made this look like something of a pain in the *** but apparently the NA process is super straight forward. Or at least, my version, since there's apparently several different iterations, internally, of these racks.

    Pull the adjusting spring & collar:




    Then undo the nut at the bottom of the pinion shaft, the spring clip at the top of the pinion, then the pinion pulls straight out. Also, the hydraulic valve body is only held on with another spring clip. Remove that, then the valve body slips straight off the pinion.






    Pop the retaining ring off the passenger side of the rack housing and the rack slides straight off. The seal that remains on the rack is going to be cut off as it's not needed.





    (note that the rack is in soft-jaws, not straight in the vise, as that would destroy the machined surface and likely cause issues with strength and durability down the line.
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  5. #5
    High Speed Low Drag aMaff's Avatar
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    Got the fittings welded to seal up the rack housing.




    Knocked off the internal rack seal, which'll keep it from trapping air and creating an internal "bumper".



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  6. #6
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    Quote Originally Posted by aMaff View Post
    I posted this in drips and drabs over in the "What have you done to your Miata today" thread, but figured I should post it somewhere on its own in case anyone's interested in doing this themselves.

    If I have one complaint about the race car it's that the steering wheel is fairly brutal on the driver. With aero and 9" slicks going through a Manual rack there's a ton of feedback. Too much feedback. And because of how heavy it is even with the Manual rack (again, 9" slicks), I haven't even wanted to run a depowered PS rack.

    Of course, power steering would fix this, but it's heavy, often messy when they boil over, and saps power from the engine. I already don't have nearly enough power, so that's out.

    However, I found out recently about a GM electric steering column that's been seeing heavy use in Rally and other offroad racing disciplines, along with a company that sells a controller that spoofs the CanBus signal, and allows you to adjust the amount of steering assist. I've been toying with the idea for a while now, but an autox buddy had one installed in his Ecotec powered Lotus 7 clone and frigging loves it. With some direct experience and some research in the bag, the time has come to start building.


    So here's the plan:
    -Snag a steering column & controller
    -Fabricate mounts and an intermediate "adapter" to go between the end of the GM rack and the input of the Miata's intermediate shaft.
    -Fix the bump-steer because hella low (not really, but the geometry is pretty d**ked right now)
    -DePower and refurb the PS rack I've had sitting on the shelf for ages now waiting for its moment to shine.
    -Add steering rack travel limiters to prevent the 15x10s rubbing on the sway-bar in paddock / grid / during big spins.


    The column in question is out of the Saturn Vue & Chevy Equinox, and is a little over 3" shorter than the stock NA steering column. I went to Pull A Part North and snagged one out of the yard, along with the full wiring harness. The nice thing about that is that they're built for far heavier cars than what I'm putting it into, so it should be plenty.




    I spent some time this weekend rotating the motor and gearbox housing on the assembly to get it above and out of the footwell. I'm not sure I'm going to be able to keep the tilting functionality, but I definitely want to keep the full, collapsible column for safety reasons. It's available, no reason not to run it. Also the mounts are within an inch or so of where the Miata's mounts are. I'm not sure if I'll try and weld brand new mounts in or make a set that bolt to the factory mounts and then bolt to the GM mounts yet, it'll depend on where everything sits once it's in the car.



    Awesome, I wish you the best of luck with this project.

    I don't think that the power steering will affect anything because mazda tunes their steering and suspension well, but I have tried GM's power steering before in the past and it is artificial + overly boosted. I hope those traits do not carry over to your mazda.

    using electric power steering will not sap power from your engine.

  7. #7
    High Speed Low Drag aMaff's Avatar
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    USPS delivered (literally) yesterday, despite the Tropical Storm. With the kids home and our power intermittent (so many chain saws running near by), I figured I'd go play with the parts in the shop.
    Doing it this way means the tilt function goes out the window (moment of silence...) but it's going to make it a lot simpler. And the angle of the Miata wheel is fine so I'm not really torn up about it. I'll just need to be careful to get the angle close-ish to stock, but it should work great.





    Roughly where the cut will need to be. There's about an inch of depth in the non-splined area of the adapter, so the weld will be on the fully cylindrical section:




    Artist's rendition:

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  8. #8
    High Speed Low Drag aMaff's Avatar
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    I set up some "parallels" to take more accurate measurements on the steering columns now that I have a better idea on how it's all going to go together so I can get a proper length for the spacer I need to make. The dimension isn't SUPER critical, 1/8" here or there won't make a massive difference, but, you know, better is better.




    Hard to see because there's a ratchet in the background, but the GM column is 3-7/16" shorter than the Miata column.




    Blue Santa stopped by today



    With the EPS and the quicker rack, I wanted to go with a smaller wheel to minimize the distance my hands need to travel for each input. I have a 350mm / 14"-ish wheel on there now, and every inch of that (hur hur) is necessary to turn the manual rack on big rubber. This is a 280mm / 11" wheel, which is an almost 25% reduction in circumference. The smaller wheel and faster rack will make a significant reduction in the distance my hands need to travel for an equivalent input to the tires. Which means I'm probably going to WAY over-turn and over correct for the first little while once the new setup goes on, but that's a training issue, and means that WHEN I want to turn in faster (which is quite a lot with the fully manual setup), I'll be able to.



    Yeah that should be a solid improvement
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  9. #9
    High Speed Low Drag aMaff's Avatar
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    Took the parts that needed to be welded "real gud" to a buddy's shop today, as I don't have a TIG machine. With the fine splines and gears I didn't want to take any chances with spatter.




    The adapter on the right (above) is really the only thing you need (in addition to fabbing mounts to the dash bar & firewall) if you want to adapt this into the factory Miata steering system if you're ok with foregoing the tilt function, which I am. I can tweak the location with the mounts if necessary, but there's nothing really wrong with a stock-ish location.



    Drilled / tapped the steering column adapter so that the weld isn't a possible single point of failure.

    Center drills are freakin' awesome for this stuff. I don't have a mill, but with the right tools and a little creativity, you can do a lot of stuff with a wobbly ol' drill press



    The bolt is half solid, half threaded, so I drilled it through to the thread tap size, then counter-bored the hold for the non-threaded shank. My drill press has a crap *** depth gauge & stop, so a little measuring and tape makes a good marker for where to stop drilling.




    Countersink to clean up the burr and make starting the tap easier.




    Tapped it. The tap goes through 1 side of the collar and a portion of the splined shaft. This is one more way the bolt will take some strain off the weld and serve as a backup should something break.




    A little thread lock on the set-screws and the shank of the bolt for the internal threads, and a nylock nut as 1 final backup to the backup of the backup for the steering system.

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  10. #10
    High Speed Low Drag aMaff's Avatar
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    With the length finally set, I can start looking at the mounting arrangement. The only one that is basically "fixed" is the upper mount near the steering wheel. The bottom can end up wherever. It took some tweaking of the various parts to get everything to fit and line up properly in the space above the pedal box, but I think I've got it where I want it.

    The motor isn't currently installed (because it's heavy and I was wrestling the whole thing in and out to work on it on the bench), but it'll be up top, pointed towards the trans tunnel.




    Incredibly, the Miata spline size for the steering wheel is the same as at least this GM... Seriously, I took the quick release off of the stock column, and slid it right on to this one. The only difference is the threaded shank is larger, but it's still a 21mm nut (like the Miata) so nothing really changes there.




    The Miata and GM column mounts weren't exactly parallel, so it took a little creativity to get everything lined up correctly.






    Next comes some serious figuring on the lower mounts. That'll take some head-scratching and beard stroking.
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  11. #11
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    Finished up the upper mount. I added gussetts because the twisting load while being driven in anger, I imagine, will be a significant, and it makes me feel better.

    This is obviously upside down. I used the stock plate for the Miata so it bolts up, and the brackets pick up the GM column's break-away mounts so the safety features built into the column work as designed should something go horribly wrong.




    As expected, getting all the geometry right so that I could use the stock mounts was a massive pain in the ***. The driver's side one especially, as it had to be worked around the brake pedal.
    As NOT expected (because I was a bit concerned, honestly, about having to re-engineer the lower mounts) it stiffened things up massively. Easily as stiff as stock, maybe better.

    Driver's side mount in progress...




    Plenty of brake-pedal clearance.




    Passenger side mount. Much more room to work with there.



    Motor installed. Plenty of room.
    Also, check it! I can get about 1" of tilt on the column




    Down:




    Up:




    I got the heavy-gauge wires for the motor installed and terminated, and installed the potentiometer in the switch box before I ran out of time.

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  12. #12
    High Speed Low Drag aMaff's Avatar
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    I got sick of the dingus-arm on the adjuster catching my pant leg or accidentally disengaging it with my shoe. I played with it some and the length and shape is 100% for clearing the dash / column shrouding, and 0% for leverage.
    This is more betterer




    After slapping a coat of paint on all the raw-steel brackets and re-installing everything, I had to put the new steering wheel on because LOOK AT IT

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  13. #13
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    Hahaaaa! It works
    I mean not that I ever doubted. Right? Right.

    The system test was successful. Sketchy AF, but the damn thing works. Like...I could turn the steering without the wheel on the QR.
    Lots of electrical tape and a small amount of "holding the ground wire onto the pin on the switch", but good enough for a test before permanent connections are made this weekend.




    I had a buddy who's way better at soldering and electronics than I over to help out getting the wiring sorted out.




    I decided that as much as possible would go into the switch panel box, just to keep everything out of the weather. The controller was secured to the box, then wired to switched power & ground through the switch box panel. We connected to the rheostat, and we were able to use a pair of unused wires for the clutch pedal switch that were already wired into the switch box (but not used) to carry the power and CANBUS signal to the ECU on the steering column. We tapped into those wires near the column and spliced the connector on.




    Before tidying up the wiring completely, we went ahead and did a systems test to make sure everything worked. Much to my surprise (because I worked on it…) it worked properly the first time!



    “Like a kid at Christmas” is a pretty accurate descriptor. The fact that the steering turns easily without the lever-arm advantage of the steering wheel was astonishing. What else can you say other than it just works, as advertised. I ended up needing to turn it down to about 1/3 power on the rheostat just so that there would be some heft in the steering system, even with the tiny steering wheel.

    A proper test is coming up at this weekend’s autocross, where we’ll spend some time tuning it in to where it’s happy on course, and happy-enough everywhere else.
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  14. #14
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    Very good thread. Good luck and let us know how the steering works!

  15. #15
    High Speed Low Drag aMaff's Avatar
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    HAHAHAHAHAHAAAAA!
    Man, it's so good. The adjustments are pretty damn sensitive. We spent the first 6 or so runs dialing out a little bit at a time until we got to the point where the previous spot was better and dialed it back up that notch.
    Video won't show much, but being able to make fine adjustments was a nice change of pace... it went from having to be muscled around the course to finally being able to have soft hands on the wheel.

    All in all: if your class allows it, or if you've got a street car without PS, this is a great bit of kit

    Video:

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