NA Miata Electric Power Steering

[amaff]

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.

[amaff]

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/purchase/product/16-5mm-36-to-34-smooth-coupler/

[amaff]

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:

[amaff]

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.

[amaff]

I'm not gonna lie, I'm friggin stoked about this. I was looking up some info on the column this morning and stumbled over this video of an offroad race truck.

[91LudeSiT]

It's funny you're going electric while everyone else is trying to go back to hydraulic.

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[iscariot]

Interested in seeing how this turns out. Also, that company uses the same enclosure I use for my electronics (Hammond 1551).

[DanBrown]

This is a cool idea.
Would you be able to compare weight differences between PS and ePS?

[amaff]

If someone can tell me what the pump, bracket, cooler, fluid and lines weigh, I can add the stock steering column weight, and then compare that to what the EPS column and wiring (specifically the 10ga direct to the batter) weigh. I pulled the PS off of my car nearly a decade ago so I don't exactly have the numbers fresh & handy.

I imagine it'll be pretty close (the motor on the EPS is about the size and weight of a starter motor), but:
a) my car is well under the class minimum weight, so I'll just take off a bit of ballast and be right back where I started,
b) it'll draw far less power from the motor
c) the weight will be more "between the axles" than the PS pump ans reservoir, and
d) I won't have to worry about fluid boiling over and the PS slowing down in the quick repeated transitions we have in Autox. That last one's not really a concern for more street-ish cars, but once you start throwing in lots of grip (and as such force on the steering components) it can become problematic

It's funny you're going electric while everyone else is trying to go back to hydraulic.

Not sure what you mean by "everyone else". I've not seen a rush of Miatas adding hydraulic PS. The biggest issue with EPS is feel, because most of the systems are way overboosted. This one will let me dial in basically as much or as little boost as I want, which should retain most of the advantages of a straight manual rack & pinion, without the power draw and potential mess of a hydraulic system. Ideally it will still have a little heft at low speeds, and not fight back as much in the higher speed stuff.

[91LudeSiT]

If someone can tell me what the pump, bracket, cooler, fluid and lines weigh, I can add the stock steering column weight, and then compare that to what the EPS column and wiring (specifically the 10ga direct to the batter) weigh. I pulled the PS off of my car nearly a decade ago so I don't exactly have the numbers fresh & handy.

I imagine it'll be pretty close (the motor on the EPS is about the size and weight of a starter motor), but:
a) my car is well under the class minimum weight, so I'll just take off a bit of ballast and be right back where I started,
b) it'll draw far less power from the motor
c) the weight will be more "between the axles" than the PS pump ans reservoir, and
d) I won't have to worry about fluid boiling over and the PS slowing down in the quick repeated transitions we have in Autox. That last one's not really a concern for more street-ish cars, but once you start throwing in lots of grip (and as such force on the steering components) it can become problematic



Not sure what you mean by "everyone else". I've not seen a rush of Miatas adding hydraulic PS. The biggest issue with EPS is feel, because most of the systems are way overboosted. This one will let me dial in basically as much or as little boost as I want, which should retain most of the advantages of a straight manual rack & pinion, without the power draw and potential mess of a hydraulic system. Ideally it will still have a little heft at low speeds, and not fight back as much in the higher speed stuff.

I really meant like FM converting the ND to hydraulic.

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[amaff]

I really meant like FM converting the ND to hydraulic.

Right. That was for packaging & electronics concerns in a V8 conversion, not because there was anything inherently wrong with it.

https://www.flyinmiata.com/V8/ND/?UID=6

Hydraulic steering conversion.
We figured this would be necessary from the start - the ND electric steering rack (the upper one in the picture) has a massive electric motor mounted on the rack. This makes packaging of the V8 basically impossible, plus we were concerned about retaining the logic of the electric controller.

[amaff]

Got the fittings welded to seal up the rack housing.

[amaff]

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

[amaff]

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:

[amaff]

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.