Electric Power Steering Conversion – Part 4

HAHAHAHAHAHAAAAA!
Man, it’s so good. The adjustments are pretty darn 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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Electric Power Steering Conversion – Part 2

Continued from Part 1.

With the column completed, I could get it mounted in the car. Woohoo, it fits! And SOMEHOW, the steering wheel spline size is the same for both the GM and stock columns. My quick release bolted right on.

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While tiedown straps are nice and simple, they’re not exactly sturdy enough for keeping a steering column in place, so it’s time to break out the cutting and welding tools.

The Miata and GM column mounts are not parallel, so it took a little creativity to get everything lined up correctly. After a little bit of measuring, I realized I could cut the shapes I needed out of a drop of 2″ square tube. Everything looks parallel in the picture, but there’s about a 1/4″ slope on 1 side of each bracket to fix the difference in angle between the stock pickup and the GM mount.

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The stock column mounting-plate made a good datum & base to fabricate from. The brackets are bolted to the GM break-away tabs as they would in the donor vehicle, retaining all of the safety features built in to the new column.

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I added a couple gussets to stiffen things up, as there will be a fair deal of torque put on this mount during competition.

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I hacked the lower mounts off of the sacrificial column, and used the stock firewall mount points as the basis for the new lower mounts. The left-side mount was by far the most difficult. It took quite a bit of jiggery-pokery to get all of the angles correct so that there was ample clearance for the brake pedal.

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There was far more room to work with on the right-hand side.

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I’d been working with the motor disconnected, as it is big and heavy, and would make things far more difficult in this stage. The time has come to put it back on. Plenty of clearance in the footwell.

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Also, check it! I can get about 1″ of tilt on the column (nearly the full stroke in the mounts)! I was fairly convinced that the tilt wouldn’t work with my install, but here we are. Finally, an NA Miata with the oft-advertised but never before actually seen tilting steering column!

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The tilting column adjuster handle is VERY much in the way when climbing around the column getting in and out of the car, so that needed to be modified to tuck it out of the way:

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I also went ahead and installed a smaller steering wheel. I went from a ~14″ / 350mm wheel to a 11″ / 280mm wheel. This effectively reduces the arc length that the driver’s hands need to travel to put in the same steering angle by about 25%.

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With all of the hardware complete, I could get a start on the electrics. I ran and terminated all of the large-gauge wires that carry power to the motor (that are connected directly to the battery with a 60 amp fuse in line), and started modifying the switch panel to accept the potentiometer. I should be able to put the controller in there as well, to keep it out of the box, and tap into a couple of spare pins in the harness going out of the box to run the controller output to the motor, making for a nice, clean install.

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Continued on Part 3

Electric Power Steering Conversion – Part 1

EDIT: Now that this is done, and has been a huge success, I want to put a quick guide & parts guide right up top for reference. This is if you take the DIY route. EPowerSteering.com also sells full ready-to-run (just fabricate mounts for your car) kits:

Compatible Steering Columns:
02 – 07 Saturn Vue
05 – 07 Chevrolet Equinox
03 – 06 Saturn Ion (only in steering column with metal ECU case!!)
Pontiac Torrent

EPS Controller
Steering Column Adapter (requires cannibalizing stock Miata column)
Dust boot (to keep water from running down into the sensors)
Fuse holder
60A Fuse (get a spare, just in case!)

When you order the controller, put a note in that you would like a 10K potentiometer adjuster. Per EPowerSteering.com, the adjustment range on the 10K is much more appropriate for smaller cars. I can attest that with the standard 100K that they ship with, my adjuster hovers around “nearly off”, and the 10K pot will give finer granularity in the lower ranges of adjustment.

 

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 came 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. I want to keep it as bolt-in as possible in case something breaks and I need to swap stock parts in.
-De-Power and refurb the PS rack I’ve had sitting on the shelf for ages now waiting for its moment to shine. With the power steering, adding in the faster rack would be good. I’m going to pair this with a smaller steering wheel to lower the distance my hands will need to travel on the wheel for a given angle of input.
-Add steering rack travel limiters to prevent the 15x10s rubbing on the sway-bar in paddock / grid / during big spins.

The steering 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 the local Pull A Part and snagged one out of the yard, along with the full wiring harness. The nice thing about this column is that they’re built for far heavier cars than what I’m putting it into, so it should be plenty. This system has seen extensive use in the offroad racing community, and I’ve seen them installed in things between ride-on lawnmowers and Unimogs. It appears to be insanely versatile.

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To get everything lined up in the right place took a lot of careful measurement. It doesn’t need to be micron-perfect, but within 1/8″ or so is the goal.

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The mounts are within an inch or so of where the Miata’s mounts are, so I’ll be able to use the stock upper mounts points (using a modified stock column mount), and will need to re-engineer the lower mounts. The plan is to weld brackets onto a stock upper column mount, and cut the lower mounts off of a sacrificial stock column.

Overall, the GM column is about 3″ shorter than the stock Miata column. This is a good thing as it will allow me to get the steering wheel in a stock location without having to modify the intermediate shaft that runs between the column and rack.

After disassembling the sacrificial stock Miata steering column, I discovered, much to my amazement, that the lower section (where it bolts to the intermediate shaft) is 3/4″ diameter. And just about every aftermarket steering component out there is 3/4″. Due to that size being ubiquitous, EPowerSteering.com sells a 16mm spline to 3/4″ shaft adapter.  I’ll use that and a section of the stock steering column to build a small adapter that will spline / bolt onto the bottom of the GM column, and spline / bolt into the stock intermediate shaft.

I took the parts to a buddy’s shop where we cut the stock steering column down to length, and TIG welded the parts together. It could have been MIGed, but with the threads and fine splines, I wanted to avoid spatter at all costs.

After it was welded, I drilled and tapped through the adapter and spline stub to run a bolt to serve as a failsafe in the event the weld breaks, as that weld essentially is a single-point-of-failure in the steering system.

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With the column setup complete, it was time to start fabbing the mounts in the car.

 

Continued in Part 2