EPAS install

#1
Recently I had a bicycle accident which re-injured some previous rotator cuff surgery, so now the Manta is much less enjoyable on the track than it was pre-injury. Because of the 6 degree caster, high ratio rack (1.5 turns L-to-L), it's a struggle to not only drive it on the street, but make the slower turns at the track. I've always had EPAS in the back of my mind, so this injury, plus discussions with Rod Brace, incented me to "go for it" and install one.

As with the theme of my McLaren copy, I'm going the frugal route, and keep costs down. I chose the Prius EPAS system knowing for sure that it had a Fail-Safe mode (meaning it doesn't require additional control features), as well as supporting YouTube information that helped me along the modification. In the end, I "feel" (not on the road yet, only in the garage) the effort required to turn the wheels is about 1/3 what it was prior to the install. Now that I've got everything in place and it works in static testing, I'll weight everything to get an idea of how much extra weight I've added.

Some photos of the change:
Comparison of the original column (911 short) along side a modified Prius column. The 911 is 9" long spline-to-spline, where the Prius is about 17" long. Because of the angles already present in the steering linkage, I did not want to increase the angles on those u-joints, so I shortened the Prius column to as close as possible to match the 911 column length:


Then I fabricated a bracket to hold the EPAS in place, utilizing the original 911 mounting points just in case I want to return back to the 911 column if things don't work out well. Results are that there is still a small amount of distortion when using the EPAS now, so I will reinforce this bracket before painting it, and most likely find a means to mount the end of the EPAS electric motor to make the mounting more rigid against the motor torque:


Lastly, reinstalled and being tested:


Sorry for any lacking details, but all of our projects are so different, that my approach or application probably couldn't be copied for any other car on this site. But being we are all getting more fragile as we grow older, I thought this may be helpful. It went much easier that I initially assumed. Had I had a steering rack that was not center-pinion, this modification probably would have been even simpler because the EPAS most likely would not have needed any shortening of the housing or shafts. My last to-do is to permanently wire it into the chassis wiring. The OEM motor input wires are 8awg (yeah!), but I'm assuming that is with full assist and perhaps at full duty cycle (for whatever that would be for the EPAS). I plan on testing with an ammeter in place to see just how much current is drawn by the system, and then use the appropriate wire size for that. I'm hoping that it will be less in the Fail-Safe mode.
 

Randy V

Administrator
#2
Good update... Although sad to hear of someone else with rotator cuff issues....
Glad to see someone else thinking along the same route I would take - re: keeping the bracket 911 friendly in case of the need to return...
I was not aware of the Prius failsafe mode. I was always looking more toward the Saturn Vue column and small control box to adjust steering effort. It’s good to know of alternatives!
 
#3
Another attribute to the Toyota (and especially the Prius) is the remote box, which allows more flexibility in mounting the EPAS, and then putting the box in close proximity somewhere else.
 
#5
Thanks Simon. I had to box the sides of the first iteration bracket to stiffen it up. Everything is nice and rigid now. I'm not finding a lot of info on this system (guessing somewhere around 45 lb/ft on the framing at best), but the OEM mounting was simply two 3mm U-brackets in the Prius dash (one of which was the column height adjustment), which surprised me. I'm looking at a tension/compression rod attached to the end of the motor to provide effective leverage to prevent any strain/fatigue at the bracket.
 
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