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  • Electric power steering rack & pinion

    Finally got one of the electric power steering rack & pinion assy’s out of the scrap box at work to play around with. Quite the serious bit of hardware! It’s got a 28mm x 7mm ballscrew with around 220mm travel, a large preloaded support bearing assy with a 22mm fine pitch toothed drive belt and a huge drive motor. The input pinion unit has an encoder & torque transducer of some sort. With no electrical power it functions as a manual rack & pinion & back-drives the ball-nut & drive motor. When powered up, I theorize that inputs from the input pinion are translated into high-power inputs into the motor/belt/ballnut to assist in pushing the rack back & forth. They work great & the onboard computers & cameras enable the automatic parking stuff that works so well in modern cars. Kinda eerie letting your car perfectly parallel park every time.

    I drug it home & stripped it down thinking that I may be able cut it down to the essentials to use it for a Z-axis drive unit for a CNC project. It would probably have the drive componts fixed & drive the ballscrew up & down connected to the Z-slide assy. I’d have to get the motor pulley off & make it fit a stepper motor though. Looking at the size of the motor harness connections, that thing uses at least 50 amps if not more like 75-100A @ 14 vdc. A CNC servo control for something like that would be hard to find. The diagonal teeth on the drive pulley/belt would make a different one hard to source so I’d just make an adapter to make it fit a NEMA23 or 34 stepper motor.







    Milton

    "Accuracy is the sum total of your compensating mistakes."

    "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

  • #2
    Last pic:

    Milton

    "Accuracy is the sum total of your compensating mistakes."

    "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

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    • #3
      Wow that's the finest tooth drive belt iv ever seen and diagonal toothed is a new one to me, lots of neat parts thanks for sharing.

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      • #4
        Thank you for going to the trouble of posting pics of it.
        Location: Saskatoon, Saskatchewan, Canada

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        • #5
          I knew many of you guys like to see cool stuff...especially cool free stuff! It'll be gloat-worthy when & if l I actually do something useful with it.
          Milton

          "Accuracy is the sum total of your compensating mistakes."

          "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

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          • #6
            raise and lower a drill press table.

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            • #7
              Electrically driven shaper?

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              • #8
                It's amazing just how things have become so much more complicated. Some years back while at a tractor wrecking yard I came across a unit on a very old John Deere tractor that was a form of "power steering". It didn't appear to be OEM at all though and I believe (WAG) it was made for an automobile originally. It consisted of a small planetary gear box (chromed brass) about 1 1/2" by 3" that had an overall reduction of ~5:1. The steering wheel was bolted to the input shaft, the case was attached solidly to the tractor and the output shaft was attached to the original steering shaft that was shortened to allow the planetary setup to fit. While it would give a greatly decreased steering effort it's downside was it also slowed steering response by the same amount of course.
                Location: Saskatoon, Saskatchewan, Canada

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                • #9
                  very nice!

                  Don't assume the current draw - that's load dependent to some degree. Make a great cat door opener. Might end up with a few manx-like cats though

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                  • #10
                    You could run it on a lower voltage to reduce the current draw or even put a resistor in series. It could be designed to put more than 10kN at the output which you will most likely not need.

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                    • #11
                      Cool. Never seen helical teeth belt.
                      (it appears that even double-helical or herringbone belts exist: https://www.rainbowprecisionproducts...-nrg-eagle-nrg )
                      Location: Helsinki, Finland, Europe

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                      • #12
                        Nice piece of kit! What vehicle is it off?

                        Ian
                        All of the gear, no idea...

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                        • #13
                          Originally posted by Arcane View Post
                          It's amazing just how things have become so much more complicated. Some years back while at a tractor wrecking yard I came across a unit on a very old John Deere tractor that was a form of "power steering". It didn't appear to be OEM at all though and I believe (WAG) it was made for an automobile originally. It consisted of a small planetary gear box (chromed brass) about 1 1/2" by 3" that had an overall reduction of ~5:1. The steering wheel was bolted to the input shaft, the case was attached solidly to the tractor and the output shaft was attached to the original steering shaft that was shortened to allow the planetary setup to fit. While it would give a greatly decreased steering effort it's downside was it also slowed steering response by the same amount of course.
                          That sound very much like a Model T Ford steering "box". Early versions were 4:1 then went to 5:1. Original 5:1s were nickel plated. I replated a lot of them for restorations.

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                          • #14
                            Several years ago worm gear drive steering column electric power steering units were arriving at my favorite scrap yard. I got 3 for a future cnc project. I thought they had a torque sensor input and the servo motor power amplifier all together. I had hoped to hack the control for cnc and have a $3 dollar servo motor-encoder and drive suitable for a bridgeport sized mill. Alas the hacking skills were way above my pay grade. I had searched for other's that had modded these units for cnc, but came up blank. Perhaps this thread will lead to the the cnc hobbyist people with the hacking skills and the desire to mod these steering units.

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                            • #15
                              Very nice piece of hardware, lots of potential uses.


                              Originally posted by ikdor View Post
                              You could run it on a lower voltage to reduce the current draw or even put a resistor in series. It could be designed to put more than 10kN at the output which you will most likely not need.
                              As Lakeside53 pointed out current draw would be dependent on load.
                              Would not lowering the voltage increase the current required for the same load.
                              Home, down in the valley behind the Red Angus
                              Bad Decisions Make Good Stories​

                              Location: British Columbia

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