O.T. Looking for a small 5K or 10K rotary potentiometer with a spring return.
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  1. #1
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    Default O.T. Looking for a small 5K or 10K rotary potentiometer with a spring return.

    As the title says, I need a potentiometer with a spring return for a DC motor I am running. I want the motor to stop with release of the potentiometer knob. Looked everywhere and can't seem to find one. Am I going to need to male my own spring?

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    I've never seen anything like that.

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    Quote Originally Posted by Shaybuilder View Post
    As the title says, I need a potentiometer with a spring return for a DC motor I am running. I want the motor to stop with release of the potentiometer knob. Looked everywhere and can't seem to find one. Am I going to need to male my own spring?
    Have you looked at a joystick potentiometer with spring return as an alternative?

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    Quote Originally Posted by Shaybuilder View Post
    As the title says, I need a potentiometer with a spring return for a DC motor I am running. I want the motor to stop with release of the potentiometer knob. Looked everywhere and can't seem to find one. Am I going to need to male my own spring?
    Got all I need.

    Grab yerself an assortment of Bournes and Alps audio-studio style SLIDE potentiomers. Cheap enuf, ten at a go.

    (At least) 20mm, 40 mm, 60, mm, 100 mm lengths.

    Slide Potentiometers

    Slide Potentiometer - Potentiometer - Alps Alpine

    Potentiometer.com Stock and Custom Potentiometers

    Now you can arrange them on standard perf-board.

    In arrays. 1, 2, 3, or 4, short to one long, for example.

    NOW they can be operated with / assisted with / returned-by springs.

    And/or "plate cams" or "gates" as with automobile shifters - cut from thin phenolic or sheet metal, to produce a result of any sort of effective resistance "step functions" and/or "curves" you need.

    Connect the sliding plate - or just the one single post on one slide-pot - to a shop-fabbed hub with ta da ignorant Kevlar weed-wacker cord.

    "Remote it" through a tube?

    And now you have anything from an ordinary-looking plain knob or lever... to the equivalent of a Joyce stick, or even an steamship "engine room telegraph" sector.

    Mind.. it is OK to use "just the one", too... compression spring OR tension spring.



    Beats all Hell out of trying to do everything with only a roughly 270-300 degree rotary motion.

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    Wouldn't be difficult to bury a spring in a custom knob , if you're after a rotary solution.

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    Quote Originally Posted by Billtodd View Post
    Wouldn't be difficult to bury a spring in a custom knob , if you're after a rotary solution.
    Used to be a stock part, "back in the day". It may still be, some niche supplier.

    There was a washer with a tab to prevent rotation that mounted under the shaft panel retaining nut. A spring hooked onto that as anchor. Spring's coils went up a clearance bore buried in the underside of the knob. Top end was anchored to the knob.

    Chapter 13, First edition, "The Electronics Bench Manual", T-Doc had a line-art drawing, IIRC. I wrote that chapter - illustrated it, mostly with camera and Benday work - and all the rest.



    K4TJ, the primo author of the rest of it, removed the chapter on detents and hardware of that sort outright to reduce printing costs, stay on "ELECTRONICS", only, second printing, onward.

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    Quote Originally Posted by thermite View Post
    ... I wrote that chapter - illustrated it, mostly with camera and Benday work - and all the rest.
    Mail him the one you used to make the photo?



    If I were doing this I'd peruse mcmaster carr for a small spring, like the ones used for drill press quill return. They do have all sorts of
    springs like that.

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    Quote Originally Posted by jim rozen View Post
    Mail him the one you used to make the photo?


    1972 was it? Nearly fifty years gone, all of that. Lot of it was Bob's "treasure", not mine!

    We did that manual on one lone IBM Selectric. White-rubber cemented each page four-up, shot it with a Robertson "darkroom camera" to reduce it to letter-size, small-print.

    ISTR I had an OSI Challenger and Bob (K4TJ) had a CPU chip with all of 256 Bytes of RAM.. a "Computer" still said "IBM", UNIVAC", or "Control Data" on the doors. Large doors. Nary a bit of that was "computerized".

    All the "original" graphics artwork was done on my drafting table in Inja ink direct to vellum, then shot on 35 mm Microfilm, hand-tray developed for paste-in. "Physical" cut-and-paste. Not electronic. All the while grumbling I had no hot-wax gear as we had at Northrop-Page!

    And then? We printed it on cheap sulphite paper. For regular loose-leaf updates.
    I had put by ten or a dozen copies when we shut-down the company. They went to mostly brown dust within about ten years!



    If I were doing this I'd peruse mcmaster carr for a small spring, like the ones used for drill press quill return. They do have all sorts of
    springs like that.
    Might not need all that much force? Wire I recall was round, a tad smaller in diameter than the spring in a retractable ballpoint pen. What yah needed, though, was a cavity that allowed for the expansion as the spiral was loaded and the spring changed radius. Also to keep rocks and dog hair from building-up.

    A slider that can be remoted inside a nice clean box and operated by a push-pull Kevlar strand is just more predictable as to spring force, Either of a stock compression or extension spring can work. "Both", even, if yah want an assymetrical centering at "hands off", slightly different range and pressure, each end of travel.

    Also easier to "customize" as to resistance and length of "throw" - given yah can wrap the "human hand" end of the Kevlar aound any diameter hub as suits yer need. Or use a lever, more directly.

    Not all that different from some of the stuff done in motorcars, actually.

    One of mine, the foot-pedal to injector control travels over a data bus.

    The other uses a "physical" link. Flexi tube housng carrying a stainless pull-cable, "gas" pedal to underhood TBI.

    Person could raid NAPA for those? OTOH, weed-wacker Kevlar is cheap and easy.

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    Quote Originally Posted by Shaybuilder View Post
    As the title says, I need a potentiometer with a spring return for a DC motor I am running. I want the motor to stop with release of the potentiometer knob. Looked everywhere and can't seem to find one. Am I going to need to male my own spring?
    Sounds like a TIG welder foot pedal:
    TIG Welding Foot Control Pedals - SSC Controls

    The imported from china ones on amazon list the resistance (sometimes)

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    Quote Originally Posted by digger doug View Post
    Sounds like a TIG welder foot pedal:
    TIG Welding Foot Control Pedals - SSC Controls

    The imported from china ones on amazon list the resistance (sometimes)
    Good catch!

    Sewing machines used similar goods even before China had electricity.

    Tons of that stuff out there, used for "real" Pilot-training simulators, kids computer games and such as well.

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    Quote Originally Posted by thermite View Post
    Good catch!

    Sewing machines used similar goods even before China had electricity.

    Tons of that stuff out there, used for "real" Pilot-training simulators, kids computer games and such as well.
    I got a "Speeding Ticket" in Home Ec class for driving my Singer too fast , it was a shop apron for dear old dad, and there was allot of "straightaways"....jeesh.

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    Quote Originally Posted by digger doug View Post
    I got a "Speeding Ticket" in Home Ec class for driving my Singer too fast , it was a shop apron for dear old dad, and there was allot of "straightaways"....jeesh.
    I've been privileged to have called many of Hong Kong's Harilela family close friends over long years.

    One of their several core biznesses, prior to War Two, was using foot-treadle machines to sew the nametags and patches for the British Army Garrison. Then the whole uniform. Thence on to greater things.

    When the Japanese invasion shut that operation down? They rubbed-down the old sewing machines with scavenged vegetable oil to make them shine - peddled them to Japanese NCO's and Officers to ship home to their Wives, Aunts, and Mothers.. who had no such luxuries!

    No more obsolete machinery!

    Then built far the larger business empire, yet....after the war.

    Enterprising folks, the lot of them. Very!

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    I have seen such pots, usually in association with remote controls for professional VTRs. Sony had controls that featured a knob with dual functions; Two Way Shuttle and Jog. In the Shuttle mode there was a center position where the knob would return when released. You would press the knob and it would enter the Jog mode where the knob turned freely and a frame by frame motion through the video was possible. The spring return was disabled. Another press on the knob and you were back to the Shuttle mode with spring return. There was an additional terminal on the pot at that center position so a definite Voltage could be established there. You may be able to get an assembly like this as a repair part. Call Sony and ask for the professional or broadcast parts people.

    I have seen a number of other pots with special features. Most of these had the special features incorporated in a separate assembly or in the knob and the pot itself is a more or less standard unit. This is the usually solution on professional, high end equipment.

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    As an operator of watchmaker lathes since 1958, I am familiar with small DC motors and the advantages of adjustable speed and the ability to immediately return to zero speed. In the old days, the lathes simply used sewing machine size universal motors and sewing machine foot rheostats. Once solid state SCR speed controls became available, I used one of those and a foot on-off switch. But then Foredom and Linemaster and Lucas started making variable foot controls with SCR guts and I still use some of those. My personal preference is the Lucas #9 LowBoy foot pedal, a 6 Amp SCR foot control that I use on a Levin D lathe with a Bodine 1/4 HP series motor. The pedal is both on-off and variable speed. I have been using it for many years. I have found that using a foot to control the motor is much better than using a hand when you are running a watch lathe, drill press, flexible shaft tool, micromotor, filing machine or 1 x 42 belt sander.

    Lucas #9 is on this page, along with a quote from my comment to Lucas after buying one many years ago. Products
    Lucas eBay listing (they also sell direct at a lower price) LUCAS RHEOSTAT #9 LOWBOY & Fishing Reel Line Winder Controler | eBay

    Levin dropped universal motors in favor of shunt motors and paired them with Minarik solid state controls and a Furnas foot switch. That was state of the art and expensive in its time. Around 35 years ago, I mounted a Derbyshire Magnus watch lathe with a shunt motor and Minarik controller and Square D foot switch and still use it. The speed control pot and forward-reverse switch are in a box that houses the motor and a Moffat flexible arm lamp, so the foot switch is just on-off. It works well and I still use it.

    Larry

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    Thanks for the replies but so far it looks like I will have to modify one with a return spring. The potentiometer is used for the speed control on a 1 1/2" scale steeple cab electric locomotive. I need a rotary motion and it needs to be able to fit into a hand held control box that is approx. 2" x 4.5 " x 7/8" high. The need for the spring return is so that the locomotive won't take off running when the main battery power is turned on if the potentiometer isn't at the zero point. I have 4 of these to build and am trying to make them as safe as possible.

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    The portable speed control has to be held in the hand. That requirement could be met with a trigger control like those used in battery and corded hand drills. In fact, I have taken apart a Linemaster foot control and found it was built around a hand drill trigger control, with the foot pedal arranged to push on the trigger.

    Larry

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    Quote Originally Posted by L Vanice View Post
    The portable speed control has to be held in the hand. That requirement could be met with a trigger control like those used in battery and corded hand drills. In fact, I have taken apart a Linemaster foot control and found it was built around a hand drill trigger control, with the foot pedal arranged to push on the trigger.

    Larry
    Or a radio control for a car.


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