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  • synchronous motors??

    I have an idea for a clock that I would like to build.
    I need a 60 rpm motor, and will gear from there.
    I don't know anything about motors really, but I'm thinking that I need a 120 vac 60 rpm synchronous motor.
    But what does that really mean?
    Synchronous to what?
    What if my line voltage varies?
    Do they have some sort of crystal that keeps RPM in line?

    Also, the motor needs to be relatively small. For instance:

    https://www.amazon.com/Synchronous-E.../dp/B012W0AMYE

    Please educate me.

    Thanks, Sid

  • #2
    It'll be synchronous to your line frequency not voltage.

    These motors were very common in the old analogue electric clocks.

    They never kept perfect time though as the supply company varies the frequency by tiny amounts to control demand, at least in the UK they do. Its only points of a Hz but it changes all the time.
    If it does'nt fit, hit it.
    https://ddmetalproducts.co.uk
    http://www.davekearley.co.uk

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    • #3
      OK, that makes sense.
      It would be optimal if I could get a more accurate motor.
      Where is Wes when I need him?

      By the way, I wonder how he is doing??

      Thanks, Sid

      Comment


      • #4
        In the US, the powerco is required to keep a long term average within a small error. (there is a move afoot to remove that requirement)

        In practice, the frequency cannot vary much at all, as every generator must be in step with the grid, or it may either turn into a motor, or else be bogged down to grid frequency by being unable to drive the whole grid by itself. Keeping accurate time good enough for any normal propose is no issue at all for synchronous motor clocks unless they get so worn that the motor cannot drive the mechanism at full speed.

        More accuracy that that can be obtained b crystal-based oscillators, of varying complexity, etc. Clocks that self-correct by receiving a time from the NIST exist. You can buy such as clocks or watches, etc. They typically sych once a day, some may synch more often.
        Last edited by J Tiers; 07-12-2019, 12:34 PM.
        1601

        Keep eye on ball.
        Hashim Khan

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        • #5
          I don't think for my purposes I need a self correcting mechanism.
          I might just buy one of the motors from Amazon and see how well it works.

          Sid

          Comment


          • #6
            Maybe just buy a timer, one of the old types with a synchronous motor and all the adjustable mechanical stops for on and off times. I see them all the time at flea markets and thrift stores. Chances are you will get what you need out of them. They are clocks after all.
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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            • #7
              Stepper motor controlled by a crystal oscillator would be a novel approach, there may be prior art however (-:

              Comment


              • #8
                Sid, are you familiar with "gearotic motion" software? Its done by Art, the founder of Mach3 cnc software. On their forum are tons of clock mechanisms people have built, the software is exceptionally useful for that purpose. It also does many types of gears, I made the helical gears for my gatling gun with the software, came out great.

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                • #9
                  Many sources for synchronous timer motors, including the older washer & dryers, all used these 60hz synchronous timer motors.
                  Max.

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                  • #10
                    I've found several that ran at different speeds, but all had the same basic package. Some were 1 rpm, I've had 3 rpm, 4 rpm- the 1 rpm can easily be made to kick over a minute hand.

                    In my experience, a clock with a synchronous motor can keep essentially perfect time. The synchronous motor is a counter really, counting the power line pulses coming in. Unless friction interferes with that, the motor will advance a gear train in perfect step with the incoming frequency. No matter if years go by, the 'count' will be exactly what the power company put through the lines over that time period. The big snag here of course is power outages, where you lose sync.

                    These things will run for decades- surpassing the life times of electronics in many cases.
                    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                    Comment


                    • #11
                      Don't forget the motors on our vinyl turntables.

                      Comment


                      • #12
                        Originally posted by Sparky_NY View Post
                        Sid, are you familiar with "gearotic motion" software? Its done by Art, the founder of Mach3 cnc software. On their forum are tons of clock mechanisms people have built, the software is exceptionally useful for that purpose. It also does many types of gears, I made the helical gears for my gatling gun with the software, came out great.
                        I have Gearotic. I used it to generate an internal tooth gear once, that I had EDM’d.
                        The gearing part I’m ok with.
                        I like the idea of a stepper with a controller. Maybe overkill? Sounds like a small Arduino board would be the ticket, although I don’t know any thing about them.

                        Comment


                        • #13
                          Nost uP boards like that do NOT have accurate clocks.... they are "accurate enough" for what they do, but not "clock" accurate. Not "cheap digital watch" accurate in many cases.
                          1601

                          Keep eye on ball.
                          Hashim Khan

                          Comment


                          • #14
                            Originally posted by sid pileski View Post
                            I like the idea of a stepper with a controller. Maybe overkill? Sounds like a small Arduino board would be the ticket, although I don’t know any thing about them.
                            The small Picmicro have the feature of running timer1 from an external crystal, the 32,768Hz watch crystal is usually used in conjunction with timer1 which will roll over every 1 second.
                            The main IC clock can also run at this speed, but if you use say, a main clock of 20Mhz in conjunction with the watch crystal, you can achieve quite an accurate clock.
                            Max.

                            Comment


                            • #15
                              99.99999% of all plug in, clocks use synchronous motors. They are made in a "tuna" style can and are widely available both new and used. They have an actual synchronous motor inside the can plus a bunch of reduction gears to produce the stated speed on the nameplate on the outside. You can get them in a wide range of external shaft speeds, usually with a clock style gear pinion on the output shaft as they are intended for use in clocks. Just search for synchronous motors and pick your output shaft speed.

                              https://www.bing.com/search?q=synchr...FORM=QBRE&sp=1

                              These motors ARE true synchronous designs and the do keep in step with the generators that supply the national electric grid. Some have stated that those generators change speed by somewhat large percentages during the day and that is 100% true. They will slow down when the load, the demand for electricity is great and they will speed up during the off hours. So the short term accuracy of all the electric clocks in the country are not very accurate IN THE SHORT TERM. They can be off by several seconds and that is a fact.

                              BUT, there is also the long term accuracy to consider. What happens is the electric companies must synchronize their generators across the country or at least over large areas of it. And they have to synchronize them to something. That something, in addition to each other, is the time signals broadcast by the NBS on the radio stations of the WWV network. Those signals are accurate to a very small degree of error and are corrected to even higher standards over longer periods. The electric generators may lose a second or two during the high demand periods of the day, but they have their speed increased during the slack times to make up those discrepancies. And they make them up EXACTLY in step with WWV. The result of this is that the LONG TERM accuracy (days, weeks, months, years) of a synchronous clock working on the power line frequency will be almost perfect. You can start at almost any point in time, any point in the year and the power grid along with those cheap, synchronous clocks will never be more than a few seconds off. A year later it will be about +/- 2 seconds. Ten years later it will still be +/- 2 seconds. One hundred years later, still the same. The long term accuracy will always be excellent and, expressed as a percentage, it will get better and better as that term increases. Just a single year gives you an accuracy of 63 parts in a billion. Ten years and that becomes 6.3 parts in a billion, etc.

                              If you need short term accuracy you need to use better equipment. But for long term accuracy the power grid is as good as the NBS and WWV, always with that +/- 2 seconds.

                              In all truth, it may not be completely that simple. But the important point is that the power companies DO make up any lost time so your cheap, electric clock is dead accurate over the long run.

                              I have been assuming mechanical clocks with synchronous motors above. But, digital clocks can also use the power line for their time reference. If they do, then they will have the exact same short term inaccuracies and long term accuracy as the mechanical clocks do. But some digital clocks can have their own, internal oscillators and they will be a lot more accurate for the short term while suffering from worse long term accuracy.

                              The popular battery powered clocks are a modern marvel. They use a crystal oscillator and again have excellent short term accuracy while suffering from worse long term accuracy.

                              I have an inexpensive digital clock here in my office. It also incorporates a WWV receiver so it uses the NBS time signals broadcast on that radio network as it's basis for telling time. It therefore has excellent short term and long term accuracy. It is to a small fraction of a second at all times. Certainly better than my ability to read it.

                              https://market.thedailymeal.com/products/westclox-70026a-lcd-atomic-digital-alarm-clock?cid=331726596&aid=1156686474919106&eid=&tid= pla-4575892519531094&ul=&mt=e&n=o&d=c&dm={devicemodel} &dt&sn&adid={creative}&k=&p={placement}&pc={target }&ap={adposition}&msclkid=bbbe703ddf261ae82cba2d17 6fb0055c




                              Originally posted by sid pileski View Post
                              I have an idea for a clock that I would like to build.
                              I need a 60 rpm motor, and will gear from there.
                              I don't know anything about motors really, but I'm thinking that I need a 120 vac 60 rpm synchronous motor.
                              But what does that really mean?
                              Synchronous to what?
                              What if my line voltage varies?
                              Do they have some sort of crystal that keeps RPM in line?

                              Also, the motor needs to be relatively small. For instance:

                              https://www.amazon.com/Synchronous-E.../dp/B012W0AMYE

                              Please educate me.

                              Thanks, Sid
                              Paul A.

                              Make it fit.
                              You can't win and there is a penalty for trying!

                              Comment

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