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  1. #11
    DAVEG's Avatar
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    Default



    What is the model of the $5 timer your are using and it's RPM ?

    - Dave

  2. #12
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    Default model of the $5 timer

    Quote Originally Posted by DAVEG View Post
    What is the model of the $5 timer your are using and it's RPM ?

    - Dave
    I'm not sure how to respond.

    This will be the fourth or fifth time in which I used a mechanically geared appliance timer to drive the polar shaft on a GEM mounted scope. No two timers were the same. All were foreign made as far as I can recall.

    I often buy a few when I see them on sale and never question the RPM or model as it doesn't matter.

    The final drive ratio matches the Sidereal rate, one rpm every 24 hours. Beyond that I'm not concerned.

    Mounting is always the same.

    The timer is mounted so the hand crafted toothed drive is tangential to an identical drive wheel mounted on the polar shaft.

    The only change, if any, is which way the timer faces. This is determined by the direction the face turns.

    There is an enormous amount of multi stage, internal gearing to step down the speed of the 120 VAC 60 cycle synchronous motor to the 1 RPD final speed needed.

    I've yet to burn up or wear one out.

    The attached photos so the timer mounted but sans the drive wheels

    Art

  3. #13
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    Art,
    In both your pictures I don't see the any of the handcrafted gears that connect the timer to the polar axis. In both pictures the polar axis looks bare and the face of timer is visible. Could you post some close up pictures showing the complete drive and how the two are connected since that is the critical part of the design in making a functioning drive.
    You also stated the motor make one rev. in 24 hours and "The timer is mounted so the hand crafted toothed drive is tangential to an identical drive wheel mounted on the polar shaft."
    How does that work out to be Sidereal rate ?

    - Dave

  4. #14
    Art Bianconi's Avatar
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    Default

    Quote Originally Posted by DAVEG View Post
    "Art, You also stated the motor make one rev. in 24 hours"
    Dave
    I never said anything of the sort! Go back and read what I wrote.


    What I said was
    Quote Originally Posted by ART View Post
    There is an enormous amount of multi stage, internal gearing to step down the speed of the 120 VAC 60 cycle synchronous motor to the 1 RPD final speed needed.
    The timer is already at the Sidereal rate. All that is needed is to provide a 1:1 ratio gearing to transfer the torque to the polar shaft.

    All the ones I have made previously were given away. There are two more currently under development. including the one whose pictures you saw.

    When I complete them I'll post pictures.

    "All the best"

    Art

  5. #15
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    Art,
    So am I understanding correctly the face of the timer is turning at 1 revolution per day and the gearing to the telescope is 1:1. If so how are you driving the telescope at Sidereal rate ? How did you attaching the "gear" to the timers ? What part of the timer was it attached too ? Also how is the drive clutched to the telescope so you can move the telescope while the drive is running.
    Can you provide the make and model of timers you have now since you stated you have couple of them and you have one pictured on your mount.

    - Dave

  6. #16
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    Default Not here, not now

    David the scope shown here is an entry level scope designed to be built and used by disadvantaged children in low income families and with a minimum of hand tools.

    It is built around slightly blemished Meade optics, the head and fork from an abandoned bicycle frame, a piece of low pressure PVC drainage pipe and a toilet flush valve based helical focuser.

    Total cash outlay is somewhere around $50 which includes the drive.

    That OTA and mount were shown as part of the tripod assembly merely as an example of the utility of the Moonlight based fixture. Someone has expressed concern that the triangular head was too large to be used with GEM mount, so I chose to address that concern. It's use with a clock drive was not meant to be the topic of lengthy dialogue.

    If you go back to the initial rendering that was attached to the opening post and load it into your viewer, it will enlarge quite a bit and the gearing of the two drive wheels should be apparent.

    Further explanations should not be needed to one with your claimed experience and background.

    Frankly, I am a bit apprehensive as to why an engineer should be having so much difficulty comprehending so simple a system.

    Should I choose to provide construction details for an appliance timer based clock drive for subscribers in this community, I will do so in a dedicated string, not hi-jack my own string for the tripod.

    I've important commitments I must address and do not have time for such an effort now.

    Art
    Last edited by Art Bianconi; 06-08-2011 at 02:58 PM.

  7. #17
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    Art,
    You have stated that your drive runs at Sidereal rate. As an engineer and an experineced telescope maker I can not figure out how this is possible. That is why I asked you this question. Your design, as you stated in your postings and from your drawing will not track at Sidereal rates. You stated "The final drive ratio matches the Sidereal rate, one rpm every 24 hours. Beyond that I'm not concerned."
    Can you also explain how you deal with backlash and play in your system. Since the timer is rotating at 1 revolution per day and is coupled to the telescope at a ratio of 1:1 any slight backlash and/or play will take many minutes to be taken up. In that time the object will have drifted out the eyepiece. This is why all the known clock drives I have either built and have seen on commerical telescopes use the gear reduction at the final drive stage and the motor turning the worm is running no slower then 1/15 rpm. This allows any play and/or backlash to be taken up quickly.

    So if I am missunderstanding something about how it your drive is workings please correct me. I'm sure others would like a detail explanation of how your drive works as well.
    You also stated that you have built a number of these drives, and they are designed to made by people with little skills and money yet you have not provided the details to show how this can be accomplished. Since you have made them I don't see what the issues is and why you can not clearly explain how to build your drive and how you have over come the issues I have raised.

    - Dave

  8. #18
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    Default

    Interesting discussion. Perhaps a thread on Sidereal time is in order. In this thread, it seems sort of like the tail wagging the dog. Sidereal Time? Solar Time? Does an inexpensive mount made of scrap parts really need to keep either? Most likely not. A simple motor that tracks for a few minutes is probably more than enough.

    Way back when I was far younger than I am today I was stationed aboard the USS Lake Champaign; a WWII aircraft carrier. We had the honor of being the prime recovery ship for a few of the earlier space efforts made by the USA. I was involved in GT5; Conrad and Cooper. Gemini 5, missed the splash down point and the Lake Champaign by far more than a country mile. The cause was an error made in a computer program. Seems while the folks at NASA were great rocket scientists, none understood the difference between a solar day and sidereal day.
    Last edited by sxinias; 06-08-2011 at 05:23 PM.
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