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Gear ratio for telescope tracking motor

  • 17-04-2021 9:15pm
    #1
    iLikeWaffles
    Registered Users, Registered Users 2 Posts: 4,325 ✭✭✭


    I'm planning to modify a tracking motor for a telescope mount. My current tracking motor and controller, off a previous mount will not fit on my new mount. The commercial tracking system for the new mount is €150 which I can't justify paying especially when I can just modify the motor I have or build a DIY tracker, the later of which will require more time and research.

    I will be modifying and 3d printing an enclosure for the motor also; the casing I have will not fit on the mount. This is all boxed off more or less but something I am not sure about is the gear ratio and how it might effect the sidereal timing.

    The project files for the 3d printed casing will need to be modified for my motor because it uses a different sized motor (MP35EA 7VDC), this is not a problem I can just scale parts of the 3d render file for the 3d printed enclosure that fits the mount (Bresser MON-2). The motor for the project is supposed to be a 28BYJ-48 motor with a belt and 2 gears configured with an arduino (small gear has 16 teeth big one 64) so 4:1, I am not too sure of the MP35EA 7VDC ratio (see note) but I do not think the controller I have will be compatible with the projects original motor 28BYJ-48, the arduino is used to calculate the speed of the motor and drive train - no need to use the arduino and instead the MP35EA motors controller connected to 5 pin din on the motor. The driven gear on this motor is too big for the new mount (hits off DEC axis).

    The question is would scaling the bigger gear in radius change the ratio or speed of rotation. I think not but I really do not know, first time dipping the toe into something like this.

    note: full drive train from MP35EA motor is 24:36:18*:90 I'm thinking this is 3.75:1 but as I said not too sure (I'm thinking small gear with 12 teeth big gear with 45 will give same ratio). I'm also not too sure what belt would fit with this ratio and also the amount of teeth on each gear to keep the timing accurate to the controller and sidereal time. Any help much appreciated.

    *on shaft


Comments

  • #2
    Turbulent Bill
    Registered Users, Registered Users 2 Posts: 1,638 ✭✭✭Turbulent Bill


    The dimensions of the teeth on the driven and driver gears have to be the same (I think), otherwise the gears won't mesh. Changing the diameter of either gear directly changes the number of teeth it has, and hence the gear ratio.

    If you need to retain a 4:1 ratio and one of the existing gears doesn't fit, you might end up changing both gears to get the even ratio. Or mess about with the control parameters to scale the motor turns to the actual gear ratio.


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