Calculate motor/gear ratio on single axis

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Discussion Overview

The discussion revolves around calculating the motor and gear ratio for a motorized dobsonian telescope. Participants explore the necessary torque calculations, the impact of friction, and the design considerations for the telescope's movement mechanism.

Discussion Character

  • Technical explanation
  • Exploratory
  • Debate/contested

Main Points Raised

  • One participant expresses difficulty in mathematics and seeks help in calculating the force required to rotate the telescope base at varying distances from its axis.
  • Another participant calculates the torque based on the force and radius, stating that the product of force and radius remains constant at 27 lb-in for the given scenario.
  • A participant shares links to resources and images related to their telescope project, indicating a desire for feedback on design.
  • One participant mentions using a 3D printer to create prototype gears and discusses the software (Onstep) intended for tracking and GoTo functionality.
  • Another participant notes a significant reduction in friction due to design improvements and questions the resulting torque calculation based on the new friction measurements.

Areas of Agreement / Disagreement

Participants generally agree on the importance of torque calculations and the impact of friction on the design. However, there are varying interpretations of how to apply these calculations to the specific design of the telescope, indicating that the discussion remains unresolved.

Contextual Notes

Participants have not fully defined the assumptions regarding the gear ratio and motor specifications, and there are unresolved mathematical steps related to the torque calculations based on changing friction levels.

Who May Find This Useful

Individuals interested in telescope motorization, gear design, or those working on similar mechanical projects may find this discussion relevant.

Skygazer
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Firstly, let me explain that I am mostly inept at mathematics. Piecing together the required information is becoming a real challenge because of that.

I am motorizing a dobsonian telescope. I have read many accounts of success and the steps involved. The places where detail is commonly left out are: defining worm gear ratio/size and stepper motor oz*in.

I understand the basic problem here, I need to find out force required to rotate the base of the telescope at different distances from it's axis. With the current amount of friction(which will change after a small redesign), I have measured that it requires approximately 2 lbs 15 ounces of force to rotate the base 9 inches from it's axis.

What I really need help with initially is how to extrapolate that data when moving closer to the axis. After that I can begin to calculate gear ratio, stepper motor strength and build my circuits. Some equation where I can input force required and distance from axis.

Any help would be GREATLY appreciated
 
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You have a force of 3 lb acting at a radius of 9 inches . This means you have a torque of 3 lb x 9 inches or 27 lb - inches .

3 lb at 9 inches = 9 lb at 3 inches = 27 lb at 1 inch etc . The product of force and radius is always 27 .

Generally though for most gear and motor calculations only the actual torque is needed .

Post a picture or drawing of your telescope mount if you can .
 
Last edited:
Thank you very much Nidum!
Here is the link to a page with a 360 degree view:
http://goo.gl/KOD0Vj
And a link to a page that has images and instructions to the same exact thing I'm attemtping:
http://goo.gl/YRX4Uk
tbehind.png
tleft.png
 
Thanks for that .

Looks like an interesting project .

Any particular design problems you want to discuss ?
 
Last edited:
It's an exciting one, that's for sure. I bought a 3D printer and plan on printing my short-term/prototype gears out of nylon. I plan on using Onstep for the actual tracking and GoTo part of the programming. http://goo.gl/eDk5K4

Most of the hard parts are completed already (meaning the software and testing by others). I've fitted the bottom axis with a lazy susan bearing like in the second link I posted. That brought friction down to 5 ounces instead of 3 lbs! Those friction pads work! So if I understand you correctly, that should equal 4.5 lb -inches? Or 72 oz*in?
 

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