Dec 21, 2013, 03:58 PM Addicted United States, CO, Parker Joined Dec 2011 1,184 Posts Question Gear ratios Hi guys, first time poster in the Robotics forum. I'm trying to calculate gear ratios. I need to increase the speed of a continuous-rotation servo. I bought a few r/c car drive gears to tinker with. I'm thinking of putting an 84-tooth on top of the servo. That will drive a 28-tooth gear. 84/28 gives me a 3x speed increase. Say I wanted to get more. I could fix the driven 28-tooth gear to another 81-tooth gear. That is a 2.9x increase. My question is say that servo rotates at 20rpm. The first stage will increase that to 60rpm. Will the second stage then increase the 60rpm by 2.9 giving me a final rpm of 174rpm? I feel like I should know this but thought I should check here. Thanks!
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 Jan 01, 2014, 10:09 PM Registered User Denver, CO Joined Dec 2005 6,459 Posts Depends on how you connect the gears. If the 81 tooth is driven by the 28 tooth, it would reduce the rpm back almost to the original rpm. So if the 81 tooth was stacked on the 28 tooth it would have to drive a second 28 tooth gear to get the rpm increase.
 Jan 01, 2014, 11:11 PM Addicted United States, CO, Parker Joined Dec 2011 1,184 Posts Thanks, Rob. I ended up driving it direct as the servo is plenty fast at 60 rpm (pan for Go Pro).

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