Shorter = Stronger

I need more steer­ing-servo power. Rather than get­ting a new servo, can’t I just use a longer arm to get more lever­age?

RC Car Action - - TECH CENTER -

Servo-arm length does af­fect how much torque is ap­plied to the steer­ing sys­tem, but you’ve got it back­ward: A longer arm will give you less torque; how­ever, you will get more steer­ing throw (as­sum­ing the steer­ing sys­tem can ac­com­mo­date it). If you in­stall a shorter servo arm, you’ll get the op­po­site: Torque goes up, but you’ll have less steer­ing throw. If your cur­rent setup re­quires you to chop off a sig­nif­i­cant chunk of travel us­ing end­point set­tings, move the servo-arm link­age closer to the out­put shaft to put more of the servo’s travel (and torque) to work. (Nerd alert: The servo’s ac­tual torque rat­ing never ac­tu­ally changes, of course. Only the amount of torque trans­mit­ted via the servo arm changes.)

Let’s say we’ve got a servo rated at 100 oun­ceinch. As the term sug­gests, this servo should be able to lift a 100-ounce weight when fit­ted with a 1-inch arm. But if we in­stalled a 2-inch arm, it would only be able to lift 50 ounces. 19

Mov­ing the steer­ing link­age away from the out­put shaft will in­crease steer­ing throw but re­duce torque—and vice versa.

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