diff --git a/src/servo.rs b/src/servo.rs
index 07b5737..3ebe73e 100644
--- a/src/servo.rs
+++ b/src/servo.rs
@@ -2,8 +2,10 @@ use arduino_hal::pac::tc1::OCR1B;
 use arduino_hal::pac::tc1::OCR1A;
 use arduino_hal::pac::TC1;
 
-const MIN: u16 = 100; // *4us =  .4ms
-const MAX: u16 = 700; // *4us = 2.8ms
+const CENTER: u16 = 375;
+const RADIUS: u16 = 185;
+const MIN: u16 = CENTER-RADIUS; // *4us
+const MAX: u16 = CENTER+RADIUS; // *4us
 const RANGE: u16 = MAX-MIN;
 
 pub(crate) trait Servo {
@@ -17,7 +19,7 @@ pub(crate) trait Servo {
 
 #[inline(always)]
 /// -1.0 full reverse, 1.0 full forward
-fn calculate_duty(speed: f32) -> u16 {
+pub fn calculate_duty(speed: f32) -> u16 {
     let speed = speed / 2.0 + 0.5;
     let duty = speed * RANGE as f32 + MIN as f32;
     duty as u16