Fall 2016 Biped Trade Off Study- Ankle Servos

Ankle Servo Selection

By: Alan Valles (Electronics and Control Engineer)
Approved by: Ijya Karki (Project Manager)

Table of Contents

Introduction

The most recent design calls for 4 servos to be utilized. Two servos will function to shift the center of mass onto the planted foot during walking motion. The remaining servos will as the ankle which will allow the robot to turn during walking motion.

Study

Since there are four different servos that have different requirements, the ankle servos will be compared. The other servos are still to be determined so that the necessary torque required to move the CoG to balance while turning is considered.

Servo	MFG	Voltage	Torque(stall)	Mass	Cost
9g	Varies	4.8-6V	18.9 oz-in	9g	Free(3.95)
ES08A	Emax	4.8-6V	21oz-in	8.5g	4.95
HS-53	Hitec	4.8-6V	16.70z-in	8g	7.19

Under ideal conditions, the CoG will be directly on top of the shaft therefore, torque requirements will be dependent based on the position of CoG and total weight of the robot. Due to these assumption, all of the servos will meet the torque requirements. Therefore, the primary constraint will be cost. This leads BiPed to utilize existing TRC inventory and select the 9g servo. If the servos were to be bought due to stripped gears on existing parts or other issues with inventory, the Emax will be purchased depending on the total budget of the robot due to other subsystems.