Spring 2017 Prosthetic Arm: Power Allocation Report

The Robot Company | CEO Professor Gary Hill

Blog Post Created by Project Manager | Bianca Esquivel

Project Documentation Written by Mission, Systems, and Test Engineer | Phuong Tran

Preliminary Information

Introduction

This report is created in response to requirements

L1-3: The Prosthetic Arm shall be able to operate for at least 16 minutes and 39 seconds (999 seconds) which is the duration allowed to play a game of minesweeper.

L2.3.1: The capacity of the battery shall be more than 943 mAh

In this report, we seek to understand the source of each quantity placed in the report.

Background

Battery Discharge Test and Servo Load Test

Link to Battery Discharge Test

Link to Servo Load Test

Power Resource Report

Test and Evaluation

Battery Discharge Test and Servo Load Test

Link to Battery Discharge Test

Link to Servo Load Test

Data

In this section, we seek to understand the reason for each quantity placed in the power report

B3: This value was from the last semester measured current draw of the hand

Link to Hand Current Draw

D3: This uncertainty was 20% because the MST engineer was not present when the measured value was taken

E3: This high margin corresponds to the high uncertainty percentage

B4: This value was calculated by 20mA (current draw from each I/O port) multiply by 20 (# of I/O ports)

Link to Arduino Micro Specs

D4: this low uncertainty results from the values were taken from Arduino manufacturer website

E4: similarly, low uncertainty percentage corresponds with low margin

B5: This value was taken from the maximum current draw of the 5V pin of the Arduino

Link to Arduino Micro Specs

C5: This value was taken from the result of the Servo Load Test

Link to Servo Load Test

D5: This uncertainty is low because we have done the test. Even though the expect current is different from the measured value, we have changed our PCB layout accordingly. In addition, the project allocation value is determined with this difference in mind.

E5: This low margin is the result of low margin percentage

E12: This is the spec from the battery chosen since we performed the Battery Discharge Test

E13: we total the margin in mA

E14: we total the expected current in mA

E15: the formula for contingency = E12 – E13 – E14

F12: This value is the capacity of the battery chosen from the Battery Discharge Test

F13, F14: These values are computed by multiplying mA value with duration of the mission (0.2775 hours – requirement L1.3)

F15: the formula for contingency = F12 – F13 – F14

Conclusion

Due to the allocation value, we pick the 11.1V 2200mAh 3S LiPo because this battery will satisfy L1.3 and L2.3.1. This decision is the result of Battery Discharge Test.

Link to Battery Discharge Test