Fall 2015 MicroBiped Level 1 Requirements

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By Paul Oo

Approved by Paul Oo (Project Manager)

Approved by Michael Balagtas (PCB Design and Manufacturing)

 

Objective

The CSULB μBiped project provides its members with the opportunity to not only design and produce a control theory project, but also to define a purpose for this project. A Biped Robot is designed to model the movement of the human lower body. The goal of this project is to prototype a μBiped that resembles a toy raptor. By customer’s request, this μBiped shall be controlled by Bluetooth on an Android phone. Due to an evolving objective, the payloads shall be determined by the customer.

Level 1 Requirements

Program Requirements:

In order to meet logistical expectations, the following program requirements have been set:

  1. According to the CSULB Fall 2014 Academic Calendar, the μBiped robot shall be tested by December 16, 2015; the date of the last day of finals.
  2. The μBiped shall be able to successfully navigate a course with obstacles, inclined path of up to 6o, and varying surfaces.
  3. According to 2014-2015 ARXTERRA µBiPed’s parts list, the project shall cost no more than $400.00.

Project Requirements:

In order to meet our objective to construct a robot that models human legs, the following project requirements have been set:

  1. In accordance with the project name, the μBiped shall travel on 2 legs.
  2. To be considered a miniaturized Biped robot, the μBiped shall range between ½ (120 mm) ±10% of Rofi’s dimensions according to the ratio of an MG92B μservo to Rofi’s servo.
  3. In accordance with customer specifications, the μBiPed shall be controlled by Bluetooth on an Android phone app.
  4. Based on evolving needs, the payloads shall be determined by the customer.

Mass Report

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By: Mesfer Aldosari

Devices Mass (g) Quantity Total Mass (g)
Arduino Micro Atmega 32u4 13 1 13
Micro Servos (MG905) 13.4 12 160.8
Sain Smart HC-SR04 Ultrasonic Sensor 8.5 1 8.5
MPU 6050 13 1 13
HC-06 1 1 1
Battery 28 2 56
Plastic 10 1 10
Total Mass 262.3

* Values given have been weighed by a scale. 

 

The table above explains what the mass of each device being used, there are seven devices in total. Which are: Arduino Micro, MG92B, Ultrasonic sensor, HC-06, MPU-6050, batteries, and 3-D PLAplastic.  The above table helps the group infer how much the robot may weigh and if they are near the mass limit.

Servo Torque Calculations

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Battery and Regulators

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By: Mesfer Aldosari

Micro biped will use two batteries LIPO 2S 350mAh to supply power to the robot.

Lithium Polymer Battery:

So after calculating the total current that is required to operate all of the component, the project needed 5 v minimum to run our project and 1500 mAh if the project was going to be ran for one hour. However, since the goal is to simply complete a track the mAh of the battery can be lowered.

So that means the project needs a battery that can provide at least 5 volts and provide enough current to power the device. In addition to providing enough power the batteries need to light enough to allow the servos to move.

 

2S Lipo battery

*Click on the link above to see the specifications at Hobby People, the following information was taken from there.

Features:

  • It has light weight which is about 28g
  • Maximum discharge rate at 10 Amps
  • Maximum pack voltage at 8.4V, Minimum pack voltage at 6V
  • Its dimension: 8 x 31 x 2
  • 7.4 volt

Capacity: 350mah

Voltage: 2S/2Cell/ 7.4V

Weight: 28g

 

Lifetime of the battery:

Battery Life = Battery Capacity in Milli amps per hour / Load Current in Mill amps * 0.70

[Battery capacity(mAh)/device consuption(mA)]*0.7

 

(350/1500)x0.7 = 0.1633

0.1633x60x2= 19 minutes is our battery last long

The factor of 0.7 makes allowances for external factors, which can affect battery life.

19 minutes without the power lost it is going to be 28 minutes

The formula used was taken from Digi-Key.com, at this link.

 

Regulators:

Micro biped will need to use at least one voltage regulator to  drop the voltage down to 5 volts from the 7.4 volts a LiPO battery provides. To do this two LM 7805s, made by Fairchild, were chosen. The LM7805 will take in 7V – 30V and has an output of 1.5A, so theoretically the LM7805s should be able to give out enough current to power the devices.

Power Budget

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By: Ameen Alattas

Devices Quintity Operating

DC volt.(v)

 Max Current

(mA)

 Operating

Current

(mA)

 Total Current

(mA)

 Power

(mA)

 Margin of error
Micro

Arduino

 1 5 50 45 45 225 0%
Servos

MG92B

 12 5 448

(Stall)

 200 2400 12000 15%
HC-SR04 1 5 15 15 15 75 0%
MPU6050 1 5 7 5.1 5.1 25.5 0%
HC-06 1 5 45 40 40 200 0%
TLC5940 1 5 120 95 95 475 5%
Total 2600.1 13000.5

* All values are measured 

As shown on the table, there are have six devices (Micro Arduino, Servos, HC-SR04, MPU6050, HC-06, TLC5940) that are operating on 5 volts.  It was chosen to use 5 volts instead of 3.3 volts for the HC-06 because the module being used has a built in voltage regulator for 5 volts to 3.3 volts.  The provided operating current and power are the actual values for all devices except for TLC5940 and servos. The TLC5940 uses current from 60-12 depending in how many servos attached to it. Since the group is using 12 servos it is assumed that it will draw about 95 mA. That’s why the 5% margin of error still  present. The servos, it depends on the weight that it will be carrying. Which will result in a current draw from 100mA-230mA. It was decided to go with 200mA for a 15% margin of error.

Servo test

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