Difference between revisions of "RaspberryTortoise"

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=== Software ===
 
=== Software ===
Software development has yet to start.
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* [[RaspberryTortoise Web Server]]
  
 
=== Power ===
 
=== Power ===

Revision as of 10:43, 12 August 2012


The RaspberryTortoise is a project aiming to develop a motorised roving vehicle from readily available components and a Raspberry Pi single board computer(soon to be readily available).

Status

This project is in active development. If you'd like to get involved contact us.

Current Objective

To interface the Raspberry Pi GPIO to control the vehicle.

Ambitions

This is a list of the things we hope to achieve with the Tortiose.

  1. Network enabled communications (wifi & SSH)
  2. Web enabled controls
  3. Visual Feedback (camera)
  4. Semi-Autonomous operations
    1. Object Detection & Avoidance
    2. Object Tracking / Chase
    3. Environment Exporation and mapping (GPS?)
    4. Area Patrol
  5. Control via Playstation controller?

Components

The current design incorporates the following components.

  1. System Controller: RaspberryPi + RaspberryPi_Buffer_Board
  2. Operating System: Raspian Setup:RPI Raspian
  3. Platform: Modified BigTrak Big Trak Autopsy
  4. Sensors: Webcam
  5. Interfaces: Installing EW-7811Un WifiDongle
  6. Software: Tortoise GitHub
  7. Power: Battery and Voltage regulation

Buffer Board

RaspberryPi_Buffer_Board is used to protect the control interfaces from the RPi.

Operating System

Raspian has been selected for is hard floating point support which 'should' provide a performance improvement.

Platform

800px-Big_trak_white_background.jpg

The chosen platform for the RaspberryTortoise is a BigTrak [1].

BigTraks were a popular motion-programmable 'robot' vehicle originally released in the late 1970s through to the 1980's.

These vehicles have been making a come-back as a 'nostalgia' toy. The are relatively cheap and contain all the key components needed to make a working robot.

Prior work has identified the major components of the original BigTrak were simple[2]. The 2010 variant of the Big Trak is superficially the same, however the control systems and power have been updated. Big Trak Autopsy.

The modern BigTrak circuits has been partially reverse engineered Big Trak Circuits. From which we've identified the primary motor drives and encoder connections.

Sensors

WebCam

Ideally this should be the [www.raspberrypi.org/archives/1254 Raspberry Pi Camera Module], however this is still under development and not available.

As an alternative, just about any Linux support webcam will do but the Microsoft Corp. LifeCam Cinema is the recommended camera.

The plan is to stream the camera imagery to the user via a webpage served from the RPi.

Interfaces

A wifi dongle is fitted to one of the RPi USB ports to provide network connectivity and remote access.

Software

Power

It is understood that the RPi draw more than 700mA then thermal fuses will kick in to protect the device from damage. If greater than 700mA is required the RPi will not be able to deliver it and external supply is used.

Power Budget

Estimated Power Consumption
device Voltage (V) Current (mA) Peak Current (mA)
RPi 5.0 200-300 300
Main Board 3.3 100 100
BT Motors 4.5 50 150
USB Wifi 5.0 100  ?
USB Camera 5.0 100  ?

Tests are required to confirm these values. It has been shown that the power consumption of an RPi can be reduced by replacing the linear regulator of the RPi[3].

Power Regulation

The RPi requires 5V and generates its own 3.3V. The motor drive requires 4.5V and the main board 3.3V. The expectation is that the motors will not be adversely affected by running from 5V and that we can use the RPi 3.3v to run the main servo board assuming the current consumption isn't too high.

The plan is to use batteries with a power regulator to generate the 5V.

LM2596 DC-DC Step Down

Batteries

Adding an RPi and associated peripherals is expected in increase the load such that more battery capacity is required to achieve 'reasonable' run-time.

Any reasonable capacity battery should do if it provides enough head room to run the power regulation module.

  • Buy a cheap cordless drill and hack it to get the battery, bonus it comes with a charger too!
  • Possible rechargable batteries [4][5]
  • Solar Cell for daylight operation or to recharge / top-up battery [6]
  • 5V 11000mAH battery used in other RPi projects [7][8]
  • DC-DC Step Down Ajustable PSU Module LM2796 Switch Regulator 4.5-35V to 1.25-26V [9]

Vehicle Interface

  • How to interface the RPi to the motor controller and sensor board.

Analysis of the Big Trak driver circuits Big Trak Circuits has identified the locations on the main board that drive the motors and sense the encoders.

These points need to be interfaced to the RPi GPIO so we can control the motors and sense the encoders.

Key Pad

We don't currently expect to use the key pad but it might be useful at some point.

There are 10 connections on the main board which somehow map to the rows and columns of the key pad via the main IC.

The keypad appears to be the same layout as the original BigTrak, its assumed to be some kind of mebrane key pad[10].

The keypad on the BTJunior has been investigated[11] and reported to be very difficult to understand and emulate. It seems plausible the bigger variant will be similarly complex.

References

  1. http://en.wikipedia.org/wiki/Big_Trak
  2. Big Trak Reverse Engineered by Robot Room
  3. http://www.raspberrypi.org/archives/260
  4. Robot Room Big Trak Motor Drivers
  5. RPi power reduction
  6. Possible Rechargable Batteries
  7. More high capacity but expensive batteries
  8. Solar Recharging
  9. http://www.newtrent.com/store/iphone-external-battery/icruiser.html
  10. DC-DC Step Down Ajustable PSU Module LM2796 Switch Regulator 4.5-35V to 1.25-26V
  11. http://www.nathandumont.com/node/248 BT Junior Hacked
  12. RPi Camera module

Resources / Research

  1. PCB manufacture
  2. Battery Chargers
  3. BigTrak updated for 2012?
  4. bigtrakisback.com
  5. Raspberry Pi tank
  6. 12V battery kit Ebay