RaspberryTortoise

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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 has reached the deploy and test stage. If you'd like to get involved contact us. To see the Tortoise head over to the YouTube Channel

Current Objective

Integrate the Encoders into the control loop.

Ambitions

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

  1. Network enabled communications (wifi & SSH) --complete
  2. Web enabled controls --complete
  3. Visual Feedback (camera) --complete
  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 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.

Imagery is streamed to the User using Motion and a Webpage.

Interfaces

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

Software

The Tortoise runs on a Raspian installation base.

Github is used to store all the bespoke software needed for the project here: Tortoise GitHub

Installation Instructions

In general the best instructions are provided in the GIt readme file.

The process is

  1. Create a vanilla Raspian image Setup:RPI Raspian
  2. Install the Wifi Dongle and Update Installing_EW-7811Un_WifiDongle
  3. Install motion, nodejs and git
  4. Download the Tortoise git repository
  5. Follow Git readme for configuration of motion and nodejs.

Power

The current design uses a 6V(4500mAH) NiMH battery which can supply 1A. This is directly connected to the RPi which in turn supplies the USB ports with the powered needed to run the Wifi Dongle and the Camera.

The Battery is also wired directly to the BT main board to provide the power to the motors.

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.

PL4-6 6V 4.5AH Lead Acid battery runs the Pi and the BigTrak without any regulation although the pi on board regulator does have to dissapate a little heat.

Alternatives include: (some may require regulation).

  • 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

The BT main board has 4 PWM inputs to drive the Left and Right motors forwards and backwards.

To control this from the RPi which only has one PWN output a small series of enables is used. link needed

These enables are attached to RPi GPIO and controlled via the motor drive software.

Basic functionality for Forward, Backward, Left and Right has been implemented.

Development of an improved Interface planned which should provide capability for more sofisticated motion control.

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