[Dprglist] Recommendations for Robot Platform

[Murray Altheim]

Carl Ott <carl.ott.jr at gmail.com> wrote:
> Hi All,
>
> Can y'all help build a short list of robot learning platforms that
> are good for coming up to speed with robot platforms? I'm looking
> for kit options with an emphasis on software - e.g. how to read
> sensors and write & implement algorithms to drive actuators.
>
> *Any recommendations for kits w/in these constraints?*
>
> 1. wheels *with encoders*
>
> 2. relatively minimal mechatronics effort & tools needed to get started
>
> 3. enough sensors or easy / off-the-shelf plug-n-play extensibility for
> DPRG style contests, e.g.
> ** line following
> ** wall following
> ** quick trip
> ** 4 square
[...]

Hi Carl,

Perhaps this is a good time to introduce myself, as I just joined the
mailing list a few days ago, having recently seen David Anderson's
autonomous robots demo on YouTube. If David is on this list I'd like to
thank him: his obvious enthusiasm and pragmatic approach is quite
inspiring. From links on his site and others I've since been reading up
on subjects like subsumption architectures, etc., and found this mailing
list.

Back in 1979 I built a robot using an 8085-based single board computer,
a couple of large DC motors and a chassis made out of aluminum and some
circular PC boards found in a surplus shop in Des Moines, Iowa, that
were apparently from the insides of a missile. It was an ambitious
project for a high school student and I never quite got the ultrasonic
sensors working properly, but it was a good learning experience, a lot
of fun, and led eventually to an IT career.

Over that career I had the fortunate experience of working at NASA
Headquarters for a few years, where as a fellow Mac enthusiast I met
David Lavery, the head of the robotics division. At the time he had a
Mars Sojourner rover sitting on his desk. I remember marvelling at the
beauty of the machining of the wheels, and wishing I had that kind of
budget (and a machine shop). While setting up a demo I also had the
opportunity to pilot a telerobotics sled under the ice in Antarctica.

Years have passed and I now live in New Zealand, where most of my
creative energy has over the past few years been in music (I have an
improvisational abstract band named Barkhausen; we just finished our
second CD).

The combination of experimenting with some DIY microcontroller-based
Eurorack synthesizer modules and the advances in the world of Raspberry
Pi has found me back into robotics. For the past few months I've been
purchasing various playthings from Pimoroni and Adafruit and doing
some experimenting.

And planning...

I decided to purchase an OSEPP tank robot ($89), with the OSEPP motor
encoder kit ($27). I also bought the OSEPP wheel kit in case I'm not
happy with tank treads. Things are beginning to arrive via the mail,
sometimes a bit of a wait on this other side of the world.

My total set of inputs and outputs are as follows:

Inputs:

   * bumpers (6 subminiature lever switches, ala Anderson's SR04)
   * infrared sensors (Sharp GP2Y0D815Z0F with Pololu carrier,
     with a range of 0.5 cm to 15 cm)
   * sonar (processed through an Ultraborg)
   * motor odometry (using OSEPP motor encoders)
   * 9-DoF orientation (Adafruit 9-DOF Absolute Orientation IMU
     Fusion Breakout - BNO055)
   * ToF/LIDAR (Pimoroni VL53L1X Time of Flight Sensor Breakout)
   * audio In (Adafruit I2S MEMS Microphone Breakout - SPH0645LM4H)
   * several state setting toggle switches, including power kill
   * Pi camera (for telerobotics)

Outputs:

   * motor controller (using a Thunderborg)
   * servo control (provided by Ultraborg, for Sonar & LIDAR)
   * audio out (Adafruit STEMMA Speaker - Plug and Play Audio Amplifier)
   * LED indicators, plus 11x7 LED Breakout
   * display screen (Adafruit Mini PiTFT - 135x240 Color TFT Add-on
     for Raspberry Pi or PiTFT Plus Assembled 320x240 2.8" TFT
     + Resistive Touchscreen)

I've been using a Raspberry Pi Zero W and a 3 B+, will probably use the
latter in the robot.

Power will be from an 18V Makita power tool battery, sourced through
the Thunderborg. I'm considering purchasing a PiJuice to separate the
motor power from the Pi, but that's not really necessary.

I'm pretty impressed by the Pimoroni Breakout Garden series of I2C and
SPI modules. In particular, the ToF modules from Pimoroni and Adafruit
(I've tried both) are amazing. The Pimoroni one has three range settings,
and on long range measures up to 4 meters with high accuracy. Mounting
one of these on a servo-controlled scanner provides an enormous amount
of functionality for quite low power, weight and cost. I'm curious to
compare how this works against an ultrasonic sensor. I will be mounting
both on top of the servo, hoping to take advantage of the pros and cons
of each.

One of the benefits of many of the Pimoroni and Adafruit modules is
that there's a python library available for each, with examples. This
has allowed me to get things up and running quickly.

Carl, I realise the total cost of my project exceeds your core budget,
but I think it'd still be quite functional with just some bumpers and
one of the long range sensors, e.g., the ToF sensor mounted to a servo
(which comes with the tank project). If tank treads are an issue for
DPRG contests OSEPP sell silicon wheels that fit on the same hubs, or
you could repurpose the OSEPP 2-Wheel Balancing Mechanical Kit by adding
a ball caster.

I also realise that the above isn't a list of resistors and capacitors
and ICs, but rather mostly finished components. I consider myself rather
old-school, but with the availability of what's effectively a LIDAR unit
for around $18 and the ability to have a tiny 3 gram circuit board provide
nine sensor types (including two kinds of compass orientation, angular
and linear accelerometers, gravity vector and ambient temperature) for
about $35, well, kinda hard to think I'd build that myself. It is 2019,
not 1979 after all. I can build a robot that is in some ways comparable
to that Sojourner robot for about $800 dollars. Amazing.

I don't have any sense yet of the kinds of projects that DPRG members
create (i.e., what might be typical).

If there's any interest in the project I would consider blogging about
it as it progresses. I can for example explain some of my experiments in
using Bluetooth as a means of mapping and orientation. These experiments
will obviously progress better once I have a functional robot.

My thanks for your patience in reading what turned out to be a long
message; I'm happy to answer any questions. I hope this has been helpful.

Cheers,

Murray

...........................................................................
Murray Altheim <murray18 at altheim dot com>                       = =  ===
http://www.altheim.com/murray/                                     ===  ===
                                                                   = =  ===
     In the evening
     The rice leaves in the garden
     Rustle in the autumn wind
     That blows through my reed hut.
            -- Minamoto no Tsunenobu