Aug 14, 2010

Meeting Date: 
Saturday, August 14, 2010

Class

Thomas Messerschmidt gave a class on "Robot hands, claws, grippers and other end effectors". His slides were going to be posted on his website.

Jim was also intrigued by the use of capacitive sensors in music toys. These sensors have really taken off recently when they became very cheap (thanks to the iPhone and its derivatives)

 

Alex showed us the motor of an automotive windshield wiper and described its potential use in robotics. You can get them for $14. These motors are very reliable, have a torque of 1700 inch/ounce and turn at 150 rpm. The shaft is not suitable for carrying loads so wheels need an independent bearing. it can be challenging to mount an encoder.

Alex continued enlightening us with his work on a SCORBOT robot arm. He discarded the 'boat-anchor'-type controller that came with the robot arm and replaced it with a Leaf Controller, surprise-surprise (for those of you that do not know Alex, he designed the controller for the Leaf project).

He described the different ways to drive a motor with an H-bridge. There are two main methods:

- sign/magnitude

- lock/antiphase

Here is a good tutorial on H-bridges.

 

 

Thomas Messerschmidt, who started the Riverside Robotics Club, showed us their initiative to define a standard robot, which can be easily built, cheap (order of $70) and easy to program.  The purpose is to built an easily-extendable platform that can be used in robot competitions. Here is a list of the components they suggest:

 

 

 

Thomas also announced an upcoming repeat of last years RobotExpo on November 6th between 1pm and 5pm.

The venue is: Woodcrest Library, 16625 Krameria Avenue, Riverside, CA 92504-5767, (951) 789-7324

The audience are kids & their moms. 

Thomas asks anyone that can show some robots to come in and show them to the public. It is fun day and you get to talk about robots to very interested people.

 

 

 

 

 

 

Here is a video of last years expo, where Anouk talked about her robots. The audience is typically young.

 

 

Thomas also is involved in a project with Tim Lewis on designing a Robot Elvis hack kit. They are hoping to make it commercially available. It is based on the BASIC STAMP microcontroller. Here Tim demonstrates controlling the neck gears:

 

 

 

 

 

 

 

 

 

 

 

Don Julien picked up a copy of Maker Magazine at one of our previous meetings and saw an article of the Makerbot. He immediately decided to build one himself and bought the kit. Today he showed us a fully working model. It didn't even work yesterday, it even worked during the meeting itself. A first in our club's history.

Makerbot is a desktop 3D printer. It 'draws' slices of a 3D object with melted ABS plastic. The end result is a 3D object.

You can find out more about Makerbot via these links:

  • Makerbot
  • Makerbot Wiki
  • RepRap - an initiative to design a 3D printer. Makerbot was derived of this
  • Blender - one of the many 3D modeling applications that can be used to design 3D models
  • Replicator - an application to slice up a 3D model in layers as prearation for the Makerbot

You design a 3D model with a modelling tool like Blender, save the model as an STL format file, then use Replicator to slice up the model in layers and produce a gcode file, which contains all the CNC instructions to drive the 3D printer.

 

 

 

 

 

 

 

Dan Mornis showed us a G1 phone he picked up from EBay, which he upgraded with Cyanogen 5.0 distribution of Android. This little gadget turns out to be packing some hefty computing power and some interesting sensors (accelerometers). You can do some serious damage with this as a mobile robot brain. This thing can also be programmed in Python. 

 

 

Unfortunately, Dan is struggling with getting a serial stream out of the phone. He is running the script below and is getting the output in the screenshot to the right. He doesn't see a direct correlation and is wondering what he might be doing wrong. If anyone could help him here ...

 

import android
import os
import time
 
print "Ready\n"
 
msg = 'u'
 
for i in range(0,5):
#os.system("echo '<%s>'> /dev/ttyMSM2" % i)
os.system("echo '<%s>'> /dev/ttyMSM2" % msg)
print i 
time.sleep(2)
for i in range(0,5):
os.system("echo '<%s>'> /dev/ttyMSM2" % i)
#os.system("echo '<%s>'> /dev/ttyMSM2" % msg)
print  msg
time.sleep(2)

Ron Rose reported on a new IR receiver / transmitter from Vishay: the  TSOP4038, TSOP58038, and TSOP5038. Read more about them here. These IR sensors measure the intensity of reflected IR light and output a pulse of which the width is representative for the distance measured. They are cheap and simple to interface to a microprocessor. These can be used for beacons (Ron seems to have a soft spot for beacons) and range sensors. The range varies from a couple of inches to several metres. This can be increased to 30 ft with a lens.

 

John Davis gave some more details about his RoboMagellan robot (see previous meeting notes for more details):

 

  • He uses OpenCV for finding the orange cone. He replaced the highUI camera capture module that comes with OpenCV and replaced it with SDL. This improved the image throughput dramatically.
  • He separates the power supply for th motors and sensors and microprocessor
  • He learned a valuable lesson from his experiments to ruggedize his robot more. It works fine on flat surface, but when negotiating the outdoors terrain, parts tend to ... part themselves from the mothership.
  • John enjoys the finer operating systems out there and runs everything on Linux. His robot comes equipped with Wifi. He uses Xming to remotely log into the robot's OS's desktop (running on Beagleboard).

 

 

 

 

 

 

 

 

Rainer Hessmer presented his recent work on Visual Odometry. Here are his notes on his web-site.

Some interesting links: