Newsgroups: comp.robotics
Path: brunix!uunet!timbuk.cray.com!hemlock.cray.com!kilian
From: kilian@cray.com (Alan Kilian)
Subject: My robot progress report
Message-ID: <1992Mar17.151351.19408@hemlock.cray.com>
Date: 17 Mar 92 15:13:51 CST

    Some folks have asked me to keep them up to date on my robot project
  so here is the first update.

  Background:
    I built a robot in high school using a 1802 processor with 256 bytes of ram.
  The platform was crappy and I had to have a tether leading to the batteries
  so I never got very far with it.

  The new robot:
    The new robot has a nice platform. Aluminum "U" channel is the main
  construction component. There are two gear boxes for the main wheels.
  The gear boxes used to be driven with those funny brushless AC motors.
  I just removed the coil from around the armature and I drive the armature
  like a pully from two DC motors.
    The DC motors have an AC tachometer built into the motor. With the help
  of a LM3900 quad opamp I convert this into a 5Vdc pulse train.
    I drive the DC motors with one MOSFET transistor and two 5Vdc coil
  Single pole double throw relays. I tried using an H bridge with bipolar
  transistors but they had two problems: 1) Too large a voltage drop through
  two transistors and my motors ran slow. 2)The best driver circuit I came up
  with for insuring no smoke and having the capability to use pulse width
  modulation used two ICs per motor. (I have since seen a circuit that uses
  one IC per motor but it's too late now).
    The relays are setup to switch the motor from forward to reverse. The
  relays coils cost 90ma each so they are set up normally for the motors
  to go forward. It costs 180ma to reverse one motor and 360ma to reverse
  both motors. It's expensive to reverse the motors so I will do most of my
  turning by stopping one motor and driving the other.
    My motors use 140ma each when running forward. I don't know what they
  use in reverse but I wouldn't expect them to use much more than that.
    I use 8 "D" sized nicad batteries 4Amp-Hours so I should be able to get
  4000/300 = 13 Hours of forward movement out of them. (300 is 140ma * 2 :-))

    I am using a Motorola MC68HC16EVB to control the robot. This is a 16Bit
  16MHZ micro controller evaluation board with a Digital Signal Processor
  subsystem. It cost $168.16 and I will be getting a rebate of $68.16 since
  I completed their DSP project. So the controller will only cost me $100.00
    This controller has 8 lines of 10Bit A/D, 2 PWM outputs 4 timer outputs
  4 event capture lines, 7 interrupt inputs 1 pulse accumulator input
  and a bunch of Digital I/O lines. And when I get another chip I get 1 line
  of D/A output. It has a serial RS232 and a PC parallel port. I write
  software on a Compac, assemble it, down load it to the EVB and debug it with
  some free software from Motorola. When it's going I can switch a switch on
  the EVB and disconnect from the debugger in the PC and have the robot move
  around on it's own. This last feature requires a modification to the EVB 
  board that I invented. Of course I'll tell you what to change if you want to
  know. 

    Here are my plans for the project over the next 6 months.
  1) Add two ultrasonic range modules from Polaroid. I got these from someone
     on this news group and I connected them to my Commode-64 and they are great
  2) Add a 2 line by 16 character LCD display panel. Epson $26.19 from Mouser
  3) Add a speech synthesizer board. $150.00 From RC Systems
  4) Add a flux gate compass. Maybe from Radio Shack.

    Here's the current sate of the machine. The platform is done. The EVB is
  mounted. The 8 motor batteries and 4 CPU batteries are mounted. The EVB can
  control the speed of the motors with the 2 PWM outputs. The EVB can sense
  the motor speeds using 2 input capture lines.

    To do this week: Add buffers to get the direction outputs to the relays.
  Add a pair of analog inputs to measure the two battery voltages. Play around
  for a few days with fixed movement to run any bugs out of the platform.
    To do next week: Get the LCD panel running if I get the data sheet.
  Get one range module running. More software to avoid objects.

    I'll let you know how it goes. If you have any questions you can either
  email them to me or post them to this news group.

    I just got an MC68HC11EVB with an 8 Bit 2MHZ processor. The same processor
  that Fred and the boys at MIT use in the 6.270 robot building course so I
  will fool around with that one also. Maybe a smaller low power robot is in
  the works. We'll see.

                         -Alan Kilian

-- 
 -Alan Kilian         kilian@cray.com 612.683.5499 (Work) 612.729.1652 (Home)
  Cray Research, Inc.           | 
  655 F Lone Oak Drive          | 
  Eagan  MN,     55121          |
