From: dwilliam@pizza.ess.harris.com (Dave Williams)
Subject: Re: My robot project.
Organization: Harris Corporation - ISD
Distribution: comp.robotics
Date: Thu, 7 Jan 1993 16:28:22 GMT

In <1993Jan4.191739.26583@n1gva> fcf@n1gva (F. C. Floberg) writes:

>ac94691@dunix.drake.edu (The Dark Kitty) writes:
>: I just thought I'd share my current project with anyone interested.
>: 

[wheelchair-based robot description deleted]

>I've toyed with the idea of robotic control in the past, and it always seemed
>that the best approach (if not the least expencive) would be to have a station-
>ary computer do the actual decision making, and have a smaller, sencory input
>and low level moter/steering control computer on board. You could the put the
>robot on a lift of some sort (or just CHAIN IT DOWN!) so it won't wheel off
>into the sunset while debugging the software.

>I'm into packet radio, so I know the gear for the communications link is abund-
>antly availible (though a bit pricey).

   Packet radio?  Hummm.  Here's one experience I've had with it:
a few years back, I was the acting TA for a Clemson Robot Lab working on a
bomb disposal robot.  The students opted to use a Packet radio link, with
the packet TNC transmitting into a pair of simple walkie-talkies.  The main
robot had a STD based computer running the control systems of the robot, 
while the operator of the robot (this was a teleoperated system) ran the 
machine by operating a remote control panel attached to a PC.  The operator
used a remote TV screen to observe the robot's position.

   The stumbling block for this system was the radio link.  The packet radio
worked very well, except for the fact that it tended to have an extrememly 
long latency time.  As a result, commands coming from the control system 
would get buffered up in the TNC, then transmitted in one long burst.  This
made the robot nearly uncontrollable, since the was nothing even approaching
real-time operations.  Unfortunately, the students hadn't discovered this
problem untill way late in the semester, and they never found out how to 
solve it.  Next year's group went with a tethered system, so we never found
out any more about the packet system.  

   Since you're familiar with packet controllers, I'll ask you:  do most 
TNC's have a way to specify transmit latency?  If we could get the TNC to
transmit packets as soon as it receives them, the packet system looks like
it could be really useful.  As is, it's just too slow a link to do any real-
time control.  (At least for teleoperated systems - something with more 
intellegence on the actual vehicle may be able to stand more latency in the
transmission link...)

Dave Williams                                   | "What time is it?" "9:00AM"
 dwilliam@jabba.ess.harris.com                  | "What day?"        "Monday"
  "Huh?  What?  Could you repeat the question?" | "Go away.  Try me Tuesday"
    <mumble mumble> opinions <mumble mumble> mine <mumble mumble mumble>
--
Dave Williams                                   | "What time is it?" "9:00AM"
 dwilliam@jabba.ess.harris.com                  | "What day?"        "Monday"
  "Huh?  What?  Could you repeat the question?" | "Go away.  Try me Tuesday"
    <mumble mumble> opinions <mumble mumble> mine <mumble mumble mumble>