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From: mikeb@ee.ubc.ca (Mike Bolotski)
Newsgroups: comp.robotics
Subject: Re: Micro rovers vs. Stompers
Message-ID: <1297@fs1.ee.ubc.ca>
Date: 2 Jul 90 21:57:41 GMT
References: <9792@pt.cs.cmu.edu>
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Reply-To: mikeb@salmon.ee.ubc.ca
Organization: Dept of EE, University of British Columbia
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In article <9792@pt.cs.cmu.edu>, gerry@cive.ri.cmu.edu (Gerry Roston) writes:
> All of this talk about small rovers strikes me as being 
> quite silly.  Let's get real folks! small rovers can not
> accomplish meaningful scientific experiments.  

While the current state of knowledge favors large rovers, the referenced
does not present a convincing argument against the fundamental implausibility
of small rovers.   There are simply far too many assumptions in the
analysis.

> Let's consider a basic issue, power.  One person suggested
> the use of solar panels. The most efficient solar panels
[ calculations omitted ]
> have a mass of about 15 kg/m^2.  For our rover, this amount
> to a mass of 3.75 kg for the solar panels ALONE.

The rover does not have to carry its own solar panels. It may well 
return to a base station to recharge.

> Since this is to be a simple rover, we will assume minimal
> computing requirements, say the equivalent of a single
> MC68020 processor.  To get ball park figures, we can look

This is another assumption.  Far simpler procesors may suffice. 

> A typical number is about 25 W.  Again, let's assume that 

Are there not low-power computers available with considerably lower
power requirements?

> of 1 kg.  To continue the analysis, let's assume that we 
> wish for the computers to remain active during the night.  If

A *major* assumption.  Why should the rover be active during the night?
Especially if a rudimentary vision system is provided (granted, this wouldn't
apply to small rovers, but to midsize ones), wandering about at night
is considerably more dangerous than in the day.

> a capacity of 325 watt hours of power.  Using silver-zinc batteries,
> which are among the most efficient, we find that we need about

How about molybdenum-lithium batteries?

> Keeping with the notion of a small rover, let's assume that the
> rover is 1/2 meter tall, giving a total volume of 0.125 m^3.
> 
> So, where are we now?  We have a rover with solar cells, batteries
> and a computer.  We can supply 34 W/hr of power and we are using
> 26 W/hr.  We also have a mass of 26.75 Kg and have consumed almost
> 10% of the available space; AND WE STILL HAVE NO LOCOMOTIVE SYSTEM
> OR EXTERNAL SENSORS!

The power and weight calculations become quite different given
a different set of assumptions. 

 
> gerry roston, field robotics center
> robotics institute, carnegie mellon university

Mike Bolotski, Department of Electrical Engineering,
               University of British Columbia, Vancouver, Canada 
mikeb@salmon.ee.ubc.ca             | mikeb%salmon.ee.ubc.ca@relay.ubc.ca