			    TRAVELLER Digest 348

Topics covered in this issue include:

  1) Re: Ground vs Grav
	by Rob_Prior@nynet.nybe.north-york.on.ca (Rob Prior)
  2) Re:Combat walkers
	by "Brendan O'Donovan" <Brendan@odonovan.demon.co.uk>

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Date: 15 Jul 1995 11:16:10 GMT
From: Rob_Prior@nynet.nybe.north-york.on.ca (Rob Prior)
To: traveller@MPGN.COM
Subject: Re: Ground vs Grav
Message-ID: <162779133.56661877@nynet.nybe.north-york.on.ca>

One thing you're forgetting with the cost comparison between ground and grav
vehicles is support infrastructure.  Look at the cost of building and
maintaining roads.  Sure, the cost of a car isn't much, but if you had to pay
for the road out of your own pocket...

(Yes, I'm aware that taxes pay for roads, and most drivers are taxpayers. 
But we're comparing the total cost of two transportation systems here.)

Air traffic control is a big problem with grav vehicles.  So are issues like
privacy.  Solutions include things like altitude restrictions and flyways. 
Flyways are much cheaper than roads - no surfacing required - and if altitude
is restricted to, say, 5m then safety is also quite good.  (Yes, you'll still
have idiots driving, but we already have that now - that's a social issue,
not a technical one.)  On automated control: six simple rules control
collision avoidance in birds, not much smarts needed there.  Even good for
gaming - failing your Piloting roll just means that you're forced the wrong
way, not crashed.

There's a HIWG document that spends six pages dicussing these issues.  These
are just some highlights.

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Date: Sat, 15 Jul 1995 10:46:21 GMT
From: "Brendan O'Donovan" <Brendan@odonovan.demon.co.uk>
To: traveller@MPGN.COM
Subject: Re:Combat walkers
Message-ID: <46@odonovan.demon.co.uk>

:From the message dated Friday 14, July 1995 :

> >>3)  Would installing contragrav improve the speed of the vehicle
> >>(after all, with contragrav on, it doesn't weigh nearly as much)?
> >
> >I don't think so. By definition I would assume a walker requires 
> >friction with the ground to push itself forward. Turn on contragrav 
> >and you might find that pushing against the ground causes the 
> >walker to tumble rather than staying upright.
> 
>    The assumption is that you would turn the contragrav on at
> a lower setting--say 50 percent of full power, thus decreasing
> the weight of the vehicle by 50 percent (or close anyway).
> 

Contra grav means that you can jump higher, but making the walker lighter will 
not improve your ground speed, as gravity is perpendicular to travel, so weight 
doesn't affect acceleration. Mass, on the other hand does affect acceleration, 
but this is not cancelled out by contra-grav. As suggested, reducing weight 
will, if anything, slow the walker down. This is because the walker can only 
move its legs so fast before the foot slips, this maximum speed is determined by 
the amount of friction with the ground. The more weight, the more friction, so 
the higher speed you can reach. Apart from jumping, contra grav would have one 
other use, it would make it easier to build a stable structure for the walker, 
by reducing stress on the legs from the weight of the upper body.

I like the idea of walkers, but they may not be as agile as anime films portray. 
The Dante robot, built to climb down into a volcano, took several days to reach 
the bottom, because of the care necessary in placing its feet. I can't remember 
the story exactly, but I've got a feeling that it fell over in the end anyway. 
The Battletech walkers are not good examples of hard science fiction, they're 
far too large to be useful as all terrain vehicles, in woods they'd trip up on 
trees, and in water they'd fall over because of drag on their legs, but slightly 
smaller walkers like the Star Wars AT-ST could have some tactical uses.
> 
> --Harold
> 

-- 
Brendan 

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End of TRAVELLER Digest 348
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