From: rwk@crl.dec.com (Bob Kerns)
Newsgroups: comp.human-factors
Subject: Re: Very poor human interface on Kubota tractor
Date: 12 Apr 92 15:02:56 GMT
Organization: Cambridge Research Lab, Digital Equipment Corp.

In article <j!sjabh.nagle@netcom.com> nagle@netcom.com (John Nagle) writes:

   From: nagle@netcom.com (John Nagle)
   Date: 9 Apr 92 16:33:54 GMT
	  The manual for current model Kubota tractors indicates how bad
   things can be outside the computer field.

Let me put this into context (but not justify it!).  My
purpose here is just to explain the situation for all
the folks who've never been near one, and illustrate the
different design constraints.  I don't mean this to
detract from the validity of your point at all.

The stuff you describe here has all been standard practice
on tractors for I'd guess fifty years.  The tractors I
encountered it on were pretty old 30 years ago, anyway.

To make sense of this, you need to understand that having
the brakes locked together is the normal configuration.
You unlock them when performing certain types of maneuvers
involving *very* sharp turns, often involving pivoting
around one rear wheel or the other.

Also, realize that tractors are not assumed to be used
by unskilled operators.  They're recognized as dangerous
heavy equipment, and I know I got a lot of safety
instruction and supervision before I was ever allowed to
even go near one, let alone operate one.

All that aside, this really all stems from engineering
constraints from a half-century ago, and could certainly
be done better now.  Still, I've never heard of anyone
being hurt due to accidents due to the brakes.  The
accidents I've heard of have come from tipover due to
steep hills, or by trying to pull stumps with the
pull coming from too high. i.e. not below the level of
the rear axle.  When confronted with enough load that
it can't rotate the wheels, it then proceeds to rotate
the tractor instead).

Tractors are low-speed devices by nature.  They must have
high centers of gravity to clear the crops (and mud, etc)
in a field.  They must be able to make extremely sharp
turns, far sharper than any road vehicle.  They must be
able to apply high torque to both wheels, even if one
wheel has no traction.  These requirements run completely
counter to safe design of a road vehicle, or even a safe
off-road vehicle.

In addition, many tractors (not the Kabota model you site)
have front wheels close together, leading to an almost
tripod-like setup.  This is superior in some situations for
fitting into certain crop row configuration, and to provide
tripod-stability (i.e. you don't get the four-legged-chair-
with-a-short-leg syndrome).  But it makes for easier tipping.

	   A roll bar is optional.

-- But a hell of a good idea, even though it may get in
the way a lot.

	  Braking involves two pedals and a lever.  The pedals apply brakes 
   separately to the left and right rear wheels.  A latch allows locking both 
   brake pedals together.  The lever operates the parking brake, but to
   operate the parking brake, both pedals must be latched together and
   depressed, the parking brake lever pulled, and the pedals released.
   Unclear what happens if this sequence is not followed.  

I believe just one of the wheels is locked, probably the left.

   positions, this being a Diesel.  The manual states that turning the key to
   "stop" will usually, but not always, stop the engine, and a separate
   emergency off pull switch is provided if the key doesn't work.

I'm a little surprised that the key switch turns off the engine at
all.  All it turns off on my boat is my alternator and the gauge
panel!  Diesels don't need electricity to run.  Just air, clean
fuel, lubrication, and cooling.  Generally, on boats, the shutoff
is completely separate from the starter circuitry.
Newsgroups: comp.human-factors