From: jimc@isc-br.ISC-BR.COM (Jim Cathey)
Newsgroups: comp.human-factors
Subject: Re: Very poor human interface on Kubota tractor
Date: 15 Apr 92 02:25:56 GMT
Organization: ISC-Bunker Ramo, An Olivetti Company

In article <RWK.92Apr13000253@taunton.crl.dec.com> rwk@crl.dec.com (Bob Kerns) writes:
>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.

Pretty much true.  Our tractors had these features.

>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.

I would not want to buy a tractor that didn't have separate
brakes for the wheels, or a differential lock.  Keep in mind
that it's the rare tractor indeed that you could get a speeding
ticket with, anywhere.

>In addition, many tractors (not the Kabota model you site)
>have front wheels close together, leading to an almost
>tripod-like setup.

Tripod steering comes in extremely handy in tight quarters.  With
four wheels, you can't actually pivot on one wheel without making
a hell of a mess with the front wheels scooping dirt, assuming they
are free enough to slide anyway.  The single front wheel (pair) has
180 degrees of turning freedom.  On the other hand, they _are_ less
stable, and might squash some row crops.  We had one of each.

>  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.

This is often the case, the parking brake is just a ratchet lock on one
of the brake pedals, just like the ratchet that exists on most parking
brake handles on cars.  You usually don't need to lock the brakes
together, unless you're really on a nasty hill or otherwise need to
really nail the beast down.

>   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.

On our diesel tractor, the key didn't stop the motor, you had to pull
_up_ on the foot throttle to kill the engine.  That or pop the clutch.
Not being electrically dependent is nice in cold weather when the
battery dies.  It is a plus for a tractor to be able to continue to run
even when it is half-dead.  A tow-start (or park it on a hill) and
you're running.  All in the best spit-n-baling-wire tradition.

I would surmise that the Kubota had an electric fuel-OFF solenoid, that
wouldn't kill the engine if the battery was dead.  (Most diesel cars
have an electrical fuel-ON solenoid, that won't let the car run if the
battery is dead.) The pull was a mechanical link to the injector pump.
Just a guess, mind you.  Ayep.

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