RE: (ET) Solid state controls

["Phil Trice" <pctrice purdue edu>]

Chris & all,
        I have a data point to offer in this area. When I was in school, I 
worked
for the city's parks dept, and had the opportunity to use a Toro
Groundsmaster tractor. This machine was targeted for mowing around
obstacles. It utilized a single pedal that controlled speed and direction. 
I
think it utilized hydrailics, but gave very smooth control over the speed 
of
the machine, and made it very easy to change direction (to stop going
forward, press the pedal as if going in reverse).
        I'm trying to think of a way to to replicate that efficiency of 
control in
my electric tractor. The real attraction for me is that there was no need 
to
stop the tractor to shift gears, no clutch, and no need to press a separate
brake. It was actually kind of a kick to drive, as I recall.

        -Phil Trice

-----Original Message-----
From: owner-elec-trak cosmos phy tufts edu
[mailto:owner-elec-trak cosmos phy tufts edu]On Behalf Of Christopher
Zach
Sent: Friday, July 19, 2002 10:19 PM
To: jbc_shop coate org; Elec-Trak List
Subject: Re: (ET) Solid state controls


Hm. I've thought about this, and for a tractor, I don't see any advantage 
to
an infinately variable speed control. In fact, I would consider it to be
somewhat of a disadvantage.

When mowing I like to set the speed to a quantum level and forget it. With
an infinite speed control, you never quite know if you're at the best speed
for mowing. Or plowing. Or tilling. With 8 motor speeds plus four gears you
have a range of 32 speeds between 0 and 9 mph. The greatest thing on the 
E20
IMHO is the cruise control lock-in.

Then there's the efficiency. Running full field/full armature is the most
efficient way to go with the elec-trak motors. Use the gears to modulate 
the
speed; don't lose 5%-10% of the power thru a controller (the relays and
solenoids are probably >99% efficient).

Also would need to make sure that any controller could *fully* support
regen. The elec-trak does have significant regen, and dumpstering it is
going to decrease your range and put a significant load on your brakes. 
I've
dropped regen on hills; the brakes have to work very very hard.

Chris