Re: (ET) Solid state controls

["Christopher Zach" <czach computer org>]

Hydrostatics are nice on an ICE based mower because you usually have to run
the engine at full speed in order to keep the blades spinning.

With a 5 speed transmission, that equals at most 4 possible mowing speeds
forward, one reverse. You have to stop every time you switch speeds, and 
you
can't fiddle with the RPMs to adjust speed since the blade will slow down
below mowing speed.

With a hydrostatic transmission, you can have multiple speeds while keeping
the engine RPMs constant for the blades. Very handy on an ICE, but not
relevant for an Elec-Trak.

The E20 and E15 have a total of eight speeds. These work in forward or
reverse at the touch of a switch, in any gear. So you wind up with a
granularity of 32 speeds if you count the four gears.

I'd say that 32 speeds is probably about the same granularity as moving the
lever on a hydrostatic transmission. Even with only eight, you pretty much
cover the range. And since the blades always spin at the same rate, you can
speed up/slow down without disturbing your mowing speed.

Personally, I normally set the cruise control for most of the lawn, and use
speed control on the last bits (like when I am zipping across the yard,
slowing down near bushes, etc). I only shift gears when going back to the
shed. For that, the added expense and complexity of a hydrostatic
transmission and/or electronic control just isn't worth it.

Chris


----- Original Message -----
From: "SteveS" <ssawtelle fcc net>
To: <elec-trak cosmos phy tufts edu>
Sent: Monday, July 22, 2002 8:51 AM
Subject: Re: (ET) Solid state controls


> It probably was hydrostatic, many higher end mowers use it and they are
> nice. I've been wondering what it would be like to couple the ET motor to
a
> hydrostatic transmission. I don't know much about them, though - I fear
the
> hydrostatic isn't very efficient, since I assume it must 'dump' pressure
> when you are at less than full speed. I bet one of you can enlighten us 
> on
> this.
>
> On solid state controls, what kind of electronic control would be
> appropriate for the motor type we have (compound, right?).  Do you PWM 
> the
> armature current, or what? 'Course, as has been mentioned, the present
> arrangement is real efficient - when the throttle is full on.
>
> SteveS
> E12S
>
>
>
> ----- Original Message -----
> From: "Phil Trice" <pctrice purdue edu>
> To: "Elec-Trak List" <>; <jbc_shop coate org>; "Christopher Zach"
> <czach computer org>
> Cc: "Phil C Trice" <pctrice purdue edu>
> Sent: Monday, July 22, 2002 8:22 AM
> Subject: RE: (ET) Solid state controls
>
>
> > 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
> >
> >
> >
>
>