RE: (ET) DC hydraulic pumps [Virus checked]

["Elie, Larry (L.D.)" <lelie ford com>]

Your point is well taken.  

As odd as it sounds, if the motors are wired in SERIES, the current is one 
is the same current as 
the current in the other, so if one motor gets hot and voltage limits, the 
other can't pass any more 
current than the bad actor.  Since the torque is proportional to the 
current, this is the easiest way 
to balance the torques to the screws.

That does not help if there is a mechanical problem, rust or whatever.  
There would have to be some 
provision to turn one screw with respect to the other to re-balance the 
system if a problem occurs.

Larry Elie


-----Original Message-----
From: Pieter Litchfield [mailto:plitch attglobal net]
Sent: Tuesday, May 20, 2003 8:28 PM
To: Discussion List Electrac tractor
Subject: RE: (ET) DC hydraulic pumps [Virus checked]


----- Original Message -----
From: "Pieter Litchfield" <plitch attglobal net>
To: "Yahoo group Gravely Tractor" <gravely-garden-tractors yahoogroups 
com>;
"Dave Reuter" <david reuter iavinc com>
Sent: Sunday, May 18, 2003 8:10 AM
Subject: [gravely-garden-tractors] RE: (ET) DC hydraulic pumps [Virus
checked]



 Dave (et al):

 While I think the idea of electric "lift cylinders" (screw jacks or linear
 actuators) on a front end loader has a lot of merit, here's a problem I
have
 trouble finding a solution to:

 One of the benefits of a hydraulic lift system is that prallel connected
 cylinders stay "in synch" automatically.  Mty lift has a right and left
lift
 as well as a right and left bucket tilt cylinder.  This is necessary since
 the use of a cylinder on each side (1) distributes the load between two
 smaller cylinders and (2) equal force on both lifting arms allows a
lighter
 lifting frame without the assembly "racking" under load.  If, for example,
 the loader had a right side lift cylinder only, it would be easy enough to
 use a bigger cylinder to lift the same amount, but without an equal
 "partner" on the other side, the lifting force would twist the loader
frame
 and possibly cause damage to the tractor as well.  Hydraulic circuits have
 the ability (by laws of physics) to balance the fluid pressure between the
 two lifting cylinders and thus provide equal lifting force to both sides
of
 the frame.

 Now - if we substitute electric linear actuators for those hydraulic
 cylinders, how can we do the same thing?  If the two actuators are made to
slightly different electric or mechanical tolerances, or if the bucket is
 loaded heavier on one side than the other, they may run at very slightly
 different speeds under load.  It won't be long before one actuator is
 positioned differently than the other and exerting a different amount of
 force on the lifitng arm assembly.  The lift frame will rack or the
 actuators will bind and stall.  I did see some paired actuators that had a
 common drive shaft running between two motors to keep them "in synch", but
 this would be awkward in the extreme on a removable bucket loader - the
 common drive shaft would probably have to run under the tractor (possibly
 with universals), where the probability of damage is high, and the loader
 would be difficult to remove.  I also have seen "indexing" actuators and
 controllers - these allow the actuator to move to a pre-determined
position.
 So perhaps a controller for two motors could move them to a predetermined
 position to  raise the lift, which would keep the two actuators
more-or-less
 in synch since at the end of each move they should end up in the same
place.
 Does such a controller exist?

 One obvious answer is to do away with two cylinder or actuators and use
one.
 There are some "real" tractor loader that use but one bucket tilt
cylinder,
 but I am stuck with the idea of two bucket lift cylinders or actuators.
But
 how can you easily keep them "in synch?"

> -----Original Message-----
> From: owner-elec-trak cosmos phy tufts edu
> [mailto:owner-elec-trak cosmos phy tufts edu]On Behalf Of Dave Reuter
> Sent: Monday, May 12, 2003 12:13 PM
> To: Pieter Litchfield
> Cc: elec-trak cosmos phy tufts edu
> Subject: Re: (ET) DC hydraulic pumps [Virus checked]
>
>
>
> Pieter,
>
> If you use a screw nut and not a ball nut the screw nut will hold due to
> the friction in the interface between the thread of the nut and screw.
When
> I used it in that application I mentioned I would load up the screw to 
> the
> 3000 lbs and leave it for hours in this position and it held fine without
> power. The only disadvantage is that it is less efficient and you have to
> power it down as well as up. But it still will be better than all the
> losses due to energy conversions that you described in your email between
> the battery, the electric motor, the hydraulic motor, and the cylinder.
>
> A company I worked for in the past was Warner Electric. They were sold to
> from what it looks like from a internet search Danaher.
>
> Here is a link to the product line for actuators. Hope this helps. There
> seems to be a few people interested so I'll post this to the group.
>
>
http://www.thomsonindustries.com/Sections/products/products_main.asp?PC=8999
> 003&L=False&IT=Contact&GI=1
>
>
>
> Dave Reuter
>
>
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