Wierd application, hypothetical question.

[Shirley, Mark R]

A stepper is an interesting idea.  I'm assuming the control
circuitry would be far different though.  And the linkage to the
control pin would be complex and/or hard to fabricate, with gears
probably involved.  Actually the newer VW turbodiesels control the 
pin I am trying to control with a stepper actuator to control the
fuel collar.  That would be a neat EFI project.  Most of those pumps
are capable of far in excess of 150HP.  Of course that's more of a 
real EFI project, with requirments of DBW, RPM input etc.

-----Original Message-----
From: Eric Bryant [mailto:BRYANTE at ghsp.com]
Sent: Wednesday, December 06, 2000 1:09 PM
To: 'diy_efi at diy-efi.org'
Subject: RE: Wierd application, hypothetical question.


> From: justin ivan [mailto:vlkslvr at hotmail.com]
> Subject: RE: Wierd application, hypothetical question.
> 
> 
> I assume that maybe by voice coil actuators you mean as in 
> speakers? Either 
> way, .5 to 1" of stroke for an electormechanical solenoid 
> really is asking 
> for too much if you need any considerable force. I could dig 
> out some of the 
> charts relating to stroke vs force that I have hiding but I 
> don't see it 
> happening.
> if it were .25 to .33 or so, you might be able to get away with it.

That's the beauty of a voice-coil actuator - you get a nearly-flat force vs.
displacement curve, while a solenoid will yield some sort of exponential
roll-off as the armature travels from the pole piece (the shape of the curve
depending on a lot of factors, of course).  

With a solenoid, it's often necessary to use some mechanical advantage in
order to keep the armature in the higher-force portion of the travel.  You
start getting non-linearities with increasing mechanical complexity (due to
lash and so on), so this turns into a difficult motion-control problem. 

A voice coil may be a bit easier than a solenoid to work with, but something
like a stepper motor will give a far-greater power density, and I think it'd
be more appropriate for this application.  At least that's where I'd
start...

Eric Bryant
mailto:bryante at ghsp.com
http://www.novagate.com/~bryante 
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