Controller Limitations

On Mon, 28 Jan 2008 14:00:15 -0800, pnachtwey wrote:


I shouldn't put things down in such an offhand manner, because I don't
have a lot of experience with things that come in boxes.

I'm currently struggling with a Teknic controller that doesn't seem to
want to let me hard limit the motor current, and which (at least I very
much doubt) will let me hard limit the current input into the box.

I'm used to control systems designs that start with a big blank
whiteboard, a difficult target to achieve, and a set of very clever
circuit designers, mechanical engineers, software engineers, and
component vendors.  So anything that doesn't give me total control over
the schematic and code comes across as being "limited to a frustrating
degree".

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

Tim Wescott wrote:

I wouldn't trust a PM motor to a controller that can't somehow limit the
drive current. Typically, current more than seven times the long-term
rated maximum current will demagnetize it nearly instantly. Performance
is greatly curtailed if the overload protection is something other than
a hard limit.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Wouldn't the current limit be in the drive?  Usually the controller
outputs +/- 10volts.  It would seem to me the current limit would be
in the drive and the voltage limit in the controller.


Don't you feel like you are re-inventing the wheel over and over.  It
takes a lot of effort to design a motion controller which all the
interfacing, sofware and diagnostics. I find it hard to believe you
can't find a motion controller some where that will do what you want.

Peter Nachtwey

On Mon, 28 Jan 2008 19:44:49 -0800, pnachtwey wrote:


When one needs to be round, another 'U' shaped, yet another rectangular
with a big bite out of one corner, and the fourth trapezoidal, when they
all go into a big sealed box that has to sit out on a runway in the
desert and operate even when the sun is shining down...

One makes custom.

There is a surprising number of applications for closed loop control that
doesn't fit into the traditional 'square box' market.  Mostly it's either
extremely critical applications (like the one cited above), very space
constrained applications, or high-volume applications (I suspect that
anything that's going to ship more than 100 units a year is getting up to
the point where it's more economical to roll your own; I should see if I
can pin that down).

At any rate, the actual control software is usually dwarfed by the rest
of the software on a board; in a custom application you can spend as much
on an interface board to translate between your systems internal
communications and an 'off the shelf' part as you would just implementing
the whole dang thing yourself.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html