Re: cost of linear actuators

On Sun, 04 Nov 2007 13:26:05 -0800, Eric Anderson <eganders@xxxxxxxxx>
wrote:

On Nov 3, 6:51 pm, default <defa...@xxxxxxxxxxxxx> wrote:
On Fri, 02 Nov 2007 21:02:01 -0700, Eric Anderson <egand...@xxxxxxxxx>
wrote:





I have an application where I have to move a 3 lb object in a 3 ft
cubic space. I am not looking at high performance or high accuracy.
It can take as much as 30 seconds to traverse the 3 ft distance and
the accuracy could be no better than 0.020 or 0.050 inch (possibly the
spec could be even looser).

Linearactuators would appear to be the best solution, but I am
finding that they are hundreds or even thousands of dollars. The
product I want to build will have to cost no more than $2,000 for a 3
axis device with controller, overhead and profit.

What is it in alinearactuatorthat costs so much that you could not
build a low cost version using a threaded rod, servo or stepper motor
and an extruded frame for a lot less?

Does anyone know of alinearactuatorthat can provide the kind of
performance I am looking for for a couple hundred dollars?

You certainly can build a "lead screw and follower"actuatorfor a lot
less than thousands - motor and couple of limit switches?

Or motor with a disk and offset pin like a crankshaft to translate
rotary intolinearmotion.

Don't overlook air cylinders. 3 feet is expensive for a cylinder but
if you can get by with a shorter cylinder with mechanical advantage
they have lots of advantages.

My OM put a satellite dish actuators on his drive way gates. Lot of
hassle running 120 out there and weather proof and in code. All kinds
of problems when something kept the gate from closing or opening
completely (like snow, ice, leaves, debris) and there was the overkill
necessary to make it work. A few air cylinders fixed it with no
hassle - 1/4" OD tubing, the actuators can stay stalled all day long
with nothing to burn out, speed is easy to adjust with a valve,
pressure is also easy to adjust. The only hard part was finding a
pressure switch that would work with the 30 PSI diaphragm pump we had
- the rest of it was hardware store parts.
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I understand that I could design the components myself. Ultimately I
expect to be building low production quantities of these and was
hoping that a linear actuator/controller combination might exist in
the marketplace so I don't have to redesign the wheel. It will be
required to work in an office environment. I have designed high-speed
line printers and automotive sensors in my career, so I could build
one of these. However, I don't want to find (as I have in the past)
that a simple, low cost solution exists that I could use out-of-the-
box and that is already being built in production quantities.
Ideally, I would like to have 3 linear actuators, 2 of which would be
on an X-Y base and the 3rd that would travel vertically from this X-Y
base (call this the Z axis). I would need to control the three with a
controller that would be programmed from a computer program I would
write for the specific application I have in mind. (I can't divulge
the purpose of this device at this time in case there are patent
issues). I need to be able to represent the position by an icon or
representation of the position using a diagram on the computer
screen. I would have be able to return to previous position (by
storing the X-Y-Z coordinates).

Many years ago there was a demonstration robot that could do that,
although probably couldn't swing three pounds around in its gripper.

It came with a keyboard and you programmed it by laboriously slewing
to the coordinate you wanted one axis at a time, storing that position
then on to the next one. When you played it back the robot would move
in all axis at the same time to get to the coordinate that you put in
memory (one axis at a time). It could also pause for a predetermined
time. It and had an RS232 connector. Forget what it was called. It
was something like $300+ back in the age of DOS.

I only came across it at work and had it do things like dial my phone
and throw switches. No idea why the company bought it. The precision
was excellent - geared stepper motors moving push pull braided steel
cables.

I'm not aware of any ready made, inexpensive, linear positioners that
meet your specs. Maybe some of the robotic or radio control groups?

Lots of hobby interest in modifying the mechanics of scanners to
become X - Y tables - but not 3 foot swings.
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