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).

Linear actuators 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 a linear actuator that 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 a linear actuator that can provide the kind of
performance I am looking for for a couple hundred dollars?

"Eric Anderson" wrote in message
ps.com...
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).

Linear actuators 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 a linear actuator that 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 a linear actuator that can provide the kind of
performance I am looking for for a couple hundred dollars?


Look at: http://www.firgelliauto.com/default.php?cPath=86

For your application, I'd consider air cylinders. Exhaust restrictors to
control speed, stops on the rods for location, solenoid valves for the
electric interface. Very low cost,especially if you look at surplus items.
Good for many 1000s of cysles without maintenance



Karl

Eric,
The cost can be attributed to feedback. Not using feedback can be dangerous
to people or machinery. You can use digital or analogue feedback. Neither is
cheap. At the very least, you must use limit switches. Please also note that
steppers are very wasteful of energy and can slip when transporting loads
during acceleration and deceleration. Hydraulic, pnuematic and pulse driven
PM Motors are good choices, some require brakes, all require feedback.
Steve

"Eric Anderson" wrote in message
ps.com...
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).

Linear actuators 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 a linear actuator that 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 a linear actuator that can provide the kind of
performance I am looking for for a couple hundred dollars?

Try Surplus Center.

Pete Stanaitis
----------------

Eric Anderson 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).

Linear actuators 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 a linear actuator that 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 a linear actuator that can provide the kind of
performance I am looking for for a couple hundred dollars?

Karl Townsend wrote:
For your application, I'd consider air cylinders. Exhaust restrictors to
control speed, stops on the rods for location, solenoid valves for the
electric interface. Very low cost,especially if you look at surplus items.
Good for many 1000s of cysles without maintenance

Given you want to position your load, not just push it into a stop, I'd
avoid air. Air is compressible, so you're essentially pushing your load
with a spring. When your feedback system says "done", you still have a
cylinder full of pressure air, which will keep it moving.
As others have said, some kind of electric motor system (screws, wires &
pulleys, etc.) looks good.

On Fri, 02 Nov 2007 21:04:26 -0700, Eric Anderson
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).

Linear actuators 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 a linear actuator that 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?

Precision, speed and power. Given your light load, low speed, and
low accuracy requirement, I see no reason why threaded rod and a small
motor wouldn't work acceptably.

With a 20-pitch thread, torque would be minimal with 3 lb thrust but
speed would be about 1500 RPM to make your speed requirement. That's
a bit fast for a steppermotor, though not out of the question. You
could also use a DCPM motor with simple rotary encoder feedback. A
suitable optical encoder is about $18 at Digi-Key. You'd also need
limit switches at ends of travel.

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