12VDC linear actuator

[Joe]

I am working on a robotics project and need to buy or build a 12VDC linear
actuator with a stroke of about 3-4 inches (~10cm) and a force of between 30
to 40 Newtons (about 6 or 7 lbs).

I have googled for linear actuator, and visited the grainger site, but they
are all 24VDC minimum and very expensive. I know I could probly build one
from a low rpm dc motor, or stepper motor, but I am not sure how.

Any suggestions for sources (I would rather buy one if the price is right),
links, or other information would be greatly appreciated.

TIA,
Joe

 

[John]

How linear does it need to be?

Automobile windshield wiper motors have low speed and high torque -
you just need to convert the 90 or 180 degree movement of the arm into
straight-line motion (the same way the wipers are driven).
The motor (including the gearcase and limit switches is under $20US:
http://www.sciplus.com/category.cfm?subsection=18&category=172

A slightly more expensive device is a stepper motor with a threaded
shaft, which is also known as a linear stepper or linear step motor.
This will require some electronics to operate the stepper motor and
some limit switches to define the ineer and outer travel limits. A 5
volt stepper motor can be powered from a 12 voult source via a
regulator. Here's on for $25US:
http://www.mpja.com/productview.asp?product=16052+MS

MPJA also has a 24 volt linear stepper for $8US. You'll have to read
the data sheet to see if it will work:
http://www.mpja.com/productview.asp?product=16385+MS

John

 

[ehsjr]

I am working on a robotics project and need to buy or build a 12VDC linear
actuator with a stroke of about 3-4 inches (~10cm) and a force of between 30
to 40 Newtons (about 6 or 7 lbs).

I have googled for linear actuator, and visited the grainger site, but they
are all 24VDC minimum and very expensive. I know I could probly build one
from a low rpm dc motor, or stepper motor, but I am not sure how.

Any suggestions for sources (I would rather buy one if the price is right),
links, or other information would be greatly appreciated.

TIA,
Joe

You also need to know the speed you need for the actuator
travel. You can build a crappy one with a threaded rod
and nut. Spin the rod, prevent the nut from turning, and
it will move linearly. Use the tpi (turns per inch) and
rpm to determine speed. The rod will reduce the speed
and increase the force, but friction losses will be high
when using a hardware store threaded rod and nut.

H&R sells a lead screw and follower. cat # TM94MEC2601
Just connect a motor to it and you're good to go, if
it's not too long for you (17").
Being made for the purpose, friction losses are low.
http://www.herbach.com/

Ed

 

[Joe]

How linear does it need to be?

Automobile windshield wiper motors have low speed and high torque -
you just need to convert the 90 or 180 degree movement of the arm into
straight-line motion (the same way the wipers are driven).
The motor (including the gearcase and limit switches is under $20US:
http://www.sciplus.com/category.cfm?subsection=18&category=172

A slightly more expensive device is a stepper motor with a threaded
shaft, which is also known as a linear stepper or linear step motor.
This will require some electronics to operate the stepper motor and
some limit switches to define the ineer and outer travel limits. A 5
volt stepper motor can be powered from a 12 voult source via a
regulator. Here's on for $25US:
http://www.mpja.com/productview.asp?product=16052+MS

MPJA also has a 24 volt linear stepper for $8US. You'll have to read
the data sheet to see if it will work:
http://www.mpja.com/productview.asp?product=16385+MS

John

Hi John,

Thank you for the suggestions, I have done business with American Sci and
Surplus before. As far as 'how linear', well, not rotary is about all I can
say at this point. I don't know what you mean by how linear. Picture a
piston in an internal combustion engine, only this reciprocates in the
horizontal direction. I could probably put some guides on either end to keep
it from flopping around too much.

I like the idea of the auto windshield wiper motors, and AS&S is cheap
compared to what I was finding in the auto parts stores today.

Thanks again for the info,
Joe

 

[Joe]

You also need to know the speed you need for the actuator
travel. You can build a crappy one with a threaded rod
and nut. Spin the rod, prevent the nut from turning, and
it will move linearly. Use the tpi (turns per inch) and
rpm to determine speed. The rod will reduce the speed
and increase the force, but friction losses will be high
when using a hardware store threaded rod and nut.

H&R sells a lead screw and follower. cat # TM94MEC2601
Just connect a motor to it and you're good to go, if
it's not too long for you (17").
Being made for the purpose, friction losses are low.
http://www.herbach.com/

Ed

Hey Ed!

It's been a long time. I was injured about a year ago and had to get out of
the wild animal business. Now you probably know who I am. I will check out
the link and see, but 17" sounds like it may be unwieldy. Maybe I can cut it
to size. All I know is that I need a low rpm DC (so I can adjust the rpm
with the voltage) motor, put a cam on the shaft, connect a rod, and see what
happens. Then I can refine it from there.
Good to know you're still here, thanks for the reply.

Joe

 

[ehsjr]

Hey Ed!

It's been a long time. I was injured about a year ago and had to get out of
the wild animal business. Now you probably know who I am. I will check out
the link and see, but 17" sounds like it may be unwieldy. Maybe I can cut it
to size. All I know is that I need a low rpm DC (so I can adjust the rpm
with the voltage) motor, put a cam on the shaft, connect a rod, and see what
happens. Then I can refine it from there.
Good to know you're still here, thanks for the reply.

Joe

Hi Joe,

Yes I know who you are - sorry to hear of the injury.
When you control the motor speed, you'll use PWM.
It's easy & effective. Controlling the voltage is
a non-starter for this.

Regarding rpm and speed: you want say 4" of travel.
The leadscrew at H&R has 18 tpi as I recall, so to
travel 4", the screw must turn 72 revolutions. If
you have a 1000 rpm motor, the actuator will travel
4" in 4.32 seconds. This only applies to the linear
acutator using the leadscrew. With a cam on a shaft
driving a rod, you'll need some gearing. H&R sells
a lot of motors - you may find something there that
will work for you. My homemade linear actuator
raises and lowers a double hung window, using a motor
I got from them for $5.95.

Ed

 

[Rich Grise]

Hey Ed!

It's been a long time. I was injured about a year ago and had to get out of
the wild animal business. Now you probably know who I am.

Dewd! Are you that guy that got his ass kicked by a wild deer? ;-D

Cheers!
Rich

 

[Troy Newton]

I'd check out Firgelli Automations (http://www.FirgelliAuto.com), they
seem to be the cheapest I've seen. I think the lowest force they have
is 120N or something around there.

Newt