12VDC linear actuator

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:

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:

MPJA also has a 24 volt linear stepper for $8US. You'll have to read the data sheet to see if it will work:

John

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.

Ed

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

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

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

Cheers! Rich

I'd check out Firgelli Automations

they seem to be the cheapest I've seen. I think the lowest force they have is 120N or something around there.

Newt

Joe wrote: