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Screw Type Linear Motion? Stepper Motor?

09/02/2015 6:53 PM

Hello: I hope you can help me find what I am looking for. Please excuse that I do not speak Engineer. I am trying to build a device to press a button, by extending a shaft, when power is applied and hold it down until power is stopped. The normally closed side of the momentary switch will automatically reverse the polarity to retract afterward. The finished device must be portable and lightweight. It will be signaled by a radio control package. I have the electronics in place for 12V R/C including a receiver / relay, but finding a subdevice to actually turn current into linear motion seems to be something reserved for big, heavy applications and highly technical fields. There has to be a simple product out there so I am asking around. What I need to do is produce about 7lb or 30N force through less than a half inch linear travel and hold it there until the control button is released. I can adjust the mounting position of the actuator in order to fine tune that dimension. Suggestions put to me have been "Stepper Motors with Screw Jack" and Stepper Motors with Captive Shafts" which, judging by what I see online, amount to the same thing. Solenoids have not worked because they do not produce much force except at the end of the stroke. So they will hold the button, but won't push the button. I DO NOT want to use a lever attached to a motor shaft as that adds slop to the system. I want a direct linear pressing of the button. It seems that manufacturers offer the right type of devices, but those I see are designed for much larger and heavier work than what I am trying to do. I am hoping to find smaller ones or that you can point me to a source. I am currently using a 12v battery but any light weight power source will work. The actuator must be no more than about 2 inches in any frame dimension. Thank you for your kind consideration of a simple hobbyist project.
Tom

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#1

Re: Screw type linear motion? Stepper motor?

09/02/2015 6:58 PM

sounds like a gun trigger for a drone

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#4
In reply to #1

Re: Screw type linear motion? Stepper motor?

09/02/2015 10:25 PM

...or worse, a "dead-man switch" detonator for an IED. Sorry, I'm not going farther on this one.

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#2

Re: Screw type linear motion? Stepper motor?

09/02/2015 7:35 PM

How about a window motor or antenna motor as used in cars? Maybe see what your local auto parts store has.

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#7
In reply to #2

Re: Screw type linear motion? Stepper motor?

09/03/2015 9:24 AM

Thank you. I will look into that.

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#3

Re: Screw type linear motion? Stepper motor?

09/02/2015 8:29 PM

Have you looked into hobby RC vehicle actuators? They may do the trick and are simple to operate and relatively inexpensive.

What exactly are you trying to actuate? Is weight a problem? Seriously, 30N of force and such a small linear travel and package using radio control really does sound like a drone gun trigger.

Please provide more information for clarification.

Jack - Defence Contractor (among other things)

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#5
In reply to #3

Re: Screw type linear motion? Stepper motor?

09/03/2015 9:10 AM

Good God! No, release switch for an animal cage. We do wildlife management. That way I can let skunks out without being right near them. Cages are already rigged with pushbutton releases.

I would tend to think terrorists wouldn't be looking for advice in this venue, but then again, the world is full of whackos. I am sure it won't be long before what you are talking about actually happens. They already have ones that will drop paint balls and whatnot. How long before somebody adapts that to... who knows what.

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#10
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Re: Screw type linear motion? Stepper motor?

09/03/2015 10:24 AM

Thanks for the feedback, you would be surprised at some of the "requests" that come through here! So you want a way to push a spring loaded button? How about a picture or two of the cage and release mechanism? If not then the cage manufacturer and model number would help us understand the intricacies of mounting and controlling the depth of throw, etc.

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#12
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Re: Screw type linear motion? Stepper motor?

09/03/2015 3:48 PM

The reason we ask is because it has already been done recently and reported by the media, so now lots of people know and are likely trying too.

Some of those large RC servos for large model planes may work, and the robotics servos would but the cost and physical size is likely going to be prohibitive for this particular application.

Have you considered just modifying the cage locking mechanism instead? Perhaps changing it to a spring loaded draw out pin that doesn't require a lot of effort to move in and out? Then even a simple solenoid would work.

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#17
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Re: Screw type linear motion? Stepper motor?

09/03/2015 7:33 PM

Maybe you should consider having your assistant perform the animal releases so that they can become fully competent and experienced?

I have had several "assistants" that I would definitely recommend for the job.

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#25
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Re: Screw type linear motion? Stepper motor?

09/04/2015 4:18 PM

Hi. I have a trap I have used frequently for small game transport. Occasionally, wind up with a skunk in it. All I have done is point the trap gate towards the nearest wooded area and opened the trap. The skunk toddles off announcing it's indignation of being in the trap. I have never been sprayed.

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#6
In reply to #3

Re: Screw type linear motion? Stepper motor?

09/03/2015 9:23 AM

Thank you. They don't seem to make one strong enough. The ones for things like airplane ailerons produce only fractions of an ounce of force. I need about 7 pounds. Anything I have found producing that much force then jumps up to things designed to shove auto parts around in a factory. They produce hundreds of pounds of force and cost thousands of dollars. If you know of an R/C supplier who has one suitable I will be grateful for the lead. It is my guess that as the technology for these "drones" grows, and they start making the really big ones for places like Amazon and what not, then parts like this will become available. Scaled up.

Thanks,

TB

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#8

Re: Screw type linear motion? Stepper motor?

09/03/2015 9:38 AM

How about a small rack and pinion arrangement, driven by a small 12V gear motor?

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#15
In reply to #8

Re: Screw type linear motion? Stepper motor?

09/03/2015 5:03 PM

I guess until the OP responds to a few of our questions, we're just pi**ing in the wind!

A few follow questions too:

  • Is there a firm size constraint? I know you stated 2" x 2" but can it exceed those dimensions?
  • Can you post a picture of where you want to install it on the cage?
  • Does it have to hold the button in or can it just activate it and return to the "safe" position?
  • A 12 VDC gear motor with a simple cam may work also?
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#9

Re: Screw type linear motion? Stepper motor?

09/03/2015 10:05 AM

Tom,

Where are you located?

I do feral cat trap / spay-neuter / release so I understand where you're coming from.

I have seen a lot of stepper motor linear positioning screws drives and they may fit your size requirements.

Let me know and maybe we can figure out a solution?

The motor below is 3" OAL and about 1.5" OD and runs off 5-9 volts but requires stepper motor driver circuitry

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#13
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Re: Screw type linear motion? Stepper motor?

09/03/2015 4:34 PM

What is the source for these? I can think of a couple of applications in my work

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#22
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Re: Screw type linear motion? Stepper motor?

09/04/2015 9:44 AM

Ebay!

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#11

Re: Screw Type Linear Motion? Stepper Motor?

09/03/2015 10:26 AM

http://www.mcmaster.com/#electric-actuators/=ys0hhf

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#14

Re: Screw Type Linear Motion? Stepper Motor?

09/03/2015 4:36 PM

Linear actuator solenoid?

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#16
In reply to #14

Re: Screw Type Linear Motion? Stepper Motor?

09/03/2015 5:06 PM

He said he tried a solenoid but it did not have the force required!

I know he could try a different one but he is working with 12 VDC R/C controllers and it may not have the available current needed to push a heavy magnet?

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#20
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Re: Screw Type Linear Motion? Stepper Motor?

09/04/2015 4:58 AM

He quoted 7 lbf, the one I linked to gives 9.9 lbf.

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#23
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Re: Screw Type Linear Motion? Stepper Motor?

09/04/2015 9:47 AM

I stand corrected. I do know that it takes a bit of current to get those solenoids to fully actuate.

I don't think he has the needed current available with the R/C equipment!

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#24
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Re: Screw Type Linear Motion? Stepper Motor?

09/04/2015 9:55 AM

The supplier states 400mA, I don't know if that's high from the point of view of R/C stuff.

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#18

Re: Screw Type Linear Motion? Stepper Motor?

09/03/2015 7:40 PM

I was once a housemate at Cornell University with a guy who was studying skunks. Once in a while he got sprayed. One of the best neutralizers is tomato juice.

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#19

Re: Screw Type Linear Motion? Stepper Motor?

09/04/2015 4:05 AM

Add a second lock to the door in the form of a 12V DC magnet and a manual override mechanism for the existing lock. During transport and normal operation use the existing lock. When the cage is set in position for a release, energize the magnet to lock the door and override the existing lock. Retire to a safe distance and de-energize the magnet to release the door. The magnet is energized for only a short time so can be powered by battery. When the cage is empty the existing lock can be reset manually. A "Single Door Electric Magnetic Lock 350lb Holding Force for Access Control" is available on e-Bay for £22.60 (about $35) + p&p (Seller information " homegarden2012 ") This product was the first hit on Google search engine (no recommendation implied) but there must be many similar products available.

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#21

Re: Screw Type Linear Motion? Stepper Motor?

09/04/2015 9:02 AM

If you enjoy building little contraptions, this might work... You would need a small electric motor (from a hobby shop or your kid's battery-operated toy), a length of threaded rod (a long threaded bolt would work), a nut with the same threads as the threaded rod, and two small gears. Mount one gear on the motor shaft. Drill a hole in the center of the other gear, large enough so it will slide freely on the threaded rod. Mount a nut to this gear. Make sure it's centered. Mount the contraption to the cage so that when the motor turns, it will turn the gear & nut. The gear and nut must be free to spin, but not free to move linearly. The threaded rod will ride back and forth along the spinning gear & nut. When the motor spins clockwise the threaded rod will move one direction (linear) and when it's reversed the threaded rod will move the other direction. (It's hard to describe this in words.)

I coached a high-school Science Olympiad team several years ago. There were events where they had to build things that were powered by mousetraps, battery motors, etc. It really was great fun! I remember several contraptions where threaded rods moved along spinning nuts to convert rotation to linear motion.

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#26
In reply to #21

Re: Screw Type Linear Motion? Stepper Motor?

09/04/2015 4:29 PM

LOL, What you are describing it indeed a screw jack. They make these things for all kinds of jobs. I am just looking for one scaled to what I need to do. That was the basis of the original post. What I have come down to is that nobody seems to actually make the size I want. Probably no commercial market. So I think I will try making one, but a little simpler than you describe. I found a plan on some hobby website and did the palm slap forehead thing. Now if I can find a motor already coupled to a threaded rod...

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#27
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Re: Screw Type Linear Motion? Stepper Motor?

09/04/2015 4:35 PM

Look on eBay.. I found tons of them!

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#28

Re: Screw Type Linear Motion? Stepper Motor?

09/04/2015 4:35 PM

Check this Site/blog for Electric Linear Motor Information. If not go to Web and look for Electric Linear Motor there are quite a few suppliers for these devices. Address:http://www.designnews.com/document.asp?doc_id=272441&

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#29

Re: Screw Type Linear Motion? Stepper Motor?

09/05/2015 10:41 AM

Seems over complicated? Just to release a gate?

I had similar with chickens who needed to be let out early in the mornings.
(having been safe on their perches from foxes etc..) and far too early for this sleepy head!

So I tied a weight with string, over a cotton real pulley, to raise the trap door when the first
chicken stepped onto the hinged release board (located inside) in front of the trap door.
A very simple arrangement for a trap door which admittedly, had to be closed (reset)
each evening, after all the chickens had retired for the night. (no problem)

Every morning they regularly let them selves out with no service from me!
The neighbours were amused, but with no power supply nor expense, it worked.
Give it a try?

jt.

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Went down this morning to the DHSS to sign my Dog on.

The woman said, "Dogs are not eligible to draw benefit".. I explained to her
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She looked in her policy book to see what it takes to qualify.

He gets his first cheque on Friday.

Damn this is a great country.

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#30
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Re: Screw Type Linear Motion? Stepper Motor?

09/05/2015 12:02 PM

That's great! Gravity is both reliable and free. Technically, I guess it's not free, since you had to lift the weight up every evening. But it's an extremely efficient and reliable way to store energy!

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#31

Re: Screw Type Linear Motion? Stepper Motor?

09/07/2015 1:42 AM
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#32

Re: Screw Type Linear Motion? Stepper Motor?

09/07/2015 5:42 PM

Try these guys: https://www.firgelliauto.com/

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