2 questions about solenoids and servos

Hi everyone,

so, as my title said, I would have 2 questions about solenoids and servos.

I need to use small 12v solenoids that can hold a push position for several minutes. But there is so many different models of solenoids that I can't find which ones can do that (without risk).
Could you please tell me what I need to search for?

About the servos, I would like to know if 270° servos are controlled in position like 180° servos or in speed like 360° servos?

Thanks in advance for your help.

Saynomore:
About the servos, I would like to know if 270° servos are controlled in position like 180° servos or in speed like 360° servos?

Post a link to the 270° servos you are thinking of using? I suspect it has position control.

The phrase "360° servo" is confusing. I think you mean a continuous rotation servo. However it is possible to get servos that move through about 360° only (i.e. one rev max) with position control. You can also get sail winch servos that can do about 3 revs with position control.

...R

Solenoids are current operated devices. So they will get hot in continuous duty use. Let that be your key in searching for which one to use.

Paul

Robin2:
Post a link to the 270° servos you are thinking of using? I suspect it has position control.

The phrase "360° servo" is confusing. I think you mean a continuous rotation servo. However it is possible to get servos that move through about 360° only (i.e. one rev max) with position control. You can also get sail winch servos that can do about 3 revs with position control.

I'm thinking of something like this model
About the 360°, that's exactly what I meant. But I thought that 360° servo was necessarily continuous servos. I ignored that some of them had position control. That's great !
Also, I didn't know the existence of sail winch servos and they seem really interesting indeed (but pricey).
Thanks for these informations.

Paul_KD7HB:
Solenoids are current operated devices. So they will get hot in continuous duty use. Let that be your key in searching for which one to use.

That's precisely because I know they can get hot that I ask for advice. I previously searched for continuous duty solenoids but the only thing I could find was some sort of car devices...

Saynomore:
I'm thinking of something like this model

There is not much info on that website. Maybe you can post a link to the servo manufacturer's website. Or if it is a clone of another make post a link to the website for the original.

...R

How big is "small"? A car door lock solenoid isn't actually a solenoid. It's a geared motor driving a rack and pinion. It holds position (against moderate loads) with no power. Should be easy to pick up cheaply on ebay.

Have you considered using a servo with a cam to push the button? Just stopping the servo rotation will keep the button pressed. You are already specifying servos for some operation.

Paul

Robin2:
There is not much info on that website. Maybe you can post a link to the servo manufacturer's website. Or if it is a clone of another make post a link to the website for the original.

Unfortunately I can't find more details or its tech sheet anywhere...

MorganS:
How big is "small"? A car door lock solenoid isn't actually a solenoid. It's a geared motor driving a rack and pinion. It holds position (against moderate loads) with no power. Should be easy to pick up cheaply on ebay.

I didn't talk about car door lock. Look at the results I get.

About the size, I need something around 20mm x 20mm x 40mm. A travel of 10mm should be enough.

I cannot use a DC motor here...

Paul_KD7HB:
Have you considered using a servo with a cam to push the button? Just stopping the servo rotation will keep the button pressed. You are already specifying servos for some operation.

...and I cannot use a servo either.

You are designing yourself into a corner. Did you look at the images from Google when you looked for solenoids? Did you find a form factor to fit your requirements? You have not disclosed how you are going to mount the solenoids. Do you intend on mounting them on the switch?

Perhaps it's time to consider replacing the switch with something more workable.

Paul

I need to use small 12v solenoids that can hold a push position for several minutes. But there is so many different models of solenoids that I can't find which ones can do that (without risk).
Could you please tell me what I need to search for?

No. Because you have not told us what you are trying to do.

I cannot use a DC motor here...

...and I cannot use a servo either.

These statements do not help much. The tell us what you think you cannot do, but give no more information about what you are trying to do.

Go read number 16 under How to use this forum - please read. It describes the XY problem rather well.

Paul_KD7HB:
You are designing yourself into a corner. Did you look at the images from Google when you looked for solenoids? Did you find a form factor to fit your requirements? You have not disclosed how you are going to mount the solenoids. Do you intend on mounting them on the switch?

Perhaps it's time to consider replacing the switch with something more workable.

I didn't talk about a switch. My goal is to push a little wooden button which have a small spring(for coming back to its original position) and I may have to hold it for minutes. And if I have to hold it for minutes I don't want my solenoids or my motor shield to burn.
This action doesn't require a lot of force.
And yes, the form factor is something rather important because I don't have much space for them(also the results where the same on the main Google search that's why I wanted to look in Google images how this stuff looks like).
I know I don't have a lot of choices available here but that's the way it is.

vinceherman:
No. Because you have not told us what you are trying to do.

These statements do not help much. The tell us what you think you cannot do, but give no more information about what you are trying to do.

Go read number 16 under How to use this forum - please read. It describes the XY problem rather well.

Well, I explained what I was trying to do in my first post:

Saynomore:
I need to use small 12v solenoids that can hold a push position for several minutes.

I didn't know that I will have to explain the whole project whereas I'm not in the "project guidance" sub-forum. I don't understand why it would matter for that question...

Look what I just told to Paul above.

I know the XY problem but I don't understand why you'd consider it's the case here.
I just want to know if I can find a small solenoid that can hold an ON position for minutes and I want to know what I need to search for. For instance I saw that some of them have a "keeping force" specification but I don't know if it's the right thing to look at. Also my continuous duty solenoids search gave me the results I talked about earlier.
And I can't use a DC motor nor a servo nor a stepper. If you know the whole project that will not change those facts.
Why would you need more informations ? I don't get it.

This action doesn't require a lot of force.

Please define "not a lot" in actual engineering units.

And I can't use a DC motor nor a servo nor a stepper.

We learn about solenoids in class at school. The reason for that is that's how Faraday himself learned about electromagnetism. They are easy to analyze with very simple equations. They are also easy to build if you are the only person in the world researching electromagnetism and don't have the ability to just order a dozen motors from China for two bucks on eBay.

But in the real world, you don't see solenoids. Pretty much anywhere you might expect to see a solenoid (such as a car door lock) the actual technology chosen is NOT a solenoid. There are a zillion different motors available in different formats which will often look a bit like a solenoid but actually fall into one of the 3 categories you have ruled out.

Unless you tell us why you can't use any of those then you are just making an XY problem.

Saynomore:
I didn't talk about a switch. My goal is to push a little wooden button which have a small spring(for coming back to its original position) and I may have to hold it for minutes. And if I have to hold it for minutes I don't want my solenoids or my motor shield to burn.
This action doesn't require a lot of force.

That sounds like an ideal role for a small servo. You could then dispense with the return spring.

I didn't know that I will have to explain the whole project whereas I'm not in the "project guidance" sub-forum. I don't understand why it would matter for that question...

Giving useful advice is not a simple YES or NO business. The context matters. The more information you provide the better will be the advice.

...R

MorganS:
Please define "not a lot" in actual engineering units.

I'm not an engineer. And I don't have the measurement device to know that.
It's roughly the pressure you need when you push on a retractable pen button. And it looks like this:
.

MorganS:
Unless you tell us why you can't use any of those then you are just making an XY problem.

Robin2:
That sounds like an ideal role for a small servo. You could then dispense with the return spring.

With my setup I can only use 2 servos, 1 DC motor and 3 solenoids. The 2 servos "spots" and the DC motor's one are already used. So I can't do that with servos unfortunately... Solenoids are my only option.

OK, so what is that setup? Some particular shield you have and you can't change it? Are you sure the shield can do all of those at the same time? Most of the multi-purpose shields can not do all of those tasks at the same time.

What is the power output available from that "setup" for one solenoid? Have you looked for solenoids in that power range and found any specs on their dynamic force? Have you enough budget (and time) to buy one and test?

Measure force with kitchen scales? Very simple and easy.

Or a stack of coins, for small weights.