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Need to pull item against a spring, fast. How to pick a "linear solenoid" ?

swatti

Dec 25, 2015
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Hi, im new and sorry for my bad english, i kinda lack the specifig "terms" needed...

I have a mechanical "gearbox" with a certain part in it, "spring-loaded" and moved by gears. I want to move this part via electricity and not the gears.

Here is the part:
https://www.dropbox.com/s/8q9ucqmhkf7cqfl/20151225_204415.jpg?dl=0

Its the black plastic "plate" there with the spring below it. It moves maybe 3-5 cm backwards.

Here it is, moved at the far back where it needs to go. Other components will stop its movement, the spring will pull it back.
https://www.dropbox.com/s/ggkd1006h8aqbh7/20151225_204427.jpg?dl=0

What i need, is SOMETHING to able to pull against that spring, aprox three to four times a second. The spring is quite strong for its size, about two to three times as powerfull as pencil spring. I maybe able find a slightly less stiff spring for this aplication.
This device would be mounted OUTSIDE the gearbox and it has multiple potential locations depending on its size. Width should not be much more then the coin in the picture, more will cause problems, length is a lesser issue.
I can use for example, use piano-wire to attach the device to the plastic part, there are options. Leave that to me.

What i have:
Lipo-battery power, 3-4 cell lipo, 11.1-14.8 volts - Comparable to RC car batteries, should have enough juice to run most things.
CONTROLL CIRCUIT. The important part! I have a friend whos able to make and program a circuit to move the device, but sadly neighter of us know what to buy as the device to move that part. We have a circuit controlling the gearbox, it has room to add thigns to it.

EDIT:
Googling things, i believe the device i need a "linear solenoid" - Preferrably one what has a hole all the way thru it so i could pull the piano-wire thru it and mount the device itself against the back of the pictured gearbox.
How do i pick to correct one and from where? Needs to ship to the cold north of Finland too.
 

Bluejets

Oct 5, 2014
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Solenoids are rated in watts as in horsepower with 1hp=746watts.
As you will be able to measure the pulling force required and you will know the time required to move the device, then you have the 2 necessary measurments to calculate this.
hp (watts) is work done in a certain time. e.g. 1hp = 550 ft.lbs per second.
Required solenoid will be larger than you imagine.

I hope this is not part of some type of weapon as I imagine this will be the only help you will get.
 
Last edited:

Alec_t

Jul 7, 2015
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If the solenoid has to pull in over a 5cm distance it will need to be pretty powerful. That implies a plunger of considerable weight/inertia; so the movement may not be fast enough for your application.
 

Bluejets

Oct 5, 2014
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Its the black plastic "plate" there with the spring below it. It moves maybe 3-5 cm backwards.

Here it is, moved at the far back where it needs to go.

Looks to me more like 10 to 15 mm.
 

swatti

Dec 25, 2015
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Did some measurements:
I overshoot the distance. Its actually mere 10mm. Bit below but lets narrow it down to 10mm.

With all parts involved i pressed down the part with a "scale" and it came at roughly 2.2 kilograms when it was at the spot it needed to be. Will that help determine the power needed?

This gearbox is a heart of what is know as an AIRSOFT gun. A permit-free TOY gun. The part here is what loads in the rounds, typically, one per each shot / cycle. I intend to load multible, as in turn it into a "shotgun"
 

Bluejets

Oct 5, 2014
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This one has a maximum pull of between 100grams and 2Kg's at distances of between 10 and 15mm so may be sufficient.( if you can believe the Chinese supplied data)
The force changes inversely with the distance.
It may pay to go to a higher wattage just to be sure.

Note the size is rather large as I said it would be.

http://www.ebay.com.au/itm/15W-DC-1...473838?hash=item5b19d5ebae:g:vSQAAOSwHjNWB99r

This is only an example. You will have to look at the data provided and make your own choice.
May be noted also that solenoids like this will have some kind of recommended duty cycle.i.e. time on versus time off, which might be lower than you think.
 

swatti

Dec 25, 2015
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Is there a differece between PULL and PUSH in terms of power etc?

My initial plan was to PUSH away from the gearbox, with the wire going thru the solenoid, or mounted at the back of the moving component in the solenoid. A pull unit would have to mounted deeper, more away from the gearbox where it does its thing.

EDIT: what does "60N" mean in terms of kilos? Or how many "N" is needed for 2 kilos?

EDIT2: Found this, is this a correct calculator?
http://www.kylesconverter.com/force/newtons-to-kilograms--force
 
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swatti

Dec 25, 2015
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This looks promising:

http://www.ebay.com/itm/JF-1264-DC-...548301?hash=item4868e5fd0d:g:3XkAAOSwHnFVpzSo

10mm and 5.5 kilos! 12volts so it would work with 11.1v lipo. "current" 500mA is a bit unkown to me, i have no idea what the current in those batteries is... A lot i presume. That unit is quite "overkill" for this so it should last if i run it under the voltages & current its meant for.
Size may end up being just a bit too large but i could use it as test-dummy atleast.

EDIT:
Ended up buying this:
http://www.ebay.com/itm/DC-12V-2A-P...329407?hash=item463efab8bf:g:U0oAAOSwPcVVwIRC

~2 kilos, 10mm, 2A and quite small. The picture shows i might be able to mount the needed wire to the back of it. A "mere" month of shipping >_<
 
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Bluejets

Oct 5, 2014
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Your online calculator is the correct one.
As for the battery, it's not how much current is in the battery but what current it can deliver.
Capacity will give you how long it can deliver this current. Note that the capacity/time deminishes the higher the current.
Battery spec sheets should show this along with any instantaneous current (which is what you will be looking for)
As the solenoid energises each stroke with the armature in the extended position, there is a rather large inrush current.
The battery will have to be able to deliver the inrush as well as the sustain current. Small batteries and those with a high internal resistance cannot handle this.
Also one must be aware of the duty cycle of the solenoid. They are initially for a low duty cycle.
i.e. they may activate and hold for quite a long period but keep cycling this at a high rate and they will heat up and possibly be damaged.
 

swatti

Dec 25, 2015
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Lipo-batteries give out quite large "burst" of power and then reduced steady current. According to numbers alone, im using this below its maximum.

We will be timing the system carefully to pull three times per cycle as fast as possible and with as little as possible wasted energy and heat generated. It doesnt need to be pulled back for very long time, so i doubt heat will be an issue.
 

Bluejets

Oct 5, 2014
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As I said previously but you apparently missed it, the most heat is generated during pull in and the more cycles you do, then the more heat is generated.
Lipo batteries do not give out large bursts of energy.
Yes, lipo batteries can deliver high current but it all depends on what lipo and what solenoid and what inrush current.
Time for three times per cycle with what time in between could be looked at as your duty cycle.
 

swatti

Dec 25, 2015
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PROGRESS! The solenoid arrived and its perfect in size atleast. Even has two screw-holes for mounting it, should be easy.

I havent used it "under heavy load" but just tapping it back and forth with a 11.1v lipo doesnt generate ANY heat, at all. Dozens of uses, doesnt even feel warm.

It seems quite powerfull so it might be able to pull the part i need. Now i just have to jury-rig it to the gearbox and see if it can pull fast enough.
 

swatti

Dec 25, 2015
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AAAAND its a fail... &%¤&#&¤#!!!

The solenoid lacks the power in the early stages to pull against the spring. Just a bit more and it would work...

As in car-tuning, solution to ALL problems... MORE POWAH!!!

http://www.ebay.com/itm/JF-1264B-DC...432582?hash=item43e3aad546:g:jSQAAOSw9N1Vyu-s

This makes TWICE the power, is a bit bigger but also able to take more amps.

Aaaaand a 3 week wait begins.

EDIT:
I do have to mention, my theory works atleast and even under load the heat doesnt seem to be an issue to worry about.
 
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