# Solenoid to squeeze small spray bottle — Understanding Newtons

Hello there,
I am building a mechanism controlled by an Arduino Uno, where a small spray bottle (very small, measuring approx 7x1x1cm, like
this one here) is contained within an acrylic tube.
One end of the tube is closed, the bottle is inside, a rod in acrylic pushes the bottle against the closed part of the tube, the spray nozzle is squeezed and it sprays water through a hole placed in the wall of the tube.

I would like to push the rod with a Push Solenoid. The solenoid would be controlled by a relay and powered with an adapter. I have tried a few with a 4N force factor; I wasn't expecting for them to work, and indeed they didn't.

Could anyone either recommend a good (and ideally small) push solenoid that could do the job, while working at 12V? I am being a bit confused by wattage and can't understand which one to pick between Amazon and RS. Alternatively it would help me a lot if anyone could let me have an idea of the amount of Newtons I'd need to make it work.

Many thanks in advance for your help!

E

Solenoids don't have an even force, the force increases rapidly towards the end
of the stroke (usually - wherever the magnetic path is most closed). 4N peak
force might mean 0.5N to start with, rising to 4N.

For pushing evenly on such a bottle a linear actuator is more likely to be satisfactory.

1 kilogram of mass presses down against the Earth with a force of approximately 9.8066 Newtons, IIRC. ;D

Thanks, more than an even action I thought I needed the uneven push in order to squeeze the bottle just like we would do with our fingers, but I guess it's a good idea to try with a linear actuator.
Will report once done

Or an RC servo motor with a cam-wheel

Hi..

suggest you measure the necessary force ( eg with a weight ) - then you'll know where to start.

regards

Allan.

ps the spray bottle needs more to squeeze as it collapses - matching the force/distance of a solenoid to some extent. Would a lever help?

Thanks Jackrae, the stepper motor and the camwheel is a very good idea.
I am thinking of building one where a stepper motor with a shaft attached to it, cut at an angle.
And then another shaft cut same angle on top of it, which can only travel vertically in order to convert rotation into linear or vertical movement.

Thanks Allan, I didn't think about doing that, a lever might help indeed.
I didn't know it was going to take so much force to simply squeeze one of those atomisers test mini bottles.

I am also considering using a liquid pump connected to a container where the perfume is.
Though as I am trying to keep everything small, I am struggling with finding a pump which can be strong enough and be connected to a nozzle atomiser.

Elso:
Thanks Jackrae, the stepper motor and the camwheel is a very good idea.
I am thinking of building one where a stepper motor with a shaft attached to it, cut at an angle.
And then another shaft cut same angle on top of it, which can only travel vertically in order to convert rotation into linear or vertical movement.

I think you may well have friction problems with that idea. An eccentric wheel operating against a small roller bearing attached to a slide rod will effectively and efficiently convert rotary motion into linear motion.

Just a quick addition to my solenoid/lever idea....

The spray bottle has an internal spring .. If you added an external spring to counteract most
of that internal spring force , ( perhaps on a lever ?) the solenoid wouldn't have nearly as much work to do...

regards

Allan.

You can actually pop off the top, unscrew a collar, and see the spring inside. Instead of trying to add another spring, you can clip the internal spring. In fact, you can remove it entirely if your actuator, whatever it may be, is affixed to the pump button.
With no spring to work against, you have a trivial amount of force to work the pump, and the pump top would follow your actuator back up.
If you already bought some kind of solenoid , then removing the spring and affixing the solenoid head to the pump top seems the simplest solution.

Thanks for all his advice!
I bought the solenoid, a tubular one from RS. At present it is at the bottom of a vertical spray small bottle of plastic. When the solenoid fires, it pushes the bottle against the top of the container in so activating the spray of the bottle. Now I only need to find an adapter that matches the solenoid's 24V 1.5A and then I will be done.