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I wanted to use solenoids in previous projects and have been let down by the fact that I can't find them here in Egypt. Plus they are a bit expensive. My question is: is there an alternative that it easy to control and cheap? If not, can you direct me to a way to easily make my own solenoids with limited materials (since I need 31 in a specific project)?

EDIT: I need to push or pull no more than 1". Please no links to buy solenoids.

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We'll need to know required forces, speeds, and duty cycles as well to recommend solutions. For example, you could use a threaded-rod linear actuator for slow but powerful actuation, or use a servo with an armature to get faster but weaker motion. – Kevin Vermeer Feb 27 '12 at 19:05
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Also, this is getting a bit off-topic, but where (and why) are you looking "in Egypt"? At the neighborhood electronics surplus store? Or at the post office? Digikey has an Egyptian-specific site at eg.digikey.com, Mouser, Arrow, Farnell, and most other major distributors ship internationally. International shipping and a week or two wait on what will likely be a $600-$1000 order doesn't seem like a major barrier. – Kevin Vermeer Feb 27 '12 at 19:19
@KevinVermeer I was looking in downtown Egypt because that's the only place (that I know of) that has stores selling electronic components. Problem is that downtown Cairo is pretty far away from where I live. If you are going to suggest Radioshack, Radioshack here doesn't sell electronic components. And about online stores, I replied about that in the answer below, however, If you can find websits that accept COD like ram.com.eg or egyrobots.com , Then I would probably buy from those. – Seif Shawkat Feb 27 '12 at 19:24
Ah, that's your problem. As Olin mentioned below, nobody buys electronics from physical stores. Get yourself a prepaid credit card, and shop at real distributors. – Kevin Vermeer Feb 27 '12 at 19:38
@KevinVermeer Ok, put the online thing aside, what is an easy way to make my own solenoids (or something similar)? Some time ago I had this idea of using parts from an old transformer but I completely forgot how I was going to do it. – Seif Shawkat Feb 27 '12 at 19:43

2 Answers

up vote 9 down vote

Solenoids are as available in Egypt as they are here in the US. DigiKey, Mouser, Farnell, and many others ship worldwide, including to Egypt. If I needed to buy solenoids, I'd be buying them from the same places you can also buy them from. Nobody buys electronic components from physical stores anymore. The entire world is accessible at the other end of the internet.

1 inch is a fairly long travel. A solenoid is basically a electromagnet with a core that can move. It is difficult to make them so that the ratio of force at the start and end of travel is not huge. The longer the travel, the harder this is. For long travels, it can sometimes make sense to use a solenoid with shorter travel and a mechanical linkage that gives higher travel at the expense of less force.

Simple solenoids aren't that hard to make yourself. Find two iron plugs, the right kind of nails or bolts can work. Find or make a cardboard or paper tube they just fit in, and glue one of them so that it is fixed. Wrap a bunch of wire around the outside of the tube. When current flows, the movable plug will be attracted to the fixed plug. However, getting this to work over 1 inch travel with reasonable force will be difficult.

Go to a local junkyard and see if you can salvage some starter solenoids. Those are really relays implemented was solenoids. Old Fords used to have them mounted on the side of the engine compartment where they were easy to remove. I still have a photographic cable release built around one of those from many years ago.

One alternative to a solenoid is some kind of geared-down motor. Hobby servo motor units can have 1 inch travel with the right arm. However, those are going to cost a lot more than solenoids.

I think in the end your best bet is to do a careful internet search to find the product that does what you want and order it. Even if a local physical store had it, it would probably be more expensive there anyway.

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What I meant is that I need anything that goes lower than 1". 2 usages were an earthquake diorama, and a clock like this one: youtube.com/watch?v=C9tW6FIX8oQ For speed, I don't need less than 3/4 of a second maybe, That might be too fast for the clock though. I was thinking to make some like the ones shown in this video youtube.com/watch?v=sR3xmof8rZY however, I don't have the tools they have and I want something that can return to normal without gravity. As for buying online, I don't have a credit card and if I were to use one, I'd be worried about shipping and taxes... – Seif Shawkat Feb 27 '12 at 19:16
... Anyways, $1 is about 6 EGP, and a $21 solenoid like this one search.digikey.com/us/en/products/F0411A/527-1000-ND/668285 is considered expensive. And I want 31 or more solenoids. EDIT: If I were to make that clock I'd make it out of foam-core board (very light). – Seif Shawkat Feb 27 '12 at 19:18
You explicitly NOT asked for places to buy solenoids, but as you mention $21 I would still suggest that you check goldmine-elec-products.com/prodinfo.asp?number=G18567 ($1.49) and goldmine-elec-products.com/prodinfo.asp?number=G18706 ($1.25) – Wouter van Ooijen Feb 27 '12 at 21:55
BTW, from what I understand some have permanent magnets which try to push the core in when energized in one direction and push it out in the other. Would a solenoid used in "repel" mode offer better force at the start of travel? – supercat Mar 8 '12 at 15:39
up vote 1 down vote

Thread and nut actuator:

@KevinVermeer - gave a very good suggestion.
He said "you could use a threaded-rod linear actuator for slow but powerful actuation ..."

Any thread and nut system can be used including used nuts and bolts if desired.

Speed need not be overly slow and unlike a solenoid you can maintain constant force over as large a distance as your wish.

Any motor can rotate a threaded rod with a nut on it.
The nut travels a distance of RPM /60/TPI inches per second.
where TPI = turns per inch of thread.
eg with a 3000 RPM motor and 30 tpi thread the travel is
inches/second = 3000/60/30 ~= 1.666 inches/second.

Force is affected by motor power.

The thread is effectively a gearbox.

You can make a quick return system by using a half nut that is held against the thread by a weight and pulls against a spring. When desired the nut is lifted off the thread and spring returned. Care needed to avoid thread damage.

Electric motors of various sorts are available from many sources including new, in toys, in printers and in many domestic appliances. Non electric motors and even eg hand cranked systems can use this method.

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Unless this thing (1) uses a leadscrew or ballscrew specifically designed for actuators, and (2) keeps the threads lubricated, 3,000 RPM operation is likely to break something. Nuts and bolts are simply not designed for this. – Kevin Vermeer Feb 27 '12 at 23:41

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