Solenoids?

[mr_fork]

I've never worked with solenoids. I want to buy around 3-5 for a mini project similar to this: http://www.youtube.com/watch?feature=player_embedded&v=g_hiz-Kx0kM (except inside a wooden box instrument)

any recommendations for the cheapest i could buy that will do the job suitably? I don't want to spend more than I have to (I'm a student ) and i don't particular get the specs for them.

thanks.

[johnwasser]

I'd look for some surplus 12V or lower DC solenoids.

A quick Google search (surplus solenoids) turned up these 6V 370 mA units for $1.59 each:
http://www.electronicsurplus.com/Item/7678/GUARDIAN%20-%20Solenoid_%20DC_%20Coil_%206VDC%200_37A%2016%20Ohms_%20-%20A420-066410-00/


Remember that you'll need a transistor to drive each solenoid.  You should also put some fairly large (100 to 1000 uF) capacitors across the power lines to provide for quick current spikes.

[retrolefty]

Keep in mind that there are several specs you might have to deal with when selecting proper solenoids for a given applications, such as:

Coil voltage
Max current draw
DC or AC
Rotary or linear plunger travel  (yes there are rotary solenoids avalible)
Total mechanical plunger travel
Plunger pulls in or pulls out with applied voltage
Pull or push-force
if the plunger has a spring return or not when de-energized.

Also keep in mind that plunger pull-in force is not constant across the the full travel range.

Lefty

[MarkT]

Or make some? http://www.youtube.com/watch?v=sRN5UhHhSxY

[retrolefty]

Or make some?

Pretty unimpressive as it really only showing you one way to wind wire onto a bobbin.
Lots of details missing to effectively design your own. Wire size and number of turns will determine the electrical requirements for the solenoid. Designing for continuous service Vs intermittent services is also a factor. Material type for plunger is important (soft iron being the best as I recall). To say nothing about the missing physical dimensions for the plunger, stops, etc.

Lefty