building a strong solenoid

[davidbenjamindix]

i want to 'build' my own solenoid to control a drawer in my woodworking project. it is a walnut box with hidden drawers that contain homemade neodymium magnetic locks. one or more of the drawers i would like a homemade solenoid to control the drawer opening and closing. i have a 4 channel 12volt DC remote control system, and one of the channels i would like to operate the solenoid with. now the drawer will be small, and i plan on building it with some type of slide or bearing (so it slides easy), and the drawer probably won't eject from the box no more than 5 or 6 inches.

i already have thin magnetic wire (i can't remember...there are 3 sizes), and have build a small solenoid before using a plastic pen tube and a nail for the core. my question is, what is the best material i should be using for the tube (where the wire coils around), including the thickness of the tube, and diameter of the tube. i also need to know the cheapest type of core that i should be using. im assuming the core is going to be pretty light so it travels in and out easily?

i also have another concern about the coil direction. how many wraps do i need....1000? should i wrap only one direction, and work out some type of switch that can change the current direction? or should i wrap both directions, use an on switch to **** the core into the tube, and use a spring to return the core after the current is removed? i'll take any advice or criticism, because im still learning, and still very inexperienced with electricity. thanks for your time!
David Dix

---------- Post added at 05:01 ---------- Previous post was at 04:20 ----------

i was just told i should just buy one. so now my question is, (im going for low cost) what kind of 12v DC solenoid should i buy? i suppose i will need a 2 way, and probably push type (because the drawer is going to be pushed out of the box). also, should i go with continuous duty?

 

[KJ6EAD]

Take a look at the solenoids, cores, coil forms and sleeves used for pinball machines. That should give you some ideas. The Pinball Resource
The coil forms and sleeves are nylon. Most of these are made to operate on 30 or 60 VDC.
Surplus source:

Solenoids have very high inertial moment. I wouldn't expect a light wood structure to last under that hammering. A motor drive might be more appropriate. Have you considered modifying the guts from a CD/DVD drive tray or carousel tray extend mechanism.

 

[davidbenjamindix]

i cant imagine how to rig up a motor to extend an object in one direction. plus, would i have a hard time converting the AC drive to DC?

 

[KJ6EAD]

It's designed to move in both directions, has it's own control chip and everything inside a CD/DVD player runs on low voltage DC.

 

[davidbenjamindix]

is there a way to speed up the motor so i get a really fast action? kinda like a surprise snapping type movement?

 

[KJ6EAD]

No. If you're looking for such speed, you'll need a spring or go back to the solenoid idea. In industry this type of motion would normally be done with an air cylinder, but that may be impractical for your project unless you have enough room for an air reservoir. It depends on how many times you need to actuate the drawer before recharging.

 

[davidbenjamindix]

well, it doesn't have to be fast. i just thought that would be a neat effect. i do need to incorporate a speed snap motion for a different project still in the works called a scare box. but anyway, back to this project. so the cd/dvd open/close tray...even if it runs off of AC, does the power actually get converted into DC to operate the opening/closing motor? or were you strictly speaking of some type of portable cd/dvd player that is completely DC?

 

[KJ6EAD]

In an AC powered CD/DVD player, everything runs on low voltage DC, mostly 12V or less. There's a power supply circuit in one corner of the unit comprised of a transformer and either a small circuit board or a portion of the main board. If your drawer is not very light (low mass), a tray mechanism will not be able to move it.

 

[davidbenjamindix]

funny thing is, i also wanted to install some type of ipod or cd player inside the box, so music/sound effects actually play when you unlock certain locks or open certain drawers.

---------- Post added at 10:39 ---------- Previous post was at 10:24 ----------

here was an idea i had about using a solenoid for a larger movement. what do you think?
**broken link removed**

 

[FvM]

I would also prefer geared DC motors to provide strong force with limited power supply. But let me refer to the original solenoid question.

I can only suggest to study the design of available solenoid drives, e.g. from a tape recorder, or surplus parts, as linked by KJ6EAD. You'll also find active production solenoids at catalog distributors. If you look sharp, you'll notice, that the solenoids have an almost closed magnetic circuit, e.g. formed by a iron case. It's the key to make a strong drive. If you just put a core into a coil, the force will be considerably weaker. For the coil, the number of ampere windings (N*I) is creating the magnetic field. So you will try to increase both, current and windings count. This involves varying the magnet wire diameter, there are of course much more then only 3 gauges. Because copper has a known resistivity, you are able to predict the coil resistance on pencil and paper.

 

[KJ6EAD]

Most available solenoids have a stroke length less than 3" so the use of a lever arm would seem good, but when you try it in a mock up, I think you'll see that lever ratios exceeding 1:1 either require a very large solenoid to actuate or a very strong pivot or both.

Take a look at some electric linear actuators like these: Linear Actuators, Linear Motors, Micro motors, Electric Motors. I wonder if an electric antenna from an auto dismantler might work for you. I thought of electric window operators but they are too strong/heavy probably.

 

[samdenson]

Let me also suggest you some stuff, you can try IP-66 here http://www.progressiveautomations.com/linear-actuators or this one, but it's expenseive http://harmonicdrive.net/products/actuators/sha/