How to build a simple solenoid?

Hi, one.

Methinks you need to specify the throw distance for this solenoid. If it just has to hold the egg, once thrown, it will consume less power than if it must exert that force over the whole throw range.

From your description, I would worry about how long that solenoid could be energized without depleting the battery. Perhaps that should be added to your requirements. You may want to devise something with a latch so that continuous energizatization is not needed.

Thanks Larry, you're right. I just forgot those things. The throw distance is only 1/2 inch. It's not continuous holding. It just release the latch that's all. I will use spring to hold the latch. What I need is really like an electronic mouse trap, since I am not allowed to touch the "trap" by hand, I can only use wire, you know what I mean. The force to release the latch is really small. The project requires 2 AA or AAA batteries only. You think that would work?

Sure. You may need an electrolytic cap to supply the pulse current needed to move the solenoid plunger. I would get a small permanent magnet and experiment with a coil whose axis is colinear with the magnet pole. You should be able to repel or attract that magnet with a short enough pulse to not warrant much worry about battery consumption. I would start with #32 magnet wire and 40 turns. For your ~3V drive, there will be an optimum turns-count somewhere if you are willing to find it. Since this is a one-shot operation, I would not spend much time trying to devise an efficient, closed path magnetic circuit unless battery power is really precious.

Larry, Can I overlap those 40 turns or make it 2-3 layers? Does it have to be very neat? Thanks again!

Both. Get the winding into as small a volume around the magnet to be moved as you can. That could mean even more layers.

Only if you want a gold star from teacher.

Welcome again.