A simple system to generate an up and down movement on a small characters head

[gonadgranny]

Hello everyone.
I want to create a small character with a head which moves up and down to give the impression of laughter.
So some sort of linear actuator.
its only a small character and so only needs a small amount of movement, maybe about 5 - 10mm.
i am wondering which is the best way to implement this.
I need to consider are the amount of power it uses. (this project will be powered by a lithium battery) so i wanna keep the power consumption down.
I also dont want to have to pay a great deal for the technology.
I was thinking of some sort of cam and motor system as that probably quite cheap and energy efficient or maybe a solenoid type actuator but these seem to use a lot of power and are heavy but simple to implement.
Any ideas would be much appreciated and any links to items on ebay for example would be great.
Thanks,
Danny

 

[Warpspeed]

I suppose the most energy efficient system might be a pendulum, or light spring with a bouncing mass, driven by a suitably pulsed electromagnet.

 

[BradtheRad]

Take a look at the desktop gizmos which have a dolphin swinging back and forth (or similar action). The circuit is very simple, consisting of a transistor which energizes a tapped inductor. The approaching magnet causes a brief pulse to the bias pin of the transistor, which in turn turns on the inductor, which gives the magnet a brief boost as it goes by. The swinging action continues as long as the battery lasts.

This type of motor uses little power, and does not take up much room. I believe I saw it used in an old programmable thermostat, driving the 24-hour clock dial. It was powered from a small 1.5V battery.

 

[chuckey]

It could be worth counterbalancing the static weight of the head. If you are a model maker it should not be that difficult. Under the head you put a "bell crank" like a see-saw. the head is supported on one end the pivot is just that. The free end has a weight on it which you adjust until the head is at its halfway position.
Frank