I need a 12Vdc bi-directional actuator (extend/retract) with a total linear in/out travel of about 5cm. Force required is about 5kg. Time to travel end-to-end <3s.

I'm thinking of visiting an auto junkyard to look for windshield wiper motor and gear train, motorized window winder, electric door lock, motorized seat adjusters, etc.

Any other possibilities?

 

Don't know whether you've any friends that are involved in biomedical engineering? They are used quite widely on patient beds. The main ones I've come across are by Linak. They have offices in the USA, perhaps they can help?

 

I would consider the auto wrecker as a possibility, the window lift or seat motors should be able to handle the 5Kg's needed.
Also you may be able to make use of the PWM controllers they have now in modern auto's, the amps are usually controlled by the CanBus, but you may be able to bypass that?
Max .

 

Try pololu.com, they have some of the linear actuators sold for hobby robotics;

http://www.pololu.com/category/127/linear-actuators

 

Firgelli is also a possibility IIRC.

 

I'd rule out electric door locks; they're pretty feeble.

 

Yeah, car door lock actuators won't move 5kg reliably and they only usually have a throw of about 25mm.