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View Full Version : [Discussion] Lightweight, Flexible Linear Actuator



dmitry
03-20-2015, 11:01 AM
Good day everybody!:happy:

I am new at this forum, and I am looking for some help and ideas on the following subject:


I am planing to make a modular lightweight linear actuator, based on dc motor that doesn't have screw drive or any gear.

It has simple components: cheap dc motor and string!

Motor rotates - string contracts- as a result, we have a linear displacement:


http://robot.kut.ac.kr/images/research_projects/exoskeleton/1.png



The advantages of such actuator: it is light! Cheap, and flexible (since the string is flexible). It can care heavy things, while being small and light.


It will also have a flexible linear displacement sensor.


Would you guys give me some ideas on what can be the practical application for such actuators?

How would somebody want to use such actuator? In what project?


If you can give me some good ideas, I will try my best to send you few of these actuators if you would like to make something with it.

Thank you for your time and ideas!

tician
03-20-2015, 05:23 PM
There has actually been quite a lot of research into string actuators, and hizook has a pretty nice breakdown (http://www.hizook.com/blog/2015/01/13/twisted-string-actuators-surprisingly-simple-cheap-and-high-gear-ratio) of it all. IIRC, the two biggest cons are difficulty getting position feedback and the limited life of the string/wire.

dmitry
03-21-2015, 12:27 AM
There has actually been quite a lot of research into string actuators, and hizook has a pretty nice breakdown (http://www.hizook.com/blog/2015/01/13/twisted-string-actuators-surprisingly-simple-cheap-and-high-gear-ratio) of it all. IIRC, the two biggest cons are difficulty getting position feedback and the limited life of the string/wire.


Good day!
Thank you for your reply!!
You are absolutely right about it's disadvantages. I do my research with these actuators for the last 4 years and I totally agree with you.

Assuming that I solved these issues. And such small actuator will be capable of providing position feedback. These days I am trying to find some particular applications for them. Something more then an actuator for robotic structure. Some wider market.

For example toys.. as Hizook mentioned. I am trying to find a use of its flexible structure.

Any conventional linear actuator is mainly based on screw drive or pneumatic. Which makes them heavy.. rigid.. and so on. Where twisted string actuator can be placed remotely and the string could even go around some objects and still provide a linear motion at the end.

I thought some of the guys form the forum could have some idea for it's implementation.

Thank you again for your interest in discussion!

tician
03-21-2015, 08:30 PM
I'm not really thinking of many uses outside of toys and/or consumer robotics (mainly hands and other manipulators) where I would trust them and where they might actually offer an advantage over existing technologies. Rigidity is usually a requirement for industrial actuators nearly as important as safety and reliability, and existing methods have been heavily refined for those purposes.

Pneumatic and hydraulic are failsafe during power loss as long as the cylinder seals, connectors, hoses, and valves do not suffer a catastrophic failure that rapidly purges the system. Screw based linear actuators are usually even safer during power loss because of the fewer components actually maintaining the failsafe capability (no seals, connectors, hoses, or valves; just a leadscrew and nut). Pulling on a load around a corner or through winding passages is much more safely and accurately accomplished with cable or chain wrapped around a capstan driven by a gearmotor.