Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: jasonhead on January 27, 2015, 02:34:04 PM

Title: Micro controllers and heat actuated design (current control) - Nylon muscles
Post by: jasonhead on January 27, 2015, 02:34:04 PM
I am building a robotic hand / arm system with the goal of using the Nylon fishing line muscles.
Like these: http://bit.ly/1ENTS0S (http://bit.ly/1ENTS0S)

My area of expertise is in software (I'm a developer), but with much less knowledge in the electronic hardware area.

Could I get some suggestions for building a system for controlling current for the heating wires?
I am thinking of an Arduino / Raspberry Pi paring - the Arduino for the analog current / movement sensor controls, and the Pi for processing sensor feedback and managing the dexterous movement complexities.

What sort of circuits would I need to build to control current flow?
I have 28 GA Nicrome 60 resistance wire for the heating "elements".

I'm thinking I will use a temperature sensor to dynamically cap the amount of current flowing to a muscle wire.

Suggestions?
Thanks
Title: Re: Micro controllers and heat actuated design (current control) - Nylon muscles
Post by: mklrobo on January 27, 2015, 03:51:15 PM
 :)  Hello!
I have played with Nitinol (muscle wires) to use for a robotic project. I could not get the
displacement of the wires that was advertised. (lilft per amp)
The heat of the wire was so small, I could not detect it, with my fingers, and I assume
that putting any temperature sensor on it may prove obtuse, because  the wire needs
room to work.
I was going to use phase control for the current control part, and a current measuring
circuit kit (Jameco sells kits) for the current.
PWM may be a more efficent way to control the current and thus, displacement.
Electronic kits are avaliable that can be plug and play, and probably provide info to
your software, that may be avaliable.
Whatever method you use, you undoubtly will have to make a current vs. displacement chart that
is in context with your control programming; This part will only come with experimentation, unless you
know someone who has already done it. (Youtube?)
Interesting project, Keep me posted.......... ;D
Title: Re: Micro controllers and heat actuated design (current control) - Nylon muscles
Post by: jasonhead on January 29, 2015, 12:49:40 PM
As someone suggested, I think I am going to go with PWM feeding into the gate input of logic level MOSFET With low internal resistance, controlling the heating of the wire.
PWM just seems to make sense as a efficient and digital way to control things.

My project site is robotics.jasonmhead.com
Title: Re: Micro controllers and heat actuated design (current control) - Nylon muscles
Post by: jasonhead on January 29, 2015, 01:36:32 PM
Here is the project intro page:
http://robotics.jasonmhead.com/project-overview-and-goals (http://robotics.jasonmhead.com/project-overview-and-goals)
Title: Re: Micro controllers and heat actuated design (current control) - Nylon muscles
Post by: bdeuell on January 29, 2015, 02:39:23 PM
This doesn't answer your question but there was a thread regarding these muscles a while back. If you haven't read it, there might be some useful information.
 
http://www.societyofrobots.com/robotforum/index.php?topic=17605.msg122301#msg122301 (http://www.societyofrobots.com/robotforum/index.php?topic=17605.msg122301#msg122301)
Title: Re: Micro controllers and heat actuated design (current control) - Nylon muscles
Post by: jasonhead on January 30, 2015, 06:56:58 PM
Thanks; I've actually communicated with that guy a bit - his site is a good resource.
Title: Re: Micro controllers and heat actuated design (current control) - Nylon muscles
Post by: mklrobo on January 31, 2015, 09:13:33 AM
 8) Awesome project!  8)
Great job on the website. I would offer an opinion, where permissible.
You might even be able to use this as a prosthetic arm. If that may
be in your future, you may be able to get finacial backing from
kickstarter, or indigogo. Good Luck!   ;D ;D