Author Topic: Linear Actuator with feedback  (Read 1951 times)

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Offline nabberukTopic starter

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Linear Actuator with feedback
« on: November 21, 2014, 06:23:29 AM »
Hi,

I'm creating an autonomous sailing boat. In order to control the main sail and rudder i would like to use linear actuators instead of servos as they have a hold position that will use minimum power.

These actuators will be controlled by a raspberri pi/arduino. The mail sail will need to be able to cope with a higher force due to the wind pulling on it.

My question is, can i create a screw threaded linear actuator fairly cheaply and be able tell it the position to be set to?

I've never really tried to build my own actuator with feedback before?

Offline jkerns

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Re: Linear Actuator with feedback
« Reply #1 on: November 21, 2014, 08:00:27 AM »
You can count revolutions of your screw to calculate the position (free rotation potentiometer, encoder, etc.) but you would have to initialize the count at one end or the other every time you power up.
I get paid to play with robots - can't beat that with a stick.

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Offline SeekingVision

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Re: Linear Actuator with feedback
« Reply #2 on: November 21, 2014, 06:20:32 PM »
If the space is available I would attach a geared down motor to a threaded rod for actuation and then use a linear resistor set as follow up. Just like real ships do! Instead of steering wheel with master rheostat have a regular servo turn it. This is a very inexpensive way to do things. Use analog comparator to turn on or off the geared motor in the correct direction through a H bridge.
Robots are our children and will inherit the Earth.

Offline nabberukTopic starter

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Re: Linear Actuator with feedback
« Reply #3 on: November 22, 2014, 09:20:37 AM »
Sorry to be a pain, I'm fairly new to this so could you provide what you mean in a bit more English or links where I can read up.

Sorry and thanks

Offline SeekingVision

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Re: Linear Actuator with feedback
« Reply #4 on: November 22, 2014, 09:49:32 AM »
Sorry for my undetailed reply but ill probably be better off drawing the circuit I'm talking about. I did a quick web search and found nothing immediately so I guess what I'm referring to isn't regularly done. I'll post a picture soon.
Robots are our children and will inherit the Earth.

Offline nabberukTopic starter

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Re: Linear Actuator with feedback
« Reply #5 on: December 22, 2014, 05:43:47 AM »
Any update on this?

Thanks

Offline Robot Attack

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Re: Linear Actuator with feedback
« Reply #6 on: December 25, 2014, 04:12:25 AM »
Hi there,

Another option would be to use a linear actuator with integrated feedback

http://store.firgelli.com/category_s/1825.htm

These guys make some that are not prohibitively expensive, depending on your budget. They work just as Seeking Vision describes, they have an internal linear resistor which they use to close the position loop.

GL!

Offline SeekingVision

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Re: Linear Actuator with feedback
« Reply #7 on: January 03, 2015, 09:34:41 PM »
Sorry no post of circuit. I can't find my old stuff since moving houses. What you can do though is try a pair of rheostats, mount one on the rudder or sail. Mount another on a simple servo. Use a LM339 quad comparator and some logic chips. The comparator reads voltage differences and outputs a logic high or low. Use two comparators for setting the high and low dead zone, reached zone, and the other 2 for the active location. I have done this before and it works great. Use standard H bridge with the setup with any power/ motor setup you want and attach the screw, geared or not. Good luck with the project.
Robots are our children and will inherit the Earth.

 


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