Society of Robots - Robot Forum
Mechanics and Construction => Mechanics and Construction => Topic started by: nabberuk 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?
-
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.
-
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.
-
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
-
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.
-
Any update on this?
Thanks
-
Hi there,
Another option would be to use a linear actuator with integrated feedback
http://store.firgelli.com/category_s/1825.htm (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!
-
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.