Linear Actuator Control

Discussion in 'The Projects Forum' started by needmog, Oct 31, 2011.

  1. needmog

    Thread Starter New Member

    Oct 27, 2011
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    Hi
    I'm new here and still have a lot to learn about electronics. I do have a small project ahead of me that I could use some assistance with. I want to control a linear 24V actuator with 12" stroke, 500lbs thrust and have 4 or 5 timed stops before it reaches it's maximum extension. Once the full extension is reached, it should automatically return to it's starting point (fully retracted) and start the cycle over again.. I have no idea what type of controller I should be looking for. Any help or advice will be appreciated.
    Thanks Gary
     
  2. mcasale

    Member

    Jul 18, 2011
    210
    12
    Is any of this hardware pre-determined, or can you use anything you want?

    I have used linear actuators that are driven by a stepper motor (or a DC motor), but the stroke is usually an inch or so. You may have to have some gears in there to get the stroke and the force. 500 lbs sounds like a lot to me.

    Most likely, you should use an MPU to do this, once you get the mechanical stuff resolved.

    Here's the actuators I've used: http://www.haydonkerk.com/Default.aspx
    These things are NOT cheap.
     
  3. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Can you post a link to the linear actuator that you were intending to use?

    Ken
     
  4. needmog

    Thread Starter New Member

    Oct 27, 2011
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    Here is the link: http://www.duffnorton.com/productdetails.aspx?id=7881
    You'll note that the capacity is less than 500 lbs, but having looked at the requirements again, I can live with that. I'm not married to this particular make or model, but just wanted to show something that I think would work for me. I'm open to suggestions, especially if a more economical alternative can be found.
    Gary
     
  5. needmog

    Thread Starter New Member

    Oct 27, 2011
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    I'm flexible in the hardware selection, other than it needs to be suitable for outdoor use. The thrust capacity can be reduced to around 200 lbs.
     
  6. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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  7. SgtWookie

    Expert

    Jul 17, 2007
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    Not knowing what your load is, you may want to pause the extension based on the percent of extension, or based on the pressure being exerted on the load. Trying to just go by the amount of time the actuator has been running will not be very accurate - but we have no clue what your application is.

    The actuators are available with potentiomenters (10k) and possibly Hall-effect sensors (the datasheet makes reference to them, but no specifics are given about the Hall-effect sensors)
    Datasheet:
    http://www.duffnorton.com/Public/18790/09_LT.pdf

    Without that kind of information, it will be difficult to make suitable recommendations. It would be best if you would describe what your application is, as best you can. Sketches/drawings can help considerably.

    In the meantime, here are a couple of related threads:
    http://forum.allaboutcircuits.com/showthread.php?t=57055 - push-button control of an actuator extension/retraction
    http://forum.allaboutcircuits.com/showthread.php?t=59451 - Extension and automated retraction of actuator w/push of a button
     
  8. needmog

    Thread Starter New Member

    Oct 27, 2011
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    My application is for a solar panel assembly (3 panels in a frame). The panel(s) is mounted on a pipe pole, which has an insert at the top that is able to rotate. Rather than getting a setup that automatically follows the sun, I want to have the panels point towards the east in the morning and have them rotate a few degrees every hour or so until they face south west, after which time they'll be getting into the shade of some trees. At that point I want to have the panels return to their starting point, ready for the next morning to repeat the cycle. Total arc of rotation is probably around 135 degrees. If I split that up into 5 stops @ 27 degrees, that would give me maximum sun exposure given the surrroundings.
    I have a 24 volt solar system, which is why I would like to stick to the 24V actuators. 200lbs thrust should be lots to turn the panel assembly on top of the pipe pole. The attached pic shows the joint where the top pipe is inserted into the pole. I'll need to add brackets for the actuator.
     
  9. Georacer

    Moderator

    Nov 25, 2009
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    What led you to choose a linear actuator for a circular movement?
     
  10. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    You also have to figure into the load calculations, not just the weight of the panels but the wind load. The wind load from your panels will probably be much higher than the actual weight of the panels.

    Like Georacer says. another type of movement would work better. Don't know if they still make them, but something on the order of an antenna rotator would work. Or a servo type motor and a worm gear box.
     
  11. needmog

    Thread Starter New Member

    Oct 27, 2011
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    I was looking at a worm gear box, but I'd have to take the whole assembly apart again in order to install it, plus it's a more expensive option.
    This way, with a couple of brackets mounted on the pole and top insert, I can use a linear actuator, which is a lot less expensive, to rotate the panels. As I said earlier I'm only rotating between 90 and 135 degrees on the horizontal plane. I'm not concerned about the wind loading because the panel assemply is centered on the pole, so both halves of the assembly get equal loading, which cancels out any load on the actuator. The actuator only has to overcome the friction of the pipe insert as it turns inside the pole.
    So, does anybody have an idea of what kind of controller I need to make this work and where I can get one?
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    Seems to me that you need an "H" bridge (it could be a couple of SPDT relays) and a way to monitor the absolute position of the actuator, as well as limit switches on either end.

    Example of a relay H-bridge:

    [​IMG]

    You might consider using a microcontroller. If you have not dealt with microcontrollers before, you should consider using something like a PICAXE.

    The PICAXE line of microcontrollers are basically a line of Microchip PIC uC's with boot loader code, which makes them easier to update and program for a novice. They run a version of Basic which is relatively easy to learn.

    You could have the PICAXE control relays to make the solar panel array turn while monitoring the voltage level from the potentiometer, and stopping the actuator when the voltage was either correct, or if it detected an error, like the signal from the potentiometer went out-of-range (open or short developed) or a limit switch was hit, or perhaps some other kind of error.

    The wiring from your panels going down is going to be a problem; it looks like you have them stretched pretty tight. You really ought to have a good bit extra around where the tube will swivel, or your wire will quickly break due to metal fatigue.
     
  13. Great Scott

    New Member

    Nov 2, 2011
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    As far as the mechanics of it goes, you could take a go kart large sprocket and band saw it in half, then either bolt or weld it around your movable section of pipe. Then you have the option of using geared motors and a chain. You could make a jack shaft to keep the motor/gearbox weight off the pole and mount it to the base. Some motor/gear box combos have encoders built into them. Check the robot supply web sites. There's lots of good stuff there.

    http://www.robotshop.com/motors-actuators.html
     
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  14. needmog

    Thread Starter New Member

    Oct 27, 2011
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    I want thank all of you that have provided me with advice and pointers so far. The PICAXE solution seems to be workable, however I'm wondering if there wouldn't be a programmable controller already out there for this type of application. Most web-sites I've gone to where they sell actuators, don't seem to say much about available controllers for them.
    BTW the issue with the wiring wrapped around the pipe has been addressed. It was an older photo.
    Thanks again
     
  15. Feign

    Active Member

    Mar 30, 2009
    50
    2
    I guess the low tech approach, rope pulley and chiming clock, is off the table?

    The manufacturer you listed has custom controllers also. I'd expect a warmer welcome from their stage and theater contact, than their main engineering contacts, due to the scale of the project.

    555 timers could drive a relay board, but are more trouble to tune than a uC. And with the uC you can few reed switch for positioning stops, and save cost for the actuator w/o servo feedback.

    What type of pole is that? Any bushings or bearing? Looks heavy and may bind. A surplus bearing and spindle from an auto cut down and fit in the top of the pole will make sure it swings. Combined with the 1800lb shear of the acme it will also stay where it's told, within reason.

    Never underestimate the effects of wind on a flat plate, That is how big is that array? If you haven't calculated it's estimated wind load already you will need to know that for your lever lengths. The compression failure mode is most likely with the screw/accuator at full extension.

    The mechanics need to be spot on, or the acme will bend. The less stroke the better, due to more support on the motor mount end. You can reduce the eccentric and side loading with parallel slides, like seen in a CNC axis.
     
    needmog likes this.
  16. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Try mounting an actuator rod to one corner of the solar panel.

    Then put a load gauge (spring with graduated markings, like a fish scale) on the actuating pipe, and see how many pounds are required to move the panel, both on no load (windless) days and high wind days.

    Due to the amount of force a 40mph wind can put on a flat surface, I'd suggest the motor solution, but in a push-pull configuration. One side would wind up chain/rope, while the other side releases chain/rope. The gearhead motors have pretty solid holding power.

    A linear actuator connected to one corner will allow the panel to be twisted (shattered), unless you use an actuator on each side.
     
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