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I'm new to this forum and I am trying to find a solution to control three small electric linear actuators I have made for my RC controlled model aircraft, they have mini 6 volt geared brushed DC motors driving a nut on a threaded rod with thrust bearings to isolate any loads to the gearbox and motor shafts, I have tested these many times in both directions and they work well without any binding.

I am a retired mechanical engineer and can handle the mechanics but require some help on the electronic control for these units, I have researched several sites, but at present have not found a complete solution.

My goal is to go all electric with this model aircraft, regards electric retracts and replace the retract servo's that would normally operate the doors, with these mini electric actuators, the servo's that normally operate the doors have a feedback from a potentiometer, the actuators I have made are too small to incorporate any feedback signal so I assume would need some form of over-current trip when reaching the end positions, and H-Bridge to reverse polarity.

The sequence required would be:

  • Doors open x three actuators operate and stop motors
  • Change polarity for next action.
  • Retracts down x three actuators and stop motors
  • Change polarity for next action.

Control to be on one channel retract switch on TX.

I'm not sure if an Arduino with motor shield could be programmed for this, as I have no experience with programming any type of micro-controller.

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  • \$\begingroup\$ A Hall sensor plus magnet (as Phil suggested) can be small and easy. Also an opto interupter plus 'flag' or opto proximity detector (reflective target). Microswitches can be quite 'micro' but electronic solutions are liable to be better long term. You could consider feeding power via a sliding contact with gap in feed rail and diodes on end sections as used in model rail layouts. || Photos would be of interest to me. Maybe a link to elsewhere? I'm doing something similar at present on a somewhat larger scale using battery-drill motor + gearbox units driving a threaded rod. Works well. \$\endgroup\$ – Russell McMahon Jan 15 '14 at 4:36
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    \$\begingroup\$ Hi,thanks for the input, as I'm not into building my own micro controllers ( I have no experience in doing this) I am looking to purchase a controller that may fit my needs, I do have images of the small actuators I have made, but cannot see anywhere on the site where I can upload images. thanks to Phil and Russ. \$\endgroup\$ – user35575 Jan 15 '14 at 13:44
  • \$\begingroup\$ Once you get a little more "rep" on this site you'll be able to post photos as part of answers or questions. Or, if you wanted, I can give you an email address that would cause attached images to be auto-magically posted to a related photo album page. \$\endgroup\$ – Russell McMahon Jan 15 '14 at 21:42
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An H-bridge with current detection sounds exactly right. You could also incorporate some kind of limit switch, either a mechanical switch, or a hall effect sensor, or an opto-interrupter, rather than relying on detecting the stall at the end of the travel. It's an extra part to buy, but perhaps more robust. You can avoid the mechanical stress from the maximum motor torque into the stops at the end of the travel and have less chance of false-positives leaving your doors half-open.

You could probably use an Arduino, but you could also just get a microcontroller which would be smaller, cheaper, and lighter. An H-bridge can be a simple as four discrete MOSFETs. There are also integrated H-bridges that have all four transistors in one package, which might save you some weight and assembly complexity. Unless this is a very large model, you can probably get away with a lighter, smaller, and cheaper solution than the Arduino motor shield.

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  • \$\begingroup\$ The OP could prototype a solution on something like an Arduino and then shrinkify it. There are also things like Ardupilot and other UAV-oriented variants on the theme. \$\endgroup\$ – RedGrittyBrick Jan 14 '14 at 23:35

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