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  1. #1

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    converting air to electric retracts.

    If anyone would like information on converting air retracts to electric i'm happy to post my research of the last few months on the topic. I've been building a Mick Reeves Lightening and wanted a much tighter retract to fit snug in the wing. I've used a screw jack system, very easy engineering to convert and have used an Arduino uno micro controller with a arduino motor shield to operate the gear doors, sequencing and retract motors. I'm new to RC Universe and this forum but would be happy to share for the benefit of all.

  2. #2

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    RE: converting air to electric retracts.

    [img]webkit-fake-url://034E32BB-0484-4731-962B-E35E658A84BA/image.tiff[/img]

    Motor shield on top of the UNO


  3. #3

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    RE: converting air to electric retracts.

    [img]webkit-fake-url://51B42D1A-41F2-4659-9863-110E32879EB7/image.tiff[/img]
    Retract mechanism note the small motor with gearbox

  4. #4

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    RE: converting air to electric retracts.

    The concept behind this conversion is nothing new but most people are afraid of the electronics associated with it. conversion of an air retract is fairly straight forward. the piston is removed and a 4mm threaded screw driven by a 6v geared motor is used to drive the gear up and down. when the screw reaches the end of it's travel the motor stalls and draws a lot of current. Its this increase in current draw that trigers the Arduino microcontroller to shut the motor down.

    The arduino UNO is the brains behind the system it's cheap and you can buy one online or at Maplins stores or electronic hobby stores. You'll also need the Arduino motor shield that fits on top of the uno. Thats it for the electronics. The motor you use will depend on the load and speed you wish to raise your gear by. i found a great source of cheap motors from this outfit www. uxcell.com . search for 6v 220rpm motors. http://www.uxcell.com/search.php?cat...selectSearch=1The arduino is programmed from a computer and if you go on you tube you'll find hundreds of tutorials on the topic. Have a look atArduino - HomePageand search on you tube for Massimo banzi tutorials. Arduino Video Tutorial 01: Get to know your Tools with Arduino CEO .... I'll post the code required for the retracts shortly once i've taken pic etc.



  5. #5
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    RE: converting air to electric retracts.

    Hi Mustang, I have converted to electric my BVM retract for my scrath built Balsa Bandit with the Electron Retracts electronic, but I need some device for actuating doors, can you help me?

    I can't see the pics.

    BR

    Jesus A. Serrano

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    RE: converting air to electric retracts.

    search the internet for gear door sequencer www.ebay.co.uk/itm/Retract-Sequencer-for-Radio-Controlled-RC-Models-/230914980304. If you want to do it within a microcontroller you need to write code.

  7. #7

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    RE: converting air to electric retracts.

    Here's a link to the system working.       http://www.youtube.com/watch?feature...&v=QQ0Qz-sYIgQ

  8. #8

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    RE: converting air to electric retracts.

    This is the code you'll need to program your Arduino UNO.  If you're familiar with code you'll get the idea.  if not i'll explain in later posts
    cut and paste from #include<Servo.h......



    #include <Servo.h> //needed to operate the servos
    #define midlimit 1700
    Servo myservoA;
    Servo myservoB;

    int Bbrake=8;//brake signal for motor B
    int Abrake=9;//brake signal for motor A
    int motorspdB=11;//PWM speed signal for motor B
    int motorspdA=3;//PWM speed signal for motor A
    int ch5;
    int motorA=12;
    int motorB=13;
    int sensorPinA = A0;    // select the input pin for the current
    int sensorPinB = A1;    // select the input pin for the current
    int switchpin = 2;
    int sensorValueA = 0;  // variable to store the value coming from the sensor
    int sensorValueB = 0;  // variable to store the value coming from the sensor

    void setup () {

      pinMode (6, INPUT);
      pinMode (13, OUTPUT);//motor B enable and direction HIGH or LOW
      pinMode (12, OUTPUT);//motor A enable and direction HIGH or LOW
      pinMode (8, OUTPUT);//Brake motor B
      pinMode (9, OUTPUT);//Brake motor A
      pinMode (4, OUTPUT);//servo A pin
      pinMode (7, OUTPUT);//servo B pin 
      pinMode (switchpin, OUTPUT);
      myservoA.attach(4);
      myservoB.attach(7);
    }
    void loop () {

      int limitA = 550; //this is the current limit for motor A
      int limitB = 300; //this is the current limit for motor B
      sensorValueB = analogRead(sensorPinB); //this reads the value of current for motorB and sets the variable sensorValueB
      sensorValueA = analogRead(sensorPinA); //this reads the value of current for motorA and sets the variable sensorValueA
      int iB = 0; //this creates and sets a variable named iB which we will use to make sure the motors stop once they reach overcurrent condition
      int iA = 0; //this creates and sets a variable named iA which we will use to make sure the motors stop once they reach overcurrent condition
      myservoA.writeMicroseconds(900);
      myservoB.writeMicroseconds(900);
      ch5 = pulseIn(6, HIGH);

      if (ch5 < midlimit) {
        digitalWrite(switchpin, HIGH);
      }
      else {
        digitalWrite(switchpin, LOW);
      }
      int updwn = digitalRead(switchpin); //this sets the value of the variable updwn which is read from transmitter switch
      int updwn2 = digitalRead(switchpin); //this sets the comparison value of updwn which is read from transmitter switch

      while (updwn == updwn2) { //the while loop here knows the current state of the switch updwn. during the while loop it will continually check 
        //the state of the switch by setting updwn2 therefore once the state of the switch changes it will exit the while loop

        if (updwn==1 && sensorValueB < limitB && iB==0) 
        {
          analogWrite  (motorspdB,255);
          digitalWrite (motorB,HIGH);
          digitalWrite (Bbrake,LOW);
        }
        else if (updwn==0 && sensorValueB < limitB && iB==0) 
        {
          analogWrite  (motorspdB,255);
          digitalWrite (motorB,LOW);
          digitalWrite (Bbrake,LOW);
        }
        else 
        {
          analogWrite  (motorspdB,0);
          digitalWrite (Bbrake,LOW);
          myservoB.writeMicroseconds(2095);
          iB++;
        }
        delay(300);
        if (updwn==1 && sensorValueA < limitA && iA==0)
        {
          analogWrite  (motorspdA,255);
          digitalWrite (motorA,HIGH);
          digitalWrite (Abrake,LOW);
        }
        else if (updwn==0 && sensorValueA < limitA && iA==0) 
        {
          analogWrite  (motorspdA,255);
          digitalWrite (motorA,LOW);
          digitalWrite (Abrake,LOW);
        }
        else
        {
          analogWrite  (motorspdA,0);
          digitalWrite (Abrake,LOW);
          myservoA.writeMicroseconds(2125);
          iA++;
        } 
        delay(200);

        sensorValueB = analogRead(sensorPinB);
        sensorValueA = analogRead(sensorPinA);

        int ch5 = pulseIn(6, HIGH);
        if (ch5 < midlimit) 
        {
          digitalWrite(switchpin, HIGH);
        }
        else 
        {
          digitalWrite(switchpin, LOW);
        }
        updwn2 = digitalRead(switchpin);
        delay(100);

      }
    }



  9. #9

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    RE: converting air to electric retracts.

    more detail on the construction of the retract gear. https://www.youtube.com/watch?v=vAoHm3Wf0Bg

  10. #10
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    RE: converting air to electric retracts.

    Nice Job, thanks for sharing. I could also see a variant as a canopy actuating system.

  11. #11

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    RE: converting air to electric retracts.

    Not sure if anyone is following this post. I'll upload a video re the Arduino board connections. Lot easier than drawing schematics.

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    RE: converting air to electric retracts.

    Ok final post, this is the link to youtube for the conecctions on the arduino. https://www.youtube.com/watch?v=4Er5Vdr5sJM 
    one other thing, within the code you have a couple of settings that may need to be changed to make your gear work properly.
    int limitA = 550; //this is the current limit for motor A
    int limitB = 300; //this is the current limit for motor B
    you may need to change values 550 and 300.  these values are the motor stall limits.  Higher values will mean that potentially your motors will still be fed power when they reach the end stops of their drive.  Lower values could mean the motors switch of even before they start to drive or as soon as any slight resistance is felt.  It's important to make sure the LEDs on the motor sheild on A and B motor terminals are not lit when the motors reach their travel end.  if they stay lit you are still drawing current from the Lipo.  if you fly for ten minutes with the LEDs lit you'll have a flat lipo when you want to lower the gear.

    The other setting in the code you may need to alter is the position the gear door servos moves to.
    myservoA.writeMicroseconds(900);
    myservoB.writeMicroseconds(900);
    myservoA.writeMicroseconds(2125);
    myservoB.writeMicroseconds(2095);

    The values 900  2125 and 2095 are the position the servo arm will move to, (open and close).  Play with the values and you'll see the arms move more or less.

    Good luck, please post a reply if you've found this forum useful.

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    RE: converting air to electric retracts.

    one other thing.  Make sure when you build your screw jack you put a thrust bearing into the design and travel end stops.  For thrust bearings i use the ones from model helicopters that attach the main rotors, the ID is 3mm so you'll ned to take the thread off your 4mm screw. If you don't have end stops you'll bend your screw jack if you get any side loads on the gear.  If you don't have a thrust bearing you'll wreck the motor in no time at all.

  14. #14

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    RE: converting air to electric retracts.

    And another foot note.  One of the main advantages of this type of gear is when the gear is fully extended and fully retracted there is no movement in the leg.  The screw jack winds the gear tight against the stops and takes all the play out.  The disadvantage is the speed it takes to raise and lower the gear and another consideration is g load.  if the aircraft is pulling significant gs the gear will stall going up... one thing to watch for.  

    The retracts are being fitted into a Mick Reeves English Electric lightning.  I'm about a couple of week away from the first test flight.  fingers crossed it goes well.  i'll post a video of the maiden flight.   

  15. #15

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    RE: converting air to electric retracts.

    Hi mustang I,m building my own electric retracts for a 90" span model could you tell me what motors and gearboxes you used and where to source them.

    I have built mine using precision rolled 5mm ACME lead screws but to keep costs down made my own lead srew nuts. I did this because I know a couple of modellers that have fitted commercial units and suffered lock up or lock down which I think is due to them being fitted with standard screw threads, which is of course what  screw threads are supposed to do when they are tightened.

    Thanks

  16. #16
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    RE: converting air to electric retracts.

    Hi Windy, I have converted to electric a BVM gear for mi scratch Balsa Bandit and I have make my own M-4x70 thread rods in the lathe. I have logged 3 fligths, today and tomorrow a few more, and no issues. I attach some pics.

    BR

    Jesus A. Serrano
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  17. #17

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    RE: converting air to electric retracts.

    Hi Jesus looks great well done.

    I haven't converted anything I just made the whole lot. I'll try to get some pics and post them.

    What motors are you using. I,m using some of the Pololu motors and gearboxs can't rememember what ratios though.
    As I said I am using acme lead screws as these aren't to expensive I could have cut my own screw threads as you have I just felt proper lead screws would be more reliable. The problem is the nuts for these are really expensive so I made my own nuts from acetal and it took just a couple of minutes each to form the acme thread. A breeze really.

    I do have a couple of friends that have fitted commercial units with standard threads and they say on occasion when they hit the end stops they do some times get jammed. So I thought I'd try to avoid that from the word go. And they work great. I have intentionally driven them into the end stops to the point of almost destroying the motor and gearbox as a test and they have never yet got stuck.

    Windy

  18. #18
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    RE: converting air to electric retracts.

    Hi Windy,

    the gear motors are from Pololu at 1:35 gear reduction:

    http://www.pololu.com/catalog/product/1091

    and the electronics is RB-45 from Electron retracts. I put a couple of "O" rings at each end stops in the threaded rod and any issues. The thread rod is made of F-210 (foral steel)
    and the pin from brass.

    Jesus A.Serrano

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    RE: converting air to electric retracts.

    Jesus a couple of pics of my retracts as promised I think your using the same motors as me then, I think with a different ratio though but can't be sure though as I can't remember .

    The other thing I also chose to do was to use a curved locking pin guide slot as I wasn't to sure of the power of the motors and with a curved slot the leaverage is basically constant over the full movement of the retract, this does make the unit a bit bulkier but I wasn't to worried about this as there's plenty of room in the wing. The oleos you see are for the moment just solid aluminium bar 20mm dia.. The wheels are Dubro 4.5" dia. not the lightest in the world but they'll do. I intend to remove the plastic hubs and make my own from ali with brakes.

    The model these are intended for is a 90" span Fairey Gannet. I have already made the contra prop unit which also has variable pitch to both props. The next challenge will be the electric folding wings, these fold in two places which should prove interesting. I intend to use a similar system to the retracts for these again controlled by the Arduino.
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  20. #20
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    RE: converting air to electric retracts.

    Windy, don't worry about the power of this Pololu gear motors, but for your Fairey I guess you must select a 50:1 reduction. I have had any minor issues with the BVM gear conversion, so my next proyect, a 2,20 m. scratch build Viper jet will fit my own retracts with a linear pin guide and a thread rod supported by two small ball bearings. Is the system used by Electron Retracts and this guys have a lot of experience. Just my 2 cents.

    Jesus A. Serrano

    P/S Very interesting proyect, retracts, contra prop unit, folding wings, wow! You have a lot of work.

  21. #21

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    RE: converting air to electric retracts.

    Jesus I think your right I do have the 50:1 Gearboxes but I have the smaller motors 6V. Although I am running them at 7.4V.

    I just looked at the Electron site, beautifully made retracts at a good price. Wouldn't have been any good to me though as i needed 95deg. because of the anhedral for the first part of the wing on the Gannet.

    Although I have got my undercarriages going up and down controlled with the Arduino and current sensing at the end points theres still a lot to figure out before its suitable to install in a plane. So thier controller for 65euro's is interesting, Can the current sensing in this unit be adjusted to suit different motors.

    A couple of photo's of the Contra Prop unit powered by two brushless motors.

    Windy
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  22. #22

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    RE: converting air to electric retracts.

    Windy i bought my motors from Uxcell online 6v 220 rpm. i use a standard m4 threaded bar. i run the motors on a three cell lipo so i'm puting more voltage through them than recommended but to date they are still wotking fine.

  23. #23

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    RE: converting air to electric retracts.

    Cheers for that Mustang I must admit I have run mine on 3 cells but thought it a bit fast so have used it on 2 cells since, but everything thing seems fine so far. Nice to hear your ok on 4mm thread I'll probably stick with the acme though because there not that expensive and are really smooth in operation and the way I make the nuts there's no backlash at all and as I said i can form the thread in each nut in less than 2 mins. Although machining the the outer part of the nut and the guide pin block takes a bit of time so all in all probably works out about the same overall time as cutting my own screws.

    The pitch on these screws is a bit courser though at 1.25mm as opposed to 0.7 for 4mm thread. but they are beautifully made though, precision rolled from 303 stainless and a 125mm length is just £14. The price of a nut though was a bit high, I think about 50 odd pounds each, which is why I decided to experiment with making my own nuts from acetal (the bought nuts are made from some plastic also), and it proved to be remarkably easy to do. And I think that the loads that these are likely to be subjected to acetal is more than adequate.

    I,m gonna copy your sketch and give it a try. This is my first foray into the Arduino and programming.

    Windy

  24. #24

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    Great thread! Hope it's still being monitored!

    I'm trying to accomplish the same tasks (control Robart electric retracts and sequence gear doors) on my TF Giant Corsair. Oregon Scale Aviation has an adequate unit, but I thought I'd dive in and try to get an Arduino Uno to do this for me, in addition to controlling LED landing lights and navigation lights. The twist: I'd like to use Futaba sBus instead of a discreet PWM channel from the receiver. Any thoughts on this?

    Thanks!

    Marsh
    Taking off is optional - landing is MANDATORY...

  25. #25

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    Hi Mustang,
    I'm a newbie on r c universe and have been reading your thread with interest, I have also made my own electric actuators and converted a set of air retracts for a scratch built turbine jet, I have also made smaller actuators to operate the retract doors, you can see some images of these on my post, (All electric retract jet ) r c universe electric jet forum, I am not sure I can use an Arduino controller as I want to use the smaller actuators I have made to control the doors rather than servo's, of course the servo's have feed back to control the end stops, however my actuators are two wire from the motors,therefore I require a control to trip over current at the end stops of the actuators, I envisage using two Electron/ Xicoy retract controllers which integrate over current trip and an H bridge to change the polarity of the motors to reverse the next retract action, one RB 45 controller to operate the three retracts and a further one to control the door actuators the controllers will allow for a delay sequence for the retracts after the doors open,do you think this system will work , or could an Arduino be programmed for this operation without feedback from the door actuators.
    I'm a retired mechanical engineer so not too sure about the electronics side, however any advice would be most appreciated.
    Regards
    Mike


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