 Joined: 04/04/2014(UTC) Posts: 22 Location: Auckland
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Hi all. I wonder if any of you electronic bofs can help me. I happened to come across a DIY project for building a simple servo controller on the Model Railroad Hobbyist magazine forum https://model-railroad-hobbyist.com/node/26088 and https://model-railroad-h...st.com/node/26088?page=1 I have a lot of old Futaba IC servos from my model RC flying days and wanted to use them for activating my Kibri loco roundhouse doors. This topic was published in 2016 on MRH and I have the feeling Pelsea is no longer there. My question is I have followed his design on a bread board as in the images but when applying 5v power, the servo will only rotate anti clockwise. Neither the pots or switch have any affect. Just can't understand what I'm doing wrong? I realise that I could probably buy a controller/driver but I get a lot of satisfaction from attempting these small DIY projects. Any help would be much appreciated.  
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 Joined: 23/07/2014(UTC) Posts: 8,464 Location: ENGLAND, Didcot
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Originally Posted by: skukuza 
My question is I have followed his design on a bread board as in the images but when applying 5v power, the servo will only rotate anti clockwise.
Neither the pots or switch have any affect. Just can't understand what I'm doing wrong?
I realise that I could probably buy a controller/driver but I get a lot of satisfaction from attempting these small DIY projects.
Any help would be much appreciated.
I would suggest putting an LED with a resistor on the output of the second timer. Use a resistor between 100 ohms and 1k for a 5V supply. Then when turning the pots you should see the brightness of the LED change. If you cannot get it to change brightness try connecting the LED to the output of the first timer to see if that is producing pulses. This would be easily done by verifying the brightness of the LED and comparing it to what brightness it shows when connected directly across the 5V.
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 Joined: 04/02/2011(UTC) Posts: 3,555 Location: Paris, France
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Hi Kevin I like a lot servo motors but unlike you I don't have the courage and patience to make a controller myself. Here is the very little I know: There are a lot of servo type but in train modeling a common type is a 5V 90° servo. For these, 2 wires bring the 0 and +5VDC while the last one bring the PWM signal (Pulse Width Modulated) to the servo. So in your case it is very easy to verify you 0 and +5VDC connections and likely the problem is with the PWM output signal of your circuit. Ideally an oscilloscope would tell you all. Here is on my layout a video on Faller Car System Stop and Direction servos on a bridge and the overall result Good luck finding the culprit Jean |
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 1 user liked this useful post by JohnjeanB
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Joined: 04/04/2014(UTC) Posts: 22 Location: Auckland
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Thanks Alan and Jean for your input. Alan I have added an LED to both the first and second timer outputs but the LED does not change brightness or frequency when rotating the pots? I'm convinced I have something wrong with my arrangement of the pots and resisters and the connection to the 556 timer? I have added an image of the MRH circuit as I see it. Let me know if you can see anything wrong.  Jean I love your layout. BTW I have subscribed to your YouTube channel. Yes I am aware of the wiring and technicalities of servos especially that they operate between 1.0ms and 2.5ms signals. Depending on the frequency the servo will rotate clockwise or counter clockwise. Thanks and regards, Kevin
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Joined: 04/04/2014(UTC) Posts: 22 Location: Auckland
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BTW I you can watch my layout on YouTube at kevin hayne.
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