81F Posted July 8, 2016 Share Posted July 8, 2016 I am in the process of dabbling with a radio controlled boat (but that is not why I'm asking) and wounder if the servos used to control the rudder can be used to operate gates, engineshed doors or even disk and crossbar signals on my model railway. If yes how would I wire them up to a switch. Link to comment Share on other sites More sharing options...
Howbi Posted July 8, 2016 Share Posted July 8, 2016 This is one to be considered.........../media/tinymce_upload/cb9c4509b7a5d37a0da3838910a5f3ce.png Link to comment Share on other sites More sharing options...
Chrissaf Posted July 8, 2016 Share Posted July 8, 2016 You need a servo control board interface. Although a Servo contains an electric motor it doesn't operate like an electric motor..A Servo has three wires:.A +6 volt (Maximum) or +5 volt DC supply voltage.A 0 volt return.And a 'Control Wire' ..... 5 or 6 volt peak to peak square wave control signal..It is the digital signal applied to the 'Control Wire' that positions the Servo arm. The digital signal is a square wave that provides a variable pulse width that ranges from 75 to 225 milliseconds. The mid point in the pulse width range is 150 milliseconds and denotes the physical servo mid position..Thus, you cannot just connect the Servo to a mechanical electrical switch and control its position with a DC voltage. You need a circuit that generates the required variable pulse width. A switch could then provide the input to the control circuit to provide the switching between clockwise and anti-clockwise Servo movement direction..There are many electronics circuits some based on NE555 timer ICs published on the net (one is published in the document hyperlinked below - see page 117). There are also ready made 'ready to run' Servo controllers that can also be purchased..EDIT: I see that HB has just published one such ready made control board. There are others, more basic and at lower cost. Google 'Servo Controller'. The 'Megapoints Servo Controller' is IMHO the Rolls Royce of Servo controllers..See Chapter 7 in this Internet PDF resource (Chapter 7 - Page 106 to Page 122 are all about Servos and Controllers):.http://www.talkingelectronics.com/EMR-1/MERG/MERG-RailwayBk-1.pdf Link to comment Share on other sites More sharing options...
2e0dtoeric Posted July 9, 2016 Share Posted July 9, 2016 Search also for 'Servo Tester', they can control up to three at a time, but all tied together, so they all move in the same direction when you turn the knob. About £3 each, depending on where you look!The one I have (for testing servos!) has a click button switch that either sweeps the servo end to end continually, goes to centre, or 'follows' the knob.For servos - for what we want as railway modellers, the dead cheap translucent blue ones that are around 4 for a £10 are perfectly adequate. Link to comment Share on other sites More sharing options...
Chrissaf Posted July 9, 2016 Share Posted July 9, 2016 The 'Blue' ones Eric mentions (I use them too) are TowerPro SG90 and can be bought for less than £2 each if you shop around on eBay. Link to comment Share on other sites More sharing options...
Chrissaf Posted July 9, 2016 Share Posted July 9, 2016 A technical correction to my earlier post. In it i said......The digital signal is a square wave that provides a variable pulse width that ranges from 75 to 225 milliseconds..This should have read:."The digital signal is a square wave that provides a variable pulse width that ranges from 75 to 225 microseconds." Link to comment Share on other sites More sharing options...
81F Posted July 9, 2016 Author Share Posted July 9, 2016 Thanks very much for the ingo have just ordered the servo tester and some servos. Link to comment Share on other sites More sharing options...
2e0dtoeric Posted July 9, 2016 Share Posted July 9, 2016 Chrissaf, your edited and corrected post about servo pulsewidths is exactly the same as the one you corrected! Link to comment Share on other sites More sharing options...
Bulver Posted July 9, 2016 Share Posted July 9, 2016 I see Chrissaf's edited post amended 'milliseconds' to 'microseconds', but not something to blink your eye or you'd miss it! Link to comment Share on other sites More sharing options...
Bulver Posted July 9, 2016 Share Posted July 9, 2016 duplicate post - how did I do that? Link to comment Share on other sites More sharing options...
Chrissaf Posted July 9, 2016 Share Posted July 9, 2016 Problem is, even my lamented correction was in error, but I hoped no one would notice. Just couldn't get my decimal point in the right place. Problem with writing posts from memory rather than looking up the reference book material first. There is no hope for me........The correct pulse width range is 0.75 to 2.25 milliseconds which is 750 to 2,250 microseconds. Thus, it is neither 75 to 225 milliseconds NOR 75 to 225 microseconds. Link to comment Share on other sites More sharing options...
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