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[Tug-Kenny RIP]

The title says it all really.

I need to know the theory of these little devices,  after all these years of boat building.   

How does one control a servo without a radio signal.  I would like to be able to throw a switch to move it a set distance clockwise and have it return to neutral when the switch is opened. Then I would like another switch to have it move in the opposite direction until switched off, where is also would return back to neutral position.  It would be nice to be able to pre-set the distance travelled.

I appreciate there are Servo controllers around so how do these work please.

Thanks guys

ken

[C-3PO]

Hi Ken,

Servos are controlled by sending them an electrical pulse of variable width. ...

The servo expects to see a pulse every 20 ms.

The length of the pulse will determine how far the motor turns. For example, a 1.5 ms pulse will make the motor turn to the 90 degree position (neutral position).

Normally the pulse would range from 1ms through to 2ms with 1.5ms being the central neutral  (90 degree) position.

This type of signal is normally referred to as PWM - Pulse Width Modulation

A very cheap way to achieve what you are after is using an Arduino - cost less than £10

Have a look at this video - the switches are push button rather than throw type - ( a very easy thing to change)

https://www.youtube.com/watch?v=Y6l4wRgkX-w

and a little about PWM & Servos

https://www.youtube.com/watch?v=YMwp3g4q2M4

For more info hit Youtube and search for PWM & Servo's - you will find hundreds of video's

Happy to help you get a working solution

Regards
C-3PO

[roycv]

Hi, if you do not mind turning a knob to move servo and then back, then a cheap servo tester will do the job, the last one I bought was 99p inc p&p! don't know how they do it but it works fine. 
Just plug in a battery and there are 3 servo outlets.  There is a choice of manual and 2 auto test ones, one a switch of servo end to end and the other continuous end to end.

Go to ebay to check, I had some 'little blue ones'.

regards Roy

[Tug-Kenny RIP]

Wow,  a good response.  Thank you.

I had a feeling it's this type of device.   I shall be researching the details and may proceed along this path.

Thanks again

ken

[Brian60]

There is a video on youtube showing servo control from a Double Pole Double Throw switch that is crosswired. Centre off throw the switch one way and servo moves to left, throw switch other way moves to the right. Dunno how they really achieved it because I only passed it in browsing for arduino stuff.

[boat captain]

There is a video on youtube showing servo control from a Double Pole Double Throw switch that is crosswired. Centre off throw the switch one way and servo moves to left, throw switch other way moves to the right. Dunno how they really achieved it because I only passed it in browsing for arduino stuff.

I wired the crane on my Grab Dredger that way. 
It is also used to operate points on model railways.

[malcolmfrary]

The really cheap and down and dirty way to move between two set points is to use a pair of the really cheap servo testers like this - https://www.ebay.co.uk/p/Multi-Servo-Tester-3ch-ECS-Consistency-Speed-Controler-Power-Channels-CCPM-D/893979761?iid=112430223970 - and a switch with a change over contact to swap between one and the other having set the required end points on each.
Or dive in with a soldering iron and some parts with a couple of circuits like this - http://www.learningelectronics.net/VA3AVR/gadgets/servo4.htm - but I suspect that the parts will cost more than the ready built tester.
 

[Tug-Kenny RIP]

I have examined the circuitry on various sites and decided to go the mechanical route.  I didn't realise the bulkiness of the circuitry that would be required to electrically control servos.  (I have to keep the weight down)

I shall remove the servo's internal electrical control board and wheel stop pin and drive it as a motor.  The controls will be with limit switches as I only need a quarter turn clockwise and return to top centre and then anti clockwise for a quarter turn.

All this will be shown on my Greek rowing ship  'Bireme'  build, as it will be needed to operate the oars movement going up and down.

Many thanks for all your thoughts as it's turned out to be a very interesting subject.

Cheers

ken

[C-3PO]

Hi Ken,

Should you want to revisit this is the future - the Arduino comes in many different shapes and sizes

Below is a picture of the Arduino Nano - weighs 7g / measures  18mm x 45 mm

You could also have specified the speed you wanted the servo to move as well as the limits


Regards
C-3PO

[Tug-Kenny RIP]

Funny you should say that, as I am very interested the Arduino and would like to have a go one day.  It seems one is only limited by imagination and the things that they can do is fascinating.

Maybe, an Arduino controlled boat is next on the blocks.   

Cheers for your help

ken

[C-3PO]

Hi Ken,

In the unlikely event you find yourself with some spare time these videos make very easy watching and and unravel the world of Arduino in quite a gentle way...

https://youtu.be/09zfRaLEasY

or

https://youtu.be/d8_xXNcGYgo

We also have a forum for RC & Arduino which is mainly model boat related - you are very welcome to join - http://rcarduino.freeforums.net/

Regards
C-3PO

[Tug-Kenny RIP]

Very interesting.  I have bookmarked them and will look into it.

ken

[roycv]

Hi now we know what it is for may I suggest that you still use a cheap servo tester. 
Put a brass rod through the control knob and then use a slow revving motor with a disc and arm attached so that the servo tester knob is rocked backwards and forwards as a piston on a steam engine.
Howes do a powerful metal geared servo to work the oars, perhaps one servo for each side all run from one tester.
Guaranteed to stay in sync and speeding up the slow revving motor can get you up to water skiing speed.
regards Roy