Technical, Techniques, Hints, and Tips > The "Black Arts!" ( Electrics & Electronics )

Operating servos that rotate 180 degrees

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roycv:
Hi all, thank you for your responses, I was trying to avoid having a servo stretcher in each installation.  Have chased one down at £8.85 + p&p.  But will be experimenting with Tx.

Any Tx ideas would be welcome I am OK soldering and circuits generally as it was a bit to do with work.

I have veroboard and a hoard of ancient electronics from my experimental days and kit assembly.  Remember making a Micron Tx and Rx's from kits back in the 80's.
I was a bit surprised how dear they were.  I have a very nice speed controller (10 amp brushed) from Bang Good that was less than £4.  You have to change the leads as they are Rx battery type, but they are cheap enough.

Any ideas about playing with the AVC pot on old Hitec Tx's?  I use these as they have a convenient 3rd. channel that is on the top and just goes where my thumb is.
kind regardsRoy


 I know I can get cheap 2.4 Ghtz rc but I use a servo adjuster type channel for tweeking a flying jib on a couple of yachts.

cos918:
Hi
Two resistors in line on the other pot wires will do it . With any servo you need to were the manufactor has put the mechaniacl stop. Some will alow more that 180 deg with out mods some wont

John

roycv:
Hi Cos, yes that works well and I have been doing that for many years, well 30 or so, but when I was making a Micron Tx all the extras were in the Tx.  Mixer etc.

I have just taken a Hitec 3 ch. 40Mhtz FM Tx apart and the answer may well lie with the AVC adjustment (volume control) but it is rather integral with the motherboard and I decided not to touch it. 

I did put a servo lead in to act as a parallel charging socket.  Rather than a low current non-intel  charge point I can use an intelligent 4 - 10 cell charger I have.
The reason for all this is that I can use standard servos which have a high torque as sail arm servos and in smaller yachts.
I have gone down the servo expander trail this time as I want something quickly and I found a UK source at a good price, I will report how I get on.
Kind regards to all who have contributed.
Roy

Hellmut1956:
If you use i.e. an Arduino UNO board from China you have the cheapest way to adapt the functionality of servos if not limited by hardware in the servos. You can get an Arduino UNO board from China extremely cheap including shipping costs! The Arduino would digitize the PWM signals from all channels of your RC receiver and generate for each of the channels individually the PWM output to the servos. You can find information about how to write the code.


Even cheaper it is with an ESP8266 based board like this one! But it is a bit more challenging it as you need to add the support for the board in the Arduino IDE, the programming tool for all this boards.


Just to emphasize: Programming the digitizing of the PWM channels is very simple: You use a clock within the microcontroller. You start the clock when the signal changes from low-high and you stop it when the signal changes from high-low. Save the value of the counter, this is a digital information of the length of a signal. You track what is the length when you pull control and dimmers maximal to get the shortest signal length and corresponding you get the maximum length. Then all you do is to generate a PWM signal on your board to control the servo by adjusting the min and max length to what you need to have your servos extended or reduced movement angle!

malcolmfrary:
Servos use a 270 degree pot as a sensor.  the 90 degree movement generally puts the required travel somewhere in the middle with plenty of room at each end.  Extending the travel does run the risk of causing the travel to go past the track end inside the pot, or into the mechanical end stop.  Both are unlikely, but a change of transmitter between, say, a Futaba and anybody elses might manage it. 
For a 180 degree task, I would use a low turn winch with an arm rather than a drum and a travel adjuster to go down from 720 (2 turns) to 180 (half a turn).  In a sail boat, of course, just using it as a drum might work well.

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