construction:electronics:servos

Servos

FrryFox wrote an article on servos, an introduction and reviews.


From: Joe Dunfee
Subject: Servomotor Control Circuit

I finally got around to converting to ASCII art a schematic for a circuit that can directly control a servomotor like those used in remote control cars. As I have mentioned before, these are also used in puppets to electronically control them. Please note that you must use a mono-space font to view it correctly, or else it will be gibberish.

         _____               +5 Volts
         |   |                  |
         V   |                  |
   ___/\/\/\_|___/\/\/\_________|
   |  5k Pot      4.3k     |    |
   |                     __|____|__
   |                    |  4    8  |
   |____________________|7         |
   |                    |          |
   |                    |   555    |
   | 1N457 Diode        |  TIMER   |
   |____|\|_____________|6         |___________
   |    |/|       |     |          |   Output to
   |              |     |          |    Servo
   |              |     |          |
   |__/\/\/\______|_____|2         |
       56k        |     |__1____5__|
                  |        |    |
                 _|_       |   _|_
          0.33mF ___       |   ___ 0.1mF
                  |        |    |
                  |________|____|
                  |
                --|--
                 -|-
                  -

Briefly, the purpose of this circuit is to generate a pulse on the output line for 1-2 milliseconds in duration, and then be off for about 10 milliseconds. As the 5k pot is turned the duration of the pulse will vary and this is what signals the servomotor to move. In actual use, I have substituted the 5k pot with two pots in parallel. One 10k that I use for the actual moving of the servomotor and another in parallel (maybe 100k) that serves as a gain control. (to adjust the sensitivity of the main control pot) I also change the 4.3k resistor for a 10k pot and it becomes the centering adjustment. A separate power supply for the circuit and the servos themselves might be recommended because they generate alot of noise. However, I use a single supply for both and add large caps to filter the noise.

    ______________________________________
    |            |                       |Red
   _|_+      ____|___                 ___|___
   ___ 5     |       |               |       |
   ___volts  |control|_______________| Servo |
    | -      |Circuit| Output  Yellow| Motor |
    |        |_______| Pin 3         |_______|
    |            |                       |
    |____________|_______________________|Black

Hope this helps. It is a very simple circuit if you know electronics, but I know many of you reading this don't know alot. However, if you have soldered a kit together, you can probably do this circuit.

From Marcwolf

Nowadays a much better and easier alternative is to use a PicAXE chip. These are single chip computers (like the Basic Stamp) but for a fraction of the price.

They are very easy to program and do not need a specialised programmer to load up the code. The programming language for them is free

This is the main site http://www.rev-ed.co.uk/picaxe/ where you can get the information.

For example - you can fet a PicAXE 08M for about $5AUD, the board for you to experimetn with $9AUD, and then a programming cable $20AUD. From there you have everything you need to experiment with.

This is an example of some tail wag code

Start:
  servo 1, 75
  pause 1000
  servo 1, 200
  pause 1000
goto Start

Now this will make the servo on PIN 1 move forward, and then move back ove a 2 second cycle. There you have a simple tail wagger.

Hope this helps someone.. and the sky is the limit on what you can do.

/home/furryfursuit/faq/data/pages/construction/electronics/servos.txt · Last modified: 2011/08/11 12:01 (external edit)

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