How to control 8 servo motors with a PC ?

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1. Introduction, remarks.

It is in fact very easy to control a servo motor with a computer. Those motors are used in RC (radio command) for airplanes, car and boats. Those motors have built in the whole electronics to control them. All you need is power (5v) and a special signal to adjust there main arm position. They generally have 3 wires :

You need to give them permanent power. Is so, they will stay in one position. To unlock them, turn the power off. To control the arm's position, you need to send , every 20Msec (no critical) a pulse of 1.5 -> 2 Msec length. The length of the signal gives the position of the arm. Sending this signal is exactly what a computer can do. But the most complicated task is to set up a high-res timer (1/100 Msec). Windows provides all the API needed to do so. We'll use the // port of the PC to control up to 8 motors (1 motor for 1 data line)

2. The electronic

No components, just wires !

What you need :

You simply have to connect all the grounds and +5V together, and each motor's data line to the LPT port data output. The LPT data lines are pins 2 to 10.

There are no buffer or transistors. You can safely omit them if you are using standard servo. Keep in mind that the computer needs only to control the servo's, through the data line, and that he doesn't need to power them.

3. The "software"

3.1 A basic soft (with Delphi 3.0)

No need to break your head against the walls, we only have to make a good delay routine, and a good LPT control routine. Some assembly needed, as win32 doesn't allow  direct outputs controls.

We simply create a timer which sends a signal every 20 Msec of a length between 1.5 and 2 Msec.

This soft is not available for downloading because it's not very useful and because I've lost it. You'd better download the full version...

3.2 The full version (also with Delphi)

This one can control up to 4 servo's (upgradable to 8) with the mouse or a joystick. You can program difference steps and save them in a text file.

It's not very useful to add a lot of comments, see the source for details...

4. Tests

Branchez tout le bazar et lancez le programme de base:

5. D’autres développements?

Ce programme devrait déjà vous permettre de faire des petits essais. Essayez aussi la version plus complète et modifiez - là comme vous le sentez. Il devrait d’ailleurs être possible, avec ce système, de commander un petit robot (max. 8 axes.. pas si mal, et plutôt dur à gérer) ou d’autres choses... A vous de jouer. A ce propos, je serais enchanté d’avoir des nouvelles, des questions, de ceux qui ont expérimenté ce système... Ou d’autres systèmes aussi d’ailleurs.

mailto:philippe.jadin@skynet.be

6. "Légal"

Cette page ainsi que son contenu peuvent être librement distribués. Les programmes disponibles en téléchargement sont évidemment freeware, et le code source peut être modifié ou réutilisé dans un autre projet. Ce serait tout de même sympa de signaler où vous avez obtenu le code...