Linking two controllers problem

i have two servo controllers with 8 channels and i have to control 12 servo motors, and i set the servo numbers 0-7 and 8-15 , i draw a line between first controller logic-level serial output to the second controller rs 232 serial input, and … the first controller works… but the second controller lights the yellow led and blinks the red led, and doesn’t work… any ideea ?

Your signal connection should go from the first controller’s logic-level serial output pin to your second controller’s logic-level serial input pin (labeled SIN). Of course the two controllers will also need their grounds connected (if they aren’t already).


on my first controller the serial input is at RS232 input… so… it cannot be the same at the second too ?

RS-232 serial and logic-level serial are similar but different protocols. The meaning of high and low voltages are inverted between the two, and the RS-232 signal voltages are much higher, and can damage logic-level serial devices.

So essentially you just have to match the output type to the input type. You could take your RS-232 signal line and split it, connecting it to both the RS-232 input pins on your two servo controllers. The signal on the logic-level output pin of your first controller has been converted from an RS-232 serial signal to a logic-level serial signal, so to use that signal you have to connect it to the logic-level serial input pin on your second controller.

Either would work fine, just don’t do both!


Thank you :slight_smile: it worked , now i have my biped robot standing up, next step is to make him walk… hard enough… :frowning: wish me luck :smiley: because i have a deadline on 20th June, for my final year project .

How can i turn a servo motor on without setting a position ??


What do you mean by turning it on without setting a position? If you want to set it to the position it’s already at when it is off, there’s no way of finding out what that is (short of adding an external sensor or tapping into the one in the servo). The closest thing you can do is to send the servo to a predetermined location before shut down and then assume it’s still there when you power up.

- Jan

I mean, when it moves to a position it keeps there even if i try to manually move the motor, i cannot, and i was wondering if i can just to power the motor to stay to the current position without to move it to somewhere, i tried with the neutral position setting but i don’t know why it doesn’t work.
I saw on the datasheet that data1 at command 0 (Set Parameters) is something like this :

bit 7 - always 0
bit 6 - servo on/off (1-0)
bit 5 - direction (0 - fw, 1 - rev)
bit 4-0 - range

So i was thinking about using this command to turn the servo on with bit 6 without moving it. And one more thing i want to know how to use the neutral position setting. can u help ?

This is what i did so far :

i thing the servos are not strong enough, coz i find difficult to make him move/walk…

waiting for suggestions…

It sounds like you’d like to be able to do the thing I said you couldn’t. The servo controller cannot know where the servo is; it can only tell it to go to a certain position or not tell it anything at all. When you change the on/off bit, it will go to wherever you last commanded, not to the location in which the servo happens to be when you turn on the bit.

The neutral setting is only relevant for non-absolute modes. (If you have a decent processor, you should be using absolute mode and do all of the calibrations in your end application.) The neutral setting sets the middle point for the 7-bit and 8-bit commands. The idea is that if you swap servos, you can just change the neutral setting and that will calibrate your new system to all of your old commands.

- Jan

thx , it’s ok now :slight_smile: i now have problems with taking a foot off the ground :frowning: 4 days left until the deadline .