Two micro servo controllers

How would I chain two micro servo controllers when using RS232-level serial?

I haven’t actually done this myself yet, but I have two micro-servo controllers I’m planning on using this way. In terms of wiring there are two ways you can go.

You can either connect the RS-232 signal line to the “COM” pin on each of the servo controllers, or you can connect the RS-232 signal line to the “COM” pin on one controller, then the “OUT” pin of that controller to the SIN pin of the second one. Actually you can connect any logic-level devices to the “OUT” pin of the servo controllers. They make a nice bridge between, say, a computer serial port and a Pololu motor controller. Of course you will also need to connect ground pins all the controllers and the device generating the RS-232 signal.

If you just wire the two controllers together in either of these ways, they will both respond to the same servo numbers. If you want to make multiple servos do the same thing, you can just connect their signal lines to the same controller output pin, but I suspect you want to control the servos all individually. By connecting just one servo-controller to your RS-232 device at a time, you can set the range of servo-address numbers it will respond to. The instructions to do this are on the last page of the user’s guide.

I was hoping that the first wiring you mentioned would work (just wire the signal to both controllers and change the addresses.) Let me know if it does work when/if you try it.

btw. Good idea on using the controller as a simple level converter.


Sadly, I won’t be trying the first wiring method any time soon. I’m retro-fitting an old 5DOF robot arm I got from work with servos (actually I eventually want to make it mobile and wireless!) and I got a Pololu micro servo controller to run the servos straight from my com port. Unfortunately I was careless and I connected power backwards to the controller, and the level-converter transistor let out a little puff of smoke. I got another one to work with now, but I think the microprocessor on my first one is still good, so I’m going to try chaining them together the second way I described.

Now, that being said, there is nothing really functionally different about the two wiring methods. The controllers are only “listening” to the serial data line, and while this does have some effect on the signal, it is small compared to the strength of the signal itself. You should be able to connect lots of listening serial devices to one line before you start to have problems. For example, for my old job I helped build a robot that had 32 servos. We used four Mini-SSCII boards to control them all, with the serial inputs all wired together.

I got it working. I took the signal and ground from the RS232 (computer side) and split it into two and it works fine.

I sent the command to set the second controller to respond to servos 8-15 and now I can control 16 servos independently. Woo.