4 Servo Motors w/ 1 NXT

[ozzie88]

Hi guys,

Is it possible to connect four servo motors to one NXT module?

I know there are only 3 output ports, however I wasn't sure if anyone found a way around this.

Thanks again!

[haydenstudios]

Hi guys,

Is it possible to connect four servo motors to one NXT module?

I know there are only 3 output ports, however I wasn't sure if anyone found a way around this.

Thanks again!

There are two ways that I know of. One of them, (which is better most likely) is to use this, it's called the Mindsensors Motor Multiplexer (Motor MUX for short).
And the other way I know of, is a little technique I invented myself. It uses three converter cables. Connect two other motors to motor ports regularly, but for the third motor port, do this
Now doing the second technique does have it's limitations. If you use it, then both motors will have to turn at the same time, and with the same amount of power. And they will have to either always turn in opposite directions, or always the same direction. Furthermore, this method will negate access to the motors rotation sensors, and will result in indefinite run if you set it to rotations or degrees, so you'll have to set it to time if you do this. The Mindsensors motor MUX is a much better option because it has none of these limitations, and the latter should only be used if your robot's ability can tolerate these drawbacks. But it is a nice and cheap alternative if you want to save money and your specific robot won't be limited by these minor annoyances. Here are two of my robots that have benifeited from the second technique: this one, and, this robot. Though using the motor multiplexer is better, you can also use my technique with sensors. Heres a robot of mine that uses this on sensors: R2D2.

[mattallen37]

Firstly, I'm gonna assume that by "servo", you mean NXT motor with encoder.

There are several options. Here are a few that I can think of:

• If you need encoder feedback:
  • Mindsensors motor mux (NXTMMX-Nx).
  • Holt data systems' motor mux (I assume it's similar to the mindsensors one, but I have no idea where to get it if you're in the States).
• If you don't need encoder feedback:
  • Use PF and an IR Link.
  • Use the mindsensors MTRMX-Nx (not very powerful, and I would not try it if I were you)
  • Make your own I2C motor controller like I did.
• If you don't need independent control:
  • Use three NXT -> RCX converter cables (like haydenstudios suggested).

Any of the above should work, but I still think that the best option all around is usually a second NXT. If you use RS-485 to communicate, there is almost no noticeable delay in the signals. You can get NXT's for around $75 USD. A second NXT would add 3 motor ports (that support encoders) as well as two sensor ports.

I agree, the mindsensors motor mux is a good solution. It isn't too expensive, and it's fairly small. It seems to work well, but not quite like the NXT motor ports. It's an I2C sensor, with a through port, so it plugs into a sensor port, and you can plug a sensor into it (no loss of ports).

Now, if you really meant servo (as in RC style servo), mindsensors sells a servo controller that can control 8 servos.

[picad]

Good day!
And why forget the interesting decision motor-MUX, detailed information on the site http://edu.holit.ua/index.php?page=shop ... 55&lang=en

[mattallen37]

That's the "Holt data systems' motor mux" that I referred to.

[mightor]

Matt,

Picad is one of the guys from Holit Data Systems. English is his not his native language, so it's possible he missed it

Regards,
Xander

[mattallen37]

Well, I meant no offense in what I said, but thanks for explaining that Xander.

[mightor]

I highly doubt any offense was taken When I am Skyping with Picad (his real name is not Picad) we use Google Translate to go between English and Ukrainian/Russian. It's a bit how Doc-Helmut does his thing on these forums

Thank goodness for Google, eh?

- Xander