Subject:
|
Mindstorms NXT
|
Newsgroups:
|
lugnet.robotics
|
Date:
|
Fri, 6 Jan 2006 23:50:32 GMT
|
Viewed:
|
2737 times
|
| |
|
|
A friend Gabe is having a hard time posting to LUGNET, so he asked me to post this
for him.
His analysis may not be completely correct, because he says the motors are like
servos with a built in rotation sensor. However, I think it's been said they can
'act like servos', because they are motors with a built in rotation sensor.
Small difference.
But, here's what Gabe said...
--------------------------------- Original Message ---------------------------------
From: "Gabriel Petrut" <gpetrut@yahoo.com>
------------------------------------------------------------------------------------
They are saying the motors are sero like with built in rotation sensor. Now for
driving the servos you will need PPM, that is Pulse Proportional Modulation signal.
That takes just one I/O from the controller, but the driver is built inside the
servo.
For DC motors you need to drive them through an H bridge, and you can have PWM
signal to change speed (that's how it is done in RCX), but this takes 2 I/O from the
controller. And the driver is inside the RCX. With this method, it is easy to stack
motors on the same port.
You can do the same with servos, considering the fact that they get the power
directly from the batteries. So, with just one I/O you can controll more that one
servo, if they are connected in parralel. Usualy, when 2 servos are connected to
work together, one has to have the signal inverted, so they have to use different
I/Os.
Regular quadrature encoders, use 2 I/O, one for chanel A and one for chanel B.
Lego rotation sensors work almost the same way, but they transform the signal to
voltage, so it can be used by the RCX.
So, thinking about all I just sayed, I would say that the motor ports have the
following wires:
- power positive for servo (9V)
- servo signal
- power ground
- channel A
- channel B
- power positive for encoder (5V)
That be considered, I don't think one can connect 2 of these motors in parralel,
because of encoder mixed signals. The motors can work in parralel, but not the
encoders. However, if one makes a Y connector, which has the connections for the
encoder only for one branch, 2 motors can be connected on the same port!
For the sensors is different, because each sensor gives out a different signal.
Remember it's digital, not analog. It all depends how much brain is incorporated
into the sensor. I believe it's at least a PIC inside all sensors. The PIC may use
up to 4 lines to send it's data to the NXT. If so, all ports may be identical, and
they work like a bus, thus more than 4 sensors may be connected. If not, then each
sensor has to have it's particular port to be connected to, which is unlikely.
After all this rambling, I have to say that a sensor extender should be fairly
easy to build. A motor extender, may be more problematic, because of the encoders.
That's my humble opinion.
Gabriel Petrut
|
|
1 Message in This Thread:
- Entire Thread on One Page:
- Nested:
All | Brief | Compact | Dots
Linear:
All | Brief | Compact
|
|
|
|
