Subject:
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Re: mindstorms NXT
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Newsgroups:
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lugnet.robotics
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Date:
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Sun, 8 Jan 2006 03:26:38 GMT
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Original-From:
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dan miller <DANBMIL99@ihatespamYAHOO.COM>
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Viewed:
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7618 times
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If they're looking to the future, I would expect it to be a digital bus,
much like something my robo-club has been thinking about. It could be I2C
or CANN-based, or proprietary (unlikely). Six wires makes sense -- ground,
bi-directional signal (2 wires; or maybe differential signal + shared bus),
power for the controllers in the sensor/motors (5V regulated), power for
analog parts (motors, LED's, sonar, 9V unregulated), and one for good luck
(usually an extra ground for noise suppression).
If so, then the encoders would be digital too, and you could imagine
daisychaining (or star config with a muxer) multiple devices on a single
port. It would just be a software matter to address them individually, and
maybe some timing considerations.
I really hope this is the case, but then again it may have been too
expensive.
When do we find out?
--- Steve Hassenplug <Steve@TeamHassenplug.org> wrote:
> 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
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Message has 1 Reply:
 | | Re: mindstorms NXT
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| (...) I just saw Lego's definiton of a servo motor. It resembles a industry servo, not a hobby servo. In the hobby servo, the closed loop is done in the servo electronics, but in the industry servo, the closed loop is done in the controller. (...) (19 years ago, 8-Jan-06, to lugnet.robotics)
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Message is in Reply To:
| | Re: mindstorms NXT
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| (...) The NXT FAQ addresses this question - it says that both the RCX and NXT will *both* be allowed in the 2006 FLL season. That should make for some very interesting decisions and comparisions. It also suggests to me that along with the MUPs we (...) (19 years ago, 8-Jan-06, to lugnet.robotics)
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