Subject:
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RE: RCX Output (Train applications)
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 16 Dec 1999 15:31:09 GMT
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Original-From:
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Avery, Amos E. <amos.e.avery@disney.NOMORESPAMcom>
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Viewed:
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680 times
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When I tried this, my train only ran at about 1/2 speed at full output from
the RCX plugged into the train power supply and batteries removed. Any
ideas why? My trains are a little old and I'm considering cleaning the
tracks. Maybe I'll try again with a new train set. Do you have any
pictures or can you show with sketches the sensor configuration or a detail
of the track layout and the plastic weggies? I'd be very grateful for any
additional info I could get. Thanks!
F'amos
-----Original Message-----
From: Ted Michon [mailto:tedmichon@home.com]
Sent: Wednesday, December 15, 1999 3:11 PM
To: Avery, Amos E.
Subject: Re: RCX Output
Amos -
We drove the trains directly from the RCX. In fact, everything in the system
was an "all LEGO" solution except for the 2 small pieces of insulating
plastic wedged between two pair of rails and for one axle in each sensor
whose end I filed a trifle to give a small bevel and eliminate the dimple
which was making the sensor button stick a little.
-Ted
"Avery, Amos E." wrote:
Wow! Did you drive the trains directly through the RCX or did you do
something different?
-----Original Message-----
From: Ted Michon [ mailto:tedmichon@home.com <mailto:tedmichon@home.com> ]
Sent: Wednesday, December 15, 1999 2:45 PM
To: Avery, Amos E.
Cc: lego-robotics@crynwr.com; Joel Shafer
Subject: Re: RCX Output
Avery-
For the Orange County (CA) Festival of Trees (South Coast Plaza, Costa Mesa,
CA December 2 - 6 ), we entered a LEGO decorated tree with 2 Railway Express
sets underneath run by an RCX (the lucky winner of the tree got the complete
Mindstorms and trains, an autographed copy of The Ultimate LEGO Book, a 5
foot diameter octagon base with a LEGO village and track layout, 150 LEGO
ornaments, 84 glass globes, and 1300 lights).
We designed the track as two concentric layouts linked by two pairs of
switches. The switches were set so that trains would run continuosly on
their track (inner or outer) in the clockwise direction but would change
tracks if run in reverse (counter clockwise). We placed one RCX touch sensor
on the outer track and one touch sensor on the inner track (it took awhile
to design the mechanics of the sensors, but we eventually got a design that
worked reliably).
Because LEGO switches isolate one rail according to the position of the
switch, we completely isolated our inner loop from our outer loop by
inserting a small piece of plastic (1/8 inch x 1/4 inch, cut from an
ordinary blister card packing) on the non-isolated rails (two total). One
RCX motor output controlled the inner loop and one controlled the outer
loop.
With this arrangement, we ran the trains independently and randomly for a
time (they looked pretty good starting up slowly, running at speed, slowing
down, and stopping) and then synchronously. In this latter mode, the outer
train started, rain 3 loops (we counted passes by the sensor), slowed a
notch, and then stopped at the outer track sensor. The inner track did the
same thing, phase delayed about 30 seconds. With both trains stopped, we
backed the outer train to clear it's sensor and then backed the inner train
to clear its sensor. Then we ran both trains backwards until one of them hit
a sensor (this switched the outer train to the inner track and the inner
train to the outer track), then ran the other track until its sensor was
hit, and then ran each independently (still backwards) to clear their
sensors. Then we repeated the whole thing.
The tree was pretty popular with kids and adults and we got a crowd whenever
we ran the trains.
I was amazed how reliable the whole thing was, though we knew better than to
leave the trains running when we weren't there.
-Ted Michon
"Avery, Amos E." wrote:
Thanks for the much-needed input. My goal was/is to eventually build a
fun, interactive multiple train layout with seemingly random events
triggered by multiple networked RCX's. It looks like I may be designing
a machine that manually turns the train rheostat to achieve my goal. The
holidays could be interesting.
F'amos
-----Original Message-----
From: Nick Taylor [ mailto:ntaylor@iname.com <mailto:ntaylor@iname.com> ]
Sent: Wednesday, December 15, 1999 11:05 AM
To: lego-robotics@crynwr.com
Cc: Joel Shafer
Subject: Re: RCX Output
Hello Joel,
Attempting to drive an RC servo directly from the RCX is NOT a good
idea! The servo is a three wire device; +4.8V to +6.0V for power
(usually the red wire), an approximately 40Hz pulse train of 1.0 to
2.0ms pulses at 0V and +5V logic levels (white or yellow wire), and
ground (black wire). The pulse train does NOT power the servo motor,
it only tells the chip in the servo where to go ... the red wire
supplies power to drive the motor until an internal pot is turned
to the point where the position of the servo equals the position
commanded by the pulse width on the white wire.
The RCX delivers a two wire output which changes polarity when a
command is sent to reverse the motor ... and the servo's logic chip
would not be very happy.
I'm sure that you could build external circuitry to let the RCX
control a servo, but I'll leave that exercise to the reader.
Play well,
- Nick -
Joel Shafer wrote:
>
> So if you need a 1, 1.5 & 2ms pulse for controlling a servo and you said
> the low setting in NQC = a 1ms pulse, are there other matching motor speed
> settings to get a 1.5 or 2ms pulse?
>
> At 05:14 PM 12/15/99 +0000, you wrote:
> > Hi F'Amos,
> > I just now put a scope on the motor output ran an NQC motor test
> > program. At OUT_FULL the motor output is about +7V DC. At OUT_LOW
> > the motor output is a pulse train of 1ms 7V pulses at about 125Hz.
> > The low level depends on the motor load ... almost 7V with no motor
> > connected and approaching 0V with a stalled motor. NQC provides
> > seven motor speeds ... and by increasing the duty cycle of the pulse
> > train the average DC level to the motor is changed.
> >
> > RC servos are also controlled by varying the pulse width. For most
> > servos a 1.5ms pulse tells the servo to go to the center position.
> > Increasing the PW toward 2.0ms turns the servo CW and decreasing
> > toward 1.0ms turns the servo CCW. The exact pulse width determines
> > the exact stopping position. Servos that are modified for use as
> > motors can never find a null position so they continue to turn
> > seeking the nonexistent null. Unless the PW sent to the servo is
> > very close to the null PW, the servo will turn at full speed. If
> > the null PW is 1500us, then a 1550us PW will result in a slower
> > speed.
> >
> > Hope this helps,
> > - Nick -
> >
> > "Avery, Amos E." wrote:
> > >
> > > --- Nick Taylor <ntaylor@iname.com> wrote:
> > > > If I'n not mistaken, the RCX output is pulse width
> > > > modulated to control motor speed, while the train controller
> > > > varies the DC voltage.
> > >
> > > Can anyone confirm the output characteristics of the RCX?
> > > It is my understanding that PWM is used to control RC servos
> > > and not to power them. Has anyone put a scope on the RCX's
> > > outputs to see what they look like? If the info is available,
> > > I'd be interested to know the exact output specs (eg. 0-9v 200ma).
> > > F'amos • <http://www.crynwr.com/lego-robotics>
>
> Joel Shafer joel@connect.net
<http://www.crynwr.com/lego-robotics>
<http://www.crynwr.com/lego-robotics>
-- Did you check the web site first?: http://www.crynwr.com/lego-robotics
<http://www.crynwr.com/lego-robotics>
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