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 17:16:54 GMT
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Original-From:
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Avery, Amos E. <Amos.E.Avery@disney/stopspam/.com>
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Viewed:
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536 times
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Wow, what an excellent description. I look forward to trying this out over
the holidays. I had one other idea that may explain my initial failure.
The track layout I was using was rather large, in fact it took up the entire
living room using nearly every piece from 5 train sets. I will try again,
thanks to your encouragement, with a smaller layout. Also, the plastic
insulation you are talking about, is that a thin plastic film cut to 1/4" x
1/8" such as scotch tape? I'm having a hard time visualizing anything other
than really thin material. Many thanks.
F'amos
-----Original Message-----
From: Ted Michon [mailto:tedmichon@home.com]
Sent: Thursday, December 16, 1999 9:20 AM
To: Avery, Amos E.
Cc: lego-robotics@crynwr.com
Subject: Re: RCX Output (Train applications)
Avery-
With 1 RCX running on AC (with batteries installed), I could run both
complete Railway Express trains (engine and 2 loaded long cars each) just
fine. We ran them at a max RCX speed setting of 4 - any higher and they were
prone to fly off the rails around curves. Because of the isloation blocks in
the layout, the loops were each electrically open at one spot so we made a
point of putting the track connector in the middle to minimize the maximum
resistance to the farthest points.
I only noticed a problem if I started both trains simultaneously at slow
speed, which was necessary when doing the track swap. So instead of using
speed 3 for this, I chose speed 4 and had no further trouble.
I don't have any processed photos yet that show the layout, but perhaps I
can give a better description. I'll start by defining some terms for the
switches. Consider a switch oriented like your right hand with the straight
side going from your wrist toward you middle finger and the curve flowing
toward your thumb and your palm flat on the layout. I'll call this a "right
hand" switch. I'll call the part the corresponds to the thumb the "curved
node", the part for the middle finger the "straight node", and the part for
the wrist where the opposite ends of the curve and straight meet the "common
node".
This particular layout was made by first making a 180 degree half circle
(imagine it at the top of the layout, if we were working on a sheet of
paper, with the open ends pointing down). Attached to the right side of the
half circle is the curved node of a right hand switch. Attached to common
node of this switch is another 180 degrees of curve (with some straight in
the middle) followed by the common node of a left hand switch. The curved
node of this second switch attaches to the remaining spot on the original
half curve.
At this point, there is a complete inner loop and two unconnected straight
nodes from the two installed switches.
Attached the straight node of another right hand switch to the straight node
of the first installed switch. Attach the straight node of another left hand
switch to the straight node of the second switch. Now add a 180 degree
section with some straight track in the middle to connect the common nodes
of switches 3 and 4 across the top of the layout. Finally, add a 180 degree
section with some straight track in the middle and on each end to link the
curved nodes of switches 3 and 4. These sections complete the outer loop.
Set all switches so that the yellow balls point to the right. This will
force a clockwise running train on the outer loop to stay on the outer loop
and a clockwise running train on the inner loop to stay on the inner loop.
When either train reverses, however, it will swap to the opposite loop.
The two small piece of 1/8 inch by 1/4 inch plastic insulation goes at the
junctions where the straight nodes of the switches meet - but only on one of
two rails in each junction. For the pair of switches on the right side of
the layout, the inner most rail gets the plastic. For the pair of switches
on the left side of the layout, the outermost rail gets the plastic.
The outer track sensor goes at the top of the outer loop on the inner side.
The inner track sensor goes at the bottom of the inner loop on the inner
side.
Power the outer loop from the bottom right corner. Power the inner loop from
the bottom left corner.
-Ted Michon
"Avery, Amos E." wrote:
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 <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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Message has 1 Reply:
 | | Re: RCX Output (Train applications)
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| This sounds interesting, but trying to understand it in the middle of class has my head swimming ;-) Any chance of diagrams and pics? I ust picked up my first trains and RIS last week, so I want to hook them together and have some fun with my cats (...) (25 years ago, 16-Dec-99, to lugnet.robotics, lugnet.trains)
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