[Robotgroup] BS2 to Sabretooth 2x10 RCMC?

Wed Aug 20 14:49:29 PDT 2008

I did have the robot on top of a box, so the wheels were moving freely.  It just freaked me out a bit because the wheels were going so fast and I couldn't send any command to stop it; I had to do it manually.

Before I connected the motors -- I didn't know that something called a "bi-color LED" actually exists -- I actually did manage to create a circuit exactly how you described.  There were some complications however:

First thing I did was hook up a simple circuit consisting of one red LED and two 10Ku resistors (thinking the higher, the better).  The resistors were connected to each battery lead.  I connected the 6v Power Wheels battery, and well, two flames appeared.  Not like campfire flames, but each one was probably big enough to light a cigarette.  

So I removed the Power Wheels battery and hooked up a 9v.  I made sure that the PLUS  and MINUS corresponded to the 6v battery.  This time, the LED lit up?  Bonnie asked if I knew what I was doing and I said yeah, everything is good.  I hooked up the 6v battery again, and this time it worked.

I wanted my circuit to have red LEDs and green LEDs to indicate direction.  However I couldn't locate a green LED at the moment, so I replaced the red LED with a white LED.  When I completed the circuit, well there was a loud pop like a gunshot and some sort of minor, yet still terrifying explosion.  It might have been the IR LED that comes with the BOE-Bot kit.  Meanwhile Bonnie is still across from me at the table checking her email this time with a funny look on her face.

Anyway, I somehow managed to engineer a circuit that lights up the green LED, and if you reverse the battery, it lights up the red LED.  I tested it with the 9v, and the LEDs weren't lighting up very brightly, so I replaced the 10Ku resistors with 1Ku resistors.  

Then I tested it with the 6v and somehow it worked and there were no explosions this time.  I may have gotten some of the details wrong, since I am going by memory, which if it involves mine, is never infallible.  So here are my possible explanations:

a) Was the LED reversed originally?  I thought that if the LED was reversed then it would cause the circuit to not complete at all?  

b) Was there static electricity in the battery that somehow dispersed, causing everything to be okay later?  Was there residue from the electrical tape, which I had wrapped around the battery leads during storage so they wouldn't cause a short, that caused the flames?

c) As I read through this, it appears that the 10Ku resistor was the difference in the 6v battery causing flames and/or exploding LEDs?  I thought a higher resistor resulted in less current?

d) The white LED was another factor that was different.

e) Or am I just really that clueless?

L. Scott Hudson

"There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things we know we don't know. But, there are also unknown unknowns. These are things we don't know we don't know." 

-- Donald Rumsfeld, describing the IBM "Rational Software" Platform

--- On Wed, 8/20/08, Paul Atkinson <pmatkinson at gmail.com> wrote:

From: Paul Atkinson <pmatkinson at gmail.com>
Subject: Re: [Robotgroup] BS2 to Sabretooth 2x10 RCMC?
To: "The Robot Group Mailing List" <robotgroup at puremagic.com>
Date: Wednesday, August 20, 2008, 5:11 PM

Another thing you can do, is put the motor base on top of a box, so the
wheels aren't on the ground. Then, no matter what the motors try to do, you
can take your time figuring things out.

You could also disconnect the motors and use a bi-color LED and appropriate
resistor in place of each motor. This way you can see a green LED increasing
in brightness for forward and a red LED increasing in brightness for
reverse. You can at least see some brightness changes that correspond to
speed. Once you are confident the LEDs are working, it should be easy to
plug the motors back in.

Paul

On Wed, Aug 20, 2008 at 3:33 PM, Gray Mack <gray_mack at yahoo.com> wrote:

> from looking at the pdf, make sure the dip switches are correct. Probably
> turn off the auto-calibrate switch (5). Check the other switches too and
> make sure you understand their significance.
>
> Put a switch between the battery and the B+ that way you can kill the
> motors quickly without disabling the logic circuits or yanking wires :)
>
> If it would help, I can bring an RC radio and receiver so we could
> eliminate the basic stamp from the test.
>
> Also, if you are ready to show it off to the masses, get on the dorkbot
> schedule as a presenter, they love in-the-works projects as much as
> completed stuff.
>
> -Gray
>
> --- On Wed, 8/20/08, LHudson <lhudson73 at yahoo.com> wrote:
>
> > From: LHudson <lhudson73 at yahoo.com>
> > Subject: [Robotgroup] BS2 to Sabretooth 2x10 RCMC?
> > To: Robotgroup at puremagic.com
> > Date: Wednesday, August 20, 2008, 1:39 PM
> > Ugh.
> >
> > It has two speeds:  really fast, and backwards really
> > fast.
> >
> > ' {$STAMP BS2}
> > ' {$PBASIC 2.5}
> > DO
> >   ' !-- Execute a Movement Command
> >   PULSOUT 13, 750
> >   PULSOUT 14, 750
> >   PAUSE 20
> > LOOP
> >
> > Anything >= 750 makes the motor go really fast.
> > Anything < 750 makes the motor go backwards really
> > fast.  Responses posted to Parallax or Lynxmotion forums
> > imply that the Sabretooth responds to the PULSOUT command in
> > the same fashion as the BOE-BOT CR servos.  Just about
> > every post seems to be resolved with "I connected it to
> > the BS2 Ground and now it works".  However I don't
> > see anything that looks like this in the wiring diagram.
> > Is this because they are using the Sabretooth 2x10 MC and
> > not the RCMC?
> >
> > Also, it is impossible to stop the motors without yanking
> > the wires leading from the RCMC to the motors.  I believe
> > that turning off the BOE also stops the motors however
> > usually I'm in some sort of panic state and forget to
> > confirm this conclusively by writing it down or something.
> > If I disconnect the wires leading from the MC to the
> > battery, the green power indicator LED remains lit.
> > However if I then switch off the BOE or disconnect the servo
> > leads, the green power indicator turns off.
> >
> > These are the documents for this MC:
> > http://www.dimensionengineering.com/datasheets/Sabertooth2x10RC.pdf
> >
>
http://www.dimensionengineering.com/datasheets/Sabertooth-2X10-RC-diagram.jpg
> >
> http://www.dimensionengineering.com/datasheets/Sabertooth-2X10-RC-DIPs.jpg
> >
> > I am using this battery:
> >
http://www.hobbymasters.com/index.asp?PageAction=VIEWPROD&ProdID=382.
> >
> >
> > Googling "Power Wheel 6 volt" returns a lot of
> > batteries that are red, but mine is Blue.  I forgot to
> > check last night to see if it was NiCD or Li.  I asked
> > Bonnie to look and and she said neither -- "Pb".
> >
> >
> > Anybody?
> >
> > L. Scott Hudson
> >
> > "There are known knowns. These are things we know that
> > we know. There are known unknowns. That is to say, there are
> > things we know we don't know. But, there are also
> > unknown unknowns. These are things we don't know we
> > don't know."
> >
> > -- Donald Rumsfeld, describing the IBM "Rational
> > Software" Platform
> >
> >
> >
> > _______________________________________________
> > Robotgroup mailing list
> > Robotgroup at puremagic.com
> > http://lists.puremagic.com/cgi-bin/mailman/listinfo/robotgroup
>
>
>
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