Subject:
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Re: parallel RCX outputs
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Newsgroups:
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lugnet.robotics.rcx
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Date:
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Sun, 23 Jul 2006 16:40:19 GMT
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Viewed:
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10779 times
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In lugnet.robotics.rcx, Juergen Stuber wrote:
> Hi Chris,
>
> Chris Magno <cmagno@rogers.com> writes:
>
> > Can I put an electric 2x4 plate across output port A and B
> > to increase the current I can draw from the brick?
>
> I think so (warning, this is based only on theoretical knowledge).
>
> > 1. when I ran a few tests with a 1x2 lamp, I would get interesting results.
> >
> > A and B forward - ON
> > A and B Reverse - ON
>
> That should be ok.
>
> Setting the power level might not work correctly,
> from looking at the ROM code it seems the PWM waveforms
> are not synchronized.
>
> Now comes the "Trying to Kill an RCX" section.
>
> > A Forward B off - very DIM
> > B Forward A off - very DIM
>
> You are using one motor output to short the other one.
>
> > A Forward B Reverse - FLASHing ON
> > B Forward B Reverse - FLASHing ON
>
> The outputs are fighting each other.
> The flashing is an interesting phenomenon, I would guess
> a thermal protection circuit triggers intermittently.
>
>
> Jürgen
If all motor ports are started and stopped together, does that synchronise the
PWM waveforms?
If not, then I don't recommend paralleling up.
If so, then I recommend paralleling up only when motors are started and stopped
together and are run at the same speed for the duration of movement. I would
also recommend that each output be given a wire to the load, so that a plate
didn't have to carry more current. I'm not sure what the over-rating factor is
on electric plates and wires, but a pole reverser switch definitely won't stand
for 12V@2.67A - I once melted one whilst controlling a robot with four 12V train
motors from a 12V 6A supply! Bear in mind that electric plates are now obsolete
- never risk what you can't replace!
I've tried parallel operation to drive a train (one wagon only as the load is
too much for the RCX otherwise). It was interesting to observe the different
behaviour, of the train motor and a slave 71427 motor that turned the driving
wheels, with different speed settings. The waveforms appeared, on an
oscilloscope, to be synchronised when I started and stopped the motors together
(commands like "On ABC").
I don't recommend using the motor from the 8421 crane with an RCX, even with
parallel outputs, as the motor can draw more than the maximum output current of
a single motor control IC (550mA at 9V from the Melexis MLX10402 data sheet).
Those motors can use up to 7.2W, which at 9V is 800mA. There might be power
interrupt disruption before cooking set in, depending on the stability of the 5V
regulating circuit when the 9V rail has high current square waves on it, but
it's not worth finding out whether a computer crash or overheat condition occurs
first! This makes me wonder why you have an application that needs parallel
outputs!
Mark
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Message has 1 Reply:
 | | Re: parallel RCX outputs
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| Hi Mark, (...) probably, I guess they would be started within the same millisecond, which would result in synchronized wafeforms. (...) It's not that bad, when the waveform is off the motor is floating. So the power control will be ineffective at (...) (18 years ago, 23-Jul-06, to lugnet.robotics.rcx)
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Message is in Reply To:
| | Re: parallel RCX outputs
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| Hi Chris, (...) I think so (warning, this is based only on theoretical knowledge). (...) That should be ok. Setting the power level might not work correctly, from looking at the ROM code it seems the PWM waveforms are not synchronized. Now comes the (...) (18 years ago, 22-Jul-06, to lugnet.robotics.rcx)
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