| |
In lugnet.robotics.rcx.java, Daniel Carvalho wrote:
> Daniel:
>
> > > I want to use rcx to control a lego train, but the fact that lejos only
> > > have 7 levels makes it dificult to set the speed.
>
> Mark Bellis wrote:
> >
> > I think at the very least you need to smooth the power output of the RCX in
> > order to turn PWM into steady voltage. I suggest a low pass filter with a time
> > constant (RC) longer than 166ms, followed by a power transistor drive circuit,
> > so that it uses a separate 9V power supply to drive the motor, not the RCX's
> > outputs.
>
> hi Mark
>
> i don't understand much about electronic. But can the lego electric
> capacitor (part number 9916) be used for this purpose?
> ...
> Daniel
The simple answer is "maybe"! If you have one handy, try it. I'm not sure
whether the RCX will cope with a capacitive load rather than an inductive one,
so I would advise you not to put the capacitor across the RCX output without a
motor in parallel. The capacitor was designed to be used with a solar cell to
average out the power from variable sunlight.
I don't know the value of the capacitor, nor whether there is any regulation
circuit attached - I would sincerely hope there is for the price, as a normal
capacitor of that size costs 50p or less!
Putting the capacitor in parallel effectively makes a tuned circuit with the
motor, so check across a range of frequencies if you're using code to vary the
PWM characteristice from the RCX - some frequencies might give weird results.
You may also motice that the train takes time to stop as the capacitor has to
discharge once the RCX outputs have turned off.
I think the effect will be similar to what I got when I used an engine that had
a gearmotor in parallel with the train motor. The gearmotor stored energy and
smoothed out the power to the train motor, actually increasing its speed for a
given RCX PWM output. RCX power level 2 of 0-7 on all three outputs in parallel
gave a reasonable shunting speed with this engine and one wagon.
At the end of the day though, the RCX was not designed to drive trains and its
power output capability is more limited than a train controller. You'll need to
parallel up all three outputs at the very least. Engines with two train motors
pulling a decent train require a more powerful controller. Don't burn out the
RCX drive transistors!
This is really crying out for a decent powerful controller that can take RCX
speed commands.
Mark
|
|
Message is in Reply To:
 | | Re: train control
|
| Daniel: >> I want to use rcx to control a lego train, but the fact that lejos only >> have 7 levels makes it dificult to set the speed. > > Mark Bellis wrote: > > I think at the very least you need to smooth the power output of the RCX in > order to (...) (20 years ago, 8-Jul-04, to lugnet.robotics.rcx.java)
|
7 Messages in This Thread:
  
- Entire Thread on One Page:
- Nested:
All | Brief | Compact | Dots
Linear:
All | Brief | Compact
|
|
|
|
