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In lugnet.technic, John Barnes writes:
> That figure was the normal operation (no load) figure. What concerned me was
> that it was a factor of almost 20 higher than the gear motors which normally
> run about 10mA. Of course, it is very easy to overlook the fact that the
> gear motor is extraordinarilly low friction, and thus draws very little
> power off load in overcoming its own mechanical losses. The buggy motor is
> of the cruder "toy" motor design which are notoriously inefficient anyhow
> and since I have never opened the casework, I don't know how "nice" the gear
> train is. So it is hard to know what the real buggy motor off load current
> would be if it were not possibly overcoming all sorts of gear train friction.
Well, check this out:
http://www.brickshelf.com/cgi-bin/gallery.cgi?f=24307
There are a few pictures of the internals of the motor. Quite a few gears!
> I will apply some juice to one stalled, and assuming I don't break
> something, let you know what the current consumption is asap.
Thanks!
TJ
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Ok, here is an extrapolated result for the short circuit (stalled) test.
The current at 9 volts would be 3.6 amps. Since I did not wish to burn up
the motor, I checked current readings at both 3 and 6 volts and also
measured the DC resistance and all things point toward 2.5 ohms. I would not
advise stalling this motor while it was running from an un-current-limited
source like a R/C rechargeable battery pack. 9 volts at 3.6 amps is > 30
watts. A motor of that physical size will heat very rapidly at that power
level. Power is proportional to the square of the voltage, so my quick test
at 6 volts for a couple of seconds was enough to start it warming
noticeably, but no harm was done. Of course, neither the off load current of
0.2 amps or the stall current of 3.6 amps tells you anything about its
efficiency at converting electrical power to mechanical power. You really
have to do the dynamometer thing for that.
JB
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In lugnet.technic, John Barnes writes:
> Ok, here is an extrapolated result for the short circuit (stalled) test.
>
> The current at 9 volts would be 3.6 amps...
Holy C..........
That's quite high (understatement) for a little LEGO motor. Do you think
it's possible that the train controller I used in my test didn't produce
enough juice? If that's the case, then the motor has a higher maximum stall
torque than I measured.
TJ
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