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In lugnet.technic, John Barnes writes:
> This is interesting information, thanks TJ. I must say that I got the visual
> impression that the buggy motors seemed to have more than a mere 2 - 3 times
> more shaft power output than the gear motors.
Yes, I did too. Judging from the performance of the RC car, you'd think the
motors would be equivalent to perhaps 8, or more, of the geared 9V motors.
The buggy can really zip along!
There was one other thing about my test. When the 9252 motor stalled, the
green LED on the train controller dimmed significantly. I wonder if it was
able to provide adequate current. Surely so! If not, then my torque results
could be low.
> The little piece of data which would add greatly to your 2 - 3
> times figure would be the current consumption. I have a nasty
> feeling that the Technic gear motor has set the gold standard
> for electric to mechanical power conversion efficiency.
I don't have a current meter (yet), but yes that would be good. Well, you
provided some current data a while back:
http://news.lugnet.com/technic/?n=7701
Was that 200mA at stall torque, or just during normal operation? Can you
test the motor at stall sometime soon? That can then be my current data
point for maximum torque. We have plenty of measurements for the geared 9v
motor for comparison.
> If the buggy motors make 3 times the torque converted to the
> same rpm, but at the expense of 10 times the power consumption
> (which I have a feeling is the case) then for battery operated
> applications like 99% of Technic/Mindstorms creations, they are
> not quite such a hot prospect.
Well, I hope my test is a little flawed, and the 9252 motors turn out better
performers. I plan on using mine!
TJ
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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.
I will apply some juice to one stalled, and assuming I don't break
something, let you know what the current consumption is asap.
JB
In lugnet.technic, Thomas Avery writes:
> I don't have a current meter (yet), but yes that would be good. Well, you
> provided some current data a while back:
> http://news.lugnet.com/technic/?n=7701
> Was that 200mA at stall torque, or just during normal operation? Can you
> test the motor at stall sometime soon? That can then be my current data
> point for maximum torque. We have plenty of measurements for the geared 9v
> motor for comparison.
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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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In lugnet.technic, Thomas Avery writes:
> In lugnet.technic, John Barnes writes:
> > This is interesting information, thanks TJ. I must say that I got the visual
> > impression that the buggy motors seemed to have more than a mere 2 - 3 times
> > more shaft power output than the gear motors.
>
> Yes, I did too. Judging from the performance of the RC car, you'd think the
> motors would be equivalent to perhaps 8, or more, of the geared 9V motors.
> The buggy can really zip along!
>
> There was one other thing about my test. When the 9252 motor stalled, the
> green LED on the train controller dimmed significantly. I wonder if it was
> able to provide adequate current. Surely so! If not, then my torque results
> could be low.
The limitation on the train controller is the wall wart - not the controller
itself. There was discussion on this in .trains a while back. Someone built
a tranformer box with about 3A output IIRC, and ran several trains with it
through an un-modified controller. There was someone else that actually
modified the controller rectifier with higher rated diodes etc, and added a
fan, but that's probably only necessary for prolonged use.
ROSCO
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