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Scaleauto motor

4015 Views 21 Replies 12 Participants Last post by  wideboy
Evening all,
I was at the shop today and they now have A scaleauto 35,000 rpm motor to fit most of our RTR cars. I have no idea what to put it in but the torque figure was amazing: 190gm/cm.(GRUNT/cm.) Over half again the power of my beloved V12/2b 25,000 motor! The prof. said the feedback has been very good on it, and it is a dollar less than the v12. (So I HAD to buy one.) Anyone tried them around here? I'll wager I'll be gearing down on my track.

Looking for a bigger hammer,
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Beppe, I agree with you. No load ratings are almost worthless. I also agree that 1 amp is insufficent for the SC07, NC4, NC6, or similar hi-performance motors.

However, stall readings are also erroneous since they do not occur in normal use. Accelerating from a stop is not the same as stall, in a DC motor. Stall implies that the motor can NOT turn, and thus the current draw is a product of resistance and voltage. However, if the arm CAN turn, the first inrush of power will cause the arm to begin rotating and stall current will never be realized. There will be a brief spike that tends TOWARD the stall current but it will never reach that level and will last only for a very brief time (milliseconds at most). If the supply is a good one, the starting current can actually be satisfied by capacitors on the output.

Using your example, 12V in a 3 ohm armature, I would expect typical current draws to range in the lower half of the stall band, even on mag cars - up to 2 amps max, with a VERY brief spike to perhaps 3A on initial startup. Also, at full speed, the motor will draw much less than 1.3A (reverse EMF will bring the current draw to near zero on ANY motor at maximum speed). Even with heavy magnets, I doubt the SC07 will draw more than .5 to .75 A at full speed.

BUT... you are correct! One amp is NOT enough for motors in this range! They will need at least 2, and preferably 3, amps to properly display themselves and have a slight excess current available.

The best measure we could ever hope for would be a standardized system whereby motors were rated at moving a set mass, under set conditions, over a given distance or time, with acceleration and speed measurements, and current draw, available using fixed voltage levels. This would give us real world numbers that might actually mean something. At the moment, motor specs are virtually worthless, and only the experiences of others are truly indicative of a motor's actual performance.
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Beppe, if Tropi ever gets 2 amps into that motor he is gonna be a very, very surprised driver.

Tropi, you are right that a motor can appear to work fine even if slightly starved for power. This is not the case if the demand is massively greater than the supply, but in this case the difference seems to be small. We seem to be talking about running a motor that is happiest on 2 amps at about 1.2 amps? Overall, it will run okay, just not at its optimum level. Perhaps a good thing - it may well be too much for the track if power was not a limiting factor?

The absolute optimum, in this case, would be a motor that drew 1.2 amps max under load and possessed the characteristics that you desired. Geared accordingly, it would then be singing happily all the time, delivering crisp response, and running cool.

Better yet.... talk the club into a high current supply....
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