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Old 01-14-2009, 09:36 AM   #1
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Default Brushless RPM

Just been looking through Losi's Xcelorin manual's and it says "RPM @ 7.2V" then listing the different RPM generated from each of their sensored motors. I have a 6.5T Xcelorin and it says the RPM should be "35136".
Thing is my 15x2 peak motor (cheap old thing) generates (apparently) 31000 rpm, so theoretically the 6.5T should be faster but not by much, but...it is.
I was wondering wheather there is a difference with the RPM ratings of brushed and brushless motors or is there any other factors which effect this.
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Old 01-14-2009, 09:38 AM   #2
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Just been looking through Losi's Xcelorin manual's and it says "RPM @ 7.2V" then listing the different RPM generated from each of their sensored motors. I have a 6.5T Xcelorin and it says the RPM should be "35136".
Thing is my 15x2 peak motor (cheap old thing) generates (apparently) 31000 rpm, so theoretically the 6.5T should be faster but not by much, but...it is.
I was wondering wheather there is a difference with the RPM ratings of brushed and brushless motors or is there any other factors which effect this.
The rpm may be similar to your brushed motor, but the brushless will have a lot more torque so you can gear it even faster if you want to. The brushless will also do this with much better efficiency and it's performance will not fade over time like a brushed motor.
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Old 01-14-2009, 10:04 AM   #3
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The rpm may be similar to your brushed motor, but the brushless will have a lot more torque so you can gear it even faster if you want to. The brushless will also do this with much better efficiency and it's performance will not fade over time like a brushed motor.
HOLLA !

Brushed is weak.
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Old 01-14-2009, 11:20 PM   #4
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Make sure you are comparing them at the same input voltage to get the rpms.

Brushed motors actually have quite a bit of torque, especially at the low end. Brushless motors develop their power at higher rpms which is why they are gears so high with extremely low FDR.

Brushed is still very competitive, but they are a LOT of work..

Brushless evens the playing field... everybody can be fast! Brush takes a lot of know-how, time and money... We are seeing a lot of folks at our track that were slow B-Main'ers now stepping up because of brushless motors. It's all about the driver now!


Have fun!

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Old 01-15-2009, 05:33 AM   #5
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Brushless motors develop their power at higher rpms which is why they are gears so high with extremely low FDR.

Jerome
Its the other way around, a low FDR equates to low motor speed, not high. The low FDR (big pinions) are because brushless has a lot of low rpm power.
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Old 01-15-2009, 08:37 AM   #6
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Its the other way around, a low FDR equates to low motor speed, not high. The low FDR (big pinions) are because brushless has a lot of low rpm power.
it really depends on the motor wind as to where the sweet spot is as far as the torque band in relation to rpm.
the 17.5 for example has a very broad torque band, almost the whole rpm range, so you can gear it to the moon without over heating it.
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Old 01-15-2009, 10:24 AM   #7
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good questions and good answers.


I have a question to add along the same lines..

How is it that one companies brushless 3500kv motor is a 10t and another companies 4600kv motor is a 13.5t?
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Old 01-15-2009, 10:38 AM   #8
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good questions and good answers.


I have a question to add along the same lines..

How is it that one companies brushless 3500kv motor is a 10t and another companies 4600kv motor is a 13.5t?
That sounds to me that one is sensored and one is sensorless.But if memory serves me correct the KV rating on a 13.5 sensored motor should be in the 3300 Kv range.

It is hard to compare sensored and sensorless as they use different wind paterns(hence the .5 at the end of all sensored motors) construction differs , rotor length and diameter differs. All of which have an impact on performance.

Take the traxxas 10t for example.It is rated at 3500 Kv which is only 200 rpm difference from 13.5 which is a 3300Kv motor.But since the Traxxas motor has a longer can and rotor it produces more torque, so it can be geared more aggresively to acheive higher top speeds.
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Old 01-15-2009, 10:46 AM   #9
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That sounds to me that one is sensored and one is sensorless.But if memory serves me correct the KV rating on a 13.5 sensored motor should be in the 3300 Kv range.

It is hard to compare sensored and sensorless as they use different wind paterns(hence the .5 at the end of all sensored motors) construction differs , rotor length and diameter differs. All of which have an impact on performance.

Take the traxxas 10t for example.It is rated at 3500 Kv which is only 200 rpm difference from 13.5 which is a 3300Kv motor.But since the Traxxas motor has a longer can and rotor it produces more torque, so it can be geared more aggresively to acheive higher top speeds.

thanks for the info. that helps a great deal.
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