Yeah, the prop loading is imperfect, and it only gives you a fixed point as an output, but I do think it gives some interesting data when it comes to motor load, which we can kinda equate to hard accel or WOT. You can use the max eff point for a given voltage to kinda create a dynamic range, but its "eh".

I was intending to address the question posed by glassDr in previous post.

Basically, if you have a fixed voltage (eg 5S) and are trying to gear to the same speed (prop rpms~=wheel rpms, ie 40mph) is it better to use a lower kv motor and overgear, or a high kv motor and gear lower?

The calc data to me says "lower gear, higher kv" is better. This makes sence to me as well as in my Novak BL example from above as well, that a 8.5 can not be ran as fast as a 5.5 on the same # of cells as after a point the motor becomes overgeared and just becomes hot (data indicates that motor will draw more amps, but eff falls, so output power does not improve.)

=> if you want a truck that does 40 on 14 cells, its more efficient to run a (8)XL and lower the gearing than run a 10xl and gear high.

Obviously there are more factors involved in actual motor selection, but this is what the calc data and my own experience tells me.

Based on this thread I have been wondering if i needed to run a 7XL instead of the 9XL in my G2R 12 cell mamba max setup. Given the same gearing (17/66) and same cell count (12 cells), Could the 7XL be more efficient in this case?

CrazyJR, now you feel my pain :) I was wondering the very same thing, but with different motors.
You'd have to change the gearing though. Aim for the same speed, and your motor temps may significantly drop.
Whatever you do, please keep us updated.

Daf

Here's another question that seems relavent to this conversation. The neu motors seem to be built with both Delta and Wye winds. The Wye wind seem to have a lower kv than the Delta. Is one wind type more efficient than the other?

As daf said, you couldn't gear it the same. Assuming both are properly geared, it doesn't mean the 9xl is inefficient, altho it may be just slightly lower. What you can't do is try to gear the 9xl for as high of speed as the 7xl is capable of w/o overgearing/overloading the motor and thus dropping efficiencies

SScream: you evil man....:mad:1 :005: I doubt and diff would be readily noticeble, all winds seem capable of v high efficiencies.

The problem is that at set voltages lower turn (higher KV) motors produce more power.

However it is possible to go down in kv but still produce the same power by using a larger motor.

My 540 8s and the 540 7l i have ordered have similar resistance and current characteristics which enable them to produce nearly the same power at a certain voltage. The pure difference ignoring the extra weight is the higher torque and lower rpm which should hopefully mean that the 540 7L will be more efficient on 3s lipo than the 8s.

I look forward to receiving my motor I have in fact bought a spare xxxt transmission in anticipation of the strain on the transmission.

What about............

Has anyone considered "driveability" or "control" differences between Kv ratings? Consider the "responsiveness" of a 1700kv motor vs a 2300kv motor or a 4600kv. The higher Kv motor would be far more reactive to throttle (or esc/trigger) inputs than the lower Kv motors.

From what I've gathered from various sources (not personal experience) the higher Kv rated motors have a somewhat higher efficiency.

Also....(although a bit off topic) How do we factor in the performance differences of using 2-pole vs 4-pole (or 8-pole for that matter) motors?

Maybe what we need is info like you'll find on this attached pdf of a Mabuchi 550 motor. It tells alot about the motors "personality".

I think with a higher rpm range the higher kv motors will feel smoother on accelleration. However i think lower kv motors that output the same power will feel more punchy as the rotating mass of the rotor will have less effect on the overal performance.

That would be PERFECT! It shows the various values at max eff, and max power. So, the user can decide what they feel is most important and make the decision based on specific data.

To a large degree, battery quality plays a big role. It looks like the graph assumes an ideal voltage source (constant voltage and zero output impedance). Pretty much ANY battery will sag and react to certain loads.

And let's not mention how the ESC handles itself. Ideally, its output should be stable no matter what, but some loads (particularly high inductive loads) are more difficult to drive due to the voltage and current phase shifting.

Argg! It's enough to give one a headache! There are simply too many variables! The motor selection is hard enough without the user being forced to make assumptions on battery quality and ESC stability.

Good point. The most efficient setup may not be the one that "feels" the best.

Ack!

Sleeb

A motor dyno would be the way to go. The graphs of the power output relative to voltage, current draw, etc plus measuring temps would be beneficial.

BUT.....

What if we could take and do an RC version of what we do in the 1:1 world?

Take one E-Revo w/4s2p Lipo's, Quark (or MM) and a Neu 1515/1Y run timed acceleration tests. For example: 0-30mph, 0-40mph, 0-50mph, 20-40mph and monitor voltage, temps, etc using something like the Medusa Power Analyzer Pro w/data logger and a Radar Gun (or maybe just acceleration for a fixed distance for simplicity) and then swap to a 1515/2.5D and re-run the tests.

Gearing swaps could be considered and several runs could be made w/various ratios and dropped into a matrix for comparison.

A major factor for me would be to see how the motor reacts/responds to mid-range acceleration. What motor/gear combo is most responsive and controlled for track use. Say your half throttle on track approaching a double or tripple jump and need power to clear it. Which combo is smoothest, most predictable and controlled? Lots of power is great but it needs to be in a useful rpm range and needs to be efficient to avoid excess heat buildup and battery drain.

that's my $3.52! Sorry for the lengthy response.

Hm. Taking the 1:1 suggestion, maybe rigging up a G-Tech would be a interesting idea? However, I'm not sure if something that light would fit in its operating parameters. If you could get a raw data dump, that might me something interesting though.

Hmmmm.... <rubs chin>

S

Did you guys read me earlier post?

Which one?