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Motor Dyno torque curves

Motor Dyno torque curves

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Old 02-08-2019, 09:49 PM
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Default Motor Dyno torque curves

so what are we looking at. The first thing i do is determine where peak efficiency is at. depending on the motor it will be be closer to 30 degrees or closer to 40 degrees. That becomes the base RPM and its different from motor to motor. it isnt a number that you can compare one motor to another. it represents the max return on investment or in our case the most efficient RPM range to start with for a given motor. its usually around 70% efficiency but because the esc is part of the equation the number has a little to do with the ESC. i always use the same ESC. a sanwa super vortex because I can change timing electronically on the fly without anything external. But it is way oversized for a stock class motor. The other thing to note is that I use a 200 amp current sensor. the resolution between points will be half as accurate as a 100amp sensor theoretically.

The second thing i do after determining the base timing is add enough boost at the right RPM to not decrease the low RPM efficiency. its around 8-12000 rpm and then i extend the torque as far out to the right as i can while retaining as much efficiency as possible. this is usually the second curve.

the third curve starts wherever it wants to start and its usually done with turbo so its full throttle only. the intention is max power under the curve from however i can get it. sometimes this results in allot of mid rpm power and sometimes it doesnt. it depends on the motor. the point is to have efficient power unless i grab allot of throttle. what I get is an ability to cool the motor while racing if I have too but I can also burn up some excess heat capacity if i need to make up some time.

so all of this creates an understanding of peak efficiency and peak power for a given motor.

lastly i run curves for a motorat30, 40, 50,60 degrees of end bell timing. I can use this data to compare it to the theoretical and set the end bell in based on the average rpm a track will need for a given motor. this tells me where the center point needs to be for the curve. I then determine how far the curve needs to extend to the right so that I dont run out of rpm.

the motor has a signature width and peak. a short track needs a high peak but the curve can be narrow. a long track needs medium peak but needs to be wide. I run a 5 minute race and manually adjust timing to where the motor doesnt overheat. I can use this data to add the thermal limits of the motor to the dyno curve. i just go back and run the motor at the timing and rpm that I discovered on the track. I can then set the motor timing to maximize the percent of duty i need to pull the car off the track at an exact temperature and it works perfect.

I can switch motors out to match the track. I think some people believe that if they look at these motor curves they will decide the one with the max power wins. it doesnt. you will notice that some motors have ridiculous peaks but are very narrow while others seem flat but very wide. the magic is in picking the right curve for a specific need.R1 21.5 brushless on 2s
first curve is 30 degrees end bell timing only
second curve is max boost

Last edited by Bry195; 02-11-2019 at 10:19 PM.
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Old 02-08-2019, 09:52 PM
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Hobbywing v10 21.5 on 2s
1st-30 degrees end bell
2nd- max efficiency (power in/power out) boosted
3rd-max power​​​​​​​
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Old 02-08-2019, 09:57 PM
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Trinity monster max certified 21.5 on 2s
1st-30 degrees endbell
2nd-max efficiency boosted
3rd-max power boosted
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Old 02-08-2019, 10:01 PM
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Trinity 17.5 monster max certified 17.5 2s lipo
the orange curve is max efficiency with a jump to max power with boost
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Old 02-12-2019, 09:40 PM
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to generalize about what you can understand about a motor think of it as a 3 stage trapezoid.
stage 1 is the 1st 1/3rd
stage 2 is the 2nd 1/3rd
stage 3 is the last 1/3rd

When i use the word timing it means ebell or boost. i will say ebell or boost if it does not apply to both.

30-40 degrees of timing
max efficiency and torque in stage 1
max efficiency in most of stage 2
minimum power in the transition from stage 2 to stage 3

40-50 degrees of timing
in most of these motors stage 1 isnt affected dramatically but the power is extended in stage 2 but the drop in efficiency towards the end of stage 2 is very sensitive to small changes in timing

47-60 degrees of timing
you lose power in stage 1 and 2 but dramatically extend the power and efficiency of stage 3

stage1 and 2 are maximized between 38 and 45 degrees and if you can set the gearing to minimize you time in stage 3 you will have a very cool running motor that doesnt fade. This is easier to do on tracks that are short.

stage 1 can remain efficient with higher timing but the longer the track is the more difficult it becomes to balance the power and efficiency of stage 1 and 2 against stage 3.

each of these motors has is very different from each other no matter what the timing is. each of them will shine in different ways but it still boils down to the slope of each stage per motor. a flat curve (stage1,2,3) is easier to apply at all tracks based on setting a current and a KV. A motor that really shines up top but is shallow in stage 2 or 3 will be very sensitive to to small changes in timing and kv in stage 1 and 2.

since some motors give big returns but are sensitive and some motors are less sensitive it give smaller returns you should be able to see why its difficult to compare what you will get out of one motor as it compares to another motor by using kv and timing alone. the power and efficiency curves are all very different but if understood and applied properly significant gains can be taken advantage if you understand the average and max rpm of a track.

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Old 02-13-2019, 09:50 PM
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Old 02-13-2019, 09:58 PM
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Since most people work from the fixed ebell settings the above power and efficiency curve can help you understand the concepts Im sharing or you can study them for your own purposes.

3 curves. 1 at 30, 40 and 50 degrees each. You can see an overall power gain from 30 to 40 but you lose peak power when you go to 50 but at 50 you get more or equal volume of power under the curve from the extension to the right.

at 50 you generate more heat at lower rpm and this is good if your average speed doesnt require you to accelerate through stage 1 of the trapezoid very often. You would do this on what i generally refer to as long tracks.

the alignment of efficiency to power gets difficult at higher timing. Staged electronic boost can eliminate this and if you look hard enough in the curves that has a series of numbers in the title you can see me playing with different methods to stage boost and turbo to eliminate artifacts of a particular motor.

dont forget that each motor creates different artifacts as well as being more or less sensitive to small changes in timing.

I chose to share and communicate in terms of power however once you understand the relationship of power and efficiency there are a couple more things to understand that may or may not add clarity or confusion but here is the other things that dramatically improve or detract from electric motor powertranes.

from a physics perspective inertia mismatch of the motor rotor to the required motion profile.
power means nothing without an understanding of how to manage heat.
after you understand power and inertia its time to understand how to generate a motion profile from a track requirement.
once you can visualize or calculate a track requirement you have to break down horsepower into seperate torque and rpm segments and determine the weight of power versus these seperate segments. Short tracks cannot be planned for completely without understanding the weight of high velocity versus lots of short accelerations. All the magic is in weighting accelerations versus max velocity.

Last edited by Bry195; 02-13-2019 at 10:13 PM.
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