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ESK8 Motor Dyno - Requests and Discussion [SERIOUS]

How did we miss this?

You’re the real MVP @Pedrodemio

Fantastic initiative! I’ll be swinging back around to Motor/ESC testing after summer and will be sure to coordinate here.

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You didn’t. It was unlisted while Pedro put this great resource together, and only listed for public view today. Discourse still counts unlisted threads as active and puts the usual timer on it.

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I was wondering myself why I missed this thread…

but then I got a cocktail or three and it didn’t bother me so much!

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I think it’s all there I just gave you the motor config. back-up… it’s prolly in the app config back-up…

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Yeah the Motor Config backup has the motor information (if the user puts it in) . And the motor resistance is in there too

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ping me tomorrow and I’ll upload the app config .xml file… I’m too high right now to power anything up…

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Added the graphs for the Boosted V3, really amazing motor with crappy bearings, and the 6355 from Aliexpress, for the price is good, but comparing with a TB6355 the performance is pretty bad, way higher resistance and also core losses

@Jc06505n Yeah, that would work, ideally I would like to see this being part of the detection process, on the results for each motor it already would show Km, Eddie losses and Hysteresis Losses, all that we need to plot those graphs, a database could be hosted on VESC tool site and have all those graphs. Unfortunately that is way beyond my capabilities

Thanks man, waiting for your tests

You know what would be cool on FreeSk8? Add motor efficiency logging, if we know the parameters I calculate here and the motor temperature, we can easily calculate how efficient the motor is at any given time. Maybe have a efficiency indicator on the remote like some cars do

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One cool thing we can now do is ride simulation using ebikes.ca Trip Simulator

https://www.ebikes.ca/tools/trip-simulator.html

Will do a guide sometime on how to convert the information we have here to use there

Unfortunately temperatures won’t be accurate until we model each motor, need the wind tunnel for that

But will help a lot with motor selection and gearing optimization

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I’m thinking I may have screwed up the core losses calculations somewhere, I can’t make the results from the Grin Trip Simulator and from my graphs to agree

For example, running a TB 6355 at 15k rpm, looking at the graphs we should have around 40 W of core losses, while if I input all the losses coefficients and spin at the same speed I got 200 W of core losses, doesn’t sound right, but also my value may be too low, time to dig in the code and see if there is any mistake, take the core losses results with reserves until I can find what is going on

Edit: kind off forgot that there is a really easy way to validate the data, just spin the motor and see the power draw, with no load almost all energy is going into core losses, will test that tomorrow and see if the results match

I didn’t take note of the power, but it was not high at all, I’m thinking my plots are right and there is some bug on the Grin simulator when entering data for our small and high rpms motors

Will probably join a bunch of batteries and maybe some wall adapters to get to 18S

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Well, I will keep updating my findings here for posterity

This is the plot of core losses torque vs RPM for my TB6355, it starts fine with a Hysteresis loss of just 0.075 N.m, a reasonable value, but is way too steep, consider that a 190 Kv at 60 A produces around 3 N.m of torque, at 12500 rpm (18S nominal speed) we have an almost 1 N.m or torque needed just to overcome the core losses, this mean 20 A of motor current just to make the motor spin

Either the current measurements are screwed up, or the bearings that are bad but not that bad cause way more drag than I imagined

Now lets look at the TB5055

And the Aliexpress 6355

The TB seems reasonable considering the bearings are also not good, but the Aliexpress one is even worse, at 18S it needs 40 A just to spin at the nominal speed

What this all means for now? That apparently at least these motors are absolute crap at high rpm, I hope people contribute with more motors measurements so we can find the good ones, but if the trend is right, none of our motors are good at high rpm

Next step is to replace the bearings on the TB6355 and see what changes

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Error found

When the current at two duty cycles is measured, I forgot to multiply by Kt, the torque per amp constant of the motor, so the graphs above actually were representing phase current vs rpm, not torque vs rpm, this is how it should look, way lower core losses all across the rpm band

Will fix all motor plots as soon as possible

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I get the logic behind voltage constant, but what’s the math to extract torque constant from the VESC measurements?

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You get the torque constant directly from the Kv, they are inversely proportional

Kt = 60 / ( 2 * pi * Kv ) = 9.55 / Kv [Nm / A]

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Wow, that’s an interesting relationship. Thanks! Blows my mind how much we can learn from these motors with just a few simple tests.

I think I will do a section explaining all the math behind the graphs

The only thing you can’t do i think that a lower Kv will produce more torque, it won’t, two equal motors, having the only difference being the Kv, can produce exactly the same torque

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@Gamer43 do you have any comment to make on the current readings at both high a low duty cycles? These current readings make no sense, first it goes down , stay relative constant and right at 90% and 95% duty cycle goes way up

If we can’t get everyone to get good readings this effort won’t work

erpm current power
700 0.4 0
2100 0.47 0.8
4616 0.36 1.1
7141 0.36 1.5
9612 0.36 2.3
12068 0.36 2.7
14512 0.36 3.4
16950 0.33 3.8
19381 0.33 4.2
21807 0.33 4.6
24230 0.31 5.4
26648 0.32 5.7
29061 0.32 6.1
31464 0.34 6.9
33864 0.33 7.6
36247 0.34 8.4
38609 0.34 9.2
40970 0.37 10.3
43368 0.52 14.9
45763 0.55 16.4

I talked a bit with @Gamer43 and I’m putting on hold the measurements you guys can do until we validate what is going on, big chance that the current measurements at low levels from the VESC are really noisy, specially at the duty cycle extremes

Unfortunately I don’t have the equipment to validate externally, so will have to figure something out

The numbers for now sound too good to be true, 96% efficiency over a big torque and rpm area

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Some new tests, I run the same motor at three battery voltages, 4S, 10S and 16S and took notes on the phase current readings in 10% duty cycle steps to see if any point deviates when you are on the extremes of the duty cycle, turns out they all deviate.

Spinning at 180 Kv motor at 16S is a bit frightening, I considered trying 20S since in theory the 100D can take without regen, but the motor might have exploded or got too hot just from core losses

@Deodand was kind enough to explain, correct me if I got wrong. Basically there is two problems, first we are measuring a really small % of the total current measurement capability, so the accuracy can/will be low, and on top of that deadtime compensation further skews the results, to a lesser effect the higher the duty cycle is.

In other words, none of the results presented here are valid :thinking:

Next step is to measure the phase current externally, see how it compares and how the deviation influences the overall theoretical performance graphs, if the effects is low, lets go ahead, everyone measure there’re motors and we keep in mind that there is a high degree of inaccuracy in the results, but can be useful for a relative comparison between motors

Unfortunately this will mean that we will have to exclude any ESC that has a notoriously noisy current reading (Hi FlipSky), but I have a FSESC MINI4.20 here and will try that

Ideally I should permute all motors and all ESCs I have here, lot of work

Cheers

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Here are the differences between the performance with the 4S and 16S measurements, not that big, and certainly usable if the overall current reading is good

Also I’m suspecting this motor I’m using for the tests have a Kv of around 160 instead of the 180 its sold as, will see if I can test it