ESK8 Motor Dyno - Requests and Discussion [SERIOUS]

[Pedrodemio]

@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

[Pedrodemio]

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

[Pedrodemio]

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

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

[Pedrodemio]

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

[hummieee]

I had similar weird current results at different duty cycle (would drop at 95%) and asked on endles-sphere and was also told it’s not accurate. Is there other data logged that could be used to figure a more accurate current draw such as watthours or amp hours and keeping other things consistent?
But with the iron losses being pretty small anyway how about just comparing the km? I think the vesc is accurate enough for that no?

[Pedrodemio]

Best way to do it is to measure the battery current and voltage with two multimeters

With that and the ERPM you can calculate motor power and motor torque, and from that calculate all the rest

This is how the folks from ebike.ca do, don’t know when, but I want to test all of that one day

[hummieee]

Why would the core losses be lower at the same rpm but with higher voltage as this graph shows?

[Pedrodemio]

These graphs aren’t actually showing that they are lower, but what effect the measurements error due to different voltages has on the efficiency plot

They should, and probably are the same , unless there is a big difference is efficient due to different duty cycles on the controller

[Paul77]

sorry if this is the wrong place to ask this, i have 2 sets of motors both TB 190 KV, the 6355 have about a 5 mph difference than the 6380’s, same gearing, wheel size, everything is the same. why would the 6355’s be able to reach a high top speed?

i have checked all my settings 10 times over and just cant figure this out.

[ShutterShock]

The real reason is just because motors kV varies between batches depending on exact number and quality of windings, often you’ll find that 190kV motors are on the lower side and actually come in at 180 something.

There’s a command in vesc tool to test kV but I can’t remember what it is

[Paul77]

That makes sense, I will look for that in the VT tonight. I will be curious to see if that is the culprit.

[ShutterShock]

I’m guessing one is high or low

[Paul77]

If that is the case my bet is the 6355 are closer to 200+ range

[rusins]

@Pedrodemio

How To Meassure on hold until we figure what is going on with the VESC measurements

Did this ever get resolved? Or are the tests good enough for comparing motors, as long as they’re done on the same hardware? I was planning on doing some tests on a Trampa Vesc 6mk3, but I could do them on my 100D if that’s what you’ve been using until now… Only got a 12s battery at the moment though.

@Pedrodemio

[Pedrodemio]

Yes, it is resolved but I didn’t go back to do the tests again, the solution is to simply to use a StormCore since it measures phase current differently, the VESC 6, at least the version I have that is one of the first revision, the phase current measurement at lower phase currents is way too noisy and completely wrong

See here

Calling owners of BIG motors

Hey dudes I’ve been modeling some new motors and came up with some weird results, basically it seems that 6396/6389 motors are really inefficient, as in they that a lot of power just to spin the motor itself For those who can, I would ask do do a simple test, run your motor at max speed, without a belt or not in a gearbox and let me know what ERPM and motor current it does under this no load condition, as well which motor you are testing and it’s Kv 6374 and above is what I need My tests are…

I plan to get back to this in the future when I have time

[rusins]

I’ll probably install Matlab later tonight so that you don’t have to bother generating all the graphs, but here is all the data from my motor tests. Also I first ran the 95% duty cycle test, and then the 35% one. Just because the 95% test normalizes all the values faster.

Edit: Matlab isn’t FOSS? Yeah, no thanks. You generate the pretty graphs please! I’ll lookup all the manufacture given motor info in a bit and add it in for you… Edit: done.

All tests done on a Stormcore 100D and a fully charged 12s Li-ion pack. FW 5.3 2021-07-14

Maytech 6355 190kv

95% duty
0.37A
55009 ERPM

35% duty
0.35A (0.44A on first test, but I guess ignore this value)
20602 ERPM

14 poles = 7 pole pairs
Manufacturer rates at 55A, 65A max.
Comments: New. Unikboards branding.

Maytech 6355 170kv

95% Duty
0.29A
48770 ERPM

35% Duty
0.32A
18208 ERPM

14 poles = 7 pole pairs
Manufacturer rates at 55A, 65A max.
Comments: slightly used

Maytech 6374 190kv

95% Duty
1.74A
53000 ERPM

35% Duty
1.05A
19790 ERPM

14 poles = 7 pole pairs
Manufacturer rates at 60A, 65A max.
Comments: new

Maytech 6880 180kv (same sized stator as 6374)

95% Duty cycle
2.25A
50000 ERPM

35% Duty cycle
1.30A
18740 ERPM

14 poles = 7 pole pairs
Manufacturer rates at 60A, 65A max.
Comments: New. Bioboards branding.

Maytech 6374 170kv

95% Duty cycle
0.92A
45860 ERPM

35% Duty cycle
0.65A
17150 ERPM

14 poles = 7 pole pairs
Manufacturer rates at 60A, 65A max.
Comments: New. Factory battle-hardened.

Maytech 6374 150kv

95% Duty cycle
0.95A
43250 ERPM

35% Duty cycle
0.85A
16125 ERPM

14 poles = 7 pole pairs
Comments: Been through hell and back. Somehow still runs great. No sensors tho. Unikboards branding.

Flipsky 6384 140kv

95% Duty cycle
0.88A
45470 ERPM

35% Duty cycle
0.80A
16969 ERPM

14 poles = 7 pole pairs
Manufacturer rates at 95A max.
Comments: New. Factory battle-hardened.

TorqueBoards 75kv direct drive

95% Duty cycle
2A
40560 ERPM

35% Duty cycle
1.65A
14840 ERPM

28 poles, 14 pole pairs.
Manufacturer rates at 80A.
Comments: Used.

Loaded x Unlimited 75kv hub motor

95% Duty cycle
1.15A
49130 ERPM

35% Duty cycle
1.05A
18060 ERPM

14 pole pairs = 28 poles, surprisingly enough
Source: this and speed calculations
Loaded unlimited hub motors experience? - #117 by glyphiks

Manufacturer rates at 20A.
Comments: New.

Can’t wait to dig into all this data and do comparisons

[hummieee]

anyone running a dyno?

at what point do these different motor sizes magnetically saturate and no longer produce torque at the same rate as the current. This below claims a max current of 95 amps and like to know what happens at 95 and beyond. MP 8074 Sensored Version Brushless Motor for Electric Skateboard scoot – Ant Innovation Technology Co., Ltd. (antinnotech.com)

@rusins results just above from all the motors could be put in hierarchy of producing the most torque with least amount of heat, the km, and couple that with the no-load losses and i believe that accurately sums up the motor’s ability to produce any amount of torque at any speed, or maybe youd need the motor’s no load losses at another speed to see their trajectory… until it saturates. if everyone is taking requests. but more so interested in how saturation plays out and just how bad it is at what current level for what diameter and length stator, which i think only a dyno will reveal.

(electrical steel is strangely #2 and i guess more value in its lower iron losses) Saturation (magnetic) - Wikipedia

[rusins]

@Pedrodemio I added info from the manufacturer about rated current & how many pole pairs. If you’re busy, I could ask someone else to generate all the graphs…

[hummieee]

Be nice to figure at what point motors saturate to decide what esc settings are worth using. Anyone got a dyno going around USA @Fosterqc

[ShutterShock]

It’s somewhere down in the middle of my long list of projects