Calling owners of BIG motors

DIY Builds
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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 still in progress, but so far it seems that compared to 6355, a 6389/6396 takes as much as 10 times the power to be spun at any given rpm, when in theory it should be close to two times more give the stator is around 2 times as long

Thanks a lot and hope to figure this out because it’s taking the sleep out of me lol

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i got 6396 but they are attached to a gear drive i can try to test later

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Thanks man, to be honest if you can’t do without, do it with the gearbox, just let me know, the values are so much higher than they should that even with some additional drag for gears and wheel bearings it will still be possible to find what is happening

Really the question here is if all bigger motors are the same and find out why this is happening

We are talking about a possible 10~20% range increase being possible just by swapping motors

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yeah i can try with a gear on easily
let me get back to you later today with the results

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@Andy87 your Inrunner freeroll video…

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Just a note but i had my Racerstar 5045 motor on a redbrick esc and a refurbished alienpower 6384 v1 to see if it was working properly.

Had them hooked up to a power source, the 5045 took half an amp to spin to the esc’s max voltage and the 6384 took a full amp.

This was on i think 20 volts though so not very similar.

Racerstar was 200KV
Alienpower is i think 170 @PixelatedPolyeurthan

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im just wondering would the can design have any impact on this? e.g. open can / closed can
also since the can also spin the shaft, i imagine 8mm and 10mm shaft would also have a difference?

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That’s a 6374 so around 750g outrunner vs. 56114 around 1100g inrunner.
Less poles and centered rotating mass definitely make some difference regarding free roll.
I‘m curious to do a range test to see how big is the difference between those two setups.

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Would explain why they get so hot!

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This is realtime data readout with a xenith and maytech 6396 on 12S. Around 4 Amps which is a fair bit

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Thanks for the data, this is better than I’m getting a similar speed, you are getting around half the losses

At higher rpm the vents could have an impact, but more testing in needed. Same for the shaft, bigger shaft = higher bearing ball speed that could have an impact, but if we have that much power being lost on bearings something is really wrong

Looking forward to it, but makes sense, less poles = less core losses, and also having less magnet mass also reduces the losses

They come with a trade off of less torque density usually

Thanks man, this is exactly the kind of data I’m looking for, and yours is almost a perfect match to what I got

My next test is taking out the big bearing, it shouldn’t have this effect, but lets see what happens

This is the data I have so far, cross check with a multimeter to rule out a wrong esc measurement, there is an error but nowhere near enough to explain the high no load current draw

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Yes indeed, 170

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What were the current draws for each?

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Just some revelations, seems like the problem is actually the VESC 6 current measurement, way off from what actually is, and that caused me to overestimate the efficiency

This is the same TB 6355 on the 100D and the VESC and both compared with the actual power with a multimeter

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So Lacroix FTW :love_you_gesture:

But keep in mind my VESC 6 is from one of the first batches and the first version

There is still a firmware comparison to be made

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yeah you should probably update everything to the newest firmware as i think some stuff around current measurement changed since FW5

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Testing it right now

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Ok, no diference whatsoever on the measurements, would be good to test a current generation VESC 6 to see if there is any diference

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maybe @Trampa would know if there’s been any changes to the current measurement hardware?

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that bearing heats things up quick too

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Interesting topic which leads to some questions.

Do you think the data (amps) of unweighted spinning motors is about the same difference as if weighted?
I mean e.g. if you have 2 motors in different sizes but with same kv and same vesc settings . Let’s say with same board, same gearing and so on. If the 6355 pulls 2A (unweighted) and the 6384 4A at max. speed, what does that mean in real world riding? Would e.g. the smaller motor need 30A and the bigger 60A motor amps under same circumstances and load?

I have some motors which I could test but don’t have a bench setup and lack of time right now. Hopefully I can do it soon.

I think it would be also interesting for you to get real kv data from people, not what the manufacture claims. Personally I never managed to get the kv number from Vesc-Tool, I tried it several times. Or I do something wrong. How is the correct way please? :pray:

I made the experience the bigger the motor the smaller the range on the same board. And on the MTB the motors often pull (almost) the max motor amps from standstill e.g. on dirt. If I set them to 80 motor amps each, they pull it. I was surprised when I saw that I always need 130-160A motor amps from standstill slightly uphill in the woods (no matter if 6374 or 6384). Also once my BMS shut off at 120A battery amps even though the vescs are limited to 100A batt amps, guess it was a voltage spike.

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