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VESC with propeller, not reaching max performance

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ogent
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VESC with propeller, not reaching max performance

Hi all, I've been using the forum a lot to troubleshoot but this is my first post :)

I'm an undergrad engineer - 

We've had a lot of problems trying to replicate T motor test data in FOC and BLDC mode

So I've been wanting to use the VESC for use in UAVs due to the potential efficiency benefits as well as wanting to be able to use reverse thrust and record data.

We've been testing these 3 motors in a wind tunnel: AT3520 (550kv, 1000W, 14x7e), AT4125(540kv, 2000W,16x8e) & AT5220 (220kv, 3000W, 19x10e).

We're running 6s , 6s and 12s respectively.

https://store.tmotor.com/goods.php?id=794

https://store.tmotor.com/goods.php?id=827

https://store.tmotor.com/goods.php?id=948

we're using the FLIPSKY 60amp 6.6 VESC

 

for the AT5220:

In BLDC mode as I understand, we should just be able to get max thrust with no tuning, there's phase advance which can affect max RPM - i've tried adjusting this to no avail - still getting a maximum of ~90,000 erpm. (instead of the expected ~110,000)

In FOC mode I've messed around with it a lot and it runs nicely up to 90,000erpm but no further.

We've also tested this motor with the smaller props and still failed to reach the correct rpm

 

For the AT3520:

We manage to almost get maximum thrust in BLDC. (this is the smallest motor) but ~10,000 less erpm on FOC. I tried field weakening and this seemed to have little effect

 

For the AT4125:

pretty meh performance all round.

 

I've probably spent 24+ hours messing around with the VESC now - I've pretty vastly underpredicted how easy it would be to get right.

 

 

 

Is there something i've missed? 

 

https://vesc-project.com/node/356 - in this forum post someone shows the VESC vastly underperforms compared to other ESCs, both FOC and BLDC. Apparently this is due to the motor "saturating". For us the high end performance is very critical for short periods of time (take off) so we don't care much about efficiency in these regions. 

 

We've purchased a "normal" ESC instead which supports reverse thrust but won't be able to measure anything without further equipment.

 

 

I've left out lots of details, but if anyone's willing to help We'd greatly appreciate this and I can send any details / data over

 

 

massive power consumption by the VESC compared to T motor data:

Picture2.png

However on the smaller motor, we do get much better agreement (on BLDC):

AT3520.png

 

maxhertz
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What power source are you running from?

It maybe that with the larger motor the batteries/PSU is struggling to supply enough current.

ogent
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Hey! We were using Lipos, two 6s 25c 5800mah in series which should be able to do 145A 

Could have done with a power supply though so we didn't have to keep on charging..

ogent

maxhertz
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With higher performance LiPos you will get less voltage sag and higher RPM.

ogent
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we only need 60a for the large motor...

Even with a smaller prop on the large motor we fail to reach expected rpm, where load would be much less.

ogent

TechAUmNu
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Have you adjusted the RPM limit from 100000erpm? It would stop you going over about 80-90k erpm if that is still set.
Are you using firmware 5.3? That should help a lot.

ogent
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I tried FOC on 5.3 since I thought the field weakening would help but I couldn't seem to get a performance benefit from it

We had the eRPM limit set to 150,000 for all tests

ogent

maxhertz
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If you measure the voltage under load, I think you will find that it is substantially less than the 50V (from a large PSU) that TMotor probably use for their 12S performance graphs.

ogent
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So I checked the voltage sagging theory anyway - At maximum achievable rpm (static) we were measuring ~43V and ~6,500rpm (our no load voltage was ~46). T motor data shows at 43V they got 7,700 rpm. 

ogent