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foc openloop not starting motor on higher erpm

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Alan oldguy
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foc openloop not starting motor on higher erpm

Hi, I have been bench testing my motor with foc openloop & found it operated my motor at the Amps & erpm I specified

until I got in to the higher rpm where it struggled to start or vibrated like mad.

My motor is a 6374 60kv with hall sensors.

I tried with 5A & 20A loads which worked until I increased the erpm to around 4-5000 erpm.

I am wanting to test the motor at around 10,500 erpm (1500 rpm) which is about half my no load rpm.

Anyone got any ideas as to what is going on or how I can remedy this thanks.

BTW had a hard job getting foc openloop to run till I discovered it didn't work with the receiver connected.

Cheers Alan

TechAUmNu
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foc_openloop is exactly what it sounds like. It just cycles the set current through the motor at the specified erpm. It has no idea where the motor is.

Therefore at higher erpm the motor will not sync with the input signal and just vibrates as the magnetic field travels round the motor.

 

If you want to test at higher erpm you can either increase the current until it works with foc_openloop. Or you can use the RPM or Duty cycle controls at the bottom of VESC Tool.

Alan oldguy
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Thanks for the explanation Tech.

I played around with the duty cycle, erpm & Amp tabs & I could get the rpm I wanted but not at the load I wanted.

Am too scared to try increasing the amps & rpm on foc openloop as when it failed on 20Amps it shook so violently

that the nuts came off the motor holder bracket & had me scrambling to disconnect the power. 

The rpm that I could reach by going from 5 - 20A was not that much of a step up & indicated that if I went to 40A

I still wouldn't get anywhere near my required 10,000 erpm.

Is there any way of getting a soft start, as this would allow the motor to get to speed.

Will suggest a soft start in foc openloop in the appropriate forum.

Thanks again. Alan 

 

Danny Bokma
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(sorry wasn't reading correctly ), but what voltage are you operating on for the power supply? And what kind of load is attached? 

TechAUmNu
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Your best bet for a constant RPM is to use duty cycle mode as it will adjust the current automatically for you. If you can't get it to stay at the RPM under load you want, then you need to increase your motor or battery current limit. Watch the current readings in the real time data tab to make sure the current limits are not limiting the motor. 

If you want to get a load of 40A on duty cycle mode, then you would need to provide a load for the motor.

 

Also if you are using foc_openloop, you don't actually need to run at the intended RPM. Since the losses in the system are more or less constant and based on the resistance of the motor and the esc over the whole rpm range. Only being slightly affected by the inductance change from increasing RPM. 

So for temperature testing you can actually just run at a low ERPM and it will give you almost identical results.

 

 

Alan oldguy
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Hi Danny, I have a 48V power supply limited to 40A. There is no load attached. I am using foc openloop to simulate a load.

 

Alan oldguy
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Thanks Tech, I am getting some pretty good results with the testing now. I am running off a 48V power supply limited to 40A.

I am testing the motor for use as an underwater thruster. The motor is in an aluminium housing filled with oil. So the reason for

wanting it to spin at it's maximum rpm under load was to see how the oil cooling worked as the motor veins pumped it around

inside the housing. By just putting the motor only  in a bucket of oil & running it at the rpm I could get to under load on foc openloop,

it told me enough about cooling & maximum continuous amp draw. Cheers Alan

vinvolc30
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hello team and Alan! Have same shaky scenario when trying to start smoothly on my el-longboard ( have 29.4V with 25A max and 5045 motor as FOC set up ) . Is there might be lowering ERPM (have -> 400 obtained after motor test) this value by some reducing(lets say 30-40%) it to make my skate start smoother without shaking of motor ? Also if make sense will it impact only start of skate or also during cruising speed(decrease it) ? *pic VESC setup attached and any ideas -> would be happy then team !

thumb_ERPM-setup.jpg

Thanx
/Alex

technicc
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Sorry for posting on an older thread.

@Alan how did you manage to make the open loop work? Can you direct me to some sort of tutorial / thread with additional information? I appreciate it.

Regards, Tomaz