Sensorelss BLDC runs properly during detection, but returns "Bad result"

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vid
Posts: 2
Joined: 30 Jan 2016, 09:02

Sensorelss BLDC runs properly during detection, but returns "Bad result"

Postby vid » 07 Mar 2016, 14:31

I have some special waterproof BLDC motors which hold up to 300bars of pressure, intended for use in rc submarine http://calypsoproject.co/en/. In order to complete automatic detection for sensorless BLDC operation motor should be without any load. These motors have built in 50:1 gear, which is unfortunately non-removable. Although the motors aren't completely free, I think that such a light load should't affect detection process. Am I right?

TI's Motorware FOC controllers went through configuration process with this motors successfully, so it should be possible to detect correct values even though the gears are always on the motors.

During detection motor runs perfectly (https://www.dropbox.com/s/9lcj06cai2s61wm/2016-03-07%2014.04.26.mp4?dl=0) but afterwards always returns bad result.

Do you have any suggestions what could be the problem?

P.S. thanks for sharing this awesome project for free :) !

jaroslavnovotny
Posts: 49
Joined: 16 Feb 2016, 13:10

Re: Sensorelss BLDC runs properly during detection, but returns "Bad result"

Postby jaroslavnovotny » 07 Mar 2016, 16:22

Hi,

what motor is inside, do you know? Size, kv, etc.
And what parameters are you using for the detection?

Can you detect other motors without problems?

Also did you try guessing the motor parameters and enter them manually and see how it performs? Thus avoiding the detection stage? Sometimes this works.

benjamin
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Re: Sensorelss BLDC runs properly during detection, but returns "Bad result"

Postby benjamin » 08 Mar 2016, 12:57

Hi,
Are you using BLDC or FOC? The FOC detection works better with a bit of load. You can try to follow this tutorial:
https://www.youtube.com/watch?v=bYYNbxPXNEU

vid
Posts: 2
Joined: 30 Jan 2016, 09:02

Re: Sensorelss BLDC runs properly during detection, but returns "Bad result"

Postby vid » 08 Mar 2016, 17:25

Hi,

jaroslavnovotny wrote:what motor is inside, do you know? Size, kv, etc.
And what parameters are you using for the detection?

Can you detect other motors without problems?


We got these motors relatively cheaply because they were prototypes. Therefore the seller didn't specify any specs (except the gear ratio and the pressure they can withstand).

Parameters for the detection process (BLDC) on the video were: current=7A, min ERPM=1200, low duty=0.1 (and of course I've also tried many other combinations).

Yes, other motors are detected without any problem.

I also tried to guess the params, but I don't have enough knowledge about BLDC or FOC to understand their correlation.

benjamin wrote:Are you using BLDC or FOC? The FOC detection works better with a bit of load.

On the video I'm using BLDC. I've also tried FOC (following that tutorial :), which returns bad result as well (R and L are measured successfully, but lambda detection won't work).
Can I see which parameters are used during the detection phase, because the motor spins perfectly while measuring for BLDC or FOC?

P.S. I have quite long cables (which I can't remove, because the motor is sealed) - could they be the problem (~1.5m)

benjamin
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Location: Sweden
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Re: Sensorelss BLDC runs properly during detection, but returns "Bad result"

Postby benjamin » 11 Mar 2016, 10:29

Do you know the motor kv and number of poles? In that case you can calculate the flux linkage like:

lambda = 60 / (sqrt(3) * pi * kv * pole_num)

rew
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Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: Sensorelss BLDC runs properly during detection, but returns "Bad result"

Postby rew » 03 Sep 2017, 14:34

For those looking here for that formula (probably me, a few months from now): it says "pole number" not "number of pole pairs".
For BLDC_tool, the number is probably 0.<something> , for VESC_TOOL (any moment now), it will be in mWb, so multiply the result by 1000 before putting it in.


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