Hi,
A friend has built his own BLDC motor... he wants me to make it spin, so I've gotten out the VESC6 to try to make it spin...
All it does is make noises. During FOC-detection it spins on the second attempt. But somehow the firmware decides not to trust it spinning. On BLDC detection I haven't been able to get it to spin. Neither in BLDC-mode, Just commanding a duty cycle or current makes it shake a bit but not spin.
The "RL" measurement succeeds, That gives 30mOhm and 2.2uH. Due to some mechanical parts not fitting, the motor is now in a "very high KV" configuration, for the desired configuration that KV is going to come down a lot, but all the windings are already there, so the inductance is going to stay around 2.2uH (at least, that's what I think, correct me if I'm wrong.).
Is the 2.2uH too low to make this work? My friend says he tried a few HK controllers and that they worked...
Update:
On BLDC mode we've gotten it to detect once. Then I guessed that the 811 that was detected was the inverse of the lambda in FOC. So I entered 1.2 mWb and now the motor runs in FOC mode.
OK. My friend has brought along his "improved" motor. We were hoping for improved efficiency over a "hobbyking" controller.
This did not turn out that way..... With the current test-setup we don't dare run the motor over about 3000 RPM.
We have now tested things with the stock VESC6 and stock firmware. The thing is... We tried it first with the FOC settings that just happened to be configured: 20mOhm and 2.0uH. That worked. The lab powersupply indicated 4A at 12V, but the VESC said it was pushing around 3A back into the powersupply....
Using Benjamin's formula: 60 / (sqrt(3) * poles * pi * kv), with a measured KV we come to a lambda of 2.07. The funny thing is that "reset to defaults" will cause the motor to work just great IN FOC MODE! I've stepped the lambda to 4 (thinking I might use poles=28 as opposed to 14 pole-pairs) Around 2.5 things start to work, at 2.0 things work also. The "default" FOC settings for R and L are 15mOhm/7uH, which are reasonable (20mOhm) and way off (0.9uH).
We're finding that when we get it to run in BLDC mode, the VESC is slightly more efficient. But in FOC mode, the VESC uses over 2x more batterycurrent (while measuring negative current).
At one poiunt we took this screenshot: http://prive.bitwizard.nl/vesc_negative2.png
Did you set an RPM limit in Vesc tool? That may explain the negative current reading as there is an option to negatively limit RPM. I would check that and maybe run it in duty cycle mode instead. I'd be interested to see this experimental motor. You should post some images of it!
First, you know how some inventors are more proud of their invention than they ought to be? Well... that is the case here. He's got a motor that requires a relatively big amount of power to spin without load (it runs on 1.5A, but should be able to run fine on 0.2A!), and he thinks its the best thing since sliced bread. If I'm wrong and it IS the best thing since sliced bread, and someone replicates his work from my pictures I'm in trouble.... So.. Sorry no pictures for now.
The "limit RPM with negative current", as I understand it will provide negative torque once you exceed the RPM limit.
Suppose I have a bike. Under Dutch regulations, the electrical assist is not allowed to work above 25km/h. So we set an RPM limit, no negative current and going downhill, or just pedaling fast, I can go faster than 25km/h, I just can't ask for electrical assistance.
Now when I give this bike to my fragile grandmother, she complains that the bike rolls on its own. It goes too fast going down the slopes coming off the bridge. Now we configure an RPM limit equivalent to 20 or 22km/h and add the negative current. Now the bike will regenerate into the battery whenever she goes downhill.
In this case when bench testing, we should not be able to keep it "regenerating" for minutes on end by hitting the RPM limit. My friend was afraid mechanical things might explode at too high an RPM. His HK controller could run safely at 2S, so we tried using the RPM limit to prevent going above the RPM equivalent to 2S. (I told him the VESC doesn't work on 2S, at least 3S). The RPM limit doesn't seem to work in FOC mode, only BLDC mode. Weird things like that too. I did not touch the "negative current" option for RPM limit. I don't know what the default is.
The thing is, VESC reports 2-3A going INTO the powersupply while in fact there is around 4A coming OUT of the powersupply. The VESC is getting seriously confused somewhere....