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electricrt / nxt_firmware_updates

Firmware updates for the E.R.T. NXT Display
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RPM fluctuation at constant throttle when field weakening is activated... Get worse as battery voltage drops. #10

Open papagino007 opened 3 years ago

papagino007 commented 3 years ago

I am currently running firmware 6.4.5E with the BBSHD BAC855/NXT/72V battery and noticed that I get a lot of RPM fluctuation at constant throttle position once Field Weakening is activate. This problem is also observed by lots of other people. This is not noticeable with a fully charged 72v battery (84V) but this problem worsen when battery voltage get lower (somewhere below 74V) and keeping constant speed with a fixed throttle position is impossible when battery voltage drops below 70V.

I have seen somewhere that the fluctuation is caused by an improperly tuned current regulator. Apparently, raising the current regulator Ki setting seems to smooth out the fluctuations.

(I have a cruise control module on my bike but can't use it for this reason)

Also, PAS doesn't take under consideration how fast you're pedaling, as it only turns ON the motor regardless of how fast you are pedaling (1 RPM or 50 RPM crank rotation will have same effect).

Would it be possible to fix these issues with the new RC6.50 Beta firmware?

Let me know if you need a beta tester....

This is Dan by the way.

electricrt commented 3 years ago

Ok let's address one at a time.

Field Weakening issue:

When does the rpm begin fluctuating?

Would you describe it such as the motor is oscillating at a certain rpm even if you maintain the same throttle position?

Do you speed limiting on?

If so, try disabling speed limiting and see if issue persist.

Are you on torque or speed mode, see if it makes any difference between the two modes

papagino007 commented 3 years ago

It is the motor RPM that's going up and down by its itself with constant throttle position, this has nothing to do with speed limiting as it will happen at any speed regardless of gear selection. No speed limit set for Sport mode... I mostly use Torque mode, but I think it is also doing this in Speed mode.

electricrt commented 3 years ago

Gotcha, this is only when field weakening is active correct? Or does it happen at literally any rpm?

papagino007 commented 3 years ago

If you turn down FW, say less than 15 or 20 in the settings, it is barely noticeable. Turning it OFF will stop the fluctuation completely. It is when you set it at 38 - 40 that it become really bad. The lower the battery voltages is, the worse it gets.

Also, it is barely noticeable when using PAS only.

I will sent you a video later showing the fluctuations...

papagino007 commented 3 years ago

Ok, I just did some test with bike on wheel stand. I re-did a throttle calibration, doing is very slowly to confirm very linear throttle response. Then with bike on wheel stand, I did the following:

I will post a video shortly showing this...

papagino007 commented 3 years ago

Video is currently being upload to YT as "Unlisted"... Should be available shortly.

Here is the link: https://youtu.be/YgbexzQHGxE

The Throttle response I get with wheel off the ground doesn't reflect what is really happening when I am actually riding the bike. When there is a load on the motor, the throttle position versus RPM is working ok, but I get the same fluctuation that you will see in the video. I am not sure why it is working on your test setup with no load, as for me, I get full RPM at only 1/5th Throttle. Again, this problem will worsen as the battery charge voltage drops, it's barely noticeable when battery is close to full charged (76 - 84V)

Maybe my setting for Ki is different on mine!

Also, something I have to mention is that my NXT display is not being supplied by the ASI BAC855 controller 5 volts output (Pin 11) , it is being supplied by a external 5V DC to DC converter. Doing this eliminates the 5V voltage sag from the controller (Pin11) as it is only rated at 50mA. You will notice that when I am doing the Throttle Calibration, my voltages is something like between 0.89V to 4.17V, I think on yours, your top end voltage will be in the 3.xx Volts range.

Hope this will help... NXT_DCtoDC

(The input and output grounds are connected together on the DC to DC converter)

electricrt commented 3 years ago

Yes, this does make sense, and I have seen this kind of rpm fluctuation before. I'm gonna suggest you try to restore settings, once I upload the new beta firmware. I also suspect it has something to do with the PID settings.