Since I finished building my prototype dual-double scooter motor powerboard about a month ago, I have been super happy with its performance. But I have had a bit of a bug in the system. I believe that bug is caused by stator saturation, but I would like if Frank or Benjamin or any of the more knowledgeable members could give me their opinion of whats going on.
Whenever I start riding, the board works flawlessly, but once I have been riding for a few minutes and the motors start to get a little warm, I begin to experience a slight braking action when I get back on the throttle after coasting. I thought I had the problem worked out at one point after changing the throttle deadband setting to 20%. But a few days later I was having the problem again. I paid close attention to the conditions that were present when it would start doing this, and it seems to be correlated with motor temperature.
I wanted temp sensors in the motors when I was building them, but could not find any. So motor temp compensation features in VESC tool are not going to help me. But I don't know if that would help anyway. It is my understanding that high torque low speed motors such as e-bike hub motors (mine are Ninebot scooter hub motors) are the most susceptible to stator saturation. It is also my understanding that when completely saturated, hall sensors cannot detect rotor position. Please correct me if I am wrong. But if that is correct, then I think what is happening is that the hall sensors are telling the VESCs I am at a standstill since everywhere on the rotor "looks the same" to the hall sensors. Until the stator de-saturates and hall sensors can detect position again, increasing the throttle will only increase the strength of a stationary magnetic field. The VESCs think I am trying to start from a standstill and increase the stationary magnetic field to try to get over a rock or something. The VESCs are not braking, but the effect is the same. I have noticed that when this starts happening when I attempt to accelerate, the action of the brakes also becomes all or none. When I command the tiniest amount of braking, I get 100% braking.
Today, I went for a long ride and this issue is now an official safety issue for me because it caused the wheels to lock up at full speed (22mph) while I was crossing the intersection of two very busy streets. I fishtailed a few times and went down hard. My transmitter slammed to the ground, batteries flew all over the road, and my board coasted into oncoming traffic. Luckily those drivers stopped and the board didn't get run over. But I felt embarrassed as traffic had stopped in all directions as I frantically tried to pick up all 8 of my transmitter batteries, the cover and a knob that came off. I am fine, but not without injury. Missing some skin on my right forearm and knee. Ya play hard, ya pay hard.
But now that this has happened, I need to figure it out and fix the problem. If what I think is happening is in fact the case, then I think this would be a non-issue if I ditched the hall sensors for encoders.
Please help guys, because honestly, I am going to keep riding, and I am going to get hurt again because this sport is too much fun for me to not do it. Nobody knows more about the VESC hardware than y'all which is why I posted in this forum.