Not sure if this is what Dean meant, but I've run into issues of cogging-resonance - very narrow RPM bands where all motors of a particular model induce fairly severe z-axis gyro noise. The motors otherwise seem fine - very smooth bearings, and very little gyro noise outside of the narrow RPM band where they seem to hit resonance. I haven't tried that many different motors, but it's been the ones with extremely sharp magnet detent (strong magnets, small air gap)that had this problem. I don't think there's any easy way to measure this on your current test setup. You would really need a torque transducer, and logging quick enough to pick up the high RPMs. Of course, a torque transducer would also let you isolate motor and propeller efficiency, which would be an awesome addition to your test results (although maybe more than most people want to know).
I've never run into EMI issue from a motor or ESC, but have from a low-cost VTx that was in very close proximity to the IMU chip on a FC. It was in a Kraken, with not too much room in the pod for physical separation. An inch was sufficient separation, but alas impossible in the tiny pod.
Yes, I've seen what you're talking about too, but believe it or not, it is an artifact not purely of the motors, but of how we drive them. One of the causes it is actually torque ripple, which is a combination of cogging torque and specific flux harmonics. This is accentuated by the trapezoidal commutation methodology used in most of our ESCs, as well as some harmonic interference between the ESC drive frequency and the commutation rate. BLHeli_32 solves some of that by making the drive frequency adjustable, so you can move it out of the range where it causes harmonic interference, and it also uses a slightly tweaked commutation method. I think more gains are possible given some looks at alternative commutation methods like sinusiodal or FOC, or maybe some sort of hybrid. There's a lot of stuff that goes in to the dynamics between motor and ESC and we have a lot of room for growth still.
Kevin:
Sep 18, 2017 at 08:27 PM
Not sure if this is what Dean meant, but I've run into issues of cogging-resonance - very narrow RPM bands where all motors of a particular model induce fairly severe z-axis gyro noise. The motors otherwise seem fine - very smooth bearings, and very little gyro noise outside of the narrow RPM band where they seem to hit resonance. I haven't tried that many different motors, but it's been the ones with extremely sharp magnet detent (strong magnets, small air gap)that had this problem. I don't think there's any easy way to measure this on your current test setup. You would really need a torque transducer, and logging quick enough to pick up the high RPMs. Of course, a torque transducer would also let you isolate motor and propeller efficiency, which would be an awesome addition to your test results (although maybe more than most people want to know).
I've never run into EMI issue from a motor or ESC, but have from a low-cost VTx that was in very close proximity to the IMU chip on a FC. It was in a Kraken, with not too much room in the pod for physical separation. An inch was sufficient separation, but alas impossible in the tiny pod.
quadmcfly:
Sep 19, 2017 at 08:48 AM
Yes, I've seen what you're talking about too, but believe it or not, it is an artifact not purely of the motors, but of how we drive them. One of the causes it is actually torque ripple, which is a combination of cogging torque and specific flux harmonics. This is accentuated by the trapezoidal commutation methodology used in most of our ESCs, as well as some harmonic interference between the ESC drive frequency and the commutation rate. BLHeli_32 solves some of that by making the drive frequency adjustable, so you can move it out of the range where it causes harmonic interference, and it also uses a slightly tweaked commutation method. I think more gains are possible given some looks at alternative commutation methods like sinusiodal or FOC, or maybe some sort of hybrid. There's a lot of stuff that goes in to the dynamics between motor and ESC and we have a lot of room for growth still.