Brushless DC motor runs fine in one direction but not another

Question

We have changed BLDC motor suppliers and are seeing a new problem. In the old system the software commanded the motor to move 5 steps of X hall counts then stop. With exactly the same electronics and software but with the new motor (which may have different hall sensors), the motor moves it's 5 steps but at a much reduced speed. We just got the motors today and don't have the full specs on it yet. Any ideas as to what could be causing the problem? I've attached 3 pics. The first one shows a scope trace on the U phase hall sensor output of the original good motor. The 2nd pic shows the same hall sensor output on the new problematic motor. The third pic shows the circuit diagram. The hall sensors are connected to J9 at the right of the diagram. J10 is the motor connector.

Thanks a great deal for any help, Fred

Answer 1

If commutation points of Hall sensors have a phase error It will adversely affect control in one direct over the other. Check with low voltage the torque vs Hall transition point, which directs polarity of drivers.

Answer 2

Check your motor specs. I know you don't have them yet but it could be what is causing your issues is that your motors specs are not the same. Thins to look for:

$$ J_m, k_t $$

Your motors moment of inertia could be higher and your motors torqu constant could be lower meaning your motor doesnt have the same power draw and takes longer to spin up.

rember

$$ T = k_t*I_m $$ where Im is your motor current... something to check out is how much current is your system drawing if its the same as your previous motor this tells you if there is an efficientcy issue.

Answer 3

The problem must be the positioning of hall sensors. Tray adjust the positioning angle of them.

Renato.

Answer 4

Each motor may have different number of pole pairs. Hall effect sensors sense degrees of an electric cycle, which may correspond to different angle of revolution. If in old motor you had 2 pairs and in the new one you have 10, you will move five times slower.

Answer 5

there are two basic hall sensor configs 60 degree and, if i recall it right, 180 degree. The only other two explanations are that of the coils miss alignment in radial or axial direction (front/back), or miss functioning hall board (inside of motor). The first one is dispatcher error (common). The second and third are mayor production errors (not so common). "it can't be what is impossible to be"