MCT8316A: The motor is driven with a high resistance torque and overspeed occurs when held in position

Hi Cherry, 

Thanks for posting thread to e2e motor drivers forum -

I've assigned this thread to a team member and we'll aim to respond as soon as possible 

Best Regards, 
Andrew 

Hi Cherry,

In open loop, motor cannot generate sufficient torque as the commutation is blindly done without knowing the BEMF zero crossings. Can you spin the motor in closed loop and try again? Also, can you provide details on the application/end equipment? 

Regards,

Vishnu 

Hi Cherry,

Cherry Zhou said:

In open loop, drive the motor to do a finger-grabbing action. When the resistance torque is high, the motor speed is zero, and the development board incorrectly reports "Abnormal Speed", causing the motor to report errors frequently and thus no longer drive the torque. At the same time, changing the chip parameters removes the "Abnormal Speed" error and the motor cannot be driven.

Sensor-less driver should only be used for applications that have low friction start up. During open-loop, if you try to grasp the motor shaft to stop it (to simulate a high load) then the driver cannot reliably find the position of the rotor (based on BEMF crossing zero detection). Sensor-less is best for driving fans, pumps, any loads that don't have too high friction at low starting speed. For high friction load, you should use Hall sensor motor and driver.

BTW, do you use Align or IPD method to start the motor?

Brian

Thanks Brian!

Cherry,

As Brian mentioned, open loop cannot generate torque. If your application demands high torque during startup, it is recommended to set higher open loop current limit. If this doesn't work, it is recommended to use sensored solution.

Regards,

Vishnu

Hi Vishnu and Brian,

Thanks for your support!

The customer uses double alignment startup and grab the object by hand with a sensorless chip. Can the device have closed-loop current control to ensure controlled motor torque for long-term operation at zero speed? 

Thanks and regards,

Cherry

Hi Cherry,

Cherry Zhou said:

The customer uses double alignment startup and grab the object by hand with a sensorless chip. Can the device have closed-loop current control to ensure controlled motor torque for long-term operation at zero speed? 

No, sensorless cannot reliably work at stalled condition -- zero speed. For this, it should be driven by sensored driver.

What exactly the real world application?

Brian

Cherry,

MCT8316A does not offer closed loop motor startup at zero speed. Sensored solution is preferred.

Regards,

Vishnu

Hi Brian and Vishnu,

Can the MCT8316Z output torque at zero speed? 

Thanks and regards,

Cherry

Cherry Zhou said:

Can the MCT8316Z output torque at zero speed? 

Yes it can!! In fact at zero speed, the motor torque is at maximum per same pwm value as there is zero BEMF to be subtracted from the VM supply.

Brian

Cherry,

Yes, in MCT8316Z torque can be generated at zero speed as the device knows the rotor position through Hall inputs. 

Regards,

Vishnu