• Locked Locked
  • Replies 3 replies
  • Subscribers 83 subscribers
  • Views 1017 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Torque issue with motorware

user3996703
Prodigy 40 points

Other Parts Discussed in Thread: DRV8305, MOTORWARE, INSTASPIN-BLDC, DRV8312

Hi!


I'm having issues with low torque output with DRV8312EVM development kit paired with F2802x control card. We also have DRV8305 booster pack card with F2802x launchpad, and the results are identical. The motor I am currently using is a dental micromotor and has the following parameters (from the manufacturer datasheet):

Rs: 0.9 ohm

L: 60 uH

Number of poles: 2

Max current: 5 A

The problem is that when I force the rotor to stop with my fingers (pretty easy to do), the rotor starts vibrating and this vibration still causes some feedback to the system, which in turn "thinks" that the rotor is still spinning -> no more current to the motor. For example on low speed (5 krpm) when stopped the speed value initially drops and the system increases the current to the motor, which causes the speed value to increase as well, but the rotor is still not rotating, only vibrating.

The motor is running very smoothly with the whole speed range, which is from 1000 to 40 krpm, only the torque is the issue. With higher speeds I can get more current to the motor when I load it.

With the same DRV8312 dev kit and with F28035 control card I can easily get enough torque with the InstaSpin BLDC solution, however the documentation for the InstaSpin-BLDC isn't as good as Motorware. Could the InstaSpin-BLDC be the better solution for this type of motor?

Where do you think I should start looking for the problem?

  • Prodigy 40 points
    Forgot to mention that the result is the same with ForceAngle on or off.
  • in reply to user3996703
    TI__Guru** 116740 points
    1. Monitor the maximum, minimum and integration of speed PI. Whether the maximum current is too small to output enough torque.
    2. Increase speed and torque PI parameters to improve dynamic response.
  • TI__Guru** 119680 points
    in my experience with dental drill type of motors yes a BLDC approach works better to get more torque. the flux of these motors are too small for good low speed torque performance.


    I think you can improve the stall performance with IS-FOC by monitoring the conditions and removing the SpeedRef during stall, but not sure if this works for you application. With ForceAngle disabled the angle into the control system will be frozen, but the speed estimate is still being used and during this time it is not guaranteed accurate, so this is why you are seeing some stimulus from the speed controller to the IqRef_A signal.