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Original question:

DRV10964: Maxon EC 9.2 starts for a few steps but stops and goes to lock

DRV10964: Old Thread got Locked... Maxon EC 9.2 starts for a few steps but stops and goes to lock.

Thomas RUFER
Prodigy 20 points
Part Number: DRV10964
Other Parts Discussed in Thread: MCF8315A, DRV10975

Tool/software:

I never got an answer on why the Motor goes to lock after 3 commutation-Steps and never reches a hand-off-point

  • 0
    Prodigy 20 points

    Hi Venkatadri

    Venkatadri Shantaram84961 said:
    The hand off point looks like shown in the data sheet page #19

    I think my point doesnt get understood:
    - The scope i posted is ALL thats happening:

    - There is NO HANDOFF POINT reached before it seems to go in Lock
    - The Graph on Page 19 as you told, shows a waveform which HAS a handoff-Point (Change from open- to closed loop):

    This does NOT happen with me. It doesnt even reach this point. Doesnt come close. 3 steps on this one coil and lock. Page 19 shows like 50-70 steps till handoff....

    As posted multiple times: The Motor gets aligned, The motor starts spinning for a FEW STEPS. See Video in first post.
    Then it goes to lock. See Video in first post.

    Venkatadri Shantaram84961 said:
    If motor never starts spinning then some other issue.

    The motor works. I tested it multiple times in our Insulin pump, with a weird chinese Drone-Motor-Controller and even with a Arduino-DIY-Solution... The motor works on everything except on a dedicated BLDC-Controller here...

    Venkatadri Shantaram84961 said:
    Initially motor start spinning in open loop, after the motor speed reaches configured hand off speed device stops divining briefly, during that moment phase voltage will be of BEMF, device measures this BEMF and calculated Kt of the device.

    As said, as posted, as shown in video: The Controler gives up accelerating the motor after 3 steps.

    So I try to explain it AGAIN:
    - Motor seems to align
    - Motor makes 3 steps on one coil
    - Motor goes to lock
    - There is no handoff reached in this 3 steps of the motor (like 3/4 turn or something like this. See Video)
    - Motor works as confirmed by driving it with multiple different DIY-Solutions

    BEMF:
    To the previous question: You are right. The cursors were of another channel with factor /10.

    So the BEMF = 370Hz and Upp 4.22V

  • 0 in reply to Thomas RUFER
    TI__Genius 16325 points

    Hi Thormas,

    Sorry for delay in replying. I am referring to the CONFIG pin Resistor divider issue. If you see motor has taken few steps and stopping.

    Let me explain the scenarios which can be happening

    1. DRV10964 will start with Align and then open loop until the hand off speed reached. Here DRV will momentarily stop driving the motor to measure Resistance and Kt and continues to closed loop

    2. The hand off point is decided by Resistor combination which applies certain %of VCC to the CONFIG Pin. Can you please check voltage on the VCC Pin. On the board (If EVM) what is R2 value? R3 is 4.7K, please check if R2 is populated and what is the value? This will provide hand off point

    Please refer to the DRV10964 Evaluation Module User's Guide (Rev. A)  Table 6.

    Possible Issue Here: R2 is DNP then CONFIG Pin is grounded, please check what is the %VCC is measured here. You may have shared schematic before, if not kindly share to me again here.

    3. In your waveform it is starting with ALIGN, Open Loop and then stopping. Possible reason is it entered a Hand off point soon but motor unable to keep Kinetic energy and motor has stopped. We need to build kinetic energy so that during motor measurement phase motor should be running and after measurement is completed device catches motor on the fly and continues to spin.

    I had seen the motor data sheet, this is a low BEMF motor and hence chose R2, R3 as per the table, preference is somewhere around 100Hz Hand off point.

    Please verify CONFIG pin value, R2, R3 value and let me know.

    Thanks and Best Regards,

    Venkatadri S

  • 0 in reply to Venkatadri Shantaram84961
    Prodigy 20 points

    Back from the competition! Slight smile

    I measured the CONF-Voltage: 0.474V as expected (See the Schematic in the old thread: 9.4% of VCC) for around 12 Hz. I was 4mV off of the thoretical value...

    I will reconfigure the voltage divider for 53% of VCC on CONFIG for around 100Hz Handoff according to Table 6 in the Eval Module User guide.

  • 0 in reply to Venkatadri Shantaram84961
    Prodigy 20 points

    I ended up with like 3.0V Config to make it able to spin. However, it only spins if there is no load on the motor. As soon as i have the normal gearing of the insulin pump assembled (Normal status of the insulin pump) the controller aligns, Spins up for like 1sec and then stops.

    I assume this is because it doesnt measure a valid backEMF in the change open- to closed-loop because the motor stops immediately with the load on it... So the backEMF is like 0 and this pushes the controller in a lock...

    I asume there is no way of disabling the closed-loop-mode and only go "blind" in open loop?

    This is what i did in my DIY-Solutions with Arduino and such: Simply drive and dont care about the result. Blind drive in open loop. Worked perfectly...

  • 0 in reply to Thomas RUFER
    TI__Genius 16325 points

    Hi Thomas,

    Open loop run is not reliable always and not efficient. Close Loop can monitor for motor stall state.

    For such applications it will be better to use DRV10975, DRV10983Q1, MCF8315A/C etc.  In this we will program the parameters (R, L, KE) to non volatile memory and provides very reliable open loop to close loop hand off.

    What is the voltage level in your application?

    Thanks and Best Regards,

    Venkatadri S