DRV8889-Q1: Stall detection work abnormal

Will,

What is the DECAY mode you are using?  It should be STRC (smart tune ripple control).

Regards,

Ryan

Hi Ryan,

Yes, I used STRC mode.

I double confirmed, the Torque value keep zero under the stall condition.

Any comments for why this happen? and how to fix it?

Hi Will,

Based on the GUI screen capture the Torque count at steady state velocity is zero. For the motor parameters and operating conditions specifically at 1/256 there is not enough SNR in the BEMF (back emf) to get any stall count. Could you please try with microsteps setting in the 1/8 to 1/32 range by changing target PPS accordingly and see if any torque counts could be achieved. Typical unloaded torque counts in the 30's would allow stall detection. Also try increasing the current to 0.3 A.

Regards, Murugavel

Hi Murugavel,

I have changed the microsteps to 1/8, 1/16. 1/32; and current also change to 0.3A, however, the Torque count change just a little to 2~5, not change to 32. 

Does this mean customer motor may not work with stall detection?

Hi Will,

The motor DC resistance is high 16 ohms (> 10 ohms) and at this low PPS the count is low. Can the customer run with higher PPS target speed? 

Regards, Murugavel

Hi Will,

Are you getting torque count in the 5 counts consistently? Also when you stall the motor does it go to zero? If so the customer can use this information to detect a stall condition using the ECU MCU controlling this device. If not customer may have to try another motor with lower DCR (< 10 ohms) with the same form factor.

Regards, Murugavel

Hi Murugavel，

My test shows the Torque count is not constant, it will change high to 10, low to ~2. When stalled, the value is not constant 0 neither, it could goes to 1, or 2.

I tried increase the speed, the Torque value goes to about ~220. and stall doesn't change the value.

I seems stall detection doesn't work well with all motor, Could you help share the stall detection requirement to the motor spec?

Thanks and Best Regards,

Will

Hi Will,

Just for comparison, could you please get one of our DRV8461EVM (Industrial, non-Automotive) and try with the customer stepper motor and see if the stall detection performance is better. See what counts are you getting for torque counts, you can try x1 and x8 if the counts are lower.

Regards, Murugavel

Hi Murugavel,

Thanks for your comments. I'm getting the EVM to verify this.

Thanks and Best Regards,

Will

Sounds good, thanks.

Hi Murugavel,

Please find the following test from EVM Torque test point. I stalled the motor at ~3s(from left side to count), the value goes down a bit, but value different is small before and after stall motor.

Another point, since customer motro spec rated voltage is 4.8V, so I connect a 4.8V  supply to EVM board, also tried increase to 5V, 6V, no big difference.

Hi Will,

Are you doing this tests with the DRV8889-Q1EVM? The rated voltage spec for the motor is specifically for a unregulated current direct drive system. All modern stepper drivers are based on full-scale current regulation so rated voltage spec. does not matter. As a matter of fact the VM must be much higher than the motor rated voltage to achieve proper current regulation. There should be another spec. for the motor known as insulation voltage which is usually much higher like even 100V.

That said the DRV8889-Q1 stall will be stable probably above 11V or 12V especially with lower DCR motors. Could you please check with at least 12V. Be sure to set the full-scale current to 0.3A or little higher than that. Thanks.

Regards, Murugavel

Hi Murugavel,

Thanks for feedback.

I increase the supply voltage to 12V, current 0.3A, I stalled the motor at ~3s, get the following Torque waveform.

The Torque value still not high to ~30.

Any further suggestion to this?

Hi Will,

Thanks for trying with 12V. There is a perceivable improvement with the torque count and able to detect stall because there is a tangible difference in counts between no stall and stall condition. The reason the count is not ~30s range is because of the motor suitability for this operating parameters. What is the end application? Are you able to detect stall consistently although the unloaded torque count is not in the 30s. 

A comparison with DRV8461EVM under the same conditions will be helpful. What is the end application? Operating VM voltage? stepper STEP speed requirements in PPS?

Regards, Murugavel

Hi Will,

Any updates with this?

Regards, Murugavel

Hi Murugavel,

Since we already goes this offline mail, I'll close this. Thanks for your support.