SLVAFO8A April   2024  – May 2024 DRV8214 , DRV8234

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction: Need for Sensorless Designs
  5. 2Ripple Counting − Concept
    1. 2.1 Ripple Counting Algorithm Details
  6. 3Case Study: Robotic Wheel Drive
    1. 3.1 Robotic Wheel Motor Operating Conditions
    2. 3.2 Tuning Parameters for Ripple Counting
      1. 3.2.1 Resistance Parameters
      2. 3.2.2 KMC and KMC_SCALE
        1. 3.2.2.1 Tuning KMC_SCALE
        2. 3.2.2.2 Tuning KMC
    3. 3.3 Robotic Wheel Motor with Ripple Counting
      1. 3.3.1 Inrush and Steady State Performance
        1. 3.3.1.1 Motor Speed Calculation
      2. 3.3.2 Soft Start
      3. 3.3.3 Loaded Conditions
  7. 4Challenges and Workarounds
    1. 4.1 Low Average Currents
    2. 4.2 Motor Inertia During Stop
    3. 4.3 Inrush
    4. 4.4 High Load Conditions
  8. 5Summary
  9. 6References
  10. 7Revision History

3.2.1 Resistance Parameters

This section refers to section 8.2.3.1.1 (Resistance Parameters) of the DRV8234 data sheet. The first step is to find the motor resistance. Using the recommended method, the robotic wheel motor's resistance was found out to be 10Ω.

Note: To perform the voltage sweep:
  1. Connect the motor directly to the power supply at a voltage just below where the motor starts to spin. For the robot wheel motor, this value was 1.2V.
  2. Read the current using a current probe, inline multimeter, or power supply readout.
  3. Calculate the motor resistance using the following equation: Motor Resistance = Voltage/Stall Current.
  4. Repeat this test across a range of voltages. Note that the motor needs to be intentionally stalled at higher voltages.
  5. Take the average of all values to calculate the value of motor resistance.

Taking the previous example of 10Ω, we have the following possible results based on the choice of INV_R_SCALE:

Table 3-2 Selection Example for INV_R_SCALE and INV_R
Bit INV_R_SCALE value INV_R_SCALE/Motor Resistance

(Actual Value)

 Rounded Value

INV_R

 Comment
00b 2 2/10=0.2 0 Do not select, since output is 0.
01b 64 64/10=6.4 6 Avoid selecting, since low bit precision.
10b 1024 1024/10=102.4 102 Can select this value.
11b 8192 8192/10=819.2 819 Cannot select this value because 819 exceeds the maximum limit for INV_R (255).

Please note that the GUI does not calculate the motor resistance automatically. The GUI selects the appropriate values for INV_R and INV_R_SCALE based on the value input for motor resistance. For details on how to use the Evaluation Module (EVM) and GUI , please refer to the EVM User Guide.