Ads1115

The controller consists of a custom printed circuit board (PCB) that connects a motor drive (drv8871, Adafruit, USA) and a 16‐bit ADC (ADS1115, Adafruit, USA) to a microcontroller. The measurement circuit was powered with 5 V and uses a reference resistance to determine the current I_LMPA flowing through the LMPA section. The measured voltage V_LMPA in the CVS section can then be used to calculate RLMPA=VLMPA/ILMPA. The signals were passed through a second order analog low pass circuit before they were picked up by the ADC. The microcontroller communicates with a control computer through a USB connection using the robot operating system (ROS) at a frequency of 10 Hz. After receiving R_LMPA, the computer calculates the necessary control input to the motor drives with PID control (K_P = 1, K_I = 0.4, and K_D = 0.4). The result was sent back to the microcontroller via the ROS message system and was transformed into an adequate pulse‐width‐modulated signal for the motor drives (more information in Figure S3, Supporting Information).

To characterize the compliance, a linear stage (8MT167‐25BS, Standa, Lithuania) was pushed in 2.5 µm steps toward a micro‐load cell (3132_0, Phidgets Inc., Canada) until a 0.125 mm displacement was reached. This displacement limit was chosen to avoid plastic deformation of the CVS catheter in the stiff states, which could lead to a bias in successive measurements. The experiments were repeated ten times for each resistance level. The output of the micro‐load cell was measured with a 16‐bit ADC (ADS1115, Adafruit, USA) and synchronized with the corresponding microsteps through a microcontroller.