If you have a CoachlabII+ from before 2010 (see bottom) it is not suitable for working with Chromebooks. You will have to use another interface.
Another possibility is, that you do not have a HID server installed, which is needed to make the USB devices work. You can find the HIDserver in the Google Chrome Webstore

If the steps follow each other too quickly, stuttering may occur as soon as the syringe is pressed. This problem appears sometimes when the command Titrate(…;Fast) is used. For a slow titration (Titrate(…;Slow)) the step motor burette should function properly. If fast titration is required, try to increase the waiting time between the steps (only possible in Author mode):

  1. Start the Coach activity ‘Acid-base titration with CMA burette’, or comparable.
  2. In the Program window, just below its title bar, drag the window edge down to open the procedure editor.
  3. Increase the value of the variable WaitingTime (for instance into 0.005).
  4. Drag the edge back to close the editor window and retry the activity.

If the ‘Titrate’ command makes the step motor moves backwards while the ‘BackMotor’ command makes it move forward: Exchange the wires connected to the outputs A1 and B1 of CoachLab II+.

This can be due to the motor itself or to the type of syringe. Check the following:

  • If the power adapter of your CoachLab II/II+ has a voltage switch, make sure it is set to 12 Volts
  • For an older type of titrator: the syringe deforms when it is pushed too hard into the titrator and clamps the piston. The syringe should be placed loosely inside the titrator.
  • For a newer type of titrator: use the supplied syringe as it has less friction.
  • Sometimes the spindle is fitted very tightly to the housing of the motor, as it causes extra friction during the motion. Try to create more space between the spindle and the housing (ca. 1-2 mm spacing) using an Allen key.