Performance of the Probe

After studying the statistics obtained during the experiment, I found the performance of the probe is not as appealing as when it is hold vertically. I have taken all the components apart and trying to figure out why. I think there are a few causes. Firstly due to the nature of the motor and the spindle, when there is no force applied on them, the tolerance in between the two components works fine. However once a force perpendicular to the tolerance is applied, it forces the motor and spindle to come in close contact in one side but with lose tolerance in the other. This in fact would lead to inaccurate performance of the motor that the output speed does not equal to the desired speed when it is high. The second conclusion I draw is that as the probe was hold horizontally, the feeling of the same force to me is different to when it was held in a more vertical fashion. Human error may have also been introduced in the experiment. As it is sometime necessary to hold the probe horizontally during a ultrasound examination, how to increase the performance of the probe might be a development point.