Jetijs,

Don't get discouraged, I think that your have great error in reading your spring scales. You should load your motor more than this so the error in your readings gets negligible in comparison to the load your motor has. Also I think that an 8mm shaft is too small for much precise readings. You'd better use a large wheel like peter does for measuring the applied torque of your motor. I am looking forward to see better results. Also I suppose that you can increase the efficiency of your motor by running it on more voltage.

How does your spring scales stand on there? without falling due to the rotation of your shaft.

Elias