I've finished adding a low speed range to my Seag C6B. It works well, but not as expected.
In its original state, the C6B has a single speed range 0 - 2000rpm.
The motor pulley is 67mm and the spindle pulley is 135mm. From this, I've assumed a motor speed of 4000rpm.
I've made a new motor pulley 83mm in diameter to achieve a modest increase in maximum spindle speed (direct drive as original design, but a countershaft pulley is now driven though not connected to the spindle). My expectation that this diameter would yield a top speed of 2500 (say +/- 5%). It's actually producing a top speed of around 3600. I'll disengage the countershaft to see if that is causing an issue tonight.
I have the same result from the low speed range which was designed for a top speed of 400rpm is actually yielding a top speed of 600rpm. (Indirect through a countershaft arrangement)
The new arrangement has a large pulley on a countershaft (135mm) which is introducing significant flywheel effect.
I don't think this is a measurement problem, at top spindle speed it is really scary!
I've assumed that the speed controller is dumb - ie it only worries about over current (ie stall) conditions and there is no tacho feedback from the spindle I can see. What could cause this gross deviation from the "as designed" expectation? I suspect the controller is the same as the Seag X3 etc.
Steve