Spindle Speed not accurate. Can I compensate?

[Toaster]

I have a small mini mill I am rebuilding:

https://centroidcncforum.com/viewtopic. ... 331#p93331

It's got a DC motor on it for a spindle. I am using this box to drive it:

https://www.amazon.com/gp/product/B07ZSXGYXL?th=1

It works just fine, but it's off by almost 50% in speed. If I command 10,000 RPM I get 15,000 clocked with a tach. If I drop it to 5000 get about 7500.

Is there any way I can compensate for this in software? Perhaps this is a PLC mod I need to do?

[Gary Campbell]

Eric...
Try this:
Make sure minimum rpm is zero
Set your max rpm in the wizard to 150% of what you have now
Check the rpm @ 25, 50, 75 and a hundred percent write down programmed vs actual to develop an averaged percentage
Apply that percentage to the max rpm as needed

[Toaster]

I checked it at every 1000 RPM from 1000-10000. Looks like I'm spinning 70% faster on average at every speed.

This spindle does have three gears (it's belt driven with three positions)

I suppose I could drop it to a lower gear range and lie to Centroid and tell it it's in high range... I would like to get it to actually work properly though