# Thread: Speeding up feed speed

1. ## Speeding up feed speed

I have just completed my cnc router and cut my first job which is great.
My problem is the max speed I can get which is only 500mm /min.

The motors and controller I purchased from eBay the controller is a TB6560 ,power supply is 24 volt 15amp and the stepper motors are Nema 34(34HST9805-37B2) ,I have attached a spec sheet for the motors.

Currently i have them wired up as Bipolar Series which i will be changing to Bipolar Parallel to increase speed.

What I need help with is from my calculations on the motors is that if wired in Bipolar Series the motor will require 247 volts @ 1.4 amps for full power and if wired in Bipolar Parallel it would be 124 volts @ 2.8 amps could someone please confirm my calculations thanks,.

If this is correct I should be able to get a large increase in speed by changing my controller and power supply as my current power supply is only 24 volts and the controller can only handle 32 volts Max.

I was looking at the Gecko G540 but its Max voltage is 50 volts which is double what I currently have.

I would require a 4 axis controller as my X axis uses two Nema motors one being slaved .
My other option would be gecko G201x drive which can handle up to 80 volts but as far as I understand I would need 4 of them and a break out board which would cost a lot.

Any suggestions would be greatly appreciated.

2. These motors have very high inductances (16 mH or more) and this drives up the max voltage that must be applied to obtain maximum power. Gecko's rule of thumb is that the max voltage (V) = 32 sqrt( I (mH) ). These large inductances can give high holding torque, but you want to be able to move them, which requires faster charging/discharging of the coils, and lower inductances. I bought the G540 with a 48V supply, then shopped for motors with ~2 mH windings. I found mine at Kysan.

3. I agree with Paul. Actually I have similar (even bigger) steppers with 20mH inductance but I am running 48V supply. I first tried to use some 80V/7 amp big Chinese drives but found the motor stalled typically around 80-150 ipm (2000-4000 mm/min). That may be consistent with your experience since I run higher voltage and maybe higher pitch lead screws (15mm/turn)?

Anyway, I switched to 203V Geckos and attribute a serious improvement to their midband resonance suppression. I can now get to 250-300 ipm reliably but beyond that the steppers just run out of steam (they have a fabulous holding torque, though). I could increase the power supply to 80V but actually I don't need it to run that fast. Well, maybe I do that sometimes.

Your cheapest solution for higher speed may actually be to use a 48V supply or even to buy a set of smaller steppers with lower inductance (\$50 each).