Centroid Community CNC Support Forum

Hi everyone,
I have a small G0704/BF20 Mill currently running acorn with steppers. I just placed an order from DMM for 3 DYN2 drives, 2 NEMA23s 400w servos (57N-DHT-A6TD1) and 1 NEMA 34 750w servo (86N-DHT-A6MD1). I asked the gentle man helping with my DMM order if I need a belt reduction drive for the servos, his reply was :
"You won't need to use any pulley and belt. Just bolt our motors directly into your existing machine and mounts and your good to go."

Does this sound right? Seems like most people use reduction belts which i'm trying to avoid unless I absolutely need. Should I just try direct mount and see how it goes? I do not have a counter weight or gas spring on my z-axis.
- Daniel

Hi Danial,

I am doing the same conversion on PM25-MV, which is very similar to the G0704. I do not believe you need a belt reduction to increase your torque/lift capacity. For assurance, you can compare your old stepper plus your belt ratio vs. the torque capacity of the new DMM motors. That should give you a very good idea where you stand.

I did a rough calculation for the z lift .75kW motor, estimated lifting load of 500lb(might be overkill), the .75 kW motor should lift with a 3.6 design factor.

Note, I ordered my z-motor with a brake. I was worried about drifting from gravity. I am still doing the wiring in the panel, however my z-axiz does drift on its own (ball screw back-drives). I'm also debating adding a c'ballance to ease the load on the z-motor (per calculation, not needed). I will try it without c'ballance 1st.

-Nick

Thanks for the reply. The z axis was one of my concerns, I Didn't realize there was a brake option. My head definitely drifts, I am not sure what the holding torque for for 750W servo is but a brake makes sense.
Best,
Daniel

DMM is probably right on. If you are using ballscrews and linear ways you may need the brake. If it's dovetail ways, likely not.
Good luck with your project.

Danial,

The brake is for holding the load up, when there is loss of power (i.e. powering the the control panel to do some work). The 750W motor has plently of holding power, for normal use.

BTW, I have dovetails on my z axis and its drifts no problem on my PM25-MV, with no motor attached.

Marty, I want to thank for all the good work you've done and published. I've learned so much from you on the electrical/controls side, coming from a mechanical background. Keep up the good work, very appriciative.

Here is my set up, still lot of work left, before power on.