Dynomotion

Group: DynoMotion Message: 10843 From: bknighton28 Date: 1/15/2015
Subject: Cnc routers and servo motor advisability and requirements

I will assembling a pro4896 router and the typical way is steppers and geckos. I have had a lot of problems with steppers in the past and converted mills and lathes to servos and snapamps and we've all been happy.

  First, does a dual motor axis work well with servos compared to steppers? Will they both be at the same place on each side instead of fighting a little and twisting the gantry?

  The machine has impressive Rapids of 1200ipm and I would like to match that if I go servo. But the torque, holding I guess, of the motor the vendor sells is 960oz in.  To match that with servos gets into amperages that exceed the snapamp based on the motors I have found. But maybe 960oz-in is overkill and a weaker servo would be right. 

  The machine uses rack and the motors have a belt reduction to the pinion. 
Group: DynoMotion Message: 10845 From: carlcnc Date: 1/16/2015
Subject: Re: Cnc routers and servo motor advisability and requirements
A cnc router at the gantry  is fine with a total "thrust" of around 150 lbs
to get  that with a 1" pinion requires 75 in lbs of torque[1200 oz in]
divide that between 2 motors and you get 600 oz in.
divide that by the 3.2:1 ratio is around 200oz in, dbl that for a safety factor and
you get a need for PEAK torque from the motor of 400 oz in

1200 in rapids you need approx 400 rpm at the the gear = 1200 rpm from motor
 does that help?
 I had a 6x10 machine with slaved motors, 1kw AC servos, ran great on kflop and snap amps
Carl
Group: DynoMotion Message: 10859 From: bknighton28 Date: 1/17/2015
Subject: Re: Cnc routers and servo motor advisability and requirements
that does help thanks. I believe I will get just two servos and try them on the dual motor axis. It looks like if I look for motors with a high torque constant the peak torque really won't be that important because it will be more than the range you were talking about anyway.