Re: [CAD_CAM_EDM_DRO] where's the torque ?

turbulatordude <dave_mucha@...> wrote:
I've been running thru the torque numbers for motors and seem to be
missing something.

A 1-1/2hp treadmill motor with 5,100 RPM has 296 oz-in torque.

On a rack and pinion. and using a 1.25" pitch, we can round the
distance per gear rotation to 4 inches. 1.25*pi=3.926, so 4 is close
enough.

When we calculate for a leadscrew, we come back to inches of table
movement. do we also do that for routers ?

I mean that we put on a 600oz-in motor, then multiply that by 5TPI to
get 3,000 OZ-IN that would mean 3,000 per inch, no ?

/// Yeah, if we were compressing a spring and wanted to calculate the kinetic force over distance. Distance traveled has nothing to do with torque. Torque, speed and power are determined by the size of the motor and the reduction being used. The pulsetrain determines the distance.///

That would make the motor 296/4=74 oz-in if it were direct drive.
using 6:1 pulleys would then multiply that up to 444 oz-in. or 444 per
inch ?

The leadscrew moves 1 inch per 5 motor rev or 0.2" per rev while the
rack moves 1.5 revs per in. Gearing up to get 5 rev's per inch would
mean a 20:1 pulley to the 1:4 rack gear. If course that would
multiply the 296 by 5 for 1,482oz-in.

Since I've seen routers and plasma cutter run with much smaller motors
and much smaller ratios (3:1 on a 350 oz-in stepper) it seems I'm
missing something.

///Steppers can get away with this because they like operating near their holding torque, very low RPM. I'd think if one designs a stepper system that never exceeded a few hundred RPM it would perform well. Servos on the other hand do not operate well at low speeds and need alot of reduction to rapid at 80% of their top speed.

The bottom line is: If you plan to use servos with a rack and pinion arrangement, you are going to need alot of reduction to do so. Example: 3000 RPM servo and 1:4 pinion to rack ratio with 100 ipm rapids. 80% of 3000= 2400 RPM. 100ipm/4=25 RPM of the pinion gear. 2400/25=96. With this config you'd need a 96:1 ratio. /// Ron

Anyone see my mistakes or what I've overlooked ?

Dave








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