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Motor size per axis?

Do you guys use the same sized motor on all 3 axis or different? Just going by the effort of the hand crank, the X and Y on my machine are substantially more effort that the Z. I'm wondering if I can save some money and go for a smaller motor on that axis...

@augustmarine

Normally for simplicity the same size motor is used however there is nothing stopping you from using different sized motors.

It is surprising the Z axis requires less effort compared to the X/Y axis, normally the Z axis has the highest load due to the mass of the spindle.

For what it’s worth, here’s my (apologetically-long) take on this question:

I’m trying not to spend more on Teknic ClearPath servos than I have to, but I’ve got to get rid of my crappy Chinese servos/finicky Gecko controllers, so I found a couple of ballscrew and liner motion force calculators online that, when used together, allowed me to figure out the maximum force the tool in the spindle will exert and the max feed rate possible using various  servo characteristics.

Besides not wanting to spend money on more servo than I need, I’m not going with a “one size fits all”  approach because all 3 of my axis’ are so vastly different from each other:

The Z has a 2:1 pulley reduction and drives a 5mm/rev ballscrew, and is only moving 59 lbs worth of spindle and  Z axis stage vertically.

The Y axis servo directly drives a 5mm/rev ballscrew and is moving 169lbs of spindle+Z-axis stuff horizontally across the gantry.

The X axis uses 2 servos that drive 20:1 planetary reducers turning a pinion down a gear rack at ~3”/rev. and moves 230lbs of everything horizontally across the machine.

A one size fits all approach can’t work here without waste.

Some of the factors considered by the calculators were the gear ratio (of everything in the system, ie: gear/pulley reduction, ballscrew ratio, etc), the mass being moved, the force being applied by the motor, desired acceleration, desired feed rate, direction of movement relative to the earth, etc.

I just fiddled with the motor variables till I got the acceleration, end force and feed rate numbers I wanted and looked at the list of ClearPath motors that had output power/force and an RPM within the needed range for that particular axis.

Presuming I did the thinking correctly, I get:

Z servo: 569W, 4850RPM, 400ipm/$443.00

Y servo: 919W, 3150RPM, 500ipm/$551.00

X servo: 735W, 2380RPM, 500ipm/$517.00

So, I end up saving $142 over a one size fits all solution that wouldn’t have given me my desired feed rate on the Z axis.

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