185 oz. Steppers on SO3

Jimf
Posts: 233
Joined: Wed Feb 11, 2015 8:58 pm

185 oz. Steppers on SO3

Post by Jimf » Mon Jan 18, 2016 7:21 pm

KAScnc wrote:That's interesting, I'm assuming your GT2 belts don't use the typical 2mm pitch? It's only like 120ish lbs tensile strength. Granted that changes depending on the type of reinforcement being used.

Typically steppers/servos are rated in holding torque, once they start moving that rating decreases a lot.
FYI. GT2 is 2mm pitch, GT3 is 3mm etc. I think I've seen them as high is 14mm pitch. That's one big set of pulleys.

900oz-in peak torque is 56lbs-in. Not sure how to convert that to tensile strength with a pulley that is about .75" diameter. I'm guessing it is less than the 120lbs belt tensile. These are 2mm GT2 purchased from Stock Drive Products. They usually have good quality belts.

Servo motors don't loose torque as you spin them faster like steppers. They have a continuous torque rating and a peak rating. Servos will spin several thousand rpm easily so you need to have gear reduction to take advantage of the available torque. I'm using 5.5:1 reduction ratio on the axis. This increases the torque significantly before you even add the mechanical advantage of the 5tpi ballscrew.

With the 5tpi ballscrew mechanical advantage, the axis has about 500lbs continuous leadscrew thrust. This Z axis could easily lift me up while moving at 50inch per minute!!!

I've been using servo motors for a number of years now. They are nice to use but much more complicated than steppers.

If anyone is interested on the formulas on how to calculate lead screw thrust, this is a example written by the owner of Geckodrives.

http://www.cnczone.com/forums/servo-mot ... .html?pp=5

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