Re: [CAD_CAM_EDM_DRO] timing pulleys

Rod McBeath <rmcbeath@...> wrote:

So, my question would be... how would a person calculate the momentum of
steel pulleys in order to appropriately size your servos? Is there an
article which deals with this? Seems to me the increased weight would be a
lot of rotational momentum added to the servos for acceleration and
deceleration.

////Depending on your exact configuration, there is generally way more than enough resistance on axies to counter any pulley momentum/back EMF issues. If the servo is not able to deal with pulley momentum, it wont be doing much of anything. ////

By the way - locally the smallest GT2 belts available are 8mm. The smaller
ones aren't carried in our area because of the heavy oilfield
industry. They have to be ordered in from Kentucky... a 3 week
wait. Since I have friends and acquaintances planning on building CNC
machines, it seems advisable to use what we can get locally, hence my
questions.

Another option would be to lighten the pulleys by drilling holes or
machining some material out of them. The problem then is balance. How
critical is balance on an NC with say 2000rpm max servo speed? Is there an
easy way to balance the pulleys?

////Well, usually a reduction is used and the smaller pulley containing less mass and balance issues would go on the servo. The larger pulley being on the lead or ball screw would not rotate anywhere near that speed. With a 5 turns in 1.000" screw (.200 lead), 2000 RPM at the screw would produce a table speed of 400 ipm, about 4 times faster than the approximate 100 ipm that most machines are run at from what I've gathered. In the case of mills anyway. Some of the routers go alot faster obviously. keep in mind also that most of the softwares like Mach2 incorporate "servo ramping", the pulse rate starts slow and increases exponentially to set speed then deccelarates then in the same manner to idle. User configured within the software.///// Ron





Rod


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