stepping down your motors

[dowling177]

Question:

How do you know how much to step down your motors (are there formulas)? Are there instances when you don't have to step down your motors?

I am building a router and driving it with belts on the x and y axis and I will be using unipolar steppers (700-1000 oz-in).

[Torsten]

Thats the $100.- question.
The most reliable way I know is when you take a Identical machine
that is aready build and running with the same motors and test its
performance then make a decision about your own machine based on that.

O.K. maybe thats a little hard to come by for us one of a kind mechanics.
Do you have the Torque curve characteristics of your motors it would be
a good start to know what kinds of useful speeds those motors will be
getting at and what torque will be left at that speed.
A better understanding of the loads required on your machine would help too.
Weight and methode of guides.
Then maybe we can find some similar machines and go from there.

Another methode is to find out a peticular load for cutting a peticular material
at a peticular feedrate.
The configure your drive to provide this and a little extra for good messure.
Then accept whatever rapids this setup will give you.

Good Luck

[Al_The_Man]

Question:

How do you know how much to step down your motors (are there formulas)? Are there instances when you don't have to step down your motors?

Many of the motor manuacturers offer design guides, either in their catalogues or on their web sites, to calculate the torque required you have to take in the relative loads of each axis and calculate the inertia required to move the load at your desired acceleration and max feed rate, Vexta for example recommend a inertia ratio between motor and load to be no more than 3:1.
If the ratio is higher than this a reduction is required. Fortunately, the inertia can be reduced by square of the reduction.
e.g. a 10:1 reduction reduces the inertia by 100.
Al