Re: Ball screw reduction ratio

Padu wrote:

Hi,

How can I calculate the reduction ration of a ball screw?

For example, let's say I have a DC motor spinning at 3000RPM, with a maximum
of 2000oz-in torque. If I couple the motor to a ballscrew that is 200mm (8")
long and has 6mm (0.236") screw lead, it's intuitive that if 3000RPM is
mantained, then the screw will travel throughout its extension in 0.66
seconds.

Let me just double check my math... 3000RPM = 50 revolutions per second. The
ball screw needs close to 33 revolutions (200mm/6mm per rev.) to travel the
200mm, therefore 33/50 = 0.66s. Therefore 3000RPM is roughly equivalent to
303mm/s.

What about torque?

This seems *awefully* fast for a ballscrew mechanism. These are
generally made for precision, not speed, though speed is a relative
thing.

Sources of ballscrew components like SKF provide engineering white
papers with design calculations. Sounds like you're doing something for
a steering mechanism. You may also want to look into rack-and-pinion
(easier mechanically), hydraulic, and pneumatic. For the latter two you
can provide positional feedback using a pot or encoder, and a PWM valve.
These might be more durable, and you'd definitely get the speeds and
torque you're looking for. The positional accuracy will depend on your
control system, and the quality/type of proportional controlled valves
you use.

-- Gordon
.