Re: small 3-axis micro stepper

--- In CAD_CAM_EDM_DRO@y..., J <jaredts@y...> wrote:

> *11" X 7-1/2" travel
> *10TPI leadscrews
> *The y-axis probably moves 35-40lbs with an empty table
> Do I have any choice but to buy a high dollar cnc controller

(geckos are high dollar to me!)? The ideal system would be able to
make cuts with a router or milling head (cutting steel would be
nice), have a 60 i.p.m. rapid and cut at around 10 i.p.m. minimum.
By the way, xylotex suggested a nema 23 powermax II 253oz-in Bipolar
motor (2.3 amps bipolar series). Thanks for any replies.

Well , the xylotex guys were on top of the game when they
recommended that powermax II motor. The basic specs seem to work out
fine for that driver.

That motor will have 2.3 amps current at 3.5 volts across 1.52 Ohms
resistance wired in series. The series connection however does
produce the largest inductance in this case 6 milli Henry if I read
it right.

In your case 60 ipm. With 10 tpi screws requires 600 RPM or 2000
full steps per second.

You can get a rough idea for performance based on the inductance
value of the coils. For each full step I have to either charge or
decay the current in the coil inductance. Given that Voltage =
inductance * (change in current/ change in time) roughly.

This can be worked several ways but lets say we need 2000 steps per
second. This means to switch the full coil current we have 2000 *
2.3amps or 4600 amps/second.

In the ideal case then V/L = 4600 so V = (4600 * .006 henerys) V=
27.6 volts.

In the real world there are switching delays . losses etc.. but at
around 30 volts you can maintain near full performance from the motor
before the torque starts to really drop off.

Two problems , For one I might be skeptical of pushing a new design
near it's limits without testing . The numbers work out on paper
provided the thermal properties can handle the load, which is hard to
say from here.

The second problem is Yoiks! Those are some fancy motors and I'll
wager you don't want to see the price tag on that model, could be
wrong but they are high tech stuff.

With that model driver I would be inclined to think more along the
lines of a 5 volt 1.5 to 2 amp motor on slightly smaller machines
110 – 140 oz. Without being able to test one under max conditions.

Brian
BSP