Re: Thanks - was: Things to check? back to basics - please

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Antonius J.M. Groothuizen"
<agroot@s...> wrote:

> Weyland:
>
> Some will flame me but...
>
> Forget Ohm's law for the steppers. You are using Gecko's to

control

> the current through the motors. The Geckos don't care what voltage
> is required, they just want the current through the stepper's

winding

> to be at a certain value.
>
> This does not apply to the input voltage of the Gecko's - too much
> and you'll blow them. When your stepper motors are turning, they
> also act as generators. The voltage they generate is called Back
> Electro-Motive Force (or Back EMF) and can be higher than the

voltage

> of your power supply. This voltage is sent back to the Gecko's and
> is why it is strongly recommended that you run the Gecko's with

less

> than their maximum voltage at your power supply.
>
> Note that since the Geckos use microstepping the 'certain value' I
> mentioned above is in reality a series of values that are repeated
> for each 'full step' of the stepper motors. The current is ramped

up

> in discrete steps, then ramped down in discrete steps to provide
> ten 'microsteps' per full step of your stepper motor.
>
> The 'iron losses' mentioned below translate to heat. What it means
> is that you have diminishing returns as the voltage multiplier goes
> up. In your example of a 4.5V motor the 75V power supply is 16.7
> times the nominal voltage - well within the boundary.
>
> Tony
>

Start with a clean sheet of paper for a minute.

you stated the motors are 4.5 volts ?
20 times 4.5 is 90, so you 'can' run these motors up to 90 volts.
you can run them at 4.5 volts, but with little power.
using the Gecko White paper, minimum voltage is 5x or in your case,
22.5 volts.

Maximum is limitd by the Gecko limit. anything between 25 and 65
volts is fine.

use the Bi-polar current setting as you are running these 8 wire
motors in parallel.

Set the Gecko for 5 amps. and check the motor specs, your motors
will be hot to the touch. This is not a problem. they should NOT
boil water. That indicates a potential problem.

Set the Gecko for full step. that way 200 pulses are 200 steps and
that should be 200 steps into a 2:1 gearing for 400 steps per
revolution into a 10 tpi leadscrew for 4,000 steps per inch.

Verify your software expectes 4,000 steps per inch.

Dave