Re: [CAD_CAM_EDM_DRO] RE Oatley Kits

petermic@... wrote:

> You've got a pretty good run down from previous reply but just to add
> the KIT number is K142 if you are looking it up.
> YEAH AND OUR DOLLAR IS REALLY LOW IN NZ.
>
> HEATSINKING! quote "the mosfets will only be warm with motor currents
> of up to 2 amps, as with motors recovered from the printer" (WRONG!!)
> "These mosfets will handle up 100v @14A but heatsinks are required."
> Yep I got caught out too, and very quickly installed heatsinks.
>
> I notice that the KCam has a motor enable output and am tempted to
> make a relay driver to disconnect the supply to the Mosfet stage.
> (the mosfet is driven by a seperate PSU for the steppers).
>
> I have a question. If I remove the supply, then re-enable the supply
> will the stepper jump a step or will it stay in the same position?

The stepper will NEVER jump just ONE step. In full-step mode, it could
jump
4 steps either way. Every 4 steps (in full step mode) the magnetic (and
current)
polarities repeat. If there is enough mechanical torque on the motor
from backlash,
belt tension, weight, table friction, etc. it is possible that the motor
may slip about
2 full steps, and then it is a tossup which way it will go when power is
reapplied.

If the motor DOES jump just one step, that is an indication that
interference from
the relay switching is causing a pulse on the step input to the stepper
driver.
For this reason and others, you will probably need to use another relay
and a
capacitor charging series resistor to bring the power up slowly before
the main
power relay closes.

Jon