Re: [CAD_CAM_EDM_DRO] LARGE Gantry table: Geckos on large servos.

Kim Lux wrote:

>Comments below.
>
>
>On Wed, 2004-03-10 at 11:55, Jon Elson wrote:
>
>
>>Kim Lux wrote:
>>
>>
>>
>>>I suspect that the motor would draw more than the rated max drive
>>>current (ie 20Amps) during acceleration.
>>>
>>>
>>>
>>>
>>>
>>Unless there is a bug in the circuit, the Gecko 320/340 cannot be made
>>to exceed
>>its own max current rating. If you turn the pot all the way up, no
>>matter how
>>large the motor, it cannot exceed 20 A.
>>
>>
>
>That was my understanding as well. That is why we *thought* we could
>run a really large servo motor if we kept the supply voltage in line.
>
>

How were you keeping the DC supply within limits? If you were running
with it at 80 V, then you needed a braking resistor to be turned on at
the slightest
rise in voltage. Did you have a braking resistor and circuit to control it?

Also, what was the inductace of the motor in question?

>BTW: the Geckos are running the same motor only smaller (ie 2 HP) on 2
>other drives with mo problems.
>
>
>
>>One weak point in those Gecko models is that they don't sense a fault to
>>ground
>>in the motor. That will blow them up for sure.
>>
>>
>
>I'll check this out immediately. By a ground fault, you mean a path
>between either of the motor terminals to its case ?
>
>

Yes, exactly.

Jon