Re: [Emc-users] Cable recommendations for Mesa boards

[Peter C. W. <pc...@me...>]

On Thu, 20 Nov 2008, Eric H. Johnson wrote:

> Date: Thu, 20 Nov 2008 15:46:08 -0500
> From: Eric H. Johnson <ejo...@ca...>
> Reply-To: "Enhanced Machine Controller (EMC)"
>     <emc...@li...>
> To: "'Enhanced Machine Controller (EMC)'" <emc...@li...>
> Subject: [Emc-users] Cable recommendations for Mesa boards
> 
> Hi all,
>
> I am running into a small problem with dropped / excess steps using the
> m5i20 board and Hostmot2 driver. The problem appears to be with the 50 pin
> cable connecting the m5i20 with the TB. The quick form of my question is,
> are there any recommended cables / manufacturers of cables to use with the
> Mesa boards in the 18" to 24" range?
>
> The longer explanation is as follows:
>
> With the Hostmot2 driver and m5i20 board, the stepper signals come off the
> P4 connector, the farthest connector from the point where the cable exits
> the computer. One loses about 8" just exiting the computer, so with an 18"
> cable, there is only about 10" left to get to the TB. Due to the panel
> layout, I really need a 24" cable from this connector.
>
> I have tried several lengths of ribbon cable, and one rounded cable. The
> best performing cable is the 24" rounded (it ought to, it cost about $20). I
> need to run about 20 cycles the length of the X axis to lose a quarter turn
> of the motor (i.e. drifts towards the min limit). The 18" flat cable will
> lose it in about 4 cycles. The stepper motion starts to get rough with a 30"
> flat cable, and anything longer (I was testing with a 54" cable) is so
> unstable as to basically not work at all. One odd thing is that with the 18"
> flat and 24" rounded cables, only the X axis demonstrates this problem, if Y
> is having any problem, it is so small that I have so far not been able to
> detect it.
>
> Past the TBs I am using Belden low capacitance cables with individually
> twisted pairs, foil shield and drain, plus an overall shield to connect the
> stepper signals to the drives. This part appears to be working fine, as
> nothing changes if I swap things around past the TBs.
>
> Any ideas or recommendations?
>
> Thanks,
> Eric
>

I'm with John here, Some thing else is going on. Step and Dir inputs 
normally not high bandwidth, and I would not expect troubles 
with even 10 foot flat cables.


Is it possible your STEP and DIR inputs have optocouplers returned to 5V?. 
This is known problem with the 5I20 (or any of our FPGA cards) outputs since 
they only swing 0 to 3.3V.


here are a couple of solutions to this depending on how you are connected to 
your step motor drivers


1. If 3.3V drive is enough for the inputs, return the anode of the input 
Optocouplers to 3.3V instead of 5V (5I20 connector pin 49 jumper option)

2. If 3.3V drive is not enough or its inconvenient to get 3.3V to the drive,
set the step and direction outputs into OPEN_DRAIN mode so you get a 5V swing




Peter Wallace
Mesa Electronics

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