PMDX-424 Tandem Motor Configuration

[broered]

Will the PMDX-424, wired to a PMDX-134 Motherboard with a ribbon cable, support a Tandem Motor configuration?

I have the PMDX-134, populated with (4) Gecko G203V's.  I want this to drive a 3-axis router with tandem x-axis (gantry) motors.  I'm anticipating the software's ability to do axis-squaring.

Thanks

[Steve Stallings]

Tandem axis drive with two motors will work with the PMDX-424, a PMDX-134, and Mach4.

Gantry squaring is planned, but not yet implemented in the Mach4 Plug-in for the PMDX-424.

[broered]

The PMDX-424 has 5 motor outputs.  The PMDX-134 has 4 motor drivers.
The PMDX-422, with 4 motor outputs, was easy to understand.  I'm not clear how mapping is achieved with the PMDX-424, using the same 26-pin ribbon cable.
Could you please explain?
(thanks)

[Bob at PMDX]

When connected to a PMDX-134, the PMDX-424 motors map to the PMDX-134 positions as follows:

PMDX-424    PMDX-134
Motor0          J1 (Axis #1)
Motor1          J2 (Axis #2)
Motor2          J3 (Axis #3)
Motor3          J4 (Axis #4)

Yeah, we really shouldn't have called the connectors on the PMDX-134 "axis" as that confuses things when you have a tandem axis.  When using a PMDX-134, ignore the PMDX-424's "Motor3a" and "Motor3b" outputs and just consider them a single "Motor3" (which is how it appears in Mach4 anyway).

In the Mach4 Configure->Mach "Axis Mapping" tab you could for example map "Motor0" to the X axis master, "Motor1" to the X axis slave1, "Motor2" to the Y axis and "Motor3" to the Z axis.  But that is just an example - any mapping of Motor0 through Motor3 to the X master/slave, Y and Z would work just as well.

Bob

[broered]

I guess I should explain that all the questions are the result of me having NOT experimented with the hardware and MACH4.  Sort of flying blind here as I try to determine an optimum hookup that will allow for the future.

From what Bob described, the PMDX-424 feeds its Motor 0 through 3 signals to the PMDX-134 through the 26-pin ribbon cable.  Creating a tandem motor configuration is done within the MACH4 software.  Signals from the PMDX-424's Motor 3B terminal block is never sent through the 26-pin ribbon cable.

If future axis squaring will be done by PMDX-424 plug-in software, then I would assume it will rely on the use of the gantry motors being connected to Motor3A and Motor3B.  Since Motor3B signals don't go through the 26-pin ribbon cable, it looks like future axis squaring will be unable to work with the ribbon cable and the PMDX-134. 

I really like the PMDX-134 concept, but I want to be wired correctly for the future. 

[Bob at PMDX]

There are two ways that the PMDX-424 will support tandem axes (and eventually, gantry squaring):

(1) Using Master/Slave mapping in the standard Mach4 configuration "Axis Mapping" tab.  All SmartBOB devices support this method for tandem motors.  In this case, you assign two of the motors to a single axis as in the example in my previous post.  The Mach4 motion planner is then in charge of feeding our plug-in the motion data needed to keep the tandem motors moving in sync during jog and GCode moves.  During homing, the SmartBOB device is responsible for moving both motors in sync.  If you have a tandem axis plus two more (for a standard x/y/z gantry machine), this uses all 4 available motors from the SmartBOB.  The step and direction connections come from PMDX-424 connectors J7 (Motor0), J8 (Motor1), J9 (Motor2) and J10 (Motor3a).  No connections are made to J11 (Motor3b).  Or you can use a ribbon cable from J6 to a PMDX-134 as you are doing.  You may also use 2 each PMDX-133 boards.  In that case, you would mount the Gecko drivers in the following PMDX-133 positions.  PMDX-133 #1 is the board that is connected directly to the PMDX-424.  PMDX-133 #2 is the board that is daisy-chained to PMDX-133 #1.


PMDX-424 Motor     PMDX-133
Motor0                    PMDX-133 #1, Axis #1
Motor1                    PMDX-133 #1, Axis #2
Motor2                    PMDX-133 #1, Axis #3
Motor3a                  PMDX-133 #2, Axis #1
- - - - -                     PMDX-133 #2, Axis #2 - NOTHING CONNECTED HERE
- - - - -                     PMDX-133 #3, Axis #3 - NOTHING CONNECTED HERE

** OR **

(2) Use the PMDX-424's hardware cloning facility.  In the Mach4 configuration "Axis Mapping" tab, map "Motor3" as the "Master" on whichever axis is your gantry axis (the "X" axis in your case).  Do not assign any motor as a "Slave" motor for that axis.  Mach4 will have no knowledge that this is a tandem axis.  The PMDX-424 will ensure that the two motors move in sync with each other during all types of motion.  Wire the step and direction signals from J10 (Motor3a) and J11 (Motor3b) to the two motor drivers on your gantry (see NOTE #1 below).  This leaves 3 other motors available (Motor0, Motor1 and Motor2) for use as you see fit (perhaps 2 more linear axis plus a rotary axis, or tool changer motor, etc.).  This will NOT work with a PMDX-134 connected to the ribbon header at J6.  It *WILL* work with 2 each PMDX-133 boards connected in series to the J6 ribbon header.  In that case, you would mount the Gecko drivers in the following PMDX-133 positions.  PMDX-133 #1 is the board that is connected directly to the PMDX-424.  PMDX-133 #2 is the board that is daisy-chained to PMDX-133 #1.

PMDX-424 Motor     PMDX-133
Motor0                    PMDX-133 #1, Axis #1
Motor1                    PMDX-133 #1, Axis #2
Motor2                    PMDX-133 #1, Axis #3
- - - - -                     PMDX-133 #2, Axis #1 - NOTHING CONNECTED HERE
Motor3a                  PMDX-133 #2, Axis #2
Motor3b                  PMDX-133 #3, Axis #3

NOTE #1:   The PMDX-424 will move the Motor3b motor in the opposite direction as the Motor3a motor by inverting the direction signal.  If your gantry needs both motors to move in the SAME direction, you will have to re-wire the connections between the Motor3b motor driver and the motor itself to reverse that motor.  Swapping the 2 wires from one phase of the motor will accomplish that.

Bob

[broered]

Bob;
Thanks for the really complete description on tandem axis support.  Mach4 and the PMDX components have far more flexibility than I ever imagined. 
 
I need to get Mach4 running so I can quit asking questions and do some real work here.