Monday, 28 October 2013

Motor Addressing

Today, bought a couple of terminal blocks which will be used to extend all stepper motor cables, and that will allow me to run with circuit boards outside of the base unit.  Only then, can I start debugging my interface circuity...


Meanwhile.... Rudi Niemeijer from the Netherlands, has also been busy hooking up an Arduino to his Armdroid clone, and seems to be experiencing similar motor addressing problems....

http://www.rudiniemeijer.nl/ort-robotic-arm/
http://www.rudiniemeijer.nl/714/
(you'll need to Google Translate these pages from Dutch)


Update:  new English pages are being maintained here

http://www.rudiniemeijer.nl/concorde-robotique-ort-robotic-arm/

Even though Rudi has a newer single interface board, the motor address logic is however roughly the same to the prototype models.


My current thinking on the addressing problems :

Motor addresses are decoded by IC6 74LS138 which selects one of eight possible outputs given an address from the interface port.  We know only six (001 - 110) of these outputs are actually used, the others are not connected.  The outputs of IC6 selects IC7 - IC12 which are 74LS175 (quad D flip-flops) used to latch the data bits.

This week... I'll be checking these addresses are correctly selecting these flip-flops.  It's quite possible the MSB (most significant bit) of the Address is not as expected, and the bit pattern needs re-arranging to suit.  But, I've not seen any examples on the internet of controlling software doing this!  Of course, another potential problem would be address lines not running in order.

The next area where the addressing can be muddled up - and only applies to the prototype variants is the wiring of the PCB interconnects.  Which is the routing from IC7 - IC12 on the interface PCB to the jumpers C1 - C12 which represent the motor drive channels for motors 1 - 6.

Finally, the physical connection of these motor channels to stepper motors assignments is another area to check.

Could be more involved... but I'll start with the above checklist....