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« on: May 19, 2022, 05:38:17 PM »
Hi,
Rimmel and I have been sharing a few PM's so that he can understand the requirements of wiring servos to Mach/ESS/BoB..
There is nothing secret about it so I thought I would post so others can see (benefit?) and/or comment.
Note that I use Delta servos and the diagram I have posted is how I have programmed and hard wired the Delta drives and the BoB is my own design.
Having said that Rimmel's Panasonic drives and MB3 breakout board should be sufficiently similar that the same scheme can be applied. Note also that there are dozens
of different ways and/or variations on how this can be done, with and without good reasons. This is just how I have done it, and with any sort of luck will be able to communicate
why I did it this way.
The first question Rimmel asked is where the 24V comes from? Firstly his MB3, and my own BoB have a 24V supply. However my Delta servos have an internal 24V supply
and I use it for the a bias source for the photodiodes. So there are two sources of 24V power. Note that the supplies share a COM. I imagine the Panasonic drives will have a similar
built-in supply.
A brief description is in order.
Not counting the two differential Step/Dir pairs there are two outputs from the BoB to two inputs of the drive. They are an Enable and a Reset. Note that I have used the internal 24V
supply, via the built-in dropper resistors, to the photodiode. If the BoB goes low then current will flow through the photodiode and thus signal the drive. Note also that the transistor in the
BoB can only sink current when the ESS drives the base high. That is to say the ESS and therefore Mach must be active before the transistor can conduct, and is fail-safe. If the ESS or Mach
give up the ghost for any reason then the Enable signal will disappear and all servos will stop.
The Reset signal is to reset the drive after a fault condition, with any sort of luck hardly ever. My Delta servos, if they fault, require either a power cycle OR a Reset in order to clear a fault condition.
I have a button (on screen) that I activate which in turn pulses the Reset output of the BoB, with its transistor switching on and sinking the photodiode current thereby signalling the drive and
resetting it.
Note also that I have just one Enable output and one Reset output and they are sent to all servos. Rimmel has commented that his MBS3 BoB outputs can sink 70mA. Each servo sources about 5 maybe 10mA
so having three servos commoned together would still only require the MBS output sink 15-30mA, well within spec.
The alarm is an output of the drive and therefor an input to the BoB. Ihave used the 24V supply of the BoB via a dropper resistor to source about 5mA. The phototransistor in the drive conducts in a fault
condition and therefore drags the BoB input low, to nearly 0V, which in turn signals (active low) the ESS.
I have one alarm input per servo so Mach and therefore I know which servo faulted. If you are trying to economise on inputs you could have all servo alarms hooked to just the one input, and that one input
would trigger an Estop. Your choice.