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Vision 570 w/ 3 shaft encoders

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Hi all, I am working on my first Unitronics project and have a 570 with the E1B snap in I/o. However I need one more shaft encoder for my project (total of 3). Can I use a M90 as the third encoder input? Is there any way to use another oplc as just remote I/o? How would I get the shaft encoder MI from the M90 into the 570? I would assume modbus but I wonder if its fast enough? Is there a better way to do all of this? Just for background the 3 encoders are monitoring the positions of the outputs of 3 motors driving 3 platforms back and fourth. The motors are controlled with vfd's over modbus as well.

Thanks for your help,


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  • MVP 2014

Hi, bit of a tough one for your first Unitronics project :(

You can use Modbus to drive the M91 as an I/O slave. Maybe that is a reasonable choice since your control system already uses Modbus for the motor drives.

However, for ultimate speed as well as simplicity.I would probably opt for CAN bus, if you only want to transfer one encoder value.

Select an M91 with CAN bus, such as the M91-2-R2C.

Set up the Vision 570 to use CAN ISC protocol

Once configured, the M91 can automatically send the encoder MI value to the V570 at an interval as short as 20ms.

Search "CAN ISC" in the Visilogic help to get all the details.

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Why not use CAN encoders & eliminate the need of a M91

Cost- - this is essentially a learning project for me, I agreed to do it for my old High School for free if they paid for the parts. The entire project had to come in at under 2k and of course I left about $500 wiggle room but that is not enough to get new or used CAM encoders from what I've found.

I think the best bet is to use the M91 as the I/o slave over CAN. I will look into that further.

I did find these...


Which will make the encoders CANopen compatible but at $200 each they are still not cheap and its just one more thing to program, power, and implement. If you think these would work way better than just using a M91 though...

Thanks again,


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  • MVP 2023

Do NOT use CAN encoders on a learning project. If the complexity of configuring CANOpen is enough to make Tim's head spin, I can't even imagine the grief a beginner would encounter.

Unless you're in love with the screen size of the V570 (and it does certainly deserve it), you may want to downsize to the V350-35-TR20 which has support for three encoders on board. Tell us the rest of the story on the project - what are you trying to do?

Joe T.

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