I have searched the Interwebs and nothing

Mitsubishi FX2n PLC's one on the robot and one on the rack both connected together by 485-BD boards they have to have two resisters one on the first PLC and one on the last PLC.



OK so when I have both resisters connected the robot wants to shoot like a race car I can only have one resister connected in order for it to work right. Why would this happen.

Because of characteristic impedance. You want to eliminate reflections - but you need to mach resistance in order to absorb it.
You posted previously one picture of panel where the cables look like snake pit? If that is true - there may be the answer. What cable you are using? Is communication cable separated from power cables? Is it grounded only on one side? etc.

Nope they are all in the same cable track and the low and high voltage is all in the same control boxes. But the cables that are in the cable track are shielded.

What is the type of robot controller?

On the rack is a FX2n 80M and on the robot is a FX2n 32MR

Make sure that you are using the correct terminal resistor 110 Ohm, 1/2W (3 brown stripes and one silver or gold), connected between RDA and RDB. Cable should be shielded twisted pair. Shield should be grounded only on one side.
Just to mention FX2N-30MR is also PLC - it is not robot controller. From that I presume that it is N:N communication.
If you are using -BD not -ADP, then you are limited to cca 50m of cable length.
Try what is happening if you connect new cable directly from PLC to PLC, avoiding power cables.

Will look into them just worried it goes fast when I connect the other resister and they have all brown lines and one gold other then that all I have are the ones with the gold, brown, orange, orange and the robot has a servo amp and a servo motor on it if that makes a difference but don't think it would.

The other one is 330 Ohm and it is used for two-pair wiring, and 110 Ohm is used for one-pair wiring. To conclude what is in one end needs to be on other end. If SDA and RDA are in short circuit, and SDB and RDB are in short circuit then it is 110 Ohm (Brown Brown Brown) and resistor should be between RDA and RDB on both sides (2 resistor in total). But if SDA, SDB, RDA, RDB are separated then it is 330 (Orange Orange Brown) and resistors should be mounted between SDA and SDB, and also between RDA and RDB, on both sides (4 resistors in total).
And definitely try connecting new shielded twisted pair cable directly, avoiding power lines, with resistors and, shield grounded only on one side.

goghie said:

Make sure that you are using the correct terminal resistor 110 Ohm, 1/2W (3 brown stripes and one silver or gold), connected between RDA and RDB. Cable should be shielded twisted pair. Shield should be grounded only on one side.
Just to mention FX2N-30MR is also PLC - it is not robot controller. From that I presume that it is N:N communication.
If you are using -BD not -ADP, then you are limited to cca 50m of cable length.
Try what is happening if you connect new cable directly from PLC to PLC, avoiding power cables.

Click to expand...

Tried it didn't help and it looks like the robot is connected to a FX2n 1PG module when it moves it lights up.

Without knowing what data is being sent from one plc to the other this could be difficult to fault find the servo is obviously controlled by registers in the plc with the servo module, assuming that the other one is sending data that is used within the plc with the servo card and giving speed/direction data then removing a termination resistor will possibly cause intermittent data loss, and this data loss is causing the robot to slow down but I find this unlikely as from your description that the problem is that it's running too fast when terminated correctly.
Communications use a protocol that would normally reject invalid data as most use a checksum to validate that the information contained in the data is valid.
422/485 communications use termination resistors at the extreme ends of the communication link to eliminate reflections in the transmission cable causing erroneous data that should be rejected and not populated into the plc memory. Normally if using communications to control a servo/s then there should be some safety programmed in to ensure that on a error of communication the servo/s will not respond for example if a remote plc sends data to another to tell it to run a motor then stop in a position based on a return communication value, failure of this communication should stop the servo.
The only other thing I can think of is that assuming that it works correctly when the termination of one of the links is removed then you have a problem on the cable or link.