MR-J Servo FAQ

Q: Are motor/drives compatible between different generations?

A: Newer drives are mostly backward-compatible with older motors. For MR-J3 and later you may need to set PC04(COP1)=-1--. HC-xF motor encoders may only work in 4-wire mode, see params OP2/OP1/COP1.


There was a custom firmware MR-J2S-B-S255 which is compatible with OBA18 encoders and some HF-KP motors. Also MR-J3-B(GA) drive seem to recognize HG-KR motors.

Q: Can a 400W amp drive a 200W motor?

A: There's a parameter "Test mode 2" (No.183) or "Design evaluation mode" (PH18,TST) which disables motor/amplifier capacity check and clears alarm 1A. For MDS-B-SVJ2 set SV017(SPEC)|=0x0800. I don't know how it will affect performance and reliability in the long run with a big capacity mismatch, but it should be safe for one step up or down. Some drives are actually physically identical, e.g. MR-J2S-10 and MR-J2S-20 differ only by a brake resistor in the. MR-J2S-70 and MR-J2S-100 are also similar, only the later is not rated for 1-phase operation.

Q: How to access hidden drive parameters?

A: Set "Parameter block" (No.19 or PA19) param value to "ABCD" and reboot the drive. Be careful not to change various calibration values.

Q: What are 2-wire and 4-wire encoder mode?

A: In 2-wire mode an amplifier talks to motor encoder via MR/MRR line in half-duplex mode. In 4-wire it send request via MR/MRR and read reply from MD/MDR.

Q: How to update MR-J2S firmware?

Some MR-J2S drives use a FLASH MCU which contain a serial bootloder. The firmware in those can be updated via RS-232 link on CN3 connector using the SHFlash.exe utility. To activate the bootloader short pins 5(MD1) and 6(3V3) on CON6 connector under the flip cover.

Q: Why update the firmware on MR-J2S?

A: MR-J2S-A, MR-J2S-CP and MR-J2S-CL use identical hardware and can be reflashed to one another. Or to replace a failed special version amp like (MR-J2S-B-S084, MR-J2S-B-PY096, ..) which may be difficult to find.

Q: How to drive HC-KFS46 and HC-KFS410 motors?

A: The manual says they need a special version of MR-J2S-70-U005/U006. It could be true for early drive vesions, but later ones have those motors in internal tables, so they will just work. The -U006/-U005 amps are locked specificaly to those motors only and won't drive any other. To unlock them set params No.157-179 to 0.

Q: Where can I find the MR-A-TM (A-TM) terminator schematic?

A: For some reason Mitsubishi didn't publish it anywhere. Here it is:

Q: What type of fiber optic cable is used for SSCNET III?

A: It seems to be a regular POF fibers with duplex PN F07 connectors. A couple of widely available TOSLINK cables with F04 connectors work just fine instead.

Q: How do absolute encoders work?

E.g. the OBA17 glass disc contains 4 sine tracks: two offset 1 period-per-turn, 16 ppt and 256 ppt. During operation the angular position is derived from those tracks via interpolation. When powered by a battery/supercapacitor the encoder probably samples only 1 ppt tracks to keep the full-turn counter consistent. 2 offset tracks allow to determine rotation direction.

Q: List of supported motors for MDS-B-SVJ2

A: Besides J2 series motors the drive also can use J2S equivalents: HC-MFS/SFS/UFS/RFS/KFS. It also knows:


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