Hi everyone,
I’ve recently assembled my AR4 robot, and while most things are functioning well, I’m encountering an issue with the J4 joint.
The problem is that J4 can only rotate in the positive direction. When I try to rotate it in the reverse direction, I get an error message saying, "J4 Collision or Motor Error."
I’ve already checked the encoders and switches, and they all work fine. All the other motors are also functioning properly.
Could anyone help me diagnose what might be causing this issue? I’ve attached photos and a video for reference.
Thank you so much in advance!
https://anninrobotics.com/wp-content/uploads/2025/08/J4-cannot-rotate-reversely.mp4
Error log:
https://anninrobotics.com/wp-content/uploads/2025/08/J4-cannot-rotate-reversely_2.avif
There could be a potential wiring issue. Can you check with a multimeter that the dir input to the driver for J4 has a solid connection from the teensy and that the signal is + in one direction and - in the other?
Thank you so much for your speedy reply!
I tested the DIR input with a multimeter, and it seems to be working properly, showing positive voltage in one direction and negative in the other. I also reconnected the wires to ensure all connections are solid. However, the issue with J4 not rotating in the negative direction persists.
To verify that the J4 wires are functioning correctly, I connected the J4 PUL and DIR wires to the J3 driver board, as shown below. With this setup, I was able to control the J3 joint to rotate in both directions using the J4 tab in the control software, which suggests that the Teensy inputs and J4 wires are working properly.
However, when I attempted to use the J3 wires to control J4 in a similar manner, the same issue occurred: I couldn’t rotate "J3" in the negative direction.
This leads me to suspect there might be an issue with the driver board. Could you provide any additional suggestions or insights on this?
Many thanks!
Ming
@ming I agree, your troubleshooting seems correct and its likely a driver issue. Can you also put J4 into open loop mode in the settings tab and verify the problem persists without the encoder being monitored. The next step might be to swap the driver with another joint and verify the problem follows to the new joint.
I set the J4 to open loop mode, the error log disappearred but it still could not rotate reversely. I also tested the J4 driver to control J3 and encountered the same issue, leading me to believe the driver might be the cause. I've ordered a new DM320T driver, which should arrive in a few days. I'll update you once I test the new driver.
Thank you so much!
Ming
Hi Chris,
I replaced the driver for J4, and it's now working well -- I can jog J4 to rotate in both directions.
But I met another new issue: after finishing the encoder and switch tests, the control software freezes everytime I click the auto-calibration button. This happens even when I chose to calibrate just one joint. Do you have any ideas what might be cuaing this problem?
Many thanks for your help!
Ming
I have noticed the same issue, but have the previous kit (not MK). The lever goes inside the J5 motor mount holes when moving backward. J4 Limit Switch Mount.STL and 10T85 switch fix this, right?
https://anninrobotics.com/wp-content/uploads/2025/08/J4-cannot-rotate-reversely_3.mp4
Thank you.
