Hey! I think this is probably a long shot but would really love if you could post more videos on AR4 robot. There are very few out there and even few mention its shortcomings and stuff.
Looks like a bug on the software, anyway, you can double check the motor and encoder wiring, another option is to delete the program and teach the points again, try also with a program that moves only the 7th axis... measure the electrical signals on the drive when the software should be commanding it
It’s just a piece of aluminum u channel. Maybe 8 inches by 3 inches. The rails came from eBay. Maybe I should do a follow up video? Even Chis asked about it. Thanks.