xArm7 poor velocity control mode

xArm/850 Troubleshooting
1

Hi uFactory. We are using xArm7 in velocity control mode from C++. Basically as follows

arm.set_mode(1);
while(true) {
    // get the qdot from our own custom software 
    std::array<float, 7> qdot_command = ...
    arm.vc_set_joint_velocity(qdot_command.data(), /*is_sync=*/false, /*duration=*/0.1);
}

Each iteration of the loop takes less than 5ms. We are generally seeing good tracking of the velocity, except some intermittent spikes as pictured in the radians/sec vs sec diagram below.

velocity spike
velocity spike1850×974 123 KB

Is there something wrong with the way we are using the API? Has anyone seen an issue like this before?Thanks.

2

Hi Mark,

Would you please provide the SN of your xArm7 to support@ufactory.cc?
What is the current firmware and ufactory Studio version?

Would you please provide C++ script with us? We will try if we can reproduce the problem.

Best regards,
Minna

3

Thanks Minna. I uploaded a minimal example here. GitHub - axbycc-mark/xarm-velocity-bug-repro: Reproduction for XArm Velocity Control Issue

Besides the XArm C++ API, it requires the Eigen library. I will follow up with the serial number by email. Please let me know if your team has any issues building the example whether your team can reproduce the problem.

4

Hi ufactory team. Is there any update on this issue or suggested workarounds? It prevents me from using the velocity control function.