Reading the documentation, it is not entirely clear to me what are the differences of the joint control modes supported in pybullet.
I try to recap them here, please @erwincoumans feel free to jump in to add more details and address holes in my understanding.
Let's assume that in all cases (excluding torque), the reference error is the following:
error = kp * (pos_des - pos) + kd * (vel_des - vel)
VELOCITY_CONTROL: This is a pure proportional control for velocity that by default has kp=0 and kd=1. Gains should be in the range [0, 1].POSITION_CONTROL (alias for CONTROL_MODE_POSITION_VELOCITY_PD): Similar to VELOCITY_CONTROL. By default it has kp=1 and kd=0. It allows to optionally specify both the target position and target velocity.TORQUE_CONTROL: It should be enabled by disabling the default motorized joints passing a force=0. Later calls using this mode will send directly the torque to the joint.PD_CONTROL: Similar to POSITION control but it allows specifying not normalized gains.
Questions:
- Is
kp ignored in VELOCITY_CONTROL?
- What is the logic behind the normalized gains in
VELOCITY_CONTROL and POSITION_CONTROL?
- Is
kd=0 by default in POSITION_CONTROL?
- Is correct that in
POSITION_CONTROL if kd=0 and a velocity reference is specified, it has no effect?
- Is the description of
PD_CONTROL correct? There's not much information about it.
- Should
PD_CONTROL with kp=0 and kd=1 behave as VELOCITY_CONTROL?
I think that a big difference of PD_CONTROL with respect to POSITION and VELOCITY is how the error is treated. I suspect that in the former case a joint force is generated, in the latter ones instead the error is minimized as constraint. Is this correct?
Related issues #2152 #1026
Reading the documentation, it is not entirely clear to me what are the differences of the joint control modes supported in pybullet.
I try to recap them here, please @erwincoumans feel free to jump in to add more details and address holes in my understanding.
Let's assume that in all cases (excluding torque), the reference error is the following:
VELOCITY_CONTROL: This is a pure proportional control for velocity that by default haskp=0andkd=1. Gains should be in the range[0, 1].POSITION_CONTROL(alias forCONTROL_MODE_POSITION_VELOCITY_PD): Similar toVELOCITY_CONTROL. By default it haskp=1andkd=0. It allows to optionally specify both the target position and target velocity.TORQUE_CONTROL: It should be enabled by disabling the default motorized joints passing aforce=0. Later calls using this mode will send directly the torque to the joint.PD_CONTROL: Similar toPOSITIONcontrol but it allows specifying not normalized gains.Questions:
kpignored inVELOCITY_CONTROL?VELOCITY_CONTROLandPOSITION_CONTROL?kd=0by default inPOSITION_CONTROL?POSITION_CONTROLifkd=0and a velocity reference is specified, it has no effect?PD_CONTROLcorrect? There's not much information about it.PD_CONTROLwithkp=0andkd=1behave asVELOCITY_CONTROL?I think that a big difference of
PD_CONTROLwith respect toPOSITIONandVELOCITYis how the error is treated. I suspect that in the former case a joint force is generated, in the latter ones instead the error is minimized as constraint. Is this correct?Related issues #2152 #1026