Motor Control Modes¶

DaMiao motors support four different control modes, each optimized for different use cases.

Overview¶

Control modes determine how the motor interprets command messages. The control mode is set via register 10 (CTRL_MODE) and must match the command format being sent.

Mode	Register Value	CAN ID Format	Use Case
MIT	1	`motor_id`	Impedance control with stiffness/damping
POS_VEL	2	`0x100 + motor_id`	Trapezoidal motion profiles
VEL	3	`0x200 + motor_id`	Velocity control
FORCE_POS	4	`0x300 + motor_id`	Position control with limits

MIT Mode¶

MIT mode (named after MIT's Cheetah robot) provides impedance control with position, velocity, stiffness, damping, and feedforward torque.

Characteristics¶

Full impedance control: Adjustable stiffness and damping
Feedforward torque: Direct torque control for compensation
Flexible: Suitable for compliant manipulation and force control
Most parameters: Requires tuning of kp (stiffness) and kd (damping)

Command Parameters¶

Parameter	Range	Description
`target_position`	Motor-specific	Desired position (radians)
`target_velocity`	Motor-specific	Desired velocity (rad/s)
`stiffness` (kp)	0-500	Position gain (stiffness)
`damping` (kd)	0-5	Velocity gain (damping)
`feedforward_torque`	Motor-specific	Feedforward torque (Nm)

Control Law¶

The motor implements an impedance controller:

τ = kp * (θ_target - θ_actual) + kd * (ω_target - ω_actual) + τ_ff

Where: - τ is the output torque - kp is stiffness (position gain) - kd is damping (velocity gain) - θ is position - ω is velocity - τ_ff is feedforward torque

Use Cases¶

Compliant manipulation: Soft interactions with environment
Force control: Precise force application
Impedance matching: Match desired mechanical impedance
Research applications: Flexible control for experiments

Example¶

motor.ensure_control_mode("MIT")
motor.send_cmd(
    target_position=1.0,      # 1 radian
    target_velocity=0.0,      # Hold position
    stiffness=20.0,           # Moderate stiffness
    damping=0.5,              # Moderate damping
    feedforward_torque=0.0    # No feedforward
)

POS_VEL Mode¶

POS_VEL mode provides position-velocity control for trapezoidal motion profiles.

Characteristics¶

Trapezoidal profiles: Built-in acceleration/deceleration
Position + velocity: Target position with maximum velocity
Simpler: Fewer parameters than MIT mode
Smooth motion: Automatic trajectory generation

Command Parameters¶

Parameter	Range	Description
`target_position`	Motor-specific	Desired position (radians)
`target_velocity`	Motor-specific	Maximum velocity during motion (rad/s)

Behavior¶

The motor moves toward the target position, limiting velocity to the specified maximum. The motor firmware handles acceleration and deceleration automatically.

Use Cases¶

Point-to-point motion: Moving to specific positions
Trajectory following: Following predefined paths
Simple control: When impedance control is not needed

Example¶

motor.ensure_control_mode("POS_VEL")
motor.send_cmd(
    target_position=2.0,      # Target: 2 radians
    target_velocity=3.0       # Max velocity: 3 rad/s
)

VEL Mode¶

VEL mode provides pure velocity control.

Characteristics¶

Velocity control: Direct velocity command
Simplest: Single parameter
Continuous motion: For constant-speed applications
No position target: Motor maintains commanded velocity

Command Parameters¶

Parameter	Range	Description
`target_velocity`	Motor-specific	Desired velocity (rad/s)

Behavior¶

The motor maintains the commanded velocity. Positive values rotate in one direction, negative values in the opposite direction.

Use Cases¶

Constant speed: Maintaining steady rotation
Velocity following: Following velocity profiles
Simple applications: When position control is not needed

Example¶

motor.ensure_control_mode("VEL")
motor.send_cmd(
    target_velocity=2.0       # Rotate at 2 rad/s
)

FORCE_POS Mode¶

FORCE_POS mode (Force-Position Hybrid) provides position control with velocity and current limits.

Characteristics¶

Position control: Moves to target position
Safety limits: Velocity and current limits for safety
Hybrid approach: Combines position and force control
Safe operation: Limits prevent excessive forces

Command Parameters¶

Parameter	Range	Description
`target_position`	Motor-specific	Desired position (radians)
`velocity_limit`	0-100 rad/s	Maximum velocity during motion
`current_limit`	0.0-1.0	Torque current limit (normalized)

Behavior¶

The motor moves toward the target position while respecting the velocity and current limits. This provides safe position control with force limiting.

Use Cases¶

Safe positioning: When force limits are critical
Obstacle avoidance: Limiting force when encountering obstacles
Human-robot interaction: Safe operation near humans
Constrained environments: Operating in tight spaces

Example¶

motor.ensure_control_mode("FORCE_POS")
motor.send_cmd(
    target_position=1.5,          # Target: 1.5 radians
    velocity_limit=50.0,          # Max velocity: 50 rad/s
    current_limit=0.8             # Max current: 80% of rated
)

Mode Selection Guide¶

Choose MIT Mode When:¶

You need compliant/impedance control
Force control is required
Research or experimental applications
You want full control over stiffness/damping

Choose POS_VEL Mode When:¶

You need smooth point-to-point motion
Trapezoidal profiles are sufficient
Simpler control is acceptable
Position accuracy is important

Choose VEL Mode When:¶

You only need velocity control
Position is not important
Constant-speed operation
Simplest possible control

Choose FORCE_POS Mode When:¶

Safety is critical
Force limits are required
Operating in constrained environments
Human-robot interaction

Switching Between Modes¶

The control mode must be set before sending commands:

# Switch to MIT mode
motor.ensure_control_mode("MIT")
motor.send_cmd(...)  # MIT commands

# Switch to VEL mode
motor.ensure_control_mode("VEL")
motor.send_cmd(...)  # VEL commands

The ensure_control_mode() method automatically: 1. Reads the current mode from register 10 2. Writes the new mode if different 3. Verifies the write was successful

Mode Compatibility¶

Commands must match mode: Sending MIT commands while in VEL mode will not work correctly
CAN IDs differ: Each mode uses a different arbitration ID
Register must match: Register 10 must match the command format