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Example Scripts

The scripts directory contains a bunch of scripts that can be used to test the motor control board and serve as examples on how to use the CAN API implemented in the python_blmc package.

Scripts that are prefixed with "leg_" are only meant for use with the hopper leg prototype #1 (note that leg #2 is not supported). The other scripts are more general and can also be used for other applications.

Besides of that, there are two types of scripts. Passive ones and active ones. The passive ones only listen for messages but do not run the motors. Therefore it is always save to call them. Active scripts do enable and run the motors. Be careful when calling them.

General Scripts

get_motor_info.py

Passive

Receive data from the board (status, motor current, position, etc.) and print it in the terminal.

read_optoforce.py

Passive

Receive data from the OptoForce sensor and print it in the terminal.

measure_msg_freq.py

Passive

Measure the frequency with which messages are received. Expects an arbitration ID as argument (i.e. only analyses messags with the given ID). Example:

measure_msg_freq.py 0x030    # measure frequency of position messages

position_ctrl.py

Active

Basic example on how to run a position controller for the motors. The angular position of the motors is given by the ADC inputs A6 and B6 (e.g. using sliders).

Takes as arguments the max. position (in mechanical revolutions [mrev]) and the gains of the PID controllers of both motors:

position_ctrl.py  max_mrev  Kp1 Ki1 Kd1  Kp2 Ki2 Kd2

velocity_ctrl.py

Active

Velocity controller for motor 1. The velocity reference is given via a slider that is connected to ADC A6. The script takes as arguments the max. velocity in krpm followed by the control gains of the PI controller:

velocity_ctrl.py max_speed P I

Leg-specific Scripts

The following scripts are only meant to be used with leg prototype #1.

leg_calibrate.py

Passive

Run this before using any of the other scripts.

Calibration procedure to determine the offsets that are used for position initialization. You are asked by the script to manually move the leg joints in positive direction until the stop and press enter while holding them there. Afterwards move the leg to the zero position (fully stretched) and again press enter.

The offset between stop and zero is automatically stored to a file "calibration_data.p" in the working directory. This file is loaded by the other scripts for the position initialization.

leg_init_position.py

Passive

Demo on how to do the position initialization. Like during calibration you are asked to manually move the joints to the stop and press enter.

When done this script starts to print the current joint positions to the terminal. This way you can verify that the calibration was done correctly (both joints should be at zero when the leg is stretched).

leg_compute_kinematic.py

Passive

Demo on how to compute forward and inverse kinematics for the leg. In each iteration the script prints:

  • the angular position of the joints
  • Cartesian position of the foot based on forward kinematics
  • again the angular position of the joints based on inverse kinematics

This is useful to check if forward and inverse kinematics are computed correctly.

Ambiguities in the inverse kinematics are solved by always using the solution where the knee points leftwards.

leg_move_sine.py

Active

Move both joints based on sine functions. The foot should move up and down on a vertical line while the knee moves on a horizontal line.

leg_foot_pos_ctrl.py

Active

Control the position of the foot. There are two modes: "slider" and "jump".

While the leg is moving, some data is logged and written to a file "logged_data.txt". Use the script leg_plot_logged_data.py to plot it.

Slider

When called with the argument "slider", the position of the foot can be controlled via sliders.

The sliders have to be connected to the ADCs A6 and B6 of the board. The A-slider sets the vertical position of the foot, the B-slider the horizontal. For the initial position (leg fully streched) set the A-slider to 0 and the B-slider to half of its range.

Jump

When called with the argument "jump", the foot will move to a slightly crouched position. As soon as it touches the ground, the leg will slowly crouch down and then immediately straighten the leg to jump. This is repeated over and over again.

In this mode touchdown detection is done by computing the force on the foot based on motor torques. Different gains for the PD controller are used depending on if the leg touches the ground or not.

leg_plot_logged_data.py

Passive

Plot data dumps from leg_foot_pos_ctrl.py.

The filename can be given as argument. Default is "logged_data.txt".