Propeller Arm Assembly Guide

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The Propeller Arm Sketch

Download the sketch for the propeller arm, 6310_PROP_22_23.zip.

The Propeller Arm in Action
The propeller arm demonstrating three PD controllers with different settings for the gains (Kp and Kd), different settings for the number of look-back steps for the derivative estimate, and different desired-angle stepsizes.
Propeller Arm Assembly

Please follow the instructions below to assemble the arm. You will be using the propeller arm for the several labs, so please assemble with care.

Calibrating the Propeller Arm

The Angle Sensor

Connect your laptop to the Teensy 4.1 and just the USB 5V supply (and NOT the large 5V 8amp supply) to the controller board. Download and unzip the Teensy propeller arm control sketch (link at top of page), upload the sketch to the Teensy 4.1, and then start the serial plotter.

Sensor Axle orientation

The angle sensor axle will correctly fit into the arm connector ONLY if the slit in the axle is aligned with the small outcropping in the connector. Unfortunately, there are two possible slit-connector alignments that fit correctly, and one mis-rotates the sensor axle by a half rotation. Watch the two videos and exam the figure below to learn how to ensure your angle sensor axle is correctly oriented in the connector.

The above two videos show the propeller arm motion and the serial plotter output when running the 6310_prop_22_23 sketch with the default settings, and with all the outputs in serial plotter "unchecked" except for Theta_m. Note that in the video on the left, when the arm is perturbed from horizontal, the measured angle jumps from -3000 to 3000 milli-radians, clearly indicating the angle sensor is incorrectly oriented. Before recording the the video on right, the angle sensor shaft was disconnected from the arm, rotated by one-half revolution, and reattached. As the video shows, With the correctly-oriented angle sensor, the measured angle changes smoothly with arm motion, from -300 to 150 milli-radians.

Angle Sensor Calibration

Setting Propellor Thrust Direction

Place your propellor control system on a tabletop (so that the arm has limited rotation), make sure your laptop is connected to the Teensy 4.1, and the USB 5V supply connected to the controller board. Then upload the sketch to the Teensy 4.1 and ONLY THEN connect the 5V 8amp supply to the controller board. Adjust the motor command in the Teensy sketch, as show in the figure below, so that the arm rotates clockwise.

Once you have verified that the arm angle sensor axle is oriented correctly, the sensor is calibrated, and the propeller thrust is in the correct direction, you are ready to start the LAB!

Leveling the Arm

Place your propellor control system so that the arm hangs off the edge of a desk or table (and can rotate freely, though be sure you've attached the purple over-rotation preventer is attached). prevlimit (so that the arm has limited rotation), make sure your laptop is connected to the Teensy 4.1, and the USB 5V supply connected to the controller board. Then upload the sketch to the Teensy 4.1 and ONLY THEN connect the 5V 8amp supply to the controller board. Adjust the motor command in the Teensy sketch, as show in the figure below, so that the arm rotates clockwise.