Variable Speed Treadmill for Studying Neonatal Rats

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Rat track logo.png
  • Nathen Schiele/ University of Idaho
  • Michele Brumley/ Idaho State University
  • Team Name Rat Pack
    Duration Fall 2018 - Spring 2019
    Faculty Adviser Dev Shrestha
    Mentor Jacob Miller

    Team Members
    • Colin Burkhalter, ME
    • Mitchell Williams, ME
    • Stephen Schoonen, BE
    • Stuart Sater, BE

    The goal of the project is to design, build, and evaluate a variable speed and variable incline treadmill for exploring the impact of locomotor activity on the development of motor control and musculoskeletal tissues. For a video introduction, follow this link

    Problem Definition[edit]


    Murine models are routinely used as an alternative to human testing for a variety of applications. Often an exercise factor is introduced to evaluate its influence in behavioral and physiological changes. Accordingly, many medical research supply companies offer commercially available, variable speed murine treadmills including the Omnitech AccuPacer, Colulbourn Treadmill, and Maze Engineering Treadmill. All these products are very cost prohibitive which prevents any poorly funded or newly-established labs to conduct murine studies involving exercise. Another limitation is the lack of a transparent belt design which is imperative for comprehensive gait tracking. While products such as DigiGait use a transparent belt, they integrate uncustomizable, proprietary gait tracking software and lack other customary features including incline adjustment. Furthermore, all available products were designed for use on fully grown subjects and lack important design considerations required for use in developmental studies. These considerations include small form factor, external controls for use in an incubator, and lower operational speeds. Therefore, Rat Track was developed using off the-shelf components and open source technology which offers customization, local construction, and lower costs. Rat Track also provides additional features and design considerations for use in gait tracking of developing murine models.


    The client has listed the project requirements in order of priority. It is anticipated that all of the following requirements will be met.

    HIGHER Priority

    • Belt size: ~12 cm width x 20 cm length
    • Belt material that could be wiped off and cleaned, will not tear easily, and possibly be replaceable
    • Variable speed control ranging from 0.5 cm/s to 15 cm/s
    • User friendly interface for speed control – preferably developed in an open-source software program or via microprocessor
    • Treadmill will be operated in temperatures from 25 to 35 degrees Celsius
    • Removable transparent walls and bumpers

    MEDIUM Priority

    • Variable ramp/incline angle from 0 to 15 degrees.

    LOWER Priority

    • Automatic timer
    • Safety features including emergency stop button
    • Transparent belt and housing for video gait analysis (video camera mounted below the belt)
    specifications matrix

    Progress Tracking[edit]

    Ratpack schedule.png


    The allocated budget was $2000

    Total Spending

    Design Considerations[edit]

    Incline Mechanism

    Ratpack Automatedassembly.gif
    Ratpack Manual assembly.gif

    Automatic Incline

    • Precise angle adjustment
    • Can be adjusted remotely
    • Provides active feedback through software
    • Allows surplus in lifting power for future design changes

    • Expensive linear actuator $140
    • Added complexity

    Manual Incline

    • Requires no user electronic interaction
    • Quicker response time
    • Simpler

    • Difficult to adjust in incubator
    • Less precise
    • May require tools to operate

    Motor Type

    Ratpack DC.png
    Ratpack stepper.png

    DC Motor

    • Less noise and shaking
    • With encoder it can be easily controlled
    • Smoother, continuous motion
    • Lower torque
    • May require more coding to maintain steady speed
    • Difficult to monitor speed without encoder

    Stepper Motor

    • Precise speed/position control
    • Relatively simple to program
    • Maintains constant speed with varying load

    • Noisy
    • 'Choppy' motion at lower speeds
    • High vibrations at low speeds

    Control Interface

    Ratpack touchscreen.png
    Ratpack buttons.png

    Touch Screen

    • Highly customizable
    • Easy to clean
    • Easy to understand
    • Sleek

    • Expensive, $50-$70
    • Relatively small screen/text
    • Potential for mis-selections


    • Simple to operate
    • Robust, solid controls
    • Low cost, ~$20 for all components

    • Potential for loose wires
    • More difficult to clean
    • Not as sleek

    Belt Material

    Clear PVC vinyl in 20, 30, and 40 gauge

    Preliminary Design

    Rat pack Main Assembly.PNG
    Angled Up.PNG
    Ratpack dissassempled design.PNG

    Project Learning[edit]

    Lab Tour
    Tour of Dr. Martins Lab to learn more about motor types and linear actuators. See full tour report here File:Ratpack martin lab tour.pdf

    Linear actuator used in a pump
    Stepper motor used in a pump

    Control Interface
    Research of different options for control interfaces. See control interface report here File:Ratrack userinterface.pdf

    Example of a touchscreen interface

    Final Design[edit]

    Overall Design
    Rat Track consists of a transparent belt elevated above a platform where a motion tracking device or camera could be placed. The belt surface can be inclined between zero and fifteen degrees and is driven by a stepper motor that can operate at speeds between 0.5 and 15 cm/s. Above the belt surface is an acrylic enclosure for containing the subject and facilitates gait tracking from the sides and front. The control box houses the majority of electronics including an intuitive touchscreen interface for setting the time and speed of the treadmill. Furthermore, the control box is separate from the treadmill and can be operated outside of an incubator or other controlled environment.
    • Incorporates simple design and widely available components for easy replication
    • Includes design considerations for use with smaller, younger subjects
    • Costs a fraction of what commercial options cost

    Control Interface
    Items Description
    Belt Tension Mechanism
    A threaded tensioning device will be implemented to ensure that the belt remains in tight to the rollers and provides a flat surface
    Belt Prototype
    The belt is made out of marine grade PVC clear vinyl and will allow for video based motion tracking from underneath. The belt can be easily replaced and cleaned.
    DC motor to power treadmill

    A stepper motor will power the treadmill at a large range of desired speeds

    Touchscreen UI

    An intuitive touchscreen user interface allows the user to control the speed, set a timer, and start or stop the treadmill.

    Containment walls/bumpers

    Acrylic walls will keep subjects from falling off the treadmill and allow video motion tracking from the side. They are also easy to clean.

    Inclination Mechanism

    Inclination angles can be adjusted to a range of 0 to 15 degrees, although the device will be optimized for 0 degree operation

    Wiring Schematic

    Wiring Schematic

    Arduino Code

    File:Arduino code.pdf


    As specified by our client, the Rat Track had to operate with linear speeds of 0.5 to 15 cm/s, with a resolution of 0.1cm/s. The formula used to control the stepper motor delay based on desired linear velocity was a function of the steps per revolution (controlled by the DM320T Stepper Driver) and the radius of the treadmill’s drive roller.

    The 106 converts the delay in seconds to delay in microseconds used in the Arduino code. However, initial tests showed that at speeds above about 12cm/s (i.e. where the delay in microseconds became smaller, and thus required more precise timing from the Arduino) were less accurate than slower speeds. In order to verify these results and form a calibration equation, speed tests were filmed using a smartphone’s slow-motion video setting. These tests were analyzed in video editing software in order to count the number of frames it took the treadmill belt to travel a set distance, marked with pieces of tape.

    The exact time taken to travel the distance between the markers was found by dividing the number of frames by the framerate (in frames per second) of the camera.

    Velocity in centimeters per second was then calculated by taking the distance between the tape markers (measured in centimeters) and dividing by the time.

    Multiple trials were run over a wide range of velocity values. The results were then plotted to find a line of best fit. The equation of this line is the calibration equation used by the Arduino to get accurate results within 0.04 cm/s. The equation already factors in the steps per revolution (800 steps) and the radius of the drive roller shaft (1.11125cm).

    Test run start position, 0 frames have passed
    Test run end position, 888 frames have passed
    Calibration data results from speed trials

    Team Members[edit]

    Ratpack colin2.JPG
    Colin Burkhalter

    Major: Mechanical Engineering
    Hometown: Hauser, Idaho
    Graduation Date: May 2019
    Future Goals:Work for the defense department

    Ratpack stu.jpg
    Stuart Sater

    Major: Biological Engineering
    Hometown: Sandpoint, ID
    Graduation Date: 12/15/19
    Future Goals: Research and development of medical imaging devices

    Ratpack stephen.PNG
    Stephen Schoonen

    Major: Biological Engineering
    Hometown: Idaho Falls, ID
    Graduation Date: 12/15/19
    Future Goals:Further my education by attending medical school

    Ratpack mitch.jpg
    Mitchell Williams

    Major: Mechanical Engineering
    Hometown: Coeur d'Alene, ID
    Graduation Date: May 2019
    Future Goals:Secure a job in the manufacturing Engineering field

    Additional Documentation[edit]

    Meeting Minutes

    File:Minutes all ratpack2.pdf


    File:Ratpack design review presentation.pdf

    File:Design Release Presentation.pdf

    File:Expo poster pdf.pdf

    File:EXPO Rat Track Presentation.pdf

    Client Interview

    File:Ratpack client interview.pdf