P17201: TigerBot VII: The Force Awakens
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Detailed Design

Table of Contents

Team Vision for Detailed Design Phase

The primary goal of this phase is to complete the detailed design of TigerBot 7, as well as, preliminary proof of concept prototypes to allow for easier implementation of concepts in MSD II.

Mechanical

Electrical

Progress Report

Electrical

Mechanical

Electrical Designs

Power Topology

Power for Tigerbot is drawn from the main.The main supplies both TEKNIC power supplies, the Odroid, and both USB hubs. There is a power board on each limb consisting of three INA195 current shunt monitors. There is a 75V to 5V LM5017 buck converter. This is shown in the schematic below.

Current Measurement

The INA195 current shunt monitors are placed in series with the power line that supplies each motor. There are three sensors in each limb. The INA195 can handle -16V to 80V. The output signal is fed to a Teensy for the feedback loop.

75v to 5v Buck Converter

A LM5017 buck converter is on each power board. The board takes in 75V and converts it to 5V to supply the encoders and transceivers. The board is still being configured for the correct settings. The buck converter is shown below under schematics.

Clearpath Integration Design

The clearpath motors require four control signals from the Teensy: A, B, Motor enable, and PWM. A and B dictate the direction of motion. Motor enable acts as an on/off switch for motor movement. The PWM signal controls the rate at which the motor turns based on its set frequency. All signals for clearpath motors are supplied by the Teensy and shifted through a transceiver.

Encoder Integration Design

The encoders are supplied by the 5V rail from the buck converter. The encoder takes in four data signals, SCLK, SSel, MISO, and MOSI. SCLK, MISO, and MOSI are all attached to each encoder and the Teensy. Each encoder has its own SSel that allows the Teensy to select which encoder to communicate with.

Force Load Cell Design

The four force load cells in each foot will transmit output data through a differential amplifier. The differential amplifier shown below shift the output voltage from 2.87V - 2.98V to 0V - 3.3V. The shifted output is fed into four Teensy analog ports.

High Level Schematic

High Level Schematic

 Power Board

Power Board

Buck Converter

Buck Converter

Motor Control

Motor Control

I2C Interface

I2C Interface

Encoders

Encoders

Force Load Cells

Force Load Cells

Teensy Interface

Teensy Interface

Refined IMU ROS topics

Refined IMU ROS topics

ROS topics and code concerning the IMUs were developed using two libraries: i2c_imu and RTIMULib2-Teensy. Something to note is that since the IMUs used are all the same (the Adafruit 9DOF IMUs), they will have the same I2C addresses. The Teensy has two i2c busses available however, so two IMUs per Teensy will keep this from being a problem. If more IMUs per Teensy later becomes required, an i2c multiplexer could be used to give them different addresses.

Example of IMU data

Example of IMU data

This data comes from using the RTIMULib2-Teensy library.
Flowchart of motor control using the Teensy

Flowchart of motor control using the Teensy

This shows the theoretical process for the Teensy to control a motor. It uses the encoder for feedback, but other sensors could be used as well.

Mechanical Designs

Over the course of the semester, countless hours have gone into the design and iteration of a humanoid robot. This process has allowed the robot to grow in complexity in necessary directions to really allow for the intended uses be possible. As more time was spent working with the designed model, compared to other industry examples, there were elements that needed to be heavily iterated to generate a complete robot assembly that will allow its intended use.

This humanoid robot has been designed with the optimization of humanoid characteristics and cost in mind. This has allowed for the engineering requirements drive by our customer to be met, while maintaining a budget that was agreed upon.

This design focuses on the assembly of six assemblies (hips, thigh, knee, shank, ankle, foot) into a complete robot assembly. Each subassembly is a complex assortment of off the shelf components and manufactured parts allowing for the motion freedom needed for the tasks this robot will be placed in.

This robot was built with as many off the shelf purchased parts as possible, as this allows the design to have completed parts used which allows more time and attention paid to the overall system level design and issue mitigation. These components include ball bearing, fasteners, ball screws, linear slides, and universal joints.

Tendon Servo Mount Plate

Tendon Servo Mount Plate

Thigh Belt Motor Standoff

Thigh Belt Motor Standoff

Thigh Motor Tekmonic

Thigh Motor Tekmonic

Bill of Material (BOM)

Electrical

Electrical BOM

Electrical BOM

Test Plans

Electrical

Force Load Cells

Tools Needed: Force load cell, DC Supply, DC voltmeter, varying weights up to 130 lbs.

Install the FLC into a stable rig to measure voltage change. Verify that there is a change in voltage when force is applied to the FSR. Measure various weights. Weights tested - 0, 10, 30, 60, 80 110, 130.

I2C

Run write operation to I2C Device and capture both SDA and SCL on oscilloscope. Compare clock to data transmitted. Measure the first 8 bits transmitted to 9DOF in comparison to SCL and record correct data transfer. Measure the returned 8 bits transmitted to the Teensy and compare to SCL.

Functional Test - Run data transfer to Teensy 200 times. Record number of times packets lost/data returned. If data transfer between two devices works, test rotation along the x, y, and z axes. Record actual to expected output for 1 degree increments. The 9DOF I2C device has been tested for both packet loss and repeatability. No additional support circuitry required.

SPI

Tools Needed: Teensy, SPI Encoder, Oscilloscope.

Connect SPI encoder to the 4 pin setup (MISO, MOSI, CLK, Enable) to the Teensy. Send packet to SPI encoder asking for current position. Record both CLK and data transferred. Compare timing of data packets to the change of the clock. Compare data returned to clock. Check the alignment of timing to clock to data returned. If both sent and received data align with clock, measure the output of the encoder in the serial monitor. Test changing the angle of the encoder for precision of the output. Set a new home position for the encoder and repeat the precision testing. Record results and measure sensitivity.

No additional support security required.

Teensy ROS Communication Limitation Assessment

Goal: Determine the limits of speed of communication between the Teensy and ROS, and what speeds would then be ideal.

Metrics:

-Control Variable(s)

-Port baud rate

-Message publishing rate

-Publisher and subscriber queue size

Success Criterion/Criteria: Teensy and ROS sends a heavy load between each other at a fast enough rate with no messages dropped and little latency.

Test Plan:

-Have the Teensy subscribing and publishing data similar to what it’ll be expected to do, like data from IMUs, current sensors, etc. ROS would then take that data and do complex math with it, while checking if messages have been dropped or if there’s significant latency.

-Adjust baud rate and other variables until message dropping and such appears, then adjust variables to next-fastest testing, and run communication for a significant length of time.

Mechanical

Overview

The intention is for validation of subsystem operation at the beginning of MSD II. Through subsequent testing of different subsystems; assembling the entirety of the robot should be straightforward and allow for idealized complete system testing. With the engineering requirements created from our customer revolving around a series of tests for complete robot design items, it is improbable and unlikely that testing can be conducted on the individual mechanical subsystems that would appropriately replace the complete system testing requirements.

Design and Flowcharts

With the continued design of the entire robot system, each subsystem (read "limb") is an element of the entire design. As seen by our images of the entire robot assembly, it does not add value to show each independent system for a testing plan.

Risk Assessment

MSD I Gate Review Worksheet

Link to document on Google drive

Plans for next phase

Phase Gantt Chart

Phase Gantt Chart

Detailed Gantt Chart

Detailed Gantt Chart

Electrical

Mechanical


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