Spring 2017 – Spiderbot – Torque Test

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Torque Testing

By: Shaun Pasoz

Electronics & Control Engineer

 

Torque testing allows the designer to see if a desired motor can output enough force to physically move a robot. To perform the test, a rig was designed in which the motor was clamped down with a fixed radius on the output shaft. Varying weights were then hung from the fixture using a very thin fishing line. This setup allowed for the force pulling the weight down from gravity to always be tangential to the fixed radius, allowing for simpler calculations of torque using the following formula:

τ=rFsin(θ)

 

The variables used to find torque are:

  • F = Magnitude of the force applied to the lever arm
  • r = Radius from axis to the point of applied force
  • θ = angle between r and F

 

Since the designed rig allows the force to always be tangential to the radius, the equation is simplified to τ=rF. To control the amount of force on the radius, the weights are used to continually increase the force. Therefore, the final equation for calculating the torque is:

τ=r*mg

 

The following tables show the data measured during the torque testing:

Motor: Sparkfun MicroGear Motor @5V
Mass (g) Current Draw (mA) Radius of Fixture (mm) Torque (Oz-In)
0 32.7 1.50 0
250 38.5 1.50 0.520
300 40.8 1.50 0.625
500 44.5 1.50 1.04
700 48.6 1.50 1.46
1000 55.1 1.50 2.08

Table 1: Sparkfun Torque Testing Data

 

Motor: Pololu MicroGear Motor @3.3V
Mass (g) Current Draw (mA) Radius of Fixture (mm) Torque (Oz-In)
0 40.1 1.50 0
500 114.8 1.50 1.04
700 128.5 1.50 1.46
900 141 1.50 1.87

Table 2: Pololu Torque Testing Data

 

Figure 2: Torque vs Mass Graph

 

Since both the radius, and the angle between the force applied and radius, the relationship between torque and mass is going to be the same for both motors. Where they begin to differ is when the other parameters of the motor are observed. For example, the current draw of the Pololu motor was over double with a 700 gram load on it. This is because the motor has been chosen to run at 3.3V instead of 5V to accommodate the customer’s needs.

 

The SpiderBot’s expected mass is 700g. The required torque to move 700g was calculated to be 1.46 ounce-inch. Both motors have a stall torque well above that, and therefore should be able to safely move the SpiderBot.  

 

With the expected load, the Pololu motor RPM was calculated at 44 RPM. This was found by putting a piece of tape on the radius and counting the revolutions for 30 seconds three times and taking the average. Repeating the process for the Sparkfun motor; it’s RPM was calculated as 33.3 RPM. Some possible deviations may occur as possible sources of error include: neglecting the weight of the weight of the fishing line that pulled the weights, and not including the various friction points in the calculations. Overall, the motors should be able to move SpiderBot without damaging the 3DoT or our PCB.

Spring 2017 BiPed – D.C. Motor Stress Experiment

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By: Abraham Falcon (Electronics and Control)

Approved By: Alexander Clavel (Project Manager)

Table of Contents

Introduction

Electronics and Control engineer job is to do an experiment on the D.C. motor to see if it can the handle the weight needed for the biped to walk. The following experiment was to determine if the chosen D.C. motor can handle the Biped’s total weight while one foot is off the ground and the other supports the entire system. The maximum stress weight of the Biped was chosen to be at 500 grams which is also what was used to determine out projects mass allocation. The test was also done to calculate exactly how much power consumption came from the D.C. motor and to determine if this would be acceptable to last up to the 30 minutes duration for the Pacman Game.

Experiment

 

Table of results:

Servo Motor Stress Weight Operating Voltage (Volts) Stress Current

(Amps)

Pololu 200:1 Plastic Gearmotor 500 grams 6 volts 100 mA

 

This experiment was done by hooking up the D.C.  motor to a battery rated at 6 volts and with a digital multimeter in series. The weight of 500 grams was attached to a custom-built pulley wheel that was attached to the shaft of the D.C. motor. Also the radius of the custom-built pulley wheel was measured out to be about 1cm.

Here is an example of the D.C. motor connection without the weight and you can see that with no load the D.C. motor runs at the highest of 62.289 mA

The setup from above picture was used but added a custom-built pulley wheel to the motor with a weight of 500 grams. The D.C. motor lifted the weight of 500 grams and the current was measured. From observation, this D.C. motor can handle the stress weight of the biped at 500 grames and the current was measured to be at its highest of 100 mA. All recorded results from this experiment is listed on the table of results above.

Here below are two pictures of the custom-built pulley wheel which was used for the experiment of Biped’s stress weight.

Conclusion

Performing this experiment, it showed that this Pololu 200:1 Plastic Gearmotor will allow for the Biped to be able to walk and also shows that for the current, the power consumption is low enough for the D.C. motor to be able to last for 30 minutes. This experiment concluded that this D.C. motor will work and it does fit our requirements for this Biped. In the references section, there is a video starting from 5:01 till 6:02 that shows how the custom-built pulley wheel was made and used for this experiment. The second reference was also a basing of the setup of this experiment to lift the weight and measure the current of the D.C. motor.

References

  1. https://www.youtube.com/watch?v=YGjBOsd9Z2g&index=2&list=FLoSP5pt7W0bsWc1xuJASmww
  2. https://www.clear.rice.edu/elec201/Book/motors.html

Spring 2017 Velociraptor: Servo Torque Test

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Table of Contents

Authors

By: Mohammar Mairena, Electronics & Control Engineer

Approved by: Jesus Enriquez, Project Manager

Introduction

The torque needed to move the different parts of the robot are specified by the Design and Manufacturing engineer. By testing the torque required at a specific location of the robot, one can prove the servo chosen will handle the stress placed at a certain location.

Analysis

Based on the measurements given by the Design and Manufacturing engineer, the servo placed at each hip will need to support 400 g at a horizontal position.

The experiment was done using a water bottle, HXT900 Micro Servo provided by Professor Hill, and a piece of string attached to the water bottle. The water bottle weighed approximately 408 grams, mimicking the weight that the servo (at the hip) will handle. The servo must rotate completely, without a stall under the 408 g load. The torque requirement at the hip was successful and rotated without a stall. Power came from the 3.3 V pin on the Arduino Uno and the current reading at 3.3 V came from the digital multimeter from the lab. At 3.3 V and under a 408 gram load, the HXT900 Micro Servo drew 180 mA of current.

Since the shaft radius of the servo is 2 mm and the weight of the water bottle is 408 grams, we can multiply them to get the Torque required at the hip. 2 mm converts to .2 cm, 408 g converts to .408 kg. Together, the torque required is .0816 kg*cm, which is equal to 1.13 oz-in.  

 

HXT900 Servo Placement Voltage Current Drawn Weight Torque Needed Shaft Radius
Hip 3.3 V 180 mA 408 g 1.13 oz-in 2 mm

 

 

Conclusion

It is important to note that at each hip, the servo will need to provide 1.13 oz-in of torque. As a result, the current drawn at each hip will be around 180 mA. Since the servos at the hips will only be used to make turns, the current drawn does not place much stress on the 3Dot battery. Max current output is 500 mA for the 3Dot Battery. The servos will not exceed the 500 mA limit.

Resources

  1. https://hobbyking.com/en_us/hxt900-micro-servo-1-6kg-0-12sec-9g.html
  2. http://www.rcuniverse.com/forum/giant-scale-aircraft-3d-aerobatic-110/2197950-how-do-you-test-servos-torque.html

Spring 2017 End of Semester Game “Pacman”

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By: Alexander Clavel

Apporved By: Game Committee

Table of Contents

Game Committee Members:

Amber Scardina – TRC President

Alexander Clavel – BiPed Project Manager

Nicholas Jacobs – Spiderbot Project Manager

Jesus Enriquez – Velociraptor Project Manager

Overview:

The BiPed and Velociraptor will participate in a game of PacMan. Both robots will start on opposite ends of a maze with the BiPed initially acting as PacMan and trying to avoid the other robot. The BiPed and the Velociraptor will attempt to collect as many “dots” or points as possible within the allotted time limit. The Velociraptor will initially act as the “ghost” and try to catch Pacman before the end of the game while also collecting points. The game will start once the Spiderbot has reached its position and begins video feed. The game will last a maximum of 30 minutes.

Rules:

–   Spiderbot will walk into the maze and then place itself above the maze for video set up

–   Biped will start off as “Pacman” while the velociraptor starts as the “ghost”

–   Both robots will start in different ends of the maze

–   There will be red dots on the ground which will be “counted” and displayed on both robots as they pass over a dot.

–   If the Velociraptor reaches and “eats” the BiPed before the 30 minutes then the raptor wins

–   If the Velociraptor does not “eat” the BiPed then the winner will be determined by who has the most dots counted.

–   There will be special grid squares to make the velociraptor vulnerable to being “eaten” and will reverse the rolls

–   If the BiPed can reach the velociraptor within the time limit then the velociraptor loses.

–   Live aerial video feed will be provided by the Spiderbot

–   Time limit of 30 minutes OR when the ghost catches Pacman OR when one group reaches 5 dots first.

–   If a robot falls over, that will count as a deducted point and they will start again at their starting area.

–   Points will be deducted at the end of the game by subtracting the endgame amount from the number of times the robot has fallen

View and Control:

–       BiPed and Velociraptor will view the gaming field through video feed provided by the Spiderbot

–       Both Robots will be controlled through the arxterra control panel

Terrain:

–       35 in x 56 in area

–       Flat paper taped across the tiled floor of the classroom

–       No physical walls

–       The Maze will be printed on paper

–       7 inch width for walkways for the robots

–       Roof with steel area for magnet and supports made of wood for the spiderbot height TBD

 

Game map to be updated , Dots to be added***

SpiderBot and Velociraptor Starting Point – Left Opening

BiPed Starting Point – Right Opening

Spring 2017 BiPed – Servo Ankle Stress Experiment

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By: Abraham Falcon (Electronics and Control)

Approved by: Alexander Clavel (Project Manager)

Table of Contents

Introduction:

Electronics and Control engineer job is to do an experiment on the servo motor to see if it can the handle the weight needed to perform the funtion of turning at the ankle. The following experiment is to know if the chosen servo motor can handle the Biped’s weight. The stress weight of the Biped was chosen to be at 500 grams as to be the maximum weight, but our actual weight should be lower than this. The experiment is also to see if the power consumption of the servo will exceed our maximum of 500 mA.

Experiment:

Table of results:

Servo Motor Servo Location Stress Weight Operating Voltage (Volts) Stress Current

(Amps)

HXT900 Micro Servo Ankles 500 grams 3.3 volts 270 mA

This experiment was done by hooking up the servo motor to the arduino and the digital multimeter in series. The weight of 500 grams was attached to a servo plastic gear with a radius of 1cm.

 

Here is an example of the servo connection without the weight and you can see that with no load the servo runs at the highest 71.961 ma.

The setup from above picture was used but added the weight of 500 grams. To simulate the weight of the ankle from Biped weight the servo was put upside down and observed if the full rotation of the gear on the servo with the weight performs well. By observing the weight on this servo, it can handle the stress weight of the biped and the current was around 270 mA.

Conclusion:

The experiment was preformed and showed that this HXT900 Micro Servo will make Biped be able to turn on the ankles and the current shows that the power consumption is under 500 mA. This experiment concluded that this servo will be effective for the ankles to turn. In the references section shows a video of the servo torque test of this type of servo chosen and this was a guide to perform this experiment.

Referrences:

  1. https://www.youtube.com/watch?v=dCgiE0xpToI&index=11&list=FLoSP5pt7W0bsWc1xuJASmww&t=168s

Encapsulation Trade Off Study

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By Edgardo Villalobos

Study on types of solar cell encapsulation.

 

Table of Contents

PLEXIGLASS

Plexiglass provides a lightweight, about 3 lbs per 8 sq. ft. with a 0.065 thickness, anti-reflective surface and is classified as a scratch resistant surface. Although plexiglass is virtually impossible to break and scratch resistant, it can scratch much easier than glass. If this material is used to encapsulate solar cells, we’d be able to acquire it from Home Depot or other similar store. This glass would then be used to cover the entire panel. To get the right shape out of the glass, we could use a dremel grinder to cut to size. The size of the glass would be the same size as the panels, which still need to be measured. The downside to using plexiglass is that each solar cell needs to be sandwiched using other materials, such as resin, which costs more.

 

Source:

[1]Plexiglass

http://www.plexiglas.com/export/sites/plexiglas/.content/medias/downloads/sheet-docs/plexiglas-optical-and-transmission-characteristics.pdf

[2]Materials

http://sinovoltaics.com/learning-center/materials/ethylene-vinyl-acetate-eva-film-composition-and-application/

[3]Materials

http://www.dunmore.com/products/solar-back-sheet.html

 

EPOXY COVERED SOLAR CELLS

Solar cells could be bought already encapsulated with a UV resistant epoxy and are usually meant to charge phones. Each cell is independently encapsulated making it easier to remove and add new cells. These cells are also polarity based, which could require wires instead of tabbing wires, also making it easier to switch cells. Using these cells would cost about the same as buying all the materials, using the plexiglass sandwich method.

 

Source:

[1]Array

http://www.samlexsolar.com/learning-center/solar-cell-module-array.aspx

Chassis Fritzing Diagram

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By Renpeng Zhang

Fritzing Diagram for Chassis.

Diagram

Description

Based on the interface definition, I created the fritzing diagram for the chassis part of the pathfinder. It consists of the Arduino Leonardo with two HC-SR04 ultrasonic sensors. It has the HC-05 bluetooth module connected to the Arduino through the TX and RX pins for the communication through a phone using the Arxterra app. Two servos is connected to the Arduino for the control of the pan and tilt of the rover. Two PCA9685 I2C expander were used for extra digital PWM and analog input pins. The VNH2SP30 motor driver is connected to the I2C expander and it’s used to control the speed of the motors. The built in current sensor of the motor driver is connected to the analog input of the Arduino for the monitoring of the current going through each motor. Battery was connected to power the motor drivers.

Spring 2017 BiPed – PCB Schematic

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By: Abraham Falcon (Electronics and Control)

Approved by: Alexander Clavel (Project Manager)

Table of Contents

Introduction:

Electronics and Control engineer is to create a custom PCB and to layout the components to be used. The PCB components are a PCA9685 PWM expander, pin headers for the LEDs and a pin header for the color sensor.

 

Eagle Cad Schematic:

The Biped PCB schematic below shows what the main components are to be use with the 3Dot board, which is the color sensor and a LED counter.

This PCB schematic is the third version and to be used on the Biped mainly for the game. Previous PCB schematics had two extra servos from the main design of the biped. As we moved forward with the design of the Biped, the customer stated that the power was the be supplied without an external battery. Power should soley be provided by the 3Dot board battery. The servos were eliminated to reduce the power consumption and therefore the PCB schematic above is the final version to be used with the 3Dot Board.

The PCB needs to communicate with the 3Dot board and the PCA9685 PWM expander will handle this. The PCA9685 PWM expander handles multiple PWM pins as the 3Dot board does not provide. Connecting multiple devices to the PCA9685 PWM expander will communicate to the 3Dot board through the I2C bus.

There will be two LEDs for the Biped to represent the eyes that are colored red and signify that the robot is indeed on. The other LED which is green is to represent a counter for collecting colored dots from the “end of semester” Pacman Game. All the LEDs connect with a 1k Ω to PWM expander, which these resistors are to limit the amount of current going through the PWM expander for protection. The LEDs are not physically connected to PCB board therefore it will use pin headers so the LEDs can freely be placed anywhere around the Biped.

For the Biped to sense the color dots from the game it will be using a Adafruit RGB Color Sensor and this sensor will also not be physically connected. The colored dots are placed on the floor therefore the color sensor must be placed on the foot to sense the color dots. The pin headers have the connection needed to connect to the 3Dot board and be powered by it. The pin headers connect to the I2C bus from the 3Dot board, which are SDA and SCL. Also from the 3dot board the power and ground can be connected to the sensor provide from 3Dot board connection. The pin headers are placed so that the color sensor can freely be placed anywhere on the biped and for this design we chose it to be on the foot.

The other components on the PCB schematic were provide from the product website, where they also provided Eagle Cad files. All the components are surface-mount devices. These components were left alone as the product works with it.

Conclusion:

The completed PCB schematic is simple but pushed our design to have less power consumption and to participate in the “end of semester” Pacman Game. The completed PCB Schematic is sent to the manufacturing engineer to layout the PCB and to be completely assembled.

Referrences:

  1. http://www.mouser.com/ProductDetail/NXP- Semiconductors/PCA9685PW118/?qs=sGAEpiMZZMvKM5ialpXrmnWDpPMxsdrM
  1. http://www.mouser.com/ProductDetail/Broadcom-Avago/HLMP-3301/?qs=sGAEpiMZZMsx4%2fFVpd5sGeS9q14uN1KF
  1. http://www.mouser.com/ProductDetail/Broadcom-Avago/HLMP-3507/?qs=sGAEpiMZZMsx4%2fFVpd5sGbU8v9L8Znih
  1. https://www.adafruit.com/products/1334

Solar Cell Current Sensing

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By Edgardo Villalobos

Custom PCB created by combining two INA3221 into one board.

 

Table of Contents

INA3221

 

Original Eagle CAD

 

Custom PCB with 2 INA3221

 

 

Three INA219 = One INA3221

 

Description

The INA3221 is a three-channel, high-side current and bus voltage monitor. It contains the setup of 3 INA219 single-channel, high-side current and bus voltage monitor.

 

Setup

The solar panel on the pathfinder rover contains 6 different panels with 6 solar cells on each panel that are setup in a certain way in series and parallel to get an output of 18 volts and 200 milliAmp from each of the panels to get a total of 18 volts and 1 amps. To test the current flowing through each of the 36 cells, we are going to use the INA3221 current sensor. As described in the INA3221 datasheet, this sensor senses current on buses that can vary from 0V to 26V. Because the INA3221 is three channels, it only measures the current running through 3 inputs, meaning we’ll need 2 per panel. The original Eagle CAD PCB layout was modified in order to get a total of six inputs that will match up perfectly with the 6 cells on each panel, meaning we will only need 6 boards as opposed to 12.

Since the these sensors can only have 4 addresses, I2C multiplexers are required.

Parameters

 

References

http://www.ti.com/product/INA3221/description

http://www.ti.com/lit/ds/symlink/ina3221.pdf

http://www.ti.com/lit/ds/symlink/ina219.pdf

http://www.switchdoc.com/wp-content/uploads/2015/04/INA3221BOB-042015-V1.0.pdf

 

Eagle CAD Files

https://drive.google.com/drive/folders/0B4jU8uMDmOoiU1dOM0tzSU1qeHM

  • Custom Eagle CAD Schematic: Current_Sensors.sch
  • Custom Eagle CAD PCB : Current_Sensors.brd
  • Original Eagle CAD Schematic : ina.sch
  • Original Eagle CAD PCB : ina.brd
  • INA3221 Eagle CAD Library : ina.lbr

 

 

 

 

 

 

Pick and Place – Updated Requirements and Mass Reports

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By: Chastin Realubit (Missions Systems and Testing)

Level 2 Requirements:

  • L2-1: Attached compartments shall not interfere with the functionality of the machine.
    • L2-1a: Wires shall be shielded or incorporate heat shrinks in all areas of the pick and place machine.
    • L2-1b: The RJ-25 cables shall be able to reach every operable part of the aluminum picking surface, while maintaining a standard of bend radii of 2 inches to prevent fatigue while running.
    • L2-1c: All microcontrollers, shields, electronics, and precision sensitive running gear shall be isolated from vibrational or other outside disturbances.
    • L2-1d: Compartments to house, wires, electronics, pumps, tape, and accessories will not occupy more space than half a foldable table.
    • L2-1e: The legs of the machine will be raised so that the cabinet can be placed.
    • L2-1f: The cabinet shall be used to hide the hardware (i.e. vacuum, Arduino, etc).
    • L2-1g: The cabinet should be formed using vacuform to make the machine look neat and professional.
    • L2-1h: The legs of the machine will enclosed with a material that can reduce the vibration of the machine to make it more accurate.
  • L2-2: The camera of the pick and place shall be used to incorporate edge detection technology (used as an alignment camera, the same as the Madell Pick and Place).
    • L2-2a: Pick and place shall incorporate edge detection to determine origins
    • L2-2b: Pick and place will have dedicated Arduino for camera system
  • L2-3: The Pick and Place will include video tutorial, written manual, sample test files.
    • L2-3a: Pick and place shall have detailed instructions on how to operate the machine through the software
    • L2-3b: Pick and place will incorporate LCD to make machine more user-friendly (Display status, component being placed etc.)
    • L2-3c: The user will be able to interface with the machine, and control the machine with an emergency power button.
    • L2-3d: The user manual should include a video to guide users on how to use it. (The video will show step by step how the user will interface with the GUI, where to download all software, and how to turn gerber file into cnc file.)
    • L2-3e: The manual will include a troubleshooting section that will help users fix the machine in case hardware was accidentally disconnected.
  • L2-4: The case should enclose the machine, and hold its weight in a manner of minimal movement when carrying.
    • L2-4a: The pick and place should be remained locked and secure to it location of setup.
  • L2-5: The machine shall be faster than human production time of 4 Hours.
    • L2-5a: Pick and place will incorporate the addition of eight additional servos
    • L2-5b: All part tape shall be managed and hassle free throughout the entire operational procedure of the machine.
    • L2-5c: All parts needed to create a 3DoT board shall be able to be picked and placed within tolerances of + or – 0.2mm.

Mass Report

Vacuum System Components Preliminary Mass (g) Uncertainty (%) Margin (±g) Expected Mass (g) Actual Mass (g)
Stepper Motor (A-Axis) 245.00 5% 12.25 245.00 247
Stepper Motor (Z-Axis) 245.00 5% 12.25 245.00 246
Vacuum Nozzle 2 5% .1 2 TBA
Z-Axis Actuator 292.00 5% 14.6 300 244.12
Detection Camera 3 5% .15 3 TBA
Project Allocation Experiment: The Z-Axis motor can still function after attaching 2000g as a load.

The vacuum will still need to be experimented on to see how much load can be placed on it.

So our preliminary allocation is 2000g
Total Expected Mass 795 g
Total Margin 39.35 g
Total Actual Mass TBA
Contingency  1165.65 g

 

Experiment:

Z-Axis Motor: We did an experiment to see the load that the Z-Axis can handle and we found that it will still carry up to 2000 g. This experiment was done so that we can see if the motor can still move up and down even with more load. This was needed because we are adding a camera on the Z-Axis and we needed the system to still function with extra weight.

Next steps:

We will now need to test the suction of the pump to check if it can carry the ICs that the 3Dot will require of us.

Power Report

Components Expected Current Draw (A) Uncertainty (%) Margin (±A) Measured Current Draw(A)
Stepper Motor (X-Axis) 1.35 5% .0675
Stepper Motor (Y-Axis) 1.35 5% .0675
Stepper Motor (Z-Axis) 1.35 5% .0675
Stepper Motor (A-Axis) 1.35 5% .0675  
Detection Camera .75 5% .0375
Display Screen .75 5% .0375  
Servo fs90r (12) .3 .05 .015  
Project Allocation 6 A (Calculated knowing that we will be using two Arduinos with separate power supplies)
Total Expected Current 3.15 A (The motors and servos will not run simultaneously)
Total Margin .36 A
Contingency 2.49 A