Spring 2016 3DOT Goliath, PCB Layout

/in , , , /by

By: Jerry Lui ( Manufacturing Engineer)

The general layout of the PCB was determined by the how sensitive the signal was, the specific wiring of IC’s to surface mounted components, and mounted surface area. Power input was placed away from sensitive signals and had a trace width of 32mm @ 1oz/ft^2 copper thickness (determined by the PCB house/fabricator) with a total temperature shift of 10C which allows total current of 1A. The trace thicknesses can be quickly determined by the following chart:

1

 

While laying out the board make sure to perform a DRC error check frequently. The included .DRU error checking file has generic limitations which may or may not adequately represent your fabrication houses’ design requirements (EagleCAD will always flag drill and VIA holes). The fabrication house will generally supply a .DRU file that can be used in place and will often allow traces to be placed closer together.

1

 

 

All of the signals were moved as far from the power input as possible in this case I have placed on the top left corner. The large power supply capacitor was also placed as close as possible to the power input and the rest of the circuit was laid out to take power from that capacitor. Also, components were placed similarly to how they were wired in the schematic as much as possible so that they are generally easier to follow and understand.

 

Note that there are red dotted lines (and blue underneath) along the perimeter that represent the ground polygon which is needed to create the ground plane (red for top layer, blue for bottom layer). The isolation width (free space between the traces and ground plane) was set to 12mils by default but was changed to 16mils as a precaution. This value is mainly determined by the fabrication house limits.

 

5

 

To place a trace on the other side of the board while you’re currently laying a trace (top to bottom) click on the middle mouse button. This will automatically create a VIA (electrically connected through hole) that connects both traces.

 

TIP: If you don’t create a ground plane first you can right-click on any GND signal and hide it. This will reduce the air-wires shown so that laying out the PCB will be easier. All GND signals will be hidden with this option but can be restored by typing “ratsnest *” in the command line.

 

TIP: Component values can be hidden by disabling the tValues layer. This makes it significantly less cluttered.

6

 

 

 

In the picture below, the ground plane has been created by hitting the “ratsnest” command. Pay close attention to capacitors during the ground plane creation. The “relief” option should be enabled so that the negative terminal can actually be soldered easily; this option is set on by default.

 

7

The mounting holes seen above were created using VIA’s. The size is determined by what screw or mounting system that’s planned on being used. In this case the size was set to 86.6mils or the standard inner drill size of a M2 screw.

 

Text such as the label “Goliath spr’16” can be placed using the “text tool” and should be placed on the tPlace or bPlace plane. Make sure to properly label components and the positive terminal, negative/ground terminal or both.

 

8

 

This is what the board will look like after being fabricated from OshPark.

9

Conclusion

Laying out a PCB can be time consuming depending on the amount of components on your board. Never use auto routing as the algorithm used is not that great. Remember to account for trace thicknesses, pin locations, and temperature limits for components.

 

 

Spring 2016 3DOT Goliath, Making Laser Tag Possible: The Receiver

/in , , , /by

By: Kevin Moran (Electronics and Control Engineer)

 

 

In this post I will be discussing my initial selection for the IR receiver and how I began testing its analog output.

 

Components:

 

Transistor: SFH 310 (Opto Semiconductor)

Resistor: 2M ohm

IR light

 

The phototransistor is a two legged transistor, with its third input being the output of the IR LED (Infrared Light).

  • When a light is shined, the electrons begin to diffuse from the emitter to the collector, this causes a voltage drop from its original 5V.
  • Unfortunately this signal is noisy and trying to use it directly for a game of laser tag would be very difficult. I present below the analog output of this transistor.

 

Arduino Plotter Graph:

 

1

 

 

Arduino Monitoring:

2

As can be appreciated from both the plotter and the monitor plots of the Arduino software, this analog signal is all over the place, the voltage drops varies depending on the distance of the LED from the receiver, and the length of time the light actually hits the receiver. Playing a game of laser tag with these results would not be very appropriate. The noise levels when no IR light is hitting the receiver are also shown on the Arduino plotter graph.

Note: The resistor value of 2M was chosen based on testing the sensitivity of the receiver with various values. 2 mega ohms turned out to be the best result

 

 

The code:

To read the analog voltage output

3

 

Eagle Cad Schematic:

4

 

 

 

Sources:

Jeff Cool: Division Manager

https://www.arduino.cc/

https://learn.sparkfun.com/tutorials/transistors

Spring 2016 3DOT Goliath, Making Laser Tag Possible: The Schmitt Trigger

/in , , , /by

By: Kevin Moran (Electronics and Control Engineer)

Since the analog output of the receiver is very noisy, my division manager suggested I use a Schmitt trigger which has 2 jobs:

 

  1. It reduces noise from the circuit through hysteresis, the time-based dependence of a system’s output on present and past inputs.
  2. It inverts the signal from the detector circuit and creates two thresholds-high and low. By changing resistor values we are able to control the high and low thresholds.

Below is the graph of a generic output using the Schmitt Trigger, as can be seen the signal is inverted, and the noise is relatively gone.

 

post

 

Now the challenge was selecting the correct Schmitt trigger that would work best with our receiver, after testing various resistor values, I made my choice between two sets of resistors.

2

I decided to go with the resistor values from Trigger 1, because It has a larger gap between the high and the low thresholds. When tested with the Phototransistor it provides a low threshold closer to 0 voltage

All values were taken with multi meter while changing the input voltage

Note: The high and low threshold change when the Resistor value connecting the receiver is changed from 100k ohms to 2M ohms (I did this in order to increase the sensitivity of the receiver)

 

Testing with Arduino Monitor:

  • When light is applied to the photo-transistor and the input is placed through the Schmitt trigger
    • High Voltage= 3.76 V
    • Low Voltage= 0.02 V

In order to make the phototransistor sensitive enough to be able to detect the IR light, I am using a 2 mega ohm resistor from the detector to the 5v supply

Both the high and low voltage thresholds are shown using the Serial Monitor

This is the result.

3

I also conducted a test on the Schmitt Trigger using a potentiometer

Components for this test:

10k potentiometer

LM358 Op-Amp

Resistors: 100k, 51k, 51k

Capacitors:  10 microF

Arduino Uno

The threshold between a high or low input from this test is 2.6V

As I varied the resistance in the potentiometer I obtained the graph provided in this slide

Based on this experiment I concluded that my Schmitt trigger was ready to be used alongside the photo-transistor.

4

 

Below is the result from this test using both the Arduino plotter and monitor

5

 

As can be seen again, a very clean signal that has only two outputs a low 0.02v and a high at 3.78v

 

Sources:

 

Jeffrey Cool: Division Manager

http://www.ti.com/lit/an/scea046/scea046.pdf

http://pcbheaven.com/wikipages/The_Schmitt_Trigger/

Spring 2016 A-TeChToP Seizure Watch PCB Layout

/in , /by

By Marena William (Manufacturing Engineer)

Overview

The 3D printed housing of the seizure watch will contain the PCB board which consists of the EDA sensor, accelometer, clock and the ATSAMB11. The electrodes’ wires will be connected to the EDA connector. Eagle CAD software was used to generate the PCB schematic and layout.

Read more

Spring 2016 3D SMD: Verification Test Plan

/in /by

By: Christine Vu (Missions, Systems, and Test)

Table of Contents

Purpose

Verification Tests will be conducted to verify the requirements based on the Verification Matrix.

Requirements for Verification Tests

Section 1 EE400D Assembly

The SMD pick and place machine shall pick up and place down all SMT components provided by any EE400D PCB up until the end of Spring 2016.

Section 1.1

Working area must be within 12.2”x15.35”(310mmx390mm) based on the Makeblock X-Y

Plotter Robot Kit.

Section 1.1.2

Surface to hold PCB shall be smooth with dimensions tolerances to be ±.001″, parallelism to .001″, and flatness to .001″ (TCI Precision, 2005).

Section 1.1.3

All pick and place processes shall begin at the bottom left corner of the PCB.

Section 1.1.4

All wires using RJ25 connectors shall have a minimum bend radius of 4x its diameter (Telecommunications Industry Association, 2001).

Section 1.2

Pick and place SMD machine shall change the orientation of each SMT component before placement.

Section 3 Software Design

Software for the SMD pick and place shall accept all EAGLE PCB files of EE400D projects up until Spring 2016.

Section 3.1

Software shall translate all EagleCAD files from EE400D PCB’s to G-Code files.

Section 3.1.1

Software shall include all x-, y-, and z-coordinates for SMD pick and place machine to read.

Section 4 Reel Feeder Design

The SMD pick and place machine shall have four 8mm reel feeders and one IC tray.

Section 4.1

All SMT resistors and capacitors shall remain in cut-tape of the reel feeders until the vacuum nozzle is ready to pick up the component.

Section 4.1.1

All reel feeders shall be installed on the working area, 12.2”x15.35”(310mmx390mm).

Section 4.1.2

Bracket to hold cut-tape of the reel feeders shall be higher than 0.04″.

Section 4.1.3

All motors used to peel off cut-tape of reel feeders must rotate 360°.

Section 4.2

IC tray shall store all IC chips required for one PCB assembly.

Section 4.2.1

IC tray shall be installed within working area, 12.2”x15.35” (310mmx390mm).

Section 5 Vacuum Head Design I

SMT component size 0402 shall be the smallest component that the pick and place SMD

machine can pick up.

Section 5.1

Vacuum system shall be able to pick up all SMT components as small as size 0402.

Section 5.1.1

Vacuum nozzle shall be smaller than 0.02″ ± 0.002″.

Section 6 Vacuum Head Design II

ATmega32u4 chip shall be the heaviest component that the pick and place SMD machine can pick up.

Section 6.1

Vacuum suction pad shall be smaller than 0.4″ ± 0.01″.

 

Summary of Verification

Verification tests will be conducted to reflect the requirements on the physical design of the SMD pick and place machine. A list of procedures will be presented in this document followed by the results and conclusion.

Verification Matrix

Verif_1

Verif_2

Verf_3

 

Verif_4

** Updated 4/29/16: Added new requirement section to consider the heaviest chip can be picked up. Dimension limitations were based on Atmel’s datasheet (2016).

List of Equipment

Applicable tools and software will be listed for each Verification test.

 

Verification Tests

EE400D Assembly

Working Area Test

Working area is defined by the area that includes  PCB to assemble, reel feeders, and IC tray. To verify that our design meets the size criteria for working area, a test will be conducted to calculate its parameters.

Requirements

Section 1 EE400D Assembly

The SMD pick and place machine shall pick up and place down all SMT components provided by any EE400D PCB up until the end of Spring 2016.

Section 1.1

Working area must be within 12.2”x15.35”(310mmx390mm) based on the Makeblock X-Y

Plotter Robot Kit.

Section 1.1.2

Surface to hold PCB shall be smooth with dimensions tolerances to be ±.001″, parallelism to .001″, and flatness to .001″ (TCI Precision, 2005).

Section 1.1.3

All pick and place processes shall begin at the bottom left corner of the PCB.

Section 1.1.4

All wires using RJ25 connectors shall have a minimum bend radius of 4x its diameter (Telecommunications Industry Association, 2001).

Section 1.2

Pick and place SMD machine shall change the orientation of each SMT component before placement.

Applicable Tools

Equipment Type Name (Brand) Tolerance
Mitutoyo S/N 12519090 Caliper 0.001”
Measuring Tape Stanley 33-425 Powerlock 25-Foot by 1-Inch Measuring Tape +/- 3%

Procedure

  1. Record the weight of the heaviest component.
  2. Calculate the required minimum diameter of the vacuum nozzle that the heaviest can be picked up.
  3. Test and measure the pressure.
  4. Attach the Z-Axis with pen attachment to the X-Y Plotter.
  5. Create an EAGLE PCB design by placing capacitors on each corner of the design. A free EAGLE version would allow 4” x 3.2”.
  6. Convert to GCode and send to Makeblock X-Y Plotter.
  7. After the sketch, measure the dimensions of the EAGLE PCB design.

 

Cable Test

A test will be conducted to determine that the bending radius will not exceed a bend radius of 4x its radius.

Applicable Tools

Equipment Type Name (Brand) Tolerance
Mitutoyo S/N 12519090 Caliper 0.001”

Procedure

  1. Connect the wires attached to the X-Axis and Y-Axis.
  2. Control the Y-Axis and move to the farthest end of the plotter with respect to the PCB until the limiting switch is hit. Record the length of the cable.
  3. Control the Y-Axis to the other side of the limiting switch. Record the bend radius as shown as the photo below.

CableTEst

Figure 1. (Wikipedia, 2007).

Product Competitiveness

Objective

To verify that our SMD pick and place machine is designed similar to an industrial machine, a test will be conducted to determine the precision of the SMT component placement.

Requirements

Section 2 Project Competitiveness

The SMD pick and place machine shall be modified from an XY Plotter to have the same error specification of Madell Corporation Model DP2006-2 (n.d).

Section 2.1

Makeblock XY Plotter motors shall be modified to pick and place with 0.002″ error tolerance.

Section 2.1.1

Resolution of all axes motors shall be less than 1.8°/step.

Section 2.1.2

Z-axis motor shall move the vacuum system at 90° with respect to the floor.

Applicable Tools

Equipment Type Name (Brand) Tolerance
Mitutoyo S/N 12519090 Caliper 0.001”

Procedure

  1. Record the length of the SMT component.
  2. On PCB, measure the distance between the centers of the capacitor/resistor pads. Record.
  3. Operate the pick and place machine by picking and placing the SMT component.
  4. Measure the distance between the SMT component pin and the pads.

Software Design

Objective

To verify Software design, a test will be conducted to verify the process of converting an EAGLE file to GCode in order to send it to the modified Makeblock X-Y Plotter Robot Kit to move. The Z-axis software will be modified to control as if it was an X-axis and Y-axis.

Requirements

Section 3.1.1

Software shall include all x-, y-, and z-coordinates for SMD pick and place machine to read.

Applicable Tools

GRemote Graphic User Interface (GUI)

Notepad++ Application

Equipment Type Name (Brand) Tolerance
Mitutoyo S/N 12519090 Caliper 0.001”

Procedure

A test for the X-axis and Y-axis motors have been conducted previously given an EAGLE file from G-Code.

https://www.arxterra.com/spring-2016-3d-smd-conversion-of-eagle-file-to-gcode-initial-process/

  1. Set-up Z-axis movement by attaching stepper motor to Z-axis structure.
  2. Connect stepper motor to Me Stepper Driver. Set switches to H H L (⅛ steps).
  3. Connect corresponding Me Stepper Driver to Port 10.
  4. Plug in Me UNO Shield and turn on switch to provide 12 V to stepper motor.
  5. Zero out Z-axis on GRemote GUI by entering “G92”.
  6. Measure initial height of Z-axis structure to the nearest 0.001 inches.
  7. On GRemote GUI, enter “Z100”.
  8. Wait until stepper motor stops running and measure the final height of the Z-axis structure to the nearest 0.001 inches.

“Z100” is a command that tells the Z-axis structure to move 100 mm when the Me Stepper driver is H H L. This procedure we will confirm the height difference of the Z-axis.

Reel Feeder Design

Objective

To verify the reel feeder design has the correct function, a test will be conducted to determine its parameters and design.

Requirements

Section 4

The SMD pick and place machine shall have four 8mm reel feeders and one IC tray.

Section 4.1

All SMT resistors and capacitors shall remain in cut-tape of the reel feeders until the vacuum nozzle is ready to pick up the component.

Section 4.1.1

All reel feeders shall be installed on the working area, 12.2”x15.35”(310mmx390mm).

Section 4.1.2

Bracket to hold cut-tape of the reel feeders shall be higher than 0.04″.

Section 4.1.3

All motors used to peel off cut-tape of reel feeders must rotate 360°.

Section 4.2

IC tray shall store all IC chips required for one PCB assembly.

Section 4.2.1

IC tray shall be installed within working area, 12.2”x15.35” (310mmx390mm).

Applicable Tools

Hardware:

Reel Feeder

Micro Servo FS-90

Equipment Type Name (Brand) Tolerance
Mitutoyo S/N 12519090 Caliper 0.001”

Procedure

Note: Photos will be attached and documented

  1. Install reel feeder to the aluminum surface. Attache reel with SMT components.
  2. Install the IC tray to the working area.
  3. Install micro servo to reel feeder bracket. Servo wheel shaft shall be placed at an angle of approximately 45°. Record Servo wheel angle.
  4. Attach Z-axis and move the X-Y-axis motors to a component. Measure the clearance around the Z-axis. Record the clearance tolerance, which includes the distance around both the reel feeder and IC tray. Measure the height of the IC tray.
  5. Operate the micro servo by turning 360°. This requires timing of the speed of the micro servo and must be determined in the Arduino Code. Record this time.
  6. Determine initial measurement of the reel on the reel feeder. Record this measurement
  7. With the cut-tape attached to the micro servo wheel shaft, reel in the cut-tape. The SMT components counteract this force by moving back.
  8. Observe the elevation of the reel feeder. Record the height of the reel feeder.
  9. Record the distance of the SMT components traveled.

Results Template

Angle of Servo Shaft Z-Axis Front (in.) Z-Axis Left side  (in.) Z-Axis Right side (in.) Z-axis Height

Vacuum Head Design

Vacuum Head Test

To verify the size of the vacuum nozzle design, a test will be conducted to determine that the size of the vacuum provides sufficient pressure to pick up an SMT component.

Requirements

Section 5 Vacuum Head Design

SMT component size 0402 shall be the smallest component that the pick and place SMD

machine can pick up.

Section 5.1

Vacuum system shall be able to pick up all SMT components as small as size 0402.

Section 5.1.1

Vacuum nozzle shall be smaller than 0.50 ± 0.05 mm.

Section 5.1.2

A solenoid valve for vacuum system shall keep a stable temperature under 160° F during Operation.

Section 6 Vacuum Head Design II

ATmega32u4 chip shall be the heaviest component that the pick and place SMD machine can pick up.

Section 6.1

Vacuum suction pad shall be smaller than 0.4″ ± 0.01″.

Applicable Tools

Equipment Type Name (Brand) Tolerance Level
Pressure Gauge Milton S921

http://www.acmetools.com/shop/tools/milton-s921

 +/- 2 psi

Procedure

  1. Determine actual mass of desired 0402 SMT component. Record under SMT component mass column.
  2. With a T-bracket, measure the pressure by connecting both ends of the vacuum tubing and pressure gauge.
  3. Turn on vacuum pump and measure pressure. Record the value under pressure column.
  4. Calculate the minimum required diameter using the equation below.
  5. Measure the diameter of the vacuum nozzle being used. Using the equation below, plug in the diameter size and calculate the maximum mass allowed.

VacuumPumpDecisionPNG

Equation 1. Obtained from (VMeca, n.d.).

IMG_20160414_163826 IMG_20160414_163852

Solenoid Valve Test

The purpose of this document is to verify that the solenoid valve can be used to control the the airflow of the vacuum system without overheating or damage to the vacuum tubing. Increased heat would affect the pressure within the tubing, thus could lead to errors in the operation of the pick and place machine.

References

Aquarium airline tubing is a Tuyau Standard type, which was found to operate at a temperature range of 86 ° F – 176° F (PennPlax, n.d. & Festo, 2016.)

Applicable Tools

Equipment Type Name (Brand) Tolerance Level
Thermometer Gun Fluke 561 Infrared and Contact Thermometer

http://en-us.fluke.com/products/thermometers/fluke-561-thermometer.html#techspecs

 ±0.5% of reading or ±1°C (±2°F), whichever is greater
12 Vdc Voltage Supply Makeblock Motor Pin connection provides approximately 12 Vdc. N/A
Multimeter Extech MN35 Mini Multimeter

http://www.amazon.com/Extech-MN35-Digital-Mini-MultiMeter/dp/B0012VWR20

 0.5 %

Preliminary Calculations

We will estimate how many times the solenoid valve should close when placing one part. We would have to time when the solenoid valve should open and close.

  • Close at PCB (discrepancy may be involved because the PCB locations vary, and the origin will be ignored because it will only be at the origin once. For the ease of this experiment, the opening and closing of the solenoid valve shall be at a minute by minute basis as shown in the calculations)
  • Open at Reel Feeder
  • Close back at PCB

Therefore, for one part to be placed, the solenoid valve must operate in 3 steps. The SMD pick and place machine estimates an assemble rate of 200 parts per hour.

200 parts/hour * 3 steps/part = 600 steps/hour

Convert to minutes:

600 steps/hour * 1 hour/ 60 minutes = 10 steps/minute

During our experiment, we will need to open and close the solenoid valve 10 times every minute.

Test Procedures & Criteria

  1. Connect the solenoid valve to operating voltage 12 Vdc. Solenoid valve should be open.
  2. Open and close the solenoid valve 10 times per minute for one hour.
  3. Every ten minutes, record the temperature of the barbed fitting hose. If the temperature goes higher than 176°F, turn off. (Tip: The temperature gun should record the temperature at the same area and distance to be consistent.)
  4. Measure and record the temperature of the solenoid valve to confirm that it is under 176°F +/- 10°F. under “Actual Final Temperature”.
  5. Cool the solenoid valve to room temperature and repeat one more time.

References

Atmel Corporation. (2016).  ATmega16U4/ATmega32U4.

URL: http://www.atmel.com/images/atmel-7766-8-bit-avr-atmega16u4-32u4_summary.pdf

Festo. (2016). Plastic Tubing, Standard O.D.

URL: https://www.festo.com/cat/en-gb_gb/data/doc_ENGB/PDF/EN/OD-TUBING_EN.PDF

PennPlax, n.d. Aquarium Decorations Betta Accessories Maintenance.

URL: http://www.pennplax.com/pennplax%20pdf/Aquarium-Decorations-Betta-Accessories-Maintenance.pdf

Vmeca, n.d. How to select the proper vacuum pump.

URL: http://www.servikatalogen.no/Katalogdata/pdf/200802-1-2-3.pdf

Wikipedia. (2007). Image of a Cable with Seven Meter Radius.

URL: https://en.wikipedia.org/wiki/Bend_radius#/media/File:Bendradius.svg

Yadav, A. , Mehta, S. , Sawant, S. , Pujari, C. , & Chaudhary, M. (2014). Pick and place robotic

system for assembly of thermostat radiator valve.International Journal of Engineering

Trends and Technology, 11(3), 111-113.

 

Spring 2016 A-TeChToP Central Sensor Suite PCB Layout

/in , /by

By Mimy Ho (Manufacturing Engineer)

Overview

The chest harness prototype of the central sensor suite will have the 3D printed case which contains a printed circuit board and a 9V battery. The PCB includes the Arduino Pro Mini, accelerometer, temperature sensors, ECG circuitry, pulse oximeter circuitry. The PCB supports and electrically connects all the sensors to the Arduino Pro Mini. The schematic and layout were generated by Eagle CAD software.

Read more

Spring 2016 A-TeChToP Critical Design Review

/in , /by

Posted By Cody Dunn (Project Manager)

This blog post contains the Critical Design Review presentations for both the Central Sensor Suite and Seizure Watch subgroups.

Read more

Spring 2016 Velociraptor: PCB layout

/in , /by

By: Mingyu Seo (Manufacturing & Design)

PCB Design:

For our design, we’ve started off by planning where our PCB is going to be mounted. Rather than placing it on top or inside the body frame, we’ve come up with mounting the PCB underneath the body to cover wires connecting all the components together. So, we have decided to mount the Arduino Micro as well as the accelerometer in order to minimize the number of wires connecting to the PCB. We decided to wire the Bluetooth toward the tail and the accelerometer on top to make sure it’ll be able to detect obstacles ahead.

Problems:

  1. The voltage regulator may cause too much heat.
  2. Minimum space to place all components
  3. Sensors mounted directly to the board must either be mounted so that they hang off the edge of the PCB, or the packages must be edited to include the physical shape of the device to avoid overlap of components.

Solutions:

  1. we will be using thru-hole heatsink method rather than PCB copper heatsink. Also by placing the voltage regulator to the corner, we will be using TO-220 Heatsink. 
  2. Due to very little space provided for PCB layout, we will have to make sure to place the power supply as far away from the Bluetooth, accelerometer, and ultrasonic sensors as possible.
  3. we have a 5.12cm x 4.8 cm PCB layout, which must incorporate Arduino Micro, Accelerometer, Bluetooth, ultrasonic sensor, 8 Servos. By placing all the sensors on one side, we will be able to mount the accelerometer off the edge of the PCB, and connect Bluetooth and ultrasonic sensor with a wire.

 

PCB Layout:

PCB layout FINAL 2

Finalized PCB layout

PCB layout FINAL

Finalized PCB layout Wiring

 

Spring 2016 Velociraptor: Material Trade-Off-Study Update

/in , /by

Requirements needed to fulfill:

  • Project Level 1 Requirement:
  1. According to the given course that the robot is to complete, the Velociraptor shall travel on multiple surfaces. Refer to course analysis for more detail.
  2. The Velociraptor shall be able to statically walk on all surfaces of the course
  3. The Velociraptor shall be able to dynamically walk on flat surfaces of the course.
  4. The Robot shall statically travel up a 6.5-degree incline according to the course analysis
  • Project Level 2 Requirement:

6. To maintain balance while performing static walking, a head and tail shall be implemented to the chassis of the           Velociraptor to even out the shifted weight when standing on one leg and           thus meet the Project Level 1, requirement

8. In order for the Velociraptor to travel on two different surfaces, the material that will be placed on the feet shall           have a coefficient of friction of more than 1.0 in accordance to the                      Course Analysis as to refrain from slipping,               and thus meet Project Level 1, requirement 3.

Actual experiments will be done to verify the feasibility of the design using our 2nd prototype.

Experiments:

  1. Material Trade – Off- Study:

a) First Experiment included the feasibility of using 3D filament Polylatic Acid (PLA) for our final robot. When we started building our 2nd prototype, including the head and tail, we’ve decided to distribute the weight of the body by placing the batteries toward the head and tail to put less strain on the servos. By using this design, we will be able to minimize weight of the chassis of the robot and use the weight of the head and tail to shift center of mass.

prototype

But putting more weight toward the head and tail, caused the bottom piece of the body that connects the head to start cracking which made us do a material trade-off-study to determine the right material for our robot.

 

material1

Trial using PLA filament

 

material2

Trial using Aluminum

 

The printing the bottom piece using the 3D filament weighed 13 grams compared to Aluminum piece which weighed 19 grams. This not only shows the feasibility of using Aluminum for our bottom piece to maximize the weight on the head and tail, verifying project level 2 requirement 6 to implement head and tail on the chassis to shift the center of mass to balance when it’s performing static walking.

 

b) The second experiment was conducted in order to verify the 3D filament PLA is feasible perform static and dynamic walking on various surfaces without slipping.

Level 1 requirement 6 states the robot should perform static walking on a 6.5 degree incline, so we’ve created inclines using various degrees to determine if the robot was able to balance and refrain from slipping at a minimum of 6.5 degrees. For our experiment, we started off by creating a slope from 4.5 degrees to 13.7 degrees and tested to determine the degree the robot starts slipping.  In order to create a similar static friction of the course, we have implemented a carpet on the incline. For experimental measurement, we’ve used a protractor to measure the angle of the slope, and for the theoretical measurement, we’ve used the length and height to calculate the slope:

inlcine

Both feet on Ground:

friction test chart 1

The chart above shows the acceptability of the 3D model, when we assembled the robot, it was able to stand with both foot on the ground up to 15.7 degrees without slipping or falling.

Figure 3b

Placed sideways on a 8.7 degrees incline, successfully balancing and refraining from slipping.

Figure 3a

Robot placed on a 8.7 degrees incline without slipping or falling.

 

 

One foot on Ground:

 

friction test chart 2

When the robot is performing static walk on incline, we’ve tested if it was able to balance on one foot without falling or slipping. As shown above, the experiment showed the robot was able to balance on one foot up to 9.7 degrees incline.

OLU 3a

By shifting the weight of head and tail toward the shifting leg, the robot is able to stand on one foot as if it’s performing static walk. It’s able to stand on a 8.7 degrees incline without slipping nor falling.

 

Conclusion

Using a thicker material for the bottom piece will not only increase printing time, but also create less space for our components to fit. But by using Aluminum for the bottom piece of the body to hold the head and tail, not only will it be able to hold up to 483 grams but also we will be able to keep enough space in the middle to mount the PCB. The test to verify the material used to refrain the robot from slipping have been successful. The robot was able to stand on both feet and on one foot up to 9.7 degrees without slipping. When the robot has to stand on an incline of more than 10 degrees, we will have to reconfigure the robot’s ideal standing position to slightly lean forward in order to make sure the center of mass stays in the middle of the robot’s body.