Our project, RoSco, has been a struggle throughout the semester. This document is a testament to our willpower and determination.
Robot Scout Rover (RoSco 2015)
Gary Fong (Project manager/Manufacturing )
Youssef Al-Shanti (Mission, Systems, and Test)
Will McKinney (Project Manager/Electronics and Control )
Todd Cook (Electronics and Control)
Table of Contents:
The project objective is to build a rover that will simulate a soldier crawling through a barbed wire course. The rover will run in a remote area shown in the course map using a single power source to simulate a scout unit which will be separated from the handler taking orders via communication device. The rover will be controlled by an application from a smartphone. Negotiations of budget resulted in the rover to cost less than or equal to $250. There is to be expected rainfall during the course run on December 16th (Reported in Weather Report)
Level 1 Requirements:
Note: The pan and tilt will be waived
In order to complete our mission objective of constructing a rover that will run a desired course, the following Level 1 requirements have been set.
- The rover shall be completed by the end of the semester, which is December 16, 2016.
- Verification: CSULB Finals Schedule
- Documentation of the rover shall be completed by December 16, 2016.
- Verification: CSULB Finals Schedule
- The rover shall traverse over tree roots measuring at .25-.5 inches high.
- The rover shall traverse over a sprinkler measured at 3-5 inches high and 3 inches wide.
- The rover shall not exceed 16 inches in height when attempting to traverse the sprinkler head.
- Verification: The height of a standard barbed wire course was researched. Barbed Wire Verification
- The rover shall travel at a speed of .5-.75 ft/s.
- Verification: The average speed of a soldier was confirmed by a call to a drill sergeant by Todd.
- The rover shall have a pan and tilt system to simulate the field of view of a soldier.
- The rover shall be completed by the end of the semester, which is December 16, 2016.
The rover’s internal hardware shall be protected from light rainfall and dripping water.
- Verification: The chassis shall have an International Protection rating of 1-1 (IP Rating) Therefore, dripping water, or light rainfall shall have no harmful effect on the equipment inside.
Level 2 Requirements:
Level 1 : The rover shall be able to traverse tree roots
- Level 2: The rover shall have the ability to lift its front tracks at least 25 degrees in order to drive over roots. This maximum height of the roots are measured to be 2.5 inches. We know our treads will be 5.5 inches so we calculated the angle of track assembly rotation to be 25 degrees.
- Level 2: The track assembly should have the ability to rotate back to its original position after surpassing the tree roots.
Level 1 : The rover shall be able to traverse a sprinkler of ~5 inches
- Level 2: Each track assembly should be approximately 140 mm to clear the sprinkler. The maximum height of the sprinkler is 127 mm. By choosing 140mm, it gives us a ½ inch clearance on the sprinklers maximum height.
- Level 2: The track assemblies shall be capable of rotating at least 90 degrees to be able to stand up. They will also be able to rotate 90 degrees back to its original position.
- Level 2: When the rover is on its four legs, it must be able to move forward. In this case, speed is not taken into consideration because soldiers need to carefully move around landmines, sharp objects, and other dangerous objects.
Level 1 : The rover shall have a field of vision with the ability to look left and right, up and down
- Level 2: The rover will use 2 MG995 servos for its pan and tilt system. These servos will be connected to the Adafruit Motor Shield.
- Level 2: The pan and tilt system shall have a mount for the Android phone. The mount will be capable of holding the Android phone while it is being rotated in the specified field of vision.
- Level 2: The MG995 servos will be programmed to look left and right, up and down.
- Level 2: The rotation will be controlled by the Arxterra app with another Android phone.
Level 1 (#6) : Height of rover shall not exceed 16”
- Level 2: In order to meet the height requirement of 16”, our group measured the worst-case scenario on the course, which was a 5 inch sprinkler head. Our rover has 2 approaches to overcoming obstacles, mainly the sprinkler and tree roots. When the rover encounters the sprinkler, it will rotate its track assemblies and stand up to a height of ~13 inches, assuming that the chassis shall be ~3 inches high, the pan and tilt ~5 inches, and the tracks ~5 inches.
The preliminary project document can be found here.
We had several suggestions for overcoming obstacles, which included bigger structure to pass over the obstacle, leaping with springs, or lifting itself with its track assemblies. We chose the lifting function with track assemblies because it was the more innovative solution from the past RoScos. Leaping with springs through charging gears, linear actuators through a separate fuel tank, or solenoid actuators were too complex to go with, so that was not an option.
Prototyping, Simulations, & Trade-off Studies
We initially had a timeline to print 3D parts in time for the CDR, but the parts did not come in time and we had to improvise using other materials. Further details can be found here.
Materials Trade-off Study
There are many different types of materials that could have been used for our RoSco, including CNC aluminum, 3D printed ABS or PLA, PVC pipe, cardboard, and etc. Suggestions from the customer drove us toward 3D printing in order to reduce costs and maintain aesthetics.
Figure 2. Comparison of the two most common 3D printing materials, ABS and PLA
We chose to use ABS because it would allow us to use acetone vapor smoothing and make the rover stronger.
Servo Trade-off Study
In order to move our track assemblies and meet our objective, we had to choose a method of rotating the wheels. We decided to rotate our track assemblies with servos because they are light weight and can supply enough torque to lift the chassis. A servo trade-off study was conducted in order to figure out the best possible servos for our rover. The servo we ended up choosing was a HD 1501mg servo because it was cheap and had a very high torque. Below is our servo trade-off study.
Motor Trade-off Study
There are numerous types of motors, but the most cost efficient way for us to obtain motors was to use the old Pololu gearmotors from other semesters. They run at 85 rpm while being supplied with 6V. We were able to calculate how fast 85 RPMs would run our 55mm diameter wheels and found it to be .64ft/sec. This worked out well for us because the speed we wanted to travel at was between .5-.75ft/sec. A copy of our Motor Trade-off Study can be found below.
Battery Trade-off Study
For us to run our motors and servos long enough to complete the course, the correct battery must be chosen. The battery should allow us to complete the course along with completing other validation tests on the day of the demonstration. This has been chosen last because we needed to know what kinds of motors, servos, and microcontroller we would be using before determining what battery we would use. The battery suggested by the customer was the NiCD 7.2V 700mAh battery.
There was only one simulation done by the manufacturing division on a specific part of the rover. One of the most important concerns for this rover and our specific configuration was whether the track assemblies would snap in half from the weight of the rover. This issue was brought up because our RoSco is almost 2.5 times heavier than previous RoScos. Below is a portrayal of the simulation done in Solidworks. 70 lbs of force was applied directly to the top of the support bracket. The bracket was able to maintain functionality after the force was applied, so a conclusion could be made that the structure of the bracket was sufficient for our project. The customer had mentioned that 3D printed ABS was different from molded ABS, so this simulation test may not have been the best.
There were many experiments that we have attempted, including waterproofing servos and field of vision test for the pan and tilt system. Only two of those experiments were highly successful and could be used as data. There is a high chance of rain in December of this year so it is important to have a rover that can run in the rain. The field of vision of a crawling soldier needed to be tested to attempt to accurately portray a soldier in this situation. Each HD1501MG servo is rated to have 15.5 kg/cm when run at 5V. A test has been done to see the actual weight our servo can lift. More information concerning these experiments and results can be found here and here.
The goal for the PCB design was to create a custom PCB that will mount onto the Arduino Uno. The custom PCB will imitate the Adafruit V1 motor-shield to drive our 6 servos and 4 gearmotors. The PCB will contain headers to plug servos and motors into. Other features of the PCB include the surface mounted resistors, capacitors, and the HC-06 bluetooth module. Further information on the PCB can be found here and here.
Arduino Software Code Design
The backbone of our project was the coding of the servo and motors syncing together to be controlled from a smartphone app control panel using blue-tooth. Details concerning the structure of the code and implementation can be found at here. The Arxterra control panel and communication was very important in allowing the rover to receive commands. Further information including problems with the HC-06 bluetooth can be found here.
Interface Matrix Definition and System Block Diagram
The system block diagram and interface matrix definition allowed us to have a complete overview of how each component would be connected. The interface matrix was important to develop because having individual pins labeled for their purpose allowed ease of use. The updated system block diagram and interface matrix can be found here and here.
One of the cornerstones of success for this project was to allow RoSco to lift itself up on four track assemblies, so there had to be a design of a leg that would allow the rover to run normally as well as run while in the second mode of operation. Details of the hardware design can be found here.
Verification and Validation Test Plans
Verification Test Plans
When the design and implementation of the rover has been completed, tests must be done to ensure that the rover is functional. These tests answer the question, “Is the rover built correctly?” Verification tests are to be done in a lab environment so that we can determine if our rover passes specific requirements without any other factors affecting our rovers performance. More on Verification test plans are found here.
Validation Test Plans
The goal of our project is to build a rover that simulates a soldier crawling through a barbwire fence. Validation tests are done to determine if our rover does the job. These tests answer the question, “is the right rover built?” as opposed to verification tests which answer, “is the rover built correctly?” Validation tests are to be done on the course on the day of the final demonstration. More on Validation test plans are found here.
The mass budget was created for the purpose of tracking the weights of specific items in the rover and where they are placed. If our rover weighs too much there are many problems that could happen. We could break our brackets, our servos may not be able to lift the weight, our motors could run slow, and our battery could run out quicker. This is why it is important to keep a mass budget so that we can determine if we are using the correct motors, servos, batteries etc.
An important part when designing a rover is keeping track of how much power is being used. In this rover we are using four motors and six servos. We need to keep track of how much current these components are using in order to choose a battery that will power it for a proper length of time. These components will have current values that you can look up on their data sheets. The values should also be tested experimentally to determine if they are correct. This is all shown in our power budget. For more information on the Power Budget, click here.
An important job for a project manager is to track costs and to build a project within a given budget. This project had problems with printed parts which ended up driving up the cost. There were many parts that were not printed out correctly due to printer errors which we had to pay for. Towards the end of the semester we did not have a lot of parts we sent out for so we decided as a group to print some of our parts from the Maker’s Society. They charged us 150$ and did not make us pay for the misprints. We should have printed it from a cheaper source but we were pressed for time. We had a budget of $250 dollars which we did not meet. Our final cost ended up at $366.43.
Project Schedule and Work Breakdown Structure
Project managers are in charge of creating schedules and assigning tasks to group members to keep the project moving along. There are tools that were used to track the schedule and delegation of tasks. Project Libre was used in this project to give an accurate schedule that the members of RoSco team can look at and determine if they are on pace to complete the project. A work breakdown structure(WBS) was used to show the delegation of tasks throughout the project. This shows exactly who has done what on the project. For more information on both the schedule and the WBS, click here.
The promotional video can be found here.