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These analyses were performed with the express purpose of determining either a components dimensions, or the material to use in its construction. this was achieved by using a myriad of methods including but not limited to: Free Body Diagrams, summation equations, impact equations, deflection equations, moment of inertia, and algebra.
The requirements for this project were used to determine which analysis needed to be performed to fully and thoroughly design the robot. A full list of the requirements can be seen below.
i. The robot must be able to go 6 miles per hour minimum.
ii. The robot must have at least 1 weapon.
iii. The robot will have at least 2 wheels.
iv. The robot can weight no more than 3 lbs.
v. The robot must come to a full stop within 60 seconds of power being disconnected.
vi. The power must have 1 physical disconnect.
vii. The material used to construct the weapon tip must have a stiffness (Young’s Modulus, E) of 7 GPa at minimum.
viii. The plates of the chassis must have a yield strength of at least 3MPa, and an ultimate strength of 4 MPa minimum.
ix. Armor and ramp/dustpan must have a minimum tensile strength of 50 MPa.
x. Damage to electronic components must be fixable or replaceable within 15 minutes.
xi. Damaged armor must be replaceable within 10 minutes.
xii. The robot dimensions will not exceed the volume of a 2 ft cube. (2ft x 2ft x 2ft).
xiii. The gear system for the arm must not move the arm faster than 100 RPM.
xiv. The spring for the weapon arm cannot have a diameter larger than 0.5 in.
xv. The latency between the controller and the receiver cannot be more than 0.005 seconds.
xvi. The robot must have at least 2 sensors that read some sort of input.
xvii. The robot must have at least 1 microprocessor that controls the sensors and processes the data from them.
A01- Minimum Chassis Internal Volume: The analysis used basic algebra and can be seen in appendix A01- Chassis Minimal Internal Volume, and was used to determine the net internal volume minimum to try and stay as compact as possible while still allowing all of the internal components room to fit comfortably and still function properly, there was a generous tolerance of +1.3 in^3 to allow for internal walls to help the components stay where they are supposed to be while the robot is in motion. The resulting dimensions for the chassis were 8 inches long, 4 inches high, and 6 inches wide. This analysis helped the robot stay within compliance of requirement iv.
A02- Theoretical Max Speed: Found in appendix A02-Max Speed, this analysis was determined by using gear ratio equations and unit conversion equations to find the theoretical top speed of the robot to make sure it would be able to reach a competitive speed as well as one for the requirements of being able to reach over 6 miles per hour, the calculations predicted a top speed of 14.4 mph. This analysis helped the robot stay within compliance of requirement i.
A03- Skid Dimensions: This analysis was performed to find the dimensions of the skids that were to go under the front of the chassis to allow it to slide on the arena floor. The process used free body diagrams, summation equation, and impact equations. This allowed for weight loss since the skid weight less than 2 wheels, and with the addition of the skids under the front of the chasses the front wheels could be discarded. The calculations can be seen in appendix A03-Skid Dimensions. This analysis helped the robot stay within compliance of requirement iii while minimizing weight so that it can comply with requirement iv.
A04- Chassis Dimensions: This analysis was performed to find the dimensions of the skids that were to go under the front of the chassis to allow it to slide on the arena floor. The process used free body diagrams, summation equation, and impact equations. This allowed for weight loss since the skid weight less than 2 wheels, and with the addition of the skids under the front of the chasses the front wheels could be discarded. The calculations can be seen in appendix A03-Skid Dimensions. This analysis helped the robot stay within compliance of requirement iii while minimizing weight so that it can comply with requirement iv.
A05- Chassis Side Wall Thickness: This analysis focuses on the max deflection and impact forces the chassis will have to endure in the arena. This was decided using deflection equations, impact equations, free body diagrams, and summation equations, as well as some calculations provided the RioBotz competitors guidebook to estimate the effective mass of an opponent’s weapon. Because the forces that the robot chassis will be experiencing will be unpredictable the calculations have been generalized to try an account for most situations that the robot may find itself in. These calculations take assumed length, width, and height to decide the thickness of the chassis walls as well and use shear force and impact forces to check to make sure the thickness will hold up to a competition. The calculations can be seen in appendix A04 and state the results of a wall thickness of 0.25 inches thick. A CAD drawing of this part can be seen in appendix B06. This analysis helped the robot stay within compliance of requirement viii.
A06- Torque on Drive Train Motors: The calculations can be found in appendix A06-Torque on Drive Train Motors, which found the amount of torsion on the motor while under a load. To do this, torque equations, as well as unit conversions were used to calculate this analysis and found that the torque on the motors was 2.58 N*m. This is useful to know how much torque is already on the motors to make sure the force against the motors (weight, friction, impact force) is within the threshold to not stall the motors or break the motor shaft. This analysis helped the robot stay within compliance of requirement vi.
A07- Claw Dimensions: The analysis used basic algebra and trigonometry as well as arc length calculation to find the dimensions of the claw arm when given the minimum horizontal length and minimum vertical length. The impact force and material calculations were performed to determine if the assumed dimensions were acceptable for the situation that the arm will be in. The calculations can be seen in appendix 07- Claw Dimensions and found the arm to have a horizontal distance of 8.75 inches and a vertical distance of 5.15 inches, with a thickness of 0.1 inches. This analysis was in alignment with requirement ii, to ensure the robot had at least one weapon. This analysis also helped determine the material the arm would be made of, considering both metals used in analysis 8 as well as the 3D filament used to print the chassis. It was determined that the Electron would be the preferred material as it only weights 0.1225 lb in comparison to the aluminum which calculated to be 0.170 lb. If weight becomes an issue in later analyses the arm may be made out of the PAHT-CF filament because its weight is only 0.0665 lb.
A08- Armor Thickness: This analysis used FBD, impact equation, summation of forces, inertia, and shear stress equations to determine the thickness of the metal armor (specifically either Electron 675-T5 or Aluminum 6061-T6). The calculations can be found in appendix 08-Armor Thickness. These calculations are following requirement viii and ix. The calculations found that the Electron armor would be preferred to the aluminum as the electron armor can withstand the forced the robot will have to endure with 1/10 of a lb less in weight. The Electron came in at 0.34 lbs while the Aluminum came in at 0.47 lbs. The thickness was rounded up to 0.15” after the electron was calculated to need 0.133” and the aluminum calculated out to 0.149”, rounding up 0.15” allows for easier access to the material needed as that is closer to a standard size than either of the original calculations. After some calculations were done on the robots total mass it was decided to forgo any armor as weight was becoming too much of an issue.
A09- Claw Gear Ratio: Through analytical experimentations with the analytical tool “Gear Generator” online, a gear ratio close to the goal ratio was determined. The original goal ratio was 6.24:1 with a tolerance of ±3 RPM, as the ideal situation would have the ring gear in the system move at a speed of 100 RPM. The found RPM for the system was 6.33:1, this was determined via a train value calculation. This ratio was accepted because not only was it within 1 RPM to the ideal one, but this ratio also allowed the largest gear in the system (the ring gear) to be within the chassis high dimensions. The ring gear posed multiple problems concerning its size throughout the analysis and decisions were made to modify the chassis with a cut out to allow a gear that was taller than the chassis. Those modification are no longer needed as the final pitch diameter for the ring gear was determined to be 3.8” with 19 teeth and the inner sun gear at 1.8” with 9 teeth. The planetary gears and the driving gear share the same dimensions with a 1” pitch diameter and 5 teeth. The outer pitch diameter of the sun gear is 3” with 15 teeth. The sun gear will be designed to have 2 different diameters and number of teeth while sharing a central axis with the planetary gear set. This analysis followed requirement xiii in determining a max speed for the gear set for the arm maneuverability system. The full analysis as well as screen shots from the analytical tool can be seen in appendix A09- Gear Ratio.
A10- Ramp Material: This analysis was performed to maintain compliance with requirement ix. The process to go through this analysis started with a FBD, and the summation of forces, then impact equations were used. The ramp dimensions were determined to be 7.5” wide with a triangular side profile of 1.00” long and 2.278” high. This allows the ramp to absorb the necessary impacts while still maintaining the minimum possible weight. The dustpan design attached to the ramp was designed to be an outstretched arm with a triangular barb at the end. The dimensions of the dustpan portion were determined to be 5.00” long and 0.5” high with a thickness of 0.25”. As for materials for the construction of the ramp and dustpan all three choice materials from the previous analyses were used and the results are as follows: Electron was calculated to be 0.5486 lb, Aluminum was calculated to be 0.3958 lb, and PAHT-CF calculated out to be 0.2149 lb. This calculation was performed assuming that the ramp and dustpan would be made of the same material. So, the ramp and dustpan arms will be made from the PAHT-CF and then a thin sheet (0.15”) of aluminum will be placed on the interior faces of the whole part to provide armor. The full analysis can be seen in appendix A10-Ramp Material.
A11- Latency between Controller and Robot: As in accordance with requirement xv, the theoretical latency of the controller to the receiver that will be housed on the robot was determined using algebraic methods. The latency at 10 meters (the assumed max distance the driver will be from the robot) was found to be 33.3 nano seconds. This was far below the minimum latency determined in the requirements of 5 milli-seconds. The calculation can be seen in appendix A 11- Controller Latency.
A12- Spring Force:The spring analysis was by far the most difficult to perform as the material had to be self-taught by the student due to the content not being taught Fall quarter. The student performed a torque analysis to determine the output torque of the gearbox, determined the spring length and force using assumed dimensions for the spring. A spring index was also determined as well as a pitch angle, coil clearance, design shear stress, deflection of the spring, and buckling calculations. All of the above listed calculation determined that a Music wire helical spring with an outer diameter of 0.25” and a free length of 2” would be sufficient for the purpose of this project. This was all in accordance with requirement xiv, and the full analysis can be seen in appendix A12-Spring Force.
A13- Claw Tip Material: This analysis was the final analysis to be performed for this robot, it was planed as such because of the weight restriction listed in 1d. requirement iv. This analysis is in compliance with requirement vii, and the calculations can be seen in appendix A13- Claw Tip. The findings were as such that the claw top will cover the last 3.7 inches of the weapon arm and will be made out of aluminum. These findings determined that the claw tip will weigh 0.124 lbs, putting the robot’s final weight at 2.978 lbs. These decisions were determined by using FBD, algebra, impact equations, and a total mass summation.
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