Prototype Testing Report
Table of Contents
Introduction
As the team nears the completion of several major prototypes at the sub-team level, including full-scale models of the Legs, Treads/Wheels, Swim, and Buoyancy systems, the development of a thorough testing strategy will allow us to critically evaluate the performance of our designs. The results of these tests will enable us to make informed and deliberate decisions in iterating our designs and move us closer to integrating our subsystems to our Level 2 goal. Consequentially, each sub-team has formulated a testing strategy focused on investigating whether we have met the goals we outlined for ourselves in our Specifications Report. Each section will include a short brief introducing the sub-team’s intentions and providing some contextual background to their current prototypes followed by a detailed test plan and a description of all prior tests completed to date. The test plan outlines the steps involved in each test procedure, any required equipment, identified safety precautions, anticipated results, and anticipated testing logistics (including time and duration). At the end of this comprehensive report, we have also updated our schedule for the remainder of the project and our projected budget.
Impact Protection Rating
HARRT would like the robot to satisfy the requirements laid out by the international standard IK code for degrees of protection provided by enclosures for electrical equipment against external mechanical impacts. The code outlines 10 levels of protection based on the impact energy of a mass onto the enclosure. Each subsystem of the robot should be assigned an IK rating based on tests. This will inform the team and its prospective stakeholders of the durability of the prototype. IK08 is the desired rating for the enclosures of electrical devices on the HARRT robot to prevent destructive impact from debris and weather effects.
Test Procedure:
- Restrain robot.
- Drop masses from heights, both specified by the code, onto the robot.
- Increase masses and heights in accordance with the ratings until failure or IK08.
Required Equipment |
Description |
| Steel balls | for dropping onto the robot |
| Meter stick | for measuring height of drops |
Safety Precautions |
| Safety Glasses |
| Avoid impact of masses with persons |
Anticipated Results
| Date | Duration | Measurement | Anticipated Results | |
| Impact Test | 5/3/22 | 2 hrs | IK rating | IK08 |
Completed Tests and Next Steps
No formal impact tests have been completed thus far. If the IK rating of the robot does not meet expectations, the material and structure of the equipment enclosures will be reworked. The IK08 expectation is for this prototype, and future versions could be updated for higher ratings.
Swim Testing
The purpose of this document is to outline the Swim Sub-Team’s testing procedure to evaluate the current Centrifugal Pump prototype. Thus far, 3 iterations of the prototype have been completed. For each prototype iteration, a similar testing procedure has been implemented, while the effectiveness of the prototype design has been improved over time. This report will highlight several components of testing, including the specific test procedure, equipment required, safety precautions, and anticipated results.
There were two main objectives of the Centrifugal Pump. First, the goal was to propel a chassis 5 mph while submerged in water. The robot was originally intended for reconnaissance during a natural disaster, such as a hurricane or tsunami. Therefore, it is important for the robot to function while exposed to water and be able to “swim” while submerged. Another main objective is that the electric components for the centrifugal pump are properly waterproofed. Given that the pump will be submerged in water throughout testing, it is crucial to ensure that the electronics and motor do not get “fried”, as a result of water contact. Thus, the team has plans to purchase an “already-sealed” motor to ensure that water-proofing can be completed, while considering the challenges of sealing a motor ourselves, within the given timeframe.
Test Procedure:
- Fill a fish tank with water.
- Prime the pump by placing it underwater for 30 seconds, such that air is removed from the interior and water is able to flow through.
- Place the pump at an angle, such that the inlet is at a lower height than the outlet.
- Use the hand drill to rotate the motor shaft, and allow water to flow through the outlet of the pump to a smaller tank.
- Measure the dimensions of the smaller tank, and the amount of water displaced by the pump. Measure the time required for a given amount of water to flow into the smaller tank.
Required Equipment |
Description |
| Large Tank | For submerging the pump and measuring flow rate |
| Sink | Filling the tank with water |
| Drill | Spinning the impeller shaft |
| Paper Towels | Drying up spilled water |
| Ruler | Measuring dimensions of the tank as well as change in water volume during flow rate testing |
| Timer | To time the speed of the water exiting the outlet pipe of the pump |
Anticipated Results
| Date | Duration | Measurement | Anticipated Results | |
| Flow Rate | 4/1/22 | 2 hrs | RPM vs flow rate relationship | linear |
| Robot Velocity | 4/21/22 | 4 hr | velocity | 5 mph |
Completed Tests and Next Steps
Thus far in our Senior Design Project, several tests have been completed, each with a different prototype design and size. In December of 2021, a test was completed with the largest, and most preliminary prototype. The goal of this test was to simply test if the pump could successfully perform its job of “pumping water.” Initially, the motor shaft was merely rotated by hand. Upon observing that water was able to enter through the inlet and exit faster through the outlet, a hand drill was used to observe this occur at an exponentially faster rate.
Ending the fall semester on this note was an exciting experience, but the sub-team knew that significantly much work was to be done to improve the design. Given the feat that was to follow of integrating the prototype with the Buoyancy prototype, the design needed to be made smaller. Additional piping was also added in order to have the inlet and outlet of the pump level with each other. Upon making the prototype half the size, another test was performed. The goal of this second test was to make observations regarding how a smaller prototype would perform, in comparison to the large prototype. Although the prototype’s new design of the inlet and outlet performed well, the prototype was too small to produce a flow rate to the level of team expectations, requiring the need for another iteration later on.
Recognizing that this second prototype iteration was far too small to produce substantial power, calculations were performed to determine a new set of dimensions that fell between the smallest and largest prototypes. In addition, the sub-team met with Prof. Rossmann to receive feedback on making the design more efficient. Upon making these changes to the CAD designs, a third test was conducted. The goal of this most recent test was slightly different – the team wanted to determine the flow rate and velocity of the “most efficient” prototype. While the same testing methodology was used, measurements of the fish tank and water height displaced were taken to compute the flow rate. The flow rate was then divided by the cross-sectional area of the outlet to determine the velocity of water flowing out of the pump. The flow rate was determined to be 1.2034e+03 cm3/s and the velocity was determined to be 5.48 mph, which surpassed the “initial goal” velocity of 5 mph.
Moving forward, the Swim sub-team began tests utilizing a motor, rather than a hand drill. Using the first purchased Bilge Pump’s motor, several parts were 3D-printed and assembled to fit the specs of the motor. Testing the pump using the above testing procedure, it was determined that the motor did not have the strength to propel water, given that the fuse would burn at 5 A. Therefore, a new motor with a stronger fuse needed to be purchased. The sub-team determined a motor with a 12 V, 16 A fuse, and re-designed / assembled the parts as appropriate to fit this much larger motor. Testing the pump, once again, determined that significantly more water was able to be propelled. The team plans to compute the forward velocity, once the Swim and Buoyancy sub-systems are assembled on the chassis.
Test Results
Results from the tests impacted subsequent iterations of the design, from an effectiveness and power perspective. From the power perspective, initial tests were conducted with a hand drill that provided 1270 RPM. These tests provided a velocity of 5.4838 MPH, which achieved the specification set forth in the Prototype Specification Report. For the next test, which utilized a sealed-motor from a Bilge Pump with a 12 V / 5 A fuse, quantitative results were not collected; however, qualitative results were. Testing with this motor determined that such a motor would not be able to propel as much water as we would have liked. Therefore, for the next iteration of the robot, a motor with a higher current fuse was utilized (12 V and 16 A). Given that this motor was stronger than the hand drill utilized in our initial test, it can be stated that the final design of the pump utilized meets the force and velocity requirements set forth in the Specifications Report.
Finally, a test was conducted to test the pump with the Buoyancy sub-system. In performing this test, it was determined that the forward velocity of the Water Movement robot was 0.5 mph, indicating that the forward velocity requirement set forth was not achieved in combination with the Buoyancy Sub-Team. This can be attributed to the weight of the chassis, that was unexpected.
Utilizing our testing results, the team hopes to advance the prototype / increase its efficiency, given more time. One observation made is the weight of the Water Movement chassis, given the immense number of parts, its size, and the heaviness of the Swim motor, which may have caused the Water Movement robot to slow down. Given more prototype development resources, a smaller motor with just as much power could have been purchased, allowing the speed of the Water Movement to increase.
Buoyancy Testing
Design a reservoir system that takes in water and distributes it to each of its 4 reservoirs. The reservoirs are located on each of the four corners of the robot. Balance is achieved by managing the amount of water that is within each reservoir. The orientation, as well as the current depth of the robot, is measured by multiple pressure sensors. The data from these sensors is then fed to a control system, to ensure a specified depth is maintained.
The objective of this test is to ensure that the buoyancy subsystem of the robot will be proficient in controlling the orientation of the robot while submerged. This control will be achieved by using four pumps, each linked to a corresponding reservoir, to vary the amount of water in each reservoir independently. The four reservoirs are located on the outer corners of the chassis. By varying the amount of water displaced by each reservoir, the net buoyant force can be changed. This can result in the chassis ascending, descending or rotating along its pitch or roll axes.
This test will be performed by submerging the chassis and reservoirs in water. All other components will be kept dry, including the pumps, with extra long tubes connecting them to the submerged reservoirs. Remote control will be used to toggle whether each motor is on, as well as the direction of each motor. Eventually, this method will be replaced with data obtained from on-board pressure sensors.
Test Procedure:
- Fill tank with enough water to allow chassis to be able to fully submerge when testing
- Place the chassis in the tank (electrical components won’t be waterproofed at this time, they’ll be outside of tank)
- Add ballasts to bring the chassis near neutral buoyancy. Since we aren’t testing with internal components, another object must be added that will displace enough water to achieve near-neutral buoyancy.
- Start to fill the four reservoirs with water, in turn chassis should start to sink over time
- Once fully submerged the perlistic pumps will be reversed drawing the water from the reservoirs and the chassis in turn should resurface
- Record the amount of time it takes the system to switch between ascension and descension.
Required Equipment |
Description |
| Voltage Provider | Power source for the motors. The overall robot does not yet have its own power supply |
| RC Controller | Enables manual control of specified parts. |
| Tank | The chassis mounted with the reservoirs will be placed in the tank filled with water to test allow for tests |
| Timer | Time how long the pumps are working to make the chassis move vertically down/up |
| Paper Towels | To allow for any spills of water from the tank |
Anticipated Results
| Date | Duration | Measurement | Anticipated Results | |
| Chassis Ascension and Descension | 4/1/22 | 1.5 hrs | vertical control | Chassis Ascension and Descension were Achieved |
| Pitch and Roll Control | 5/10/22 | 2 hrs | flat orientation | Pitch and Roll control achieved |
| Sensor Control performance | 5/10/22 | 2 hrs | – | Sensor control |
Completed Tests and Next Steps
The Buoyancy sub-team thus far in Senior Design has decided on three different tests for the prototype. The first test was the chassis ascension and descension which was just recently completed on April 1st of 2022. The goal of this test was to prove that the reservoirs mounted on the chassis had the ability to fill up enough that the robot was able to sink underwater, and able to empty the reservoirs to allow for resurfacing of the robot. Upon completion of the test it was determined that the reservoirs were in fact able to be filled up and emptied to allow for ascension and descension of the chassis. However, the chassis has yet to be implemented with the swim team and the reservoir size may need to be increased upon integration to achieve neutral buoyancy. The test also excluded any internal chassis components, so even more water must be displaced.
Continuing onto the next two tests, the Buoyancy sub-team began tests on the Pitch / Roll Control and Sensor Control performance. This was done after the Swim and Buoyancy sub-teams had combined to the level 2 team goal as the chassis had to be fully assembled to assure that both a flat orientation was able to be obtained and the sensor control performance would work when fully integrated.
Test Results
Results from the first test of chassis ascension and descension led to the iteration of increasing the reservoir size from 4” to 6” and the number of reservoirs needed from 3 to 4. This was due to a recalculation of the buoyant force that would be needed in each of the reservoirs. Therefore, to achieve this as well as the size increasing the need for a fourth reservoir was also added to assure that the iteration would work under the maximum mass the robot was calculated to be (~14kg). This would then be re-tested when making the design iterations and retested when integrated with Swim sub-team.
Additionally, a test was conducted with the Swim sub-team in May 2022. In performing these tests, it was determined that a flat orientation was maintained, the sensor control performance worked, and chassis ascension and descension was achieved.
According to the results of our testing, we hope to increase the speed the fluids within the reservoirs are moved. This will increase the speed in which the buoyant forces are adjusted. While testing, it was seen that as the pressure increased, the speed in which the reservoirs are drained decreases. Higher pressure pumps should increase the maximum depth the robot can operate as well as increase the speed in which the reservoirs are filled and emptied.
General Safety Precautions
- Safety Glasses
- Elevating the electronics to separate them from potential pump or reservoir spills
Legs Testing
This report will identify what will be tested within the legs sub-team, and how the leg will be tested in these areas. A prior report detailed the specifications regarding the expected operation of the legs; the tests detailed in this report are meant to evaluate how well the system fulfills those expectations. The legs are made of a hip and knee joint, each with one rotational degree of freedom. As of March 28, 2022, a full leg prototype has been assembled and testing can begin.
Our objective is to make sure the leg can close and open to a desired angle and over a certain time. There are four specifications that can be effectively tested: fold time, bending range, carrying capacity, and tolerance of the angle measurement. The other specification detailed in the report is cost, which is not a feature of the robot and cannot be tested. Fold time will be used to create a system model which will then be used to design a closed loop control scheme. Bending range will simply inform us on the range of angle values that can be given to the system when in operation. The tolerance of the angle measurement will be used in refining the controller, but more importantly as a pass/fail test as to whether the angle sensors are precise enough for our purposes. If the sensors are too imprecise, the operation of the legs will run into difficulties especially when connected via the treads. The carrying capacity test will be used to gauge the robot’s effectiveness in meeting the metrics that were outlined for it earlier in the project.
Test Procedures:
Fold Time:
- Manually fold the leg fully
- Set voltage and current
- Measure time it takes to reach some angle
- Return to folded position
- Change voltage and current and test again
- Repeat 1-5 starting from fully extended position
- Repeat 1-7 with different attached weights
Bending Range:
- Measure angle of joints when fully folded and extended with built-in angle sensors to find exact values that will be used in the system
Carrying Capacity:
- Begin with manually folded leg
- Secure hip mount to test table in an inverted orientation
- Attach weight to lower leg-wheel interfacial shaft
- Extend knee and hip joints (simultaneously?)
- Repeat 1-4 with increasing weight until stall torque is reached non-destructively on one or both motors
Tolerance of Angle Measurement:
- Under closed loop control, specify a desired angle of a joint
- Measure angle that the leg achieves with external tools
- Repeat and compare values to find range of angles that system accepts as the same
Required Equipment |
Description |
| Clamp | to attach leg to tabletop |
| Timer | for Fold Time test |
| Protractor | for Tolerance of Angle Measurement test |
Anticipated Results
| Date | Duration | Measurement | Anticipated Results | |
| Fold Time | 4/1/22 | 1 hr | time | 3 s |
| Bending Range | 4/1/22 | 1 hr | degree | 150 (hip)
200 (knee) |
| Angle Tolerance | 4/8/22 | 2 hrs | degree | 0.5 degrees |
| Carrying Capacity | 4/15/22 | 2 hrs | mass | 5 kg (per leg) |
Completed Tests and Next Steps [as of 4/4/22]
The only tests done so far have been superficial ones just to see whether the leg mechanisms work at all (which they do!). The tests outlined in this report will allow the team to make quantitative assessment and improvement of the system. If any of these tests show that the legs will not fulfill the metrics expected of them, the team will make the necessary hardware changes or goal reassessment to align the prototype with our goals. We expect the legs to meet the metrics, in which case next steps will be designing the control scheme and integrating more fully with wheels/treads and eventually the water movement sub-teams.
Test Results
The fold time was highly successful for the knee; to avoid damaging any components, it was never given full power, but it can both extend and fold in under two seconds even when given a limited voltage. The hip was less successful, as the motor in the hip joint struggled greatly with lifting the full weight of both sections of the leg. In the hip joint, both the motor and power transmission hardware were taxed by testing while the leg was suspended above the ground. The most feasible mode of testing the legs was to operate them while attached to the chassis which was elevated sufficiently to suspend the leg entirely. The result is that instead of the legs pushing against a solid surface to support the chassis, each leg was asked to manipulate its own considerable weight, not unlike a crane trying to lift its carrier using its boom. A control scheme was never fully implemented, so the robot could not rest on and actuate all four legs at once, so the fold time of the hip was not found. The 200 degree bending range of the knee satisfied the expectations from CAD models, whereas the range for the hip of 120 degrees was slightly less than originally anticipated. The angle tolerance was worse than expected not because the sensors were faulty but because the hardware in the joints tended to loosen or wear quickly; the set screws slipped regularly and the PLA of the legs seemed to plastically deform due to bearing stresses from the metal hub mounting screws; future iterations of the legs should be made with a more robust material like aluminum. The carrying capacity was not tested.
Treads/Wheels Testing
The primary objective of this section is to specify the Treads/Wheels Sub-Team’s testing strategy to evaluate the performance of the tread assembly and the Leg-Wheel interface. The Tread Assembly includes the sprocket, a modified Christie suspension, roller wheels, skid wheels, structural spars, and tread linkages. The Leg-Wheel interface incorporates the motor, gear, and belt assemblies into the lower leg, designed in tandem with the Legs Sub-Team. This interface powers both the wheel and the Tread Assembly, depending on the system deployed by the end-user of the overall product. As of March 28, 2022, the Leg-Wheel interface has been fully assembled and preliminary testing has begun. The Tread Assembly, after having gone through several iterations, is approaching its first completed system-level prototype. With each test and iteration, we have focused on improving ease of manufacturing, space efficiency, and general effectiveness. This report will highlight several aspects of our testing procedure, the equipment required, safety precautions, anticipated results, and projected timeline and budgets.
The primary objective of the ground clearance tests is to determine the maximum obstacle dimensions the system can traverse without increased risk to becoming stuck. These tests are primarily relevant to the Tread Assembly. When the legs of the robot use wheels as their end effectors, the maximum ground clearance is the maximum articulation length of the leg, which can each move independently. The Tread Assembly allows for superior weight distribution over a given surface area at the cost of increased complexity and size, leading to potential snags and hindrances if encounter obstacles catch exposed parts in such a way that movement becomes restricted. The performed tests aim to evaluate, in part, the potential of such risks occurring.
The objective of ground speed tests is to determine the maximum speed that the robot can reach in a controlled environment. The robot will be tested on asphalt and and will have a test area taped off to ensure safety. The robot will be provided the maximum voltage, allowable by the motor, with markings to determine the approximate distance. Additionally, through the use of bluetooth, the RPM of the motor can be better evaluated using the motor encoder. There will be a safety switch engaged to stop power supply to the motor prior to exiting the marked out testing zone. This test can be conducted on various terrains, however preliminary testing will be performed on finished concrete or asphalt. It is important because the robot’s speed is large enough to generate sufficient momentum, theoretically derived values, for the obstacles that the robot may encounter. Additionally, the robot must maintain speed and have accurate variable speed control to be best deployed in disaster relief scenarios.
The objective of the angle of traversable slope test is to ensure that the robot can traverse obstacles and non-flat terrain in completing its mission path. Given the desire for the robot to operate in difficult terrain, the robot must be able to scale and descend slopes while still maintaining traction. 40 degrees on a “grippy” terrain was chosen as a fair evaluation of the robot’s ability to perform, as a small obstacles may cause the robot to lift upward and larger obstacles or changes in environment may require the same obstacle traversion.
Ground Clearance:
- On the fully assembled tread system, place in a neutral, unloaded position.
- Load the system using weights until the suspension reaches maximum compression or until the system can no longer move downwards due to component interference. Keep the system level.
- If there is interference, make note of the interfering site. This will be the point of reference designated as the LIP (Lowest Interfering Point).
- Continue loading the system until all suspension columns have reached maximum compression or are inhibited by other interfering points. The resulting weight is the maximum load before the suspension “bottoms out,” which correlates to the “Suspension Weight Capacity” specification.
- Unload the system and allow it to return to a neutral position
- Measure the distance from the ground to the LIP. This is the maximum ground clearance.
- To determine the ground clearance at specific loads, place the desired load onto the system, evenly, and measure the distance between the ground and the LIP after the suspension has been compressed by the added weight.
Ground Clearance Safety Precautions
- When managing heavy weights, ensure proper lab safety is observed. Wear close-toed shoes and be cautious when handling weights so as to not drop them on exposed limbs and vulnerable surfaces.
- When actively compressing the suspension, avoid placing your hands, fingers, or other body parts into the path of the suspension to avoid pinching, crushing, and other forms of bodily harm.
Ground Speed:
- Place the robot in controlled terrain (specified in general description above)
- Ensure the robot will collect data from the motor encoder using a bluetooth dongle to collect data or hardwired to a computer
- Run the motor at maximum allowable voltage for test run
- Analyze the PPR (pulse per rotation) of the motor driving the treads system and convert to a linear velocity using controls concepts
- Repeat trials to ensure accuracy (for further tests the terrain may also vary between tests)
Ground Speed Safety Precautions
- Clear a trial run area for the robot free of people and objects. Use of a remote start or delay would also help to ensure the safety of team members and observers. Additionally a remote kill switch should be implemented to avoid damage to the robot or the surroundings.
- Limit the time of the trials to ensure that the distance is relatively known.
Angle of Traversable Slope:
- Place robot on slope/base of slope and orient/afix to guide system so it is stable
- Wire robot to receive and send input, output, and power to respective connections
- Have platform at top of ramp to allow for slowdown of robot
- Run motors at maximum voltage necessary to traverse slope without stalling
- Repeat trials
Required Equipment |
Description |
| Calipers | for measuring compression distances |
| Weights | for loading the suspension system |
| Encoder | in the motor to determine PPR |
| Ramp | test ability of motors to provide torque while performing Angle of Traversable Slope specification |
| Guide Rails/Retainment Mechanism | prevent assembly from losing stability before test is performed |
Anticipated Results
| Date | Duration | Measurement | Anticipated Results | |
| Ground Clearance | 4/1/22 | 2 hrs | distance | 25 mm compression (front)
35 mm compression (rear) |
| Ground Speed | 4/1/22 | 1 hr | velocity | 2 m/s |
| Angle of Traversable Slope | 4/1/22 | 1 hr | slope angle | 35 degrees |
Completed Tests
Test |
Results |
Analysis |
||||
| Ground Clearance (Treads) | 65 mm uncompressed
35 mm at maximum compression |
These results indicate we have fulfilled our ground clearance specification across all ranges of use. We extrapolate that the current design should, at a minimum, be able to handle obstacles up to 30 mm in height. | ||||
| Suspension Weight Capacity |
|
Having originally designed the robot such that it could support up to 40 kg at Level 1 implementation (all systems integrated), the old suspension proved that it would be unable to meet this goal. As a result, the design of the suspension was changed to add additional larger and stiffer springs into the lower suspension column. Further, due to the shift to the year-end goal of achieving a Level 2 design, the minimum weight to be supported was changed to 20 kg to reflect that at Level 2, the suspension would only be intended to integrate with the Legs system.
Using the new suspension, almost 30 kg could be supported before overcompression becomes irrecoverable. This phenomenon occurs when the suspension is loaded from a neutral state and is compressed to a steady-state point below the level of maximum compression. Manually compressing the suspension at these loads (overcompressing; applying additional force and then removing the applied additional force) will result in the suspension not being able to return to the steady-state point it had achieved after being loaded from a neutral position. In a practical setting, exceeding this limit of recoverable compression means that any obstacles hit while carrying the corresponding load will result in suspension “creep” where the suspension will eventually reach a maximally compressed state and become non-functional. This phenomenon is likely to occur due to a large amount of internal friction within the suspension causing significant damping. Reducing the discrepancy between absolute weight capacity and effective weight capacity can likely be achieved by converting the lower part of the suspension column to metal to reduce friction between PLA layers of nesting suspension parts. After integration with the Legs team to create a Level 2 chassis, it was determined that the track system was shorter than the length of the chassis designed by the Legs sub-team. As a result, future work would have increased the length of the spar, allowing for additional suspension columns to be inserted into the design, further increasing the weight capacity of the suspension. With these results in mind, it is the conclusion of the Treads/Wheels subteam that this suspension design has effectively met the targeted specifications. |
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| Angle of Traversable Slope | Carpeted surfaces: 50˚
Polished Wood: 16˚ |
These tests were conducted on an unloaded track system in a static position. As a result, these values represent the best-case scenario for our design. Integration with other systems will raise the center of gravity of the overall system, effectively reducing the angle of traversable slope. As a result, the Treads/Wheels subteam is not confident that the current design will be able to meet the original specification. Future improvements to the system may include the addition of soft-rubber textures (either via spray-on coating or via sheets attached to the treads) to improve grip on smoother surfaces. While full-system tests were unable to be performed for the produced Level 2 chassis, if the legs could be articulated such that the center of gravity actively tips forward of the center of the spar, these test results may see some improvement. | ||||
| Ground Speed |
|
These results show that when using wheels, the current design is able to meet the outlined specifications. However, when the treads are used, the ground speed of the system significantly decreases. Further, internal friction significantly drops the reliability of the treads being able to achieve the indicated speed. As a result, the Treads/Wheels subteam conducted an investigation to determine the performance-limiting factors. The team found that, due to a large portion of the design relying on 3D printed PLA components, warping due to thermal stresses and continued usage combined with excessive friction between certain components, the treads were unable to achieve the desired ground speed. The team observed that some of the axles in the lower leg, which were responsible for transmitting power to the treads, were slightly misaligned, causing uneven tension in their connecting belt. This problem was further exacerbated by how the tread system was cantilevered from the leg, adding increased pressure on one of the axles. The treads also appeared to have inconsistent tension; they were more taught on one side of the sprockets than the other. Further, the treads also experienced significant friction with the track tensioners. As a result, future steps would have likely included the installation of the same self-aligning flange bearings used in the spar into the lower leg. This would alleviate some of the frictional losses in the cantilevered drivetrain and would reduce the likelihood of misaligned shafts. |
Qualitative testing includes the following:
- Fitment of Tread/Wheel sub-team lower leg assembly confirmed with Leg sub-team upper leg assembly
- Intended actuation of suspension achieved
- Subsystem mostly assembled and integrated
General Safety Precautions
- When removing material from 3D prints, proper designs were ensured to the minimal necessary use of tools.
Team Level Updates