Functional Specification Table
| Spec ID | Requirement | Threshold (Shall) | Objective (Should) | Validation Method | Notes |
| S-001 | Operation Instructions | N/A | N/A | Include instructions on cart operation | |
| S-002 | Warning Labels | N/A | N/A | Observation | Visible warning labels to prevent injury from dangerous components |
| S-003 | Emergency Stop | Stopping Distance ≤ 8 ft | Stopping Distance ≤ 5 ft | Record the distance that the cart took to come to a complete stop, from 3 mph | Do research on stopping distances |
| S-004 | Water Resistance | IP = 3 | IP = 4 | Use a hose to spray water from all directions on the cart’s electrical housing, for 5 min. | |
| S-005 | Solid Ingress | IP = 3 | IP = 4 | Use a 1mm diameter rod to check for penetration, in the electrical housing. | |
| E-001 | Operation Time | t ≥ 10 min | t ≥ 30 min | Timer, GPS Speedometer phone App | Allows enough time for proof-of-concept demonstration |
| E-002 | Solar Charging | Battery Charged 70% in 3 hours of sun | Battery Charged ≥ 90% in 3 hours of sun. | Multimeter or battery monitor and stopwatch | This shows that the system will charge the battery to the expected level. |
| E-003 | Travel Speed | Speed ≥ 3 mph | Speed ≥ 5 mph | GPS Speedometer phone app | Based on average walking speed |
| E-004 | Carrying Capacity | 45-55 lbs | 65-75 lbs | Scale, GPS speedometer phone app, timer | Allows users to transport 5 gallons of water plus one energy medical bag or an MSF RISK kit |
| E-005 | RF Signal Connection | Distance ≥ 5 | Distance ≥ 10 | Distance tracking app on a phone | |
| E-006 | Ride Quality | N/A | N/A | Pass/Fail test with and without vibration isolators. Record the among of marbles left for both cases. Pass if less marbles fall out with the vibration isolators. | Protect the contents inside of the cart. (Related to suspension) |
| E-007 | Climbing Capability | 5 degrees ≤ | 15 degrees ≤ | Observe that the cart can start up and drive, loaded with its max carrying capacity, 10 feet up a 15 degree or steeper slope. | |
| E-008 | Multiple-Terrain Capability | Drive through gravel with a granule size of 5 – 75 mm with the max carrying capacity loaded | Drive through sand with a granule size of 0.05 – 2 mm with the max carrying capacity loaded | Observe that the cart can start up and drive, loaded with its max carrying capacity, 10 feet through sand with a granule size of 0.05 – 2 mm. | The cart needs to be able to drive down backroads so multiple terrain capability is required. |
| E-009 | Control Response | Response time ≤ 3 seconds | Response time ≤ 1 second | Observe the time it takes for the cart to perform the task at 3 distances from the remote control within our maximum range. | |
| E-010 | Stability | 5 degrees ≤ | 15 degrees ≤ | Observe that the cart can start up and drive, loaded with it, s max carrying capacity, 10 feet perpendicularly to the slope. | |
| E-011 | Scaled Power System | N/A | N/A | Pass/fail the battery power system will be scaled to the full-scale version | |
| P-001a | Weight of Demo Cart (w/o cargo) | w ≤w ≤ 110 lbs | w ≤≤ 90 lbs | Using a scale, we will weigh the cart. | |
| P-001b | Weight of Full-Scale Cart (w/o cargo) | w ≤w ≤ 170 lbs | w ≤≤ 150 lbs | Using scale and research on appropriate battery sizes | |
| P-002 | Charging by Outlet | N/A | N/A | Charger will be hooked up to batteries and we will verify through observation that the charge is increasing | |
| D-001 | Motor Housing | N/A | N/A | Observation | To protect the motor from rocks and other debris that might get kicked up at it during operation. |
| C-001 | Cost of Materials | Cost < $1,500 | Cost < $2,000 | Spreadsheet and Bill of Materials |
Detailed Functional Specifications:
- Safety (S)
S-001: Operation Instructions: The cart will come with a user manual containing basic instructions on how to operate it safely as well as warnings for improper use. For the device to be useful, the operator must be able to understand how to operate the cart. These instructions will include information on how to move the cart using the remote control, how to charge the cart with solar power, and how to charge the cart using an outlet.
S-002: Warning Labels: The cart will be labeled near the electrical equipment and drivetrain with warnings in English, French and Spanish to protect the user from electrical shock or injury from fast-moving components. This device is meant to be helpful, but it could be harmful if not operated properly. It is important that the user is aware of the potential dangers of mishandling the cart, so the warning labels are meant to aid in this. According to the Médecins Sans Frontières (MSF) website, a significant number of MSF’s missions are in Francophone countries as well as Spanish-speaking countries. Thus, the warning labels will have English, French and Spanish translations to increase the likelihood that the warning can be read and understood by the user. This will be measured by observing that there are warning labels on the cart.
S-003: Emergency Stop: The cart shall come to a complete stop within 8 ft or less, from 3 mph. The cart should come to a complete stop within 5 ft or less, from 3 mph. The average walking speed is about 3 mph so we want to make sure that the cart will stop efficiently and smoothly from 3 mph. To ensure that neither the user nor the cargo undergoes unnecessary risks. The stopping distance will be recorded on a flat asphalt surface, the cart will be traveling 3 mph and the distance measured will be the distance that the cart took to come to a dead stop, from the spot where the brakes were fully engaged.
S-004: Water Resistance: The housing for electrical components shall be designed to meet an IEC Water IP rating of 3 and should be designed to meet an IEC Water IP rating of 4. To protect the electrical components from shorting and to protect the user from electrical shock, the housing must be appropriately resistant to water. This will be validated by using a hose to spray water from all directions on the cart’s electrical housing, for 5 min.
S-005: Solid Ingress: The housing for electrical components will be designed to meet an IEC Solid IP rating of 4 and should be designed to meet an IEC solid IP rating of 5. To protect the electrical components from shorting and to protect the user from electrical shock, the housing must be closed off to small objects and dust. This will be validated by using a 1mm rod to check for penetration in electrical housing.
- Effectiveness (E)
E-001: Operation Time: On flat ground asphalt and within the range of 1-5 mph, the demonstration cart shall operate for a time of at least 10 minutes and should operate for at least 30 minutes. This amount of time will be enough for a proof of concept of the cart’s function. This will be measured using a stopwatch to time how long the cart can operate and using a GPS speedometer smartphone app placed on top of the cart to monitor the cart’s speed.
E-002: Solar Charging: In three hours of direct and mostly continuous sunlight, the solar charging system shall charge the battery which will be at a 50% to at least 60% capacity and should charge the battery to at least 80% capacity. According to our calculations, the solar system should be able to provide a charge capacity of 47.9 Ah to a battery within 5.8 hours of sun, which is the average hours of sun Seattle sees in a day. In three hours of sun, the solar system should be able to provide a charge capacity of 24.7 Ah. This is about 82% of the battery’s Ah rating of 30 Ah. A threshold value of 60% was selected so that inefficiencies in the solar cells and in the battery, charging could be well accounted for. This will be tested and measured by placing the solar panel charging system and battery outside in direct sunlight and monitoring the battery voltage and/or capacity using a multimeter or battery monitor. A stopwatch will be used to keep track of the time that the solar panels are exposed to direct sunlight.
E-003: Travel Speed: The cart shall operate with a max speed of at least 3 mph and should operate with a max speed of at least 5 mph. The average walking speed is about 3 mph so this will allow the cart to stay within the range of the user. Operating a little faster around 5 mph would be optimal so that if the cart needs to maneuver around any obstacles and catch up to the user it would be able to do so. The speed of the cart will be measured using a GPS speedometer within a phone app of a flat asphalt surface.
E-004: Carrying Capacity: Starting from 0 mph the cart shall be able to carry 45-55lbs and still reach 3 mph and the cart should be able to carry 65-75lbs and still reach 3 mph within 45 seconds. This specification shows that the cart will be able to carry a reasonable weight for the doctors in MSF. The smaller range is based on the estimated weight of a 5-gallon bucket of water and 1 emergency medical equipment bag. The larger range is based on the weight of MSF’s RISK kit which is the equivalent of a mini operation room. Being able to start from 0 mph and reach 3 mph ensures that the cart can still function properly while carrying the weight.
E-005: RF Signal: The cart shall be able to detect the RF signal no less than 5 feet and should be able to detect the RF signal no less than 10 feet. This specification ensures that we will be able to control the cart from a distance if needed and shows the strength of the connection. By using a distance tracker on the cart, we will be able to determine the distance that the cart can be operated from the remote control.
E-006: Ride Quality: The cart will ensure the contents inside of it are safe. This specification is to ensure that if there are sensitive materials inside the cart, they can be safe while being inside the cart. This is related to the suspension of the cart when operating and the cart is serving its function of transporting materials safely. This will be validated by driving the cart 10ft on a gravel road with a granule size of 5-75mm with steel spacers in place of the vibration isolators. A bowl of marbles will be placed in the cart for the duration of the test and the number of marbles remaining in the bowl will be recorded. Repeat the test with the vibration isolators and recorded the number of marbles remaining in the bowl. This is a pass-fail test, if the number of marbles remaining is greater with the vibration isolators than without, the test fails.
E-007: Climbing Capability: The Cart shall be able to climb a 5-degree hill and should be able to climb a 15-degree hill. Due to the different environments, the cart may be working in, it needs to be able to transport cargo up substantial hills. To validate that the cart will be able to transport gear up hills, the cart will be recorded starting up and driving 10 ft up a hill with a 15-degree slope.
E-008: Multiple Terrain Capability: The Cart shall be able to travel through gravel unloaded and should be able to get through at full load capacity. This specification is to ensure that cart can get through gravel and still be fully operational even at maximum load capacity. To validate this specification, we will have the cart go through gravel at both unloaded and fully loaded and through observation verify that it is fully functional and operational through the gravel.
E-009: Control Response: The control response shall be less than 3 seconds and should be less than 1 second. This specification ensures that the time lag is minimized and so that the user can operate the cart in a safe manner. To validate the control response, we will be testing the time lag at the cart at 3 different distances from the remote control within our range.
E-010: Stability: The cart shall traverse laterally on a 5-degree slope and should traverse on a 15-degree slope. For the safety of both the user and the contents of the cart, it shouldn’t tip over when traveling sideways on a hill. To validate that the cart will be able to transport gear up hills, the cart will be recorded starting up and driving 10 ft perpendicularly on a hill with a 15-degree slope.
E-011: Scaled Power System: The demo-cart power system will be designed in such a way that it accomplishes a proof of concept for that of a full-scale cart with a greater duration of use. The demo cart will only differ from the designed full-scale cart in that it will have a smaller battery capacity. For the full-scale cart, we have designed it to use a 24 V battery with a capacity of 100 Ah to allow for about 5 hours of constant use at full load between charges. For the demo cart, we have designed it to use a 24 V battery with a capacity of 24 Ah, which will allow for about 1.2 hours of constant use at full load between charges. Both the demo and the full-scale cart will be designed with 200 W of solar power. This specification will be validated by a graphical comparison between the demo-carts duration of use and solar charging test results and the full-scale cart’s expected duration of use and solar charging test results.
- Physical Characteristics (P)
P-001a: Weight of Cart: The weight of the demo cart w/o cargo shall be equal to or less than 110 lbs. and should be equal to or less than 90 lbs. To ease the transportation of the cart when it is not moving under its own power, and to reduce the stress reduce the stresses on the electrical components when the cart is in use. The weight of the cart needs to be as light as possible. The total weight will be measured using a scale.
P-001b: Weight of Cart: The weight of the full-scale cart w/o cargo shall be equal to or less than 170 lbs. and should be equal to or less than 150 lbs. To ease the transportation of the cart when it is not moving under its own power, and to reduce the stress reduce the stresses on the electrical components when the cart is in use. The weight of the cart needs to be as light as possible. The total weight will be measured using a scale and predicted weights of full-scale batteries based on appropriate battery weights available for purchase.
P-001: Charge by Outlet: The cart will be able to charge using a standard wall outlet. Due to the lack of control of weather and the time of year when the cart is being used, the strength of the sun will vary and not always be able to provide adequate charging. Providing the option for the user to charge the cart by outlet provide a more reliable and faster way of charging the cart batteries when outlets are available.
- Durability (D)
D-001:Motor Housing: The motor will be housed. This is to protect the motor from any rocks or debris that might get kicked up while it is being operated. This is important to increase the life span of the cart and to reduce maintenance. This specification will be measured by observation.
- Cost (C)
C-001: Cost of Materials: The cost of materials should not exceed $1,500 and shall not exceed $2,000. The costs of electric-powered transportation devices with battery storage of 24 Ah (i.e., scooters and go-karts) are in the $2k-$7k range. A cost of materials of $2,000 would be low enough to compete with these products. This specification will be measured by keeping a costs spreadsheet and bill of materials