Objective: To design an ultra-portable human-powered vehicle
Major Considerations:
1) Has to be cost-effective (< $300)
2) Has to use as many off-the-shelf parts as possible (to ease manufacturability and parts procurement)
3) Has to be less than 20 lbs
Solution: Vincii is a portable four wheeled vehicle operated by means of human power. Unlike bicycles, Vinci offers more portability because of its much smaller size (around the size of a carry-on luggage). Because it is human powered, the vehicle does not require any power source besides the operator’s hand movements which are identical to using the handles of an elliptical trainer. This vehicle addresses a critical need for daily commuters, enabling them to travel short distances quickly, and to easily carry the device when not being used – all at an affordable price.
Major Considerations:
1) Has to be cost-effective (< $300)
2) Has to use as many off-the-shelf parts as possible (to ease manufacturability and parts procurement)
3) Has to be less than 20 lbs
Solution: Vincii is a portable four wheeled vehicle operated by means of human power. Unlike bicycles, Vinci offers more portability because of its much smaller size (around the size of a carry-on luggage). Because it is human powered, the vehicle does not require any power source besides the operator’s hand movements which are identical to using the handles of an elliptical trainer. This vehicle addresses a critical need for daily commuters, enabling them to travel short distances quickly, and to easily carry the device when not being used – all at an affordable price.
Design Process
The pictures below illustrate how Vincii is intended to be used. The picture on the extreme right is how the user would pull it along when it is not being used.
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The major motivation for choosing hand-propulsion over the conventional leg-propelled method (bicycle) was the increased leverage it offered. The bicycle was taken as the gold standard as Vincii's value proposition is to provide the same efficiency the average bike provides, with greatly improved portability.
Three things determine the speed of a bike (holding the energy input by the rider constant):
1) The size of the wheel
2) The gear ratio
3) The length of its crankarm
Since portability was of paramount importance, the wheel size had to be small. This meant having to compensate for the loss in mechanical advantage by some other means. This is where the long handlebars come into play. These handlebars greatly increase the leverage that was lost when the small wheels were swapped for large bicycle wheels. The fact that the human arm can't generate as much force as the leg was also taken into account during the design.
Three things determine the speed of a bike (holding the energy input by the rider constant):
1) The size of the wheel
2) The gear ratio
3) The length of its crankarm
Since portability was of paramount importance, the wheel size had to be small. This meant having to compensate for the loss in mechanical advantage by some other means. This is where the long handlebars come into play. These handlebars greatly increase the leverage that was lost when the small wheels were swapped for large bicycle wheels. The fact that the human arm can't generate as much force as the leg was also taken into account during the design.
A preliminary sketch showing an exploded view of Vincii
The initial design used plywood pedestals. This turned out to be a very bad idea as it soon collapsed under the rider's weight
Some features that Vincii possessed:
1) Four wheeler vehicle having the rear wheels as drive wheels. 2) Front wheels are skateboard trucks which helps in changing direction based on the user’s position on the vehicle. Leaning right will turn right and vice versa. 3) Rear wheels are trike freewheels, converted to drive wheels. 4) The drive shaft is coupled to a bicycle chain-sprocket system. The cranks of the bicycle chain ring is attached with four bar linkages (instead of pedals). The crank arm of the four bar linkage is extended upwards so that they can be moved back and forth by hands. The movement pattern of the hands are similar as in an elliptical trainer with handles on it. 5) The vehicle can be operated in coast mode just as a bike, thus, cranking is not always required to continue motion. 6) Because of the coast feature, the two rear wheels can be freely rotated as the device is carried like a carry-on luggage. 7) The two crank arms can be folded while carrying the device. |
Vincii when folded
To develop the crank arm's swinging motion (similar to an elliptical trainer), the crank-rocker theory was applied.
The two images above present the four bar mechanism’s formulas. The values for T1, T2 and T3 needs to be +, - and – for getting a crank-rocker mechanism out of the four bars. These formulas were used to verify if the assigned values for the link lengths are appropriate.
After a number of iterations for possible link lengths and simulating it in the online four bar linkage simulator (also based on our system constraints), the values of 6.3”, 2”, 6.5” and 5.8” for the links (q, s, l, p) were ascertained to be the best dimensions. |
Design for a proposed plastic fairing that will be vacuum formed, inspired by a Lamborghini
A slightly modified version of the fairing, enveloping the whole vehicle
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Shows the calculation for mechanical advantage. As can be seen Vincii has more mechanical advantage compared to a conventional bicycle
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Shows a slightly modified design. The handlebars are angled outward so that it doesn't collide with the rider's legs when in motion
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Vincii v2.0 was upgraded to an all aluminum chassis to increase structural rigidity while keeping the weight of the vehicle down
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Fabrication and Assembly
Similar to Zippy, Vincii's fabrication also required the use of some complex industrial equipment and tools. It was entirely manufactured at TechShop San Jose.
The tools included, but were not limited to:
The tools included, but were not limited to:
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1) Tormach CNC router
2) Shopbot CNC router 3) Vacuum former 4) TIG welder 5) Sandblaster 6) Drill press |
7) Metal lathe
8) Vertical bandsaw 9) Cold saw 10) Spray paint 11) English wheel 12) Powder coater |
Shows a bearing housing that connects the chassis to the two handlebars. This was a fairly complex part that required the use of a Tormach CNC router and some intricate aluminum TIG welding.
Vincii, entirely assembled. There were multiple problems with this version, chief of which were that the chassis was not structurally sound, and the handlebars were too flimsy.
Vincii v2.0
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All the parts laid out, prior to assembly
Shows a test board that was set up to test the four-bar linkage theory prior to assembly. It functions to test the theory as early as possible so a solution can be devised if it turns out to be faulty, as opposed to waiting till the whole vehicle comes together, where failure could be catastrophic.
The all-aluminum chassis that was developed to deal with the structural issues. This chassis was strong enough to be able to take a 240b person and still function normally.
DFM and DFA analyses were done in parallel with the design, to ease manufacturability and assembly. The added benefit was when it is ready for mass production, the fabrication techniques don't have to be revamped.
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Vincii's BOM
The three pictures below show the sequence of making the ABS plastic fairing.
A wooden mold is made using a Shopbot CNC router. The CNC router can only machine up to 3 inches in depth. Due to this limitation, multiple MDF boards were machined separately and then glued one on top of the other. Some wood bondo was applied to the entire mold in order to smoothen it out. It is now ready for vacuum forming.
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The entire mold was too big to fit inside the vacuum former. So, a front and a back fairing were made and subsequently attached together as shown. Obviously this cannot be done for the production version but for prototyping purposes, this was adequate.
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The fairing, when fitted to Vincii. Although it seemed like a good idea at first, the ABS fairing ended up making the vehicle look cheap and inauthentic. It was discarded soon after.
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Credits: S.G.M. Hossain, Lee Rajkhowa