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Getting technical on the Patents
Three Wheeler Challenge 1 - Roll Axes
All three wheelers are more sensitive to weight location than four-wheel cars. How and where weight is located can cause the vehicle to tip or roll easier. This is because there are three roll axes creating a triangle, instead of four (like a typical car) which create a square.
The closer the weight is to any triangle side, the more likely it is to tip over or roll on that axis.
As you look at the seating in a three-wheeler, is it close to that line? If so, the variable weight of passengers is impacting stability.
Seating location
Dragonfly moves the variable weight seating forward deeper inside the triangle, farther away from the side roll axis. This makes the three-wheeler inherently more stable with different loads.
The forward seating means passengers are located between the front wheels to a larger degree, especially in the foot/leg area. To make ingress/egress possible, Dragonfly employs a forward opening canopy in front of the wheels. Conversely, a typical three-wheeler will have the door behind the front wheel, like a four-wheel car.
Variable Weight moves the Center of Gravity
Variable weights are loads that change and can influence a three-wheeler's stability in daily use.
For example, there may be 2 riders at 250 lbs each (500 lbs total), or conversely, there may be a single 150 lb rider, resulting in a ‘Variable’ weight of 350 lbs. In a three-wheeler, this could be 20% of the vehicle weight.
If there is one passenger, the Center of Gravity (CG) shifts off center, towards the left roll axis. This is good for a left turn but causes additional roll tendencies on a right turn.
With two passengers, the extra weight moves the CG rearward, closer to the left and right roll axes, making the vehicle less stable.
Large variability in the weighting makes it difficult for engineers, resulting in design compromises and additional stability controls which attempt to reduce inherent issues. This is not an issue for 4 wheels but is critical with 3 wheels.
Dragonfly's goal is to eliminate these issues through forward seating.
Challenge 2- Single rear wheel drive limits traction
With higher power motors and the high torque of electric, it can be easy to spin the one rear drive wheel in a three-wheeler. If the one wheel loses traction in a turn, the vehicle can spin-out quickly and unexpectedly. Unlike four-wheel cars, there is no second rear wheel for traction. The roll-over effect of variable weighting (as discussed above) becomes another major concern in this dynamic.
Mitigation via a wider rear tire helps, but if roads are wet, hydroplaning on the wide rear wheel becomes an even greater concern.
Some three-wheelers use a single driven rear wheel because it does not require a differential (making it more simplistic), and the mechanicals are easier to route if the engine is in the rear.
Dragonfly drives power through the front wheels, which immediately and directly doubles the traction. And if one front wheel does spin, there is another on the same axis for stability. This is a clear solution to the rear-wheel-drive traction challenges.
Challenge 3- Motor Location
With existing three-wheelers, there are two typical motor layouts with rear wheel drive, and one with front wheel drive. These layouts are similar to traditional four-wheel cars.
For Dragonfly, the first two options are eliminated because of traction issues as discussed above, in challenge 2. Option 3 is not viable because as seats are moved forward to create variable weight stability, the seating overlaps the traditional engine location.
As a solution, Dragonfly places the motor in parallel with or behind the seats, and routes power forward to the front wheels. This allows engineers to design weighting and balance based on the fixed weight of the motors and other components while maintaining forward seating and front wheel drive. Space limitations and other design concerns such as doors and steering routing are also addressed.
Dragonfly is the first to take this rear engine / front wheel drive approach. The ICE (gasoline) model has a single rear motor, and the
E-Series (electric) is intending to use dual rear motors.
The Dragonfly design doesn't make sense on a 4-wheel car; however, it addresses the unique challenges of a three-wheeler.
The three tech elements of the unique design
Three wheelers are unique with specific engineering challenges that do not apply to traditional four-wheel approaches. Dragonfly has engineered for these challenges through 3 key design elements:
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- Forward seating in order to put variable passenger weight closer to the ideal location for stability,
- Front wheel drive for double the traction,
- Mid/Rear engine placement behind the front wheels with a drive train that routes power forward to the front wheels in order to support stability and traction goals.
With this arrangement, very unique shapes, doors, and driving excitement levels emerge. It offers a new view on vehicle designs.
We hope these concepts will be adopted by all three-wheeler manufacturers, essentially creating a new class of vehicles. The concepts apply to one, two, three, or four passenger three-wheeler designs, and any body styles.