To organize all thoughts in selecting 3- or 4-wheel, I will make a decision matrix and select all criteria that must be considered.
When discussing a 3-wheel design we will be considering both a tadpole/teardrop shape and a delta shape as shown below.
The 4-wheel datum is a vehicle rear-wheel drive vehicle, with Ackermann steering in the front, and brakes in all wheels.
- Delta off the menu, reasoning below
The only thing that delta does better than the other designs is that its steering would be simpler. You can see that even taking small corners it just falls over and damages the car. This video shows what I'm talking about: https://youtu.be/QQh56geU0X8 This effect is due to the cars difficult to balance weight transfer and it being very prone to oversteer. This huge disadvantage makes it nearly impossible to recommend over anything else.
More information on why tadpole is just a better 3 wheel option can be seen at this article summary: 3 vs 4 Wheel Task 2 , link to the original article is also included in that page.
Criteria | Weighting | 4-Wheel | Tadpole | Notes |
|---|---|---|---|---|
Suspension | 0 | This criteria is broken up into the design, manufacturability, and assembly of the front and rear suspension. Both will be factored into the final decision. | ||
Front | 0 | |||
Design | 0 | |||
Manufacturability | 0 | |||
Assembly | 0 | |||
Rear | 0 | |||
Design | 0 | |||
Manufacturability | 0 | |||
Assembly | 0 | |||
Steering | 0 | This criteria is broken up into the design, manufacturability and assembly of front, rear, or all-wheel steering. In this case, we will use the best scoring implementation of the three steering types. Consider this a child decision matrix. | ||
Front | 1 | 0 | 0 | Delta wins due to the simplicity of only having 1 wheel in front, and tadpole and 4 wheel remain identical due to both having 2 wheels up front -Malcolm |
Design | 0 | 0 | Delta only has to connect to one wheel, while tadpole remains virtually the same due to also being connected to 2 wheels -Malcolm | |
Manufacturability | 0 | 0 | Delta has very few components just have to make sure it maintains positive caster, and again, tadpole is the same as 4 wheel -Malcolm | |
Assembly | 0 | 0 | Delta takes up very little space, and is not complex, so stuff could be built around it, although car shape might limit potential space -Malcolm | |
Rear | 1 | 0 | ||
Design | 0 | 1 | Tadpole now has the rear advantage, as it only has one wheel, and delta loses that advantage -Malcolm | |
Manufacturability | 0 | 1 | Rear steering only would be difficult to design for in general, but again tadpole benefits here from only having 1 wheel, although being able to maintain a positive caster while also wrapping the steering all the way around the car could prove difficult -Malcolm | |
Assembly | 0 | 0 | The | |
All-Wheel | 1 | 0 | ||
Design | 0 | |||
Manufacturability | 0 | |||
Assembly | 0 | |||
Brakes | 0 | With the assumption that the implementation of brakes will be relatively equal between different wheel allocations (only front, only back, all wheels), we will only look at the over arching difficulty. Brake wheel allocations is being worked on by Ayush. | ||
Design | 0 | |||
Manufacturability | 0 | |||
Assembly | 0 | |||
Stability | 0 | Min is researching the stability. 3 Wheel Vehicle | ||
Handling | 0 | |||
Chassis | 0 | |||
Aerobody | 0 | Connor Hawkins left a comment on the 3- vs. 4-Wheel Car co-op task page which would be another consideration for this criteria. | ||
Battery Box | 0 | |||
Motor Allocations | 0 | Typically, for tadpole design the vehicle is rear wheel drive - Evan Dodd Consider the number of motors and if a differential would be required https://www.youtube.com/watch?v=gIGvhvOhLHU&t=282s |
Resources:
https://engineerdog.com/2015/09/09/engineering-a-3-wheel-vehicle-chassis/