Now that I have an account I can discuss some basics of engines, transmissions and so on. In short a technical discussion:
Where to begin? As with any engineering problem we begin with what the limitations are for our project:
1) A combustion engine with a maximum fluid capacity of 50cc (cubic centimeters) to avoid hurdles with VDOT/DCVA/MVA.
2) The ability to operate on biodiesel (typically used vegetable oils passed through a strainer to remove the larger carbon chains)
3) Optional electric start
4) Inexpensive. Both engine and frame must be easy to come by
5) Target price. The resultant 'scooter' (the vehicle we are targeting) must fall within a price range that is affordable and competitive. For example, scooters may be purchased via mail order for close to $1500 (Northern Tools sells them, 2 are all electric)
6) Uncomplicated. We aren't building the bat cycle here.
7) Limited speed/acceleration: The scooter should not be able to exceed 40mph on a straight level road in no wind conditions.
So, let's talk power: 50cc displacement will garner about 1hp (this is a very back of the napkin equivalency). Can one horse push around itself and one rider and a backback at 20-35mph. Transmission will probably have to operate in one of three ways:
a) Direct drive over a chain or belt with a clutch on the engine or,
b) A torque converter on the engine, adds weight, cost.
c) Friction drive where the engine has a small wheel that is pushing against the rear tire and drives it with friction.
If we choose option a) we'll need the driven part of the transmission (think rear sprocket on a bike) to be big enough to handle a certain hill grade with a certain weight.
Option b) is the most efficient in terms of operation. But again, it adds weight and complexity. Performance under differing conditions will be best at high RPMs (because the drive wheel drives the belt in the torque converter to reach a certain RPM to engage the driven wheel).
Option c) requires a strong spring to push the driver wheel attached to the engine against the tire without wearing it out while still allowing for reasonable acceleration. Inherently and from personal experience, the power losses are pretty big with a moderate grade (i.e. an uphill).
More to follow....
