Tadpole Trike, Dymaxion Drivetrain (design)

[skyl4rk]

I am wondering if anyone has any thoughts about a Dymaxion drivetrain for a small tadpole trike. The drivetrain would have a subframe with the motor and rear wheel which pivots on the main frame, so that steering is accomplished with the rear wheel.

The rear subframe would be complex, it has to have suspension, motor, drivetrain, controls and rear wheel all on a moving subframe. The front end could be simple, in fact a trailer axle with the addition of appropriate springs and shocks would probably be adequate for a light vehicle.

The body could be Dymaxion shaped with improvements, such as a smoother surface area than the original. A Pillbug with a narrow tail would be a good design to emulate. The body could be molded or could be developed from flat surfaces. It would cover the wheels. For a small trike, the forward part of the body could be lifted up as a door with the hinge at the very front of the vehicle.

The motor/drivetrain could be a number of types, electric motor/chain or hubmotor, light gas motorcycle take off, small diesel with cvt (Comet type).

The subframe would be a welded steel box that included some type of suspension for the wheel, motor and transmission mounts, and a roller and track system that allows the entire subframe to swing right and left to allow for steering.

http://www.youtube.com/watch?v=fO80IjrO9d8

[skyl4rk]

Here is a build of the original design, I think that for a smaller, more efficient engine, the entire assembly (engine, drivetrain, wheel) could turn, which might simplify things a bit.

http://www.youtube.com/watch?v=wZdpO2kP_q8

[akumabito]

It looks heavy, and rear-wheel steering is very unstable, even more so in a trike.. definitely not a configuration I'd be aiming for..

[JasonG]

Sorry to be negative, but stay away from a rear steerer.
Spend some high speed time in a forklift or drive a car in reverse to get an idea of the issue.

[akumabito]

hah, yeah, forgot about turning a car in reverse. It can be scary as hell, to say the least, even at moderate speeds. You can try it in your car, just get it up to 10 Mph in reverse, then do a sharp turn.. scary, I tell ya! don't try it at higher speeds or with a tall vehicle like a van or SUv - you might actually roll it!

[gasstingy]

Emulating the Dymaxion body design is an ambitious project but doable, if you can build a body from scratch. Personally, I'd have to join the naysayers about rear wheel steering though. Turning a corner in town would swing the rear of the car way out to make the front go where you want it to go. Since it is virtually unheard of to do that, vehicles near you would not be expecting it and it would be too easy to hit someone while trying to make a turn.

[skyl4rk]

I have spent quite a bit of time driving a three wheeled "hilo", the type where the drive wheel is connected to a steering bar, and you stand on a shelf behind the drive wheel with the forks and fork wheels forward. Myself and other workers at the warehouse were very skilled in speeding through aisles of pallets and flying onto trucks to drop pallets off.

However, that was at speeds of well under 20mph.

If you are going down a road at cruising speed and you turn the wheel hard (in any car) you will be going off the road. Is it possible that driving with rear wheel steering is something that can be learned?

One down side of a standard front steering tadpole trike is that when turning sharp corners, the rear wheel has a tendancy to break loose from the road at high speeds. Using the rear wheel as the steering wheel could increase that tendancy. Using that wheel as the driving wheel might also have an effect, although the weight of the engine could compensate.

[skyl4rk]

http://www.youtube.com/watch?v=D7POp3jvikY