RWS Trike

I have been living in Milan for last 3 years and I didn’t see either a single trike or a recumbent bike, for sure out of the city and also other countries we might see more recumbents, inspite all great advantages f recumbent bikes which the most important of them could be comfort and less aerodynamic drag,  but thinking and searching about the reasons  that recumbent are not as popular as normal upright bikes, lead to some obvious facts:

• Recumbent bikes are usually more expensive than normal upright bikes… or at least you cannot find a cheap one as easy as finding a cheap upright bike.
• Riding a recumbent requires some practice and not many people are keen on new experiences…
• Recumbent bikes seem too sporty for an urban environment. And they are not easy to stop and start in constant traffic interruptions.

Considering these facts; Main objective of the new design is to:

• simplicity
• Affordability:  to make it possible to classify it as a low-cost bicycle. My goal for the price is a Trike around 200 euro
• Make it easy to ride with a normal appearance and ordinary rider pose without any need to wear sporty costumes…

I have simplified the concept over and over again and the right now MSA-Trike is as simple as possible while I think I have not compromised so much of its functionality…

The lean steer effect has been applied to design by tilting the head tube a bit forward and it is proportional to the steering angle.  Amount of this lean-steer effect has been adjusted for the average speed of 15 Km/h

Regarding the power transmition, I had a concept about a hub gear which would installed directly on the front wheel without any need to chain, here I simplified it for prototyping and the result is a 2 speed planetary gear set that could be easily prototyped.

Planetary gear ratio depends on which part is fixed and which part is moving:

Planetary gears are usually made of A ring gear, a sun gear, and a set of 3 or 4 planetary gears that are linked together.

I have used ring/Sun/Planetary Gears with relatively 42/18/12 teeth.

Working out the gear ratio of a planetary gear train can be tricky. Let's denote the following:

Tr	Turns of the ring gear
Ts	Turns of the sun gear
Ty	Turns of the planetary gear carrier
R	Ring gear teeth
S	Sun gear teeth
P	Planet gear teeth

The turning ratio is as follows:

( R + S ) ×T_y = (R × T_r )+( T_s × S)

 By default I would fix outer ring by a disk brake, In this case the gear ratio is 3.33( 1 +42/18) but there is this opportunity to release the brake and let the outer ring to rotate, in this case output ratio differs from fixed configuration and it’s suitable for starting  the bicycle movement.

By using a disk brake which in our case is used as a clutch, we can let the disk and consequently the ring gear to rotate… depending on the brake pressure ,gear ratio would change from 3.33 to 1.00 and it happens in a linear way.

I already know that there is some waste of energy due to friction, I still have not calculated the  amount of this wasted energy, so till performing a proper calculation and test, let’s say that we use this gear set just as a 2 speed gearbox. High gear of 3.33 and low gear ratio of 1.00

 2 different ratio modes  would be achieved like this: (Note that in this design the pedal is used as the planetary carrier. So the driving components are 3 planetary gears and the sun is driven component)

High Gear:

If we hold the ring gear in a fixed position, T_r will always be zero. So we can remove those terms from the above formula, and we get:    T_s /T_y = (R+S)/S=(18+ 42/18) =3.3          

With the fixed disk & Ring gear, and the planet gears connected to the pedals as driving elements, turning the pedals and consequently the set of 3 planetary gear carrier, would cause the sun gear and consequently the hub and wheel, to turn 3.3 times.

low gear:

According to the formula, and considering that planetary gear carrier as the driving  element, if  We let the disk and ring gear to rotate, the sun gear would turn with a less angular velocity, at its extreme if we let the ring to turn freely, it would be  ring that rotates with a low gear ratio but higher torque, and the sun gear would not turn at all. As you see it literally mean that by controlling of ring’s rotation we can adjust the ratio of rotation of sun gear and hub and wheel in a linear manner.

Again to avoid any kind of waste we let the ring to rotate freely without any friction but we would limit the rotation by a freewheel bearing that doesn’t allow the ring to overrun the hub and the sun gear… this would result an equilibrium of

Tr	=Ts	=Ty

And the gear ratio equals to T_y  / T_s  =1 which is a convenient ratio to gain speed while starting the bicycle movement.

I am also very keen to know if linear gear change would work efficiently or not, so in very near future  I am going to make a prototype of this gear set.

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PS: I am also planning another experiment with this concept Trike:

As you see the seat  is slightly inclined toward forward; I cannot assert that this is a optimum configuration  in terms of comfort, but the reason I did it like this, is my understanding that  in current recumbent seats, the rider doesn’t have so much maneuverability, as the body weight is being supported by the back and therefore the rider can not move the body  and lean as free as an upright bike. With this concept and shifting some of the rider’s weight on the feet, it might be easier to move the body and have a better control over the vehicle. We can walk for hours and hours with the whole weight of the body on the feet, I guess it also wouldn’t be so tiring for the feet to bear few percentage of the body’s weight during a short urban ride for the sake of the safety and also avoiding so called “leg suck” problem.