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 Sociable (side by side) Tadpole Trike Design

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bhakuniabhi Posted - 04/18/2014 : 14:24:14

I am working on a project where my problem statement is to "build a hybrid three wheeled vehicle (tadpole config and side by side seating) which is to be driven by two riders and may alternatively or simultaneously be driven by electrical power as well". I am currently working on the human powered drive - basically determining what gear ratios to work with and what torque ranges to expect. I have tried to find some text on this but I am unable to get some good useful info on the design. I am planning to transfer the power by both driver to a jackshaft and then back to the rear wheel from there. Can someone suggest me how to calculate the torque required to pedal the vehicle upto a desired speed. I am highly confused at this point of time and am running late due to this. SO please help.

Abhimanyu Singh Bhakuni
Bachelors in Engineering (Manufacturing Processes and Automation)
University of Delhi, INDIA
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xarvox Posted - 05/07/2014 : 02:49:10
Unless your endevour is purely academic, stuff like expected torque isnt really your bigger problem..

You will recieve the torque that two cyclists can deliver, about 50NM, but you cannot accurately calculate the required torque for a specific speed since you can pull the same top speed with a wide spectrum of power input.
The acceleration is of course dependent on the torque, but it also depends on total weight, rotating weight (wheels), rolling resistance, aerodynamics, temperature and elevation above sealevel.
It might even depend on wether youre heading home or to work.. ;)

To make things a bit easier for you, have a look at bicycles that do the same speed as your intended goal and use that gear ratio.
This method fails to take weight and aerodynamics into account, but you will get a rough estimate thats probably more exact than guesswork alone.

I would suggest that you use freewheels on your jackshaft, so both riders can pedal independantly.
This could also be a good place to install your electric motor, thru a third freewheel on the jackshaft.

I would have the motor turn the jackshaft at around the same speed as the cyclists can turn it when making about 80-90 rpm on the pedals (cadence) and use a single gearing system between the rear wheel and jackshaft.
This will probably give you the least headache and a very simplistic transmission.

Im currently building a similar project, alltho a delta configuration without the electric assist, but you might get inspired.. :)
Don S Posted - 04/19/2014 : 13:42:01
Bicycles use the method of calculated gear inches, which is basically just the distance that a tire of a given diameter (in inches) would travel in one revolution. Another way to think of it is that if the chain ring and rear cog were the same size and your trike had a 20" rear tire, than one revolution of the cranks would advance your trike 20 gear inches or a distance of 20 X pi inches. (metric conversions necessary) . The selected gearing varies based on rider fitness and cycling experience, the terrain, and vehicle design. There are likely too many variable involved (CdA and Crr. etc.)to be able to calculate the torque required to reach a given speed with an untested design but it takes a strong rider to continually produce 1/2 hp. You can find usable estimates for rider power outputs and the other variable to determine a maximum estimated speed and then, using cadence, calculate the gear inches required to equal that speed and determine the gear ratios required in your design.

"it's important to understand what makes them fast. It's more important to understand what keeps them from going faster." DS

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