Cleaning out my garage of the summer projects has turned into finally organizing all my landscaping tools. So it's taking longer that I wanted, but it will ultimately be better. Hopefully, I'll finish my chore this week so I can work on the lawnmower disassembly next week.
Meanwhile, I've been working on figuring out the drive system. First thing was to figure out the gearing between the front and rear wheels. I had already arbitrarily selected a 36-tooth sprocket (choice was between 36 and 44 for the bore diameter I wanted). This turned out to a good choice. In order for the rear wheel to rotate at the same rate as the front wheels, the rear sprocket should have 28 teeth--a standard sprocket size--to the front's 36 tooth.
The basics of the drive system so far is: the pedals (w/ front derailleurs) are chained to freewheels (w/ rear derailleurs). The freewheels are coupled to a common shaft that would drive the main transmission chain. This is where things get a little fuzzy.
I want the drive to have two modes, road and mud, with an easy way to switch between them. The road mode will initially be geared 1 to 1 to the freewheels shaft with the final ratio determined after actual testing. The mud mode would be significantly geared down to increase torque output at the wheels.
To keep the weight down, I want to do this with timing pulleys and belts and use sprockets and roller chain only to interface to the wheels.
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