“A big problem I see in a bicycle PTO is stability. The stand has to be much mor than the standard already on the cycle. It would have to be independent of the cycle for weight reasons. In which case you wind up with a ready frame missing ony a crank and gear chain. Would be far easier and most likely cheaper to build the whole thing than repurpose a bicycle.
BTW what is the price of a old style bicycle?”
The quote above by @jtd is from a conversation on reusing stuff lying around to do routine things that might otherwise be outsourced at some cost, or be bought readymade as finished and probably packaged goods, thus adding in some, very real but mostly overlooked, sense, to the human energy burden on the planetary ecosystem.
In particular, it arises from a nice looking jugaad that was circulated, of bicycle parts being added to a small grinding mill. The video suggests that women who are too busy to get out and about for a walk or to the gym could thus get the equivalent of a home gym machine, while grinding the atta needed for the day.
Apart from all the questionable assumptions in that premise, it seems it’s probably a good idea to examine and create awareness of the possibility of dual usage of any such device as a bicycle, rather than proposing a design that demands dismantling the bike and using the parts to make a different gadget.
Of course, it is possible that mass manufactured items like a bicycle frame might be cheaply and easily sourced anywhere in India, and so the project might become one of repurposing rather than reusing or recycling (a word I was trying to avoid, since not many people appreciate my fondness for puns). That needs to be examined first, while creating such designs.
The engineering part of this discussion, the reason for the subject title, is that existing gadgets usually have a particular motion that is accessible, such as the rotary motion of the bicycle. The motion that is needed by the new design might be in a different axis or of a different kind, such as a pure linear motion, or an oval etc. The conversion mechanism that enables this is called a Power Take Off, or PTO, literally the accessible part of the inbuilt transmission, that can be used to extend the transmission and deliver the desired motion for the new end purpose.
It should be noted that plug in designs for bicycles to drive water pumps for agriculture have been around for decades. The bicycle is not dismantled, it is lifted and placed in a frame for the period it is needed, and can then be lifted out and wheeled away.