Sam Shepherd, MEE, did a thesis in which he modified a professional product development cycle for use by engineers so that it could be used by farmers to make tools for themselves. His thesis was focused on the development of an electric lay-down work cart. You can find his paper here: Product Development for Small Scale Farms
Shepherd's modified product development cycle was a success in that it brought about the creation of a working work cart. His cycle still needs to be optimized for use by small scale farmers. It is my opinion that it is still too time consuming for realistic adoption by farmers. It would still be useful for an engineer or someone not invested in farm work. You can find his process here: Shepherd Eppinger Product Development Cycle, Improved. I highly recommend reading through his comments there. My main complaint with his cycle is that it begins too abstractly, without any idea of what the product will be. Realistically, in my opinion, farmers generally know what they need but can't afford it. I discuss that in the Simplified Product Development Cycle Version 1.
Simplified Product Development CycleVersion 1
You can view version 1 of my simplified product development cycle here: Simplified Product Dev Cycle v1
Version 1 was an outline with some good ideas but had many flaws. Shepherd himself gave some great feedback on it which allowed for a second version to be created.
Version 2 can be found here: Simplified Product Dev Cycle v2
This is a living document and should be commented on thoroughly by anyone interested. It is still in outline form. Ideally the cycle would be an outline followed by a write-up of each step. There is a massive amount of documentation from Shepherd's work cart which utilized his development cycle and he has given permission for it to be uploaded.