I have read a few threads on this forum about the use of tractors and found good food for thought. I am looking at buying 10 acres in the next couple of years. I plan to rent the equipment that I originally need to do any earth moving or very repetitious work that can best and most quickly be done with very expensive equipment. Given the size of land, my age and the things that I want to do, I can see the need to have some kind of utility vehicle to make life not only easier but to save wear on my body. I would like to suggest this idea for your critique:
A steel frame about 6' by 6' (1.7m by 1.7m) - or 4' by 4', etc. and about 2' (60cm) tall mounted on tracks (tank tracks, not wheels). Each track has 2 electric motors. There is an additional electric motor mounted to a pto for accessories or to operate a hydraulic pump if necessary. The top of the frame is covered by steel or wood, and is nothing but a platform, save an area for a driver (the device could even be controlled remotely). Under the top platform is an area to carry batteries and mount tanks to carry water or nutrients for crops - water can be added for nothing more than additional weight. The top platform would also have a small crane/mechanical arm to facilitate loading and unloading. The generic nature of the moving platform would be such that accessories from many other brands of tractors could be used. Top speed would be about 10 mph (16kph) The platform should be capable of carrying at least a thousand pounds - (450 kg) when not pulling a plow, ect in additional to handling the weight of the platform itself. I don't know how to use any CAD software yet, but what I am imagining would look like the attached photo, with the exception that the tracks would be mounted under the vehicle to give it more ground clearance. A very bare bones, utility vehicle that could easily be modified for almost any purpose.
I choose electric motors to reduce the complexity of the vehicle - no transmission needed, no drive train, no dinofuel, etc. Electric motors have very few parts, and with a little bit of training, can be repaired by most people. There also would not be any obnoxious smells. Electric motors also lend themselves more readily to use a remote control. Can you imagine sitting on a lounge under an umbrella, sipping lemon tea while plow or mowing your land? It still would require some additional electronics to make it safe but I am enamored by the idea.
Perhaps and ideal situation - if plow, tillers, seeders, disks, etc could be mounted underneath the platform rather than being dragged behind the vehicle to minimize the area required to make turns.
What are your thoughts? The platform would be useful for any situation - a general permie community or someone who has to grow a large area of one or two crops. The only reason I am looking into the mono crop situation is to grow something that can be processed either into alcohol or biodiesel for fuel for my vehicles. Also, for growing one staple that can be used to feed a variety of animals, supplemented by other things as necessary.
Cost? Just by poking around to some mfg sales rooms in China, I think 4 x 5hp low rpm motors would be about US$1,500. The rest of the expense - metal, welding, track and suspension, I have not looked into yet.
Thanks! That is good feedback. With most farm tractors I have seen, weight is not viewed as a problem because it usually equates to traction. Secondly, by using tracks instead of wheels, the surface area that the weight is applied to is increased substantially - psi of contact area goes way down - 120 kg over 960 in2 (track area) vs. 120 kg over 60ish in2 (sorry but don't know how to calculate the area of the contact region between a round tire and flat surface. I would probably use 48 v motors - 2000 watts - 250-300 rpm max - to get the power that I need to plow, etc, though I know that the weight of things would be the same. Perhaps 2 motors would be adequate, or 2 x 2000 watts or even 2 x 1000 watts. I have to get info on power needed to pull the accessories I would need. I think your calculation of a battery is too small. It certainly would not be the cheapest option to plow or till a field - I am also certainly not Bill Gates - but it does provide a versatile solution to a myriad of problems faced on a homestead including lifting, transporting goods, soil preparation and crop management, while impacting the environment minimally. The battery pack would even serve as an portable/emergency power source for other appliances and machines.
I've gotten to poke my nose into a few projects that were similar in concept over the years. One of the most promising projects was intended as part of an overhaul for large scale farming and land management to address farming in regions prone to field erosion by creating a practical system of semi-automated 'mini-tractors' that would then work fixed width terraces. (The robots would allow a single 'driver' to oversee a dozen or more 'tractors' at a time which would then be able to effectively operate in narrow terrace bands that traditional tractors would be too wide to work in. The narrow terrace method being ideal for how easy it is to convert an existing hill side to without the need to move excessive volumes of material or requiring bank reinforcement.)
One thing that can greatly increase the flexibility and usefulness of an electric tractor system is the ability to quick-swap the batteries. Unlike the electric car a tractor can frequently benefit from the 'excessive' weight of the traditional deep cycle lead acid battery, but systems that aren't designed to quickly and easily pull the batteries from the unit and replace them with freshly charged ones are then stuck out of action while the cells are slowly recharged. If you design your batteries such that one person can pull up to a 'swap point' and quickly transfer the batteries then you have greatly increased the work cycle of the unit. While this does mean you have to pay that much more for your battery collection, it does have the added benefit of being able to treat them in a far more friendly manner to extend their life cycle before they need to be refurbished.
It is however much harder to design a system that works well for swapping. Electrical safety issues and all that, and handling swaps with potentially wet/muddy environments. This means you have to be very careful with your material selection choices and connector styles. A 'hands off' swap is ideal, but keep the system simple. Shorting out a battery because you're tired is not a fun way to end a hard work day.
And remember, your 'swap station' doesn't have to be a fixed location. It can just as easily be portable, such as a trailer you haul to the site and leave near the current work area, or a second 'tractor' dedicated to hauling cells between the charge station and work area.
Also, I wouldn't suggest planning to use water as dead weight for additional traction. Water is only a good option if you're working in conditions where you expect you might need to drop it for whatever reason, but otherwise I would suggest designing your bed to support easily adding additional battery racks for when you need more weight. They'll give you the extra mass along with the extra juice you need to haul them around and keep working.
You have the right idea with the lifetrack, but, yes, I hope to make it electric, and will likely not have it use so many different attachments - the purpose is to do routine work, not work that is done only one time, or every five years or so. The reason for using electricity is to make it more agreeable to indoor work, inside a greenhouse. Also, I am more familiar with electric motors than I am with gas or diesel - electric motors have very few parts, so easy to repair...I will keep on asking questions I wish I could find an electric motor guru now.