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Discussion Starter #1 (Edited)
Dear EV experts,

I'm new to the forum and to EV's in general. I'm amazed to find so much experience here, which is why I would want your help with the small project I'm creating.

Let me sketch you my situation.

I work for an NGO in the Democratic Republic of Congo. We're working with small and very poor farmers in a very remote region. They do all their work manually. Some form of mild mechanisation is highly welcome. The "walk behind tractor" or "roto-tiller" serves as the starting point.

  • fuel (gas) costs a lot here in the interior (2200 francs / liter, that is: 1.8 euros /l or $4.9 / gallon); diesel is cheaper, but still off-limits (about 20% less the price), which is why we don't like IC engines
  • big tractors are too big; people don't have the cash to invest, nor the technical skills. Getting such a machine to the interior (via the Congo river) is prohibitively costly
  • farm fields are tiny: the average field is around 1 acre (half a hectare)
  • we already have several solar panels (to charge the 12V batteries of our big radio and our P.A. system) and could add some more
  • this situation had us decide on designing a simple, small, low-cost electric tractor
The are several back-breaking tasks for which we seek mild mechanisation and for which the tractor should be used:

  • removing roots from trees that have been cut down (slash-and-burn farming is the main type of farming here)
  • removing big chunks of slash (burned branches of, say, two meters)
  • cutting or pushing down weeds and small trees on fallows (every 2 to 3 years, a fallow is re-used; it has then grown a lot of biomass)
  • tilling
  • weeding
  • fertilizing
  • harvesting
  • pulling a cart with produce to the warehouse
Main subsistence crops grown:

-corn, cassava (manioc), rice, beans, groundnuts


Our idea is to train a few people to operate the tractor, and to help others use it. Costs are carried by the cooperative which we have created.

The tractor should be (I know this will be a tall order):

  • multifunctional
  • durable
  • relatively powerful (we've done some tests pulling roots with a Yamaha 125 DT, which worked; the DT boasts 17hp)
  • low-cost (functional: no gadgets!)
  • extremely simple to operate and to maintain
  • should be possible to build the machine in Kinshasa, by local technicians
The tasks it has to perform are short-duration tasks; a capacity to work during 1 hour is already OK.

We made a tentative sketch of what it could look like, which I attach to this post. (Don't mind the simplicity of this drawing).

Now since we've got no expertise whatsoever on EV's, we'd highly appreciate your first impressions, advice, or input.

If the eventual tractor were to work well, we have network resources (contacts at major agricultural and international development organisations) which may help replicate it and make a real program out of it.

Thanks!

PS: I found Woody's E-tractor project, which is great, but of an other order. /woodys-tractor-project-39910.html
 

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Hi and welcome.

I was also thinking the one wheel drive would be unstable, expecially slow speed in the field.

I would be tempted to go with two wheels on the same axle but possibly driven by two geared motors, like the ones use on powered wheel chairs but bigger. If the angled gear drive was by worm and wheel gearing then you would get a big reduction ratio in a compact space and it would remove the need for braking thus aiding simplicity. The tractor could be controlled by separate power controls on each hand grip for each wheel so it would steer like a tank with skid steering.

The wheel hubs could be on bearings on the drive shafts and drive would be transmitted from the shaft to the hub by means of a drive peg from a flange on the drive shaft to the hub. That would allow the tractor to freewheel and be towed manually to and from a job.
 

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I think simple and cost effective are paramount in this design. Solid axle with two wheels and chain and sprocket for gear reduction. At this speed and weight brakes are probably not needed. Steering would just be physical manhandling, I don't think you are doing much more than spinning it around at the end of a row.
 

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Spinning around a two wheel tractor like that is difficult if the axle is solid. With that approach a simple ratchet freewheel would be useful as used in some rotavator designs.

The other thing to consider is whether the tractor is to be funded by an organisation that can afford a good and reliable design made from new parts or if it will need to be made from locally sourced parts of variable quality and possibly preused.

Also if there is to be only one tractor that will be different to one that will be the concept for a short production run that could add value to the community tasked with its supply.
The later case would be better with a reliable supply of parts where as the former could be made of anything that comes to hand.
 
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I think what you need is something like this. These are everywhere around here and are very robust and have lots of torque to dig into the ground. I am sure someone could make one with detachable tools too. Maybe they already have one. Remove the gas motor and put on a nice DC sepex motor and use like 24 volts and simple contactor control. Either on or off. Use the gearing on the tractor for speed control like is done with the gas engine anyway. I turn it on and turn up the throttle and go. I never throttle up or down while using this tiller. It will dig through anything.

Pete :)
 

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Discussion Starter #8
Interesting design but maybe prone to tipping over? I wonder if a more typical two side by side drive wheel design might be better? Low speed torque is of course a DC series motor specialty, that and low cost is why I chose it for my AMPhibian project.
Your project is very interesting, and already offers a good view on the capacity we're looking at. In one of the videos you show how you pull a log through the forest, in a for me highly impressive way! Our chunks of wood are often smaller, but if the tractor can handle a log that big, many of our farmers would be exhilirated.

I read that the DC series motor (is that a "universal motor") demands a lot of maintenance, especially for the brushes? But it's probably the one we need, because of its superior traction at low speeds. (Frankly, I have no clue on electric motors).
 

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Given the speed of even a 36-48v motor there would need to be about 30:1 reduction to a 25" diameter wheel to get a reasonable working speed of 10mph at 4000rpm. The reduction may even need to be more, say 50:1 to bring that speed down to 6mph. Much easier to obtain such reduction with a worm wheel gearbox then a chain.

Even a single worm reduction on an axle would do it and it would be both robust and sealed from the environment for a long life.

It would mean having to buy in an expensive component but could be viable if it was a production run.
 

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I think what you need is something like this. These are everywhere around here and are very robust and have lots of torque to dig into the ground. I am sure someone could make one with detachable tools too. Maybe they already have one. Remove the gas motor and put on a nice DC sepex motor and use like 24 volts and simple contactor control. Either on or off. Use the gearing on the tractor for speed control like is done with the gas engine anyway. I turn it on and turn up the throttle and go. I never throttle up or down while using this tiller. It will dig through anything.

Pete :)
That sort of thing would make an idea candidate for a one off conversion or a perhaps a conversion kit if other similar tractors were easily obtainable.

Not so easy if they needed to be made from scratch for production.

Plenty of food for thought.
 
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The DC motor has brushes to replace but almost never need to be replaced. You'd want a SepEx DC motor so you don't have the issue of motor speed runaway if you use just manual contactor on/off switching. The SepEx motor is just as robust and will run at a specific speed and will try to keep that speed even when a load is applied. It is an excellent choice for your application.

Pete :)
 

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Discussion Starter #12
Hi and welcome.
Thanks.

I was also thinking the one wheel drive would be unstable, expecially slow speed in the field.
Sure. JRP3 and Woodsmith, as said, the design is completely open. I will at each step quickly re-design, so you can view your input graphically.

I would be tempted to go with two wheels on the same axle
I'll draw, because it's also one of JRP3's suggestions. Which makes 2 of you.

but possibly driven by two geared motors, like the ones use on powered wheel chairs but bigger. If the angled gear drive was by worm and wheel gearing then you would get a big reduction ratio in a compact space and it would remove the need for braking thus aiding simplicity. The tractor could be controlled by separate power controls on each hand grip for each wheel so it would steer like a tank with skid steering. The wheel hubs could be on bearings on the drive shafts and drive would be transmitted from the shaft to the hub by means of a drive peg from a flange on the drive shaft to the hub. That would allow the tractor to freewheel and be towed manually to and from a job.
I've thought about this, and have a design ready. The steering via the wheels' motors would be very easy to handle. But I have put it on hold, because it may be too complex and perhaps too costly. Let's not forget that the fields are tiny, and the jobs not too intricate.

But all ideas remain open and welcome!
 
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That sort of thing would make an idea candidate for a one off conversion or a perhaps a conversion kit if other similar tractors were easily obtainable.

Not so easy if they needed to be made from scratch for production.

Plenty of food for thought.
My point, why make from scratch when you more than likely could buy them for less. There are many manufactures of walk behind tractors world wide. I'd almost bet he could get them there. Just gotta do your homework.

Pete :)
 

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To aid options, what sort of resourced and facilities would there be to work within?
Is the preference towards adapting and converting exisiting machinery or developing something from scratch?
 
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Modify what you have. Don't go reinvent one. Cost is a big factor and I am sure there are plenty of very good used walk behind tractors available to modify. The mod should be pretty easy. I was correct, you can get these that have removable attachments for different needs. Perfect for your needs.
 

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Discussion Starter #17
I think simple and cost effective are paramount in this design. Solid axle with two wheels and chain and sprocket for gear reduction. At this speed and weight brakes are probably not needed. Steering would just be physical manhandling, I don't think you are doing much more than spinning it around at the end of a row.
I think you are on the right track. Low cost and simple. Turning is the only operation that may require some force by the farmer, but they're used to heavier things, so that shouldn't be the problem.
 

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I read that the DC series motor (is that a "universal motor") demands a lot of maintenance, especially for the brushes? But it's probably the one we need, because of its superior traction at low speeds. (Frankly, I have no clue on electric motors).
Brushes are the only real wear item, other than bearings, but should last a very long time. EV's typically estimate replacement around 60,000 miles of use or more.
 

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Discussion Starter #20
Spinning around a two wheel tractor like that is difficult if the axle is solid. With that approach a simple ratchet freewheel would be useful as used in some rotavator designs.
In fact, the tiny wheel in my first design, is a such a freewheel. Turning this one-big-wheel tractor would be very easy. But spinning-over may be a prob.

The other thing to consider is whether the tractor is to be funded by an organisation that can afford a good and reliable design made from new parts or if it will need to be made from locally sourced parts of variable quality and possibly preused.
Well, for this prototype we'll use new parts for the frame, but all the rest will be locally sourced. The Congolese are masters in finding decent used stuff or in re-furbishing it (and they're also masters in quoting you a hefty price once they know you're "NGO").

Also if there is to be only one tractor that will be different to one that will be the concept for a short production run that could add value to the community tasked with its supply.
The later case would be better with a reliable supply of parts where as the former could be made of anything that comes to hand.
I prefer a kind of "open-source", ultra-basic design, that can serve any motor one finds.

If ever there were to be more than one of this to be made, it would still be manufactured locally, with few parts being sourced abroad.
 
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