# Two-wheel electric tractor for Africa - your expertise needed!



## congofarmer (Jan 22, 2011)

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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## JRP3 (Mar 7, 2008)

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.


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## Woodsmith (Jun 5, 2008)

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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## JRP3 (Mar 7, 2008)

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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## Woodsmith (Jun 5, 2008)

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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## JRP3 (Mar 7, 2008)

A narrow track width and moderate weight shouldn't be that hard to spin. Tip it slightly to unload the outer wheel and spin it around on the inner. The chain and sprocket design allows use and reuse of fairly standard items with minimal fab and machine work.


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## Guest (Jan 22, 2011)

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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## congofarmer (Jan 22, 2011)

JRP3 said:


> 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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## Woodsmith (Jun 5, 2008)

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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## Woodsmith (Jun 5, 2008)

gottdi said:


> 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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## Guest (Jan 22, 2011)

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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## congofarmer (Jan 22, 2011)

Woodsmith said:


> Hi and welcome.


Thanks.



Woodsmith said:


> 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. 



Woodsmith said:


> 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. 



Woodsmith said:


> 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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## Guest (Jan 22, 2011)

Woodsmith said:


> 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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## Woodsmith (Jun 5, 2008)

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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## Guest (Jan 22, 2011)

This one is available worldwide. http://www.paddyricetransplanter.com/walk-behind-tractor.htm


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## Guest (Jan 22, 2011)

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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## congofarmer (Jan 22, 2011)

JRP3 said:


> 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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## JRP3 (Mar 7, 2008)

gottdi said:


> 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.


That may not be the case depending on his location.


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## JRP3 (Mar 7, 2008)

congofarmer said:


> 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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## congofarmer (Jan 22, 2011)

Woodsmith said:


> 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.



Woodsmith said:


> 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"). 



Woodsmith said:


> 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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## congofarmer (Jan 22, 2011)

gottdi said:


> 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


Pete, thanks, this is one of the inspirations for our tiny tractor. In fact, all roto-tillers, walk-behind tractors, and one-wheel tractors have been the inspiration. 

However, it's not difficult to design a similar frame from scratch. We have many people here who know how to weld, and the sheer number of car, truck and motorbike mechanics is mind-boggling. They are highly skilled (especially when you have to use creative skills) and they don't ask a lot of money for their work.


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## JRP3 (Mar 7, 2008)

Woodsmith said:


> 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.


Run a 48 volt motor at 24V to cut motor speed in half.


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## congofarmer (Jan 22, 2011)

gottdi said:


> 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


True, if only we could find these here. But we haven't. As said, all the metal-work would not be too costly and relatively easy. The electric parts shouldn't be too difficult either. The main problem is the choice of motor and batteries, deciding on how to reduce gears and which kind of transmission we'll use, and the general outlay of the design (where to put the wheels? How to make it turn?, etc...).


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## congofarmer (Jan 22, 2011)

Woodsmith said:


> 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?


Well, given that we have some room to play (both in terms of cash and human resources and time), we might want to develop something from scratch. 

It would also facilitate getting a fund for any replication program (but this is the distant future), because "innovative" concepts get money easier than "adaptations" or modifications of existing designs. (That's my experience).


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## congofarmer (Jan 22, 2011)

gottdi said:


> This one is available worldwide. http://www.paddyricetransplanter.com/walk-behind-tractor.htm


Gottdi, if there isn't a dealer, we will never import it. Import costs for Congo-Kinshasa are one of the highest in the world. 

Sadly, there are no walk-behind tractors in Congo. Perhaps they can be found in Congo-Brazzaville, but we'll have to check this out.


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## toddshotrods (Feb 10, 2009)

Nice project. What type of materials and fabrication capabilities would be available? For example, do you have steel angle iron or tubing available for building the frame? Do you have the materials and skilled labor to work with it? Are there electric forklifts or some type of common machinery you will be getting the motors from, or wil they be sourced new? More info from you will narrow the options and ideas down to those more applicable for you.

I agree with the two wheel, side-by-side, design. It's the most practical, most stable for the intended purpose. I actually had an antique walk-behind tractor when I was a teenager. Got it from a neighbor to build a gokart, but never did. It had a plow on it.  I imagine it would have been ideal for what you need.

Gotta go back to work now, but I'll be back later with more input and ideas. I agree with the thought that muscling it around to change direction wouldn't be that big of a deal. I used to do that all the time with tillers in the garden.


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## Woodsmith (Jun 5, 2008)

How about a two fold design?

First off you need a design for a simple motive impliment, the simplest is the two whell tractor. They are fairly easy to design and make with scraps to suit the local resources and needs.

Secondly you could look at a simple motive power source. A sepex motor with a simple means of control and a battery cradle that can be easily constructed and used to replace any equipemnt that otherwise has a small petrol engine.

The two would give you a locally made tractor. The power unit on its own would be a conversion system for existing equipment with a greater range of application.
Depending on what salvageable machinery is available then either a sprocket or a geared output with something in the region of 20:1 to 50:1 depending on application.


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## Jimdear2 (Oct 12, 2008)

This is a wonderful idea, a lot of american small farmers used equuippment ilke this for the household gardens (your 1 acre plot). You might read this article that compares a couple of currently available machines.

I do want to stress that a build it youself project i.e. making something out of off the shelf components is quite possible. But I would think that anything built like that would probably have a very limited life under the circumstances you describe. I am sure that some of the international agencies could help with engenieering and design.

http://www.motherearthnews.com/Mode...Behind-Tractors-Comparison.aspx#ixzz1BmkYpcY4

The BCS is a tough machine and has many (I've heard up to around 300)attachments. I can only think that you would want something currently in production (look at their transmission warrenty). You might contact the manufacturer in Italy to see if the machine could be made available electrically powered, in kit form or less engine for conversion.

The other machines of this quality such as Gravely and Allen Bradley are no longer in production and have become collectors items.

I have heard mention of Honda producing a walk behind. You might check with their power products division. Again ask if it is available as an electric or without power plant ready for conversion.

Ther is still a lot of small farmer equippment made in Eastern Europe, maybe you can find something there.

My feelings are whatever you do, you would want to stay in the 12 to 24 volt range. Dependin on how many units you plan even a custom (Extra Tough) motor and controller package could be developed. You would for sure want something like a sepex setup so a blown belt or chain wouldn't equal a blown motor.

The speed of most of these tractors were controlled by the transmission gear chosen so the controller could be a sealed single speed thing. Just on/off.

As a last resort look at China, go to Ali Baba

Hope this helps, 
Jim


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## Harold in CR (Sep 8, 2008)

If your welders are as good as you say, and you have cars and trucks all around you, why not cut down a car differential and axles ?? You can attach pulleys, sprockets, gears, right on the input shaft, and the housing will already have "spring pads, to attach a section of cut down car or truck chassis. 

This is done all the time. 

I would cut the axles so one end is cut on two sides, and fits into a single cut out on the center of other half. Clamp in an Angle piece, and weld and turn, to keep it straight. You will never break that joint with what you are trying to do. You could even put the joint inside a strong tube and just weld the ends of the tube. That way, you don't take out the strength of the axles where you cut them. 

Tires and wheels should be easy to change out. This could turn into a common design for selling or renting out, so to speak ??


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## Jimdear2 (Oct 12, 2008)

Here are a couple of thoughts.

A lot of make do tractors were constructed from reinforced car or light truck frames with two and even three transmissions and tall mud and snow tires.

You say you have a lot of people with good mechanical skills. Do a Junk Yard Wars type competetion. With one rule, the components have to be plentiful.


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## congofarmer (Jan 22, 2011)

Before replying to the new input, first a quick pic of the two-wheel design. I know this isn't a great innovative concept, but I like to sketch the things we discuss. Even if they're extremely simple.

This is many people's suggestion, and I think I'd agree with its simplicity:


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## JRP3 (Mar 7, 2008)

That looks good. Another idea might be to take your design and put a tray or basket over the battery or on the front for carrying heavy objects such as rocks or wood. Maybe you could clarify this but I get the feeling that some of the posters are overlooking the realities of your area, where finding some scrap metal, chains, sprockets, and maybe even old motors are one thing but shipping in new or even used previously built tractors are an order of magnitude more difficult and not cost effective. Cheap labor means anything that can be built on site is going to be a better choice.


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## congofarmer (Jan 22, 2011)

JRP3 said:


> Maybe you could clarify this but I get the feeling that some of the posters are overlooking the realities of your area, where finding some scrap metal, chains, sprockets, and maybe even old motors are one thing but shipping in new or even used previously built tractors are an order of magnitude more difficult and not cost effective. Cheap labor means anything that can be built on site is going to be a better choice.


Well, the situation is nuanced. Kinshasa is (perhaps) Africa's second biggest city, with an estimated 10 million inhabitants. 

If you search well, you will find almost anything, including perhaps a walk-behind tractor and a new, imported, highly expensive electric motor. But this requires a real search, and there are few channels in which you can work. You mostly depend on luck.

There are no real dealers of quality products, except for a few houses like Iveco and Yamaha. And even they have very limited stocks and choice of products. What is more, their price is consistently much higher than if you were to buy in the U.S. or E.U. 

This is due to excessive taxes (on imports) and Congo's problematic logistics. 

In short, we're touching one of the key reasons as to why the country is in a bad fix, and develops so slowly. 


On the other hand, Kinshasa is a gold-mine for the so-called "récup" - that is all kinds of used goods that can be found, repaired, refurbished, adapted, what have you. There are literally tens of thousands of people in the informal economy who depend on this sector.

It's here that we're looking into finding the materials for our little experiment. 

But then suddenly, when it comes to, for example steel products and the skills needed to manufacture something - there is no problem. Most basic steel products are to be found new (or, again, recup): tubes, plates, bars, t-frames, etc... Welding and metal workshops are plenty. 


In short, as a starter, I could say that it's best to source everything locally. Importing is simply out of the question - unless you can rely on a person who can bring the object in his luggage from Europe or the US to Kinshasa. Else, importing is simply a losing proposition.

Let's not dramatise the situation: there are people here who succeed in building huge boats (barges) with very powerful engines and everything that this requires. It's doable, but you need some creatives and people who can search stuff for you. In this sense, the e-tractor is not a big project; in fact, I don't see any problem in finding the necessary materials. 


On a final note: electric components should be kept to a minimum (not too many controllers, etc). But I can buy them here (EU) and take them with me in my luggage. But all the other materials: sourced locally.


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## JRP3 (Mar 7, 2008)

Electrical components could be as simple as a solenoid. You could do something a bit fancier with a few solenoids to switch between 12 and 24 volts, a simpler version of this:
http://www.poormansev.com/id24.html


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## toddshotrods (Feb 10, 2009)

Due to time constraints, my CAD models are even more rudimentary than yours, but will hopefully get the points across.

I think you should build a sturdy steel basket main frame that would hold the motor and batteries, handle all the torque reaction and stresses, and balance the weight of the motors and batteries evenly over the axle. Considering the tasks you have in mind, I would want to make the tractor as naturally balanced as possible placing as little stress on the operator as possible. Long, wide, handlebars will allow the operator to easily counterbalance forward and backward, and maneuver the tractor easily. For tasks where you need more proactive counterbalancing, you can have bolt on caster wheels.

A standard size main frame would also allow you to develop different drop in powertrain combinations. So, for example, if you had two different motors you could have a drop-in powetrain cradle for each one. That way if one was down for the service the tractor could its work with the back-up powertrain. Attachments and accessories could be contracted out to fit the frame, and simply (ideally) just bolted on when they arrived.


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## congofarmer (Jan 22, 2011)

toddshotrods said:


> Due to time constraints, my CAD models are even more rudimentary than yours, but will hopefully get the points across.
> 
> I think you should build a sturdy steel basket main frame that would hold the motor and batteries, handle all the torque reaction and stresses, and balance the weight of the motors and batteries evenly over the axle. Considering the tasks you have in mind, I would want to make the tractor as naturally balanced as possible placing as little stress on the operator as possible. Long, wide, handlebars will allow the operator to easily counterbalance forward and backward, and maneuver the tractor easily. For tasks where you need more proactive counterbalancing, you can have bolt on caster wheels.
> 
> A standard size main frame would also allow you to develop different drop in powertrain combinations. So, for example, if you had two different motors you could have a drop-in powetrain cradle for each one. That way if one was down for the service the tractor could its work with the back-up powertrain. Attachments and accessories could be contracted out to fit the frame, and simply (ideally) just bolted on when they arrived.


Exactly. Thank you for the drawings. This is the most elegant and simple solution. It can be easily made with the steel materials at hand here.


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## JRP3 (Mar 7, 2008)

Should the weight be set further forward since attachments at the rear would shift the balance back?


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## toddshotrods (Feb 10, 2009)

congofarmer said:


> Exactly. Thank you for the drawings. This is the most elegant and simple solution. It can be easily made with the steel materials at hand here.


Surely.  I forgot to mention that I was also thinking with the idea of importing needed supplies like pillow block bearings to mount the axles, sprockets, chains, etc, in your suitcase as you said. The tractor itself is a product of the area, the rest is open to interpretation.


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## JRP3 (Mar 7, 2008)

That could be a heavy suitcase


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## toddshotrods (Feb 10, 2009)

JRP3 said:


> Should the weight be set further forward since attachments at the rear would shift the balance back?


Not for a universal design. You can always shift the weight with counterweights, attachments, etc. IMO, you would want the basic design to be as naturally balanced as possible. That way your not fighting to achieve a natural balance, just adapting to the situation.


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## Wiredsim (Jul 4, 2008)

What kind of batteries are available in the local market? Lead Acid deep cycle like Marine or better yet Golf cart batteries? I don't see the weight of Lead acid as being as much of a negative for this usage. Looking at that basket like design you could balance the cart with one battery on either end and the motor in the middle. 

You could definitely use Parallel to Series switching as a method to control speed. If you used solenoids as mentioned above it would only be limited by your number of batteries, such as 4 x 6, 3 x 8 or 2 x 12. 2 speeds would probably be enough if you designed full speed to be just faster then a normal walking gait.

What kind of electric motors are available? Golf cart motors? Motors from 
electric forklifts? Motors are heavy to ship and not easy to build locally unless there is already an established manufacturer. Golf Cart motors will easily give you the power you need with a fairly low RPM. You're going to want a motor that runs in the 2-4k rpm (lower the better) at the full voltage and can handle the amps needed at the lower voltages.

I'm surprised there isn't more interest in the Rototiller functionality. Surely pulling objects isn't the only need? 

Aftermarket car parts available? Motorcycles or scooter parts? I think Chain or Belt drive parts common from other purposes is going to be your best bet for replacement parts and get the reduction you need. If the motor runs at 2000rpm for example, you will need an ultimate reduction of roughly 50:1 to get to walking speed (~3mph). Scooter gearboxes often give you a 5:1 reduction, than another 10:1 on chain drive gets you the rest of the way.


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## JRP3 (Mar 7, 2008)

Might need to use a jack shaft setup to get the gear reduction needed, though there are some motors built for lower RPMs.


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## Wiredsim (Jul 4, 2008)

After thinking about your challenge, I suspect the only readily sourced motors on the local market with enough power will be used Alternators. This is actually a reasonable solution, as they are quite powerful depending on the model.

Here are a couple of resources about how to convert:

http://www.rcgroups.com/forums/showthread.php?t=905411

http://www.endless-sphere.com/forums/viewtopic.php?f=30&t=16328

A couple of cliff notes for you:

You need a Sensorless Brushless controller, such as a RC ESC to drive the stator. This is extremely simple to setup, you just disconnect the voltage regulator and connect the three wires to the controller. You can also add Hall sensors easily to these to improve the low speed torque and starting ability. I think it would be fine without if you are able to get the motor up to speed without a load, using a clutch of some kind (even a belt clutch using a tensioner could work).

You need to supply voltage to the rotor, the torque you get at a given RPM is greatly dependent on your rotor voltage/current. If you use a simple Brushed controller for the Rotor, you can vary this dynamically. However I think a simple DC-DC converter will get you what you need, it looks like the rotors usually saturate at around 5-9volts. If it is a switchable DC-DC converter all the better (or you could use two and switch one in and out of the circuit to get two speeds). A Rheostat is another way to adjust the voltage to the rotor. 

You will want to run this at a higher speed then I mentioned before, depending greatly on the particular model of Alternator used. Truck, Marine, Bus and other large commercial Alternators are better then car units. However just about any unit will get you a decent amount of power.

The nice thing about this is that you can easily bring a large amount of controllers and DC-DC converters in your luggage, as they are small and light. All that remains would be the batteries as a local challenge. However even car or truck batteries will work as a worst case scenario.

Good luck!

*Here is a good example picture*


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## Wiredsim (Jul 4, 2008)

Here are a couple of links about electric tractors that already exist:

General info:

http://www.eeevee.com/tractors/TNF_article.html

GE Elec-Trak tractor:

http://www.builditsolar.com/Projects/Vehicles/ElecTrak/ElecTrak.htm

http://www.crystel.com/Elec-Trak/E-20 Tractor.html










The Sunhorse:

http://www.freepowersys.com/suhorse.htm


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## jk1981 (Nov 12, 2010)

It seems to me your design has to use readily available parts that are simple to modify and will work so long as they're nearly right since you're unlikely to find the same part twice if something needs replacing.

To me that says something simple like a lightly modified car or light truck starter motor (possibly with an alternator fan grafted on for cooling) for power, possibly one per wheel to make turning easier and to give more go and a simple chain reduction drive from motorcycle parts, gear it for slow walking speed. It's robust, easy to clean/service and there are no oil seals to get right. Use the starter solenoids from a car for on-off forward control, they're plentiful and simple.

Mechanically you need to look at where the load attaches and how the thing balances if you're to get decent traction since it'll be pretty light (100-150kg at a guess). You may need to have the man-handle in one position for maneuvering around the yard or load carrying (well balanced) and another for pulling (unbalanced until the load is applied). To make best use of the battery's weight.

A parallel (or series if you can find 24V motors) set of 2 or 3 similar sized car batteries or a large tractor/truck battery are likely to be the cheap option (care needed to balance them before connection). Ok it's crude and the they wont last forever but you have the lead to trade against your next ones once they're done and again, they're going to be much easier to find locally than proper deep cycle batteries. So long as it's well balanced (low but giving sufficient ground clearance) the weight is a good thing for traction. Low voltage is safer. Wherever you put the batteries if they're flooded wet cells they'll need to be kept as near level as possible and any spills that may occur need to be able to drain away safely.

I guess you can get agricultural tyres but if you can't then angle iron paddles bolted to bald car tyres or welded direct to steel rims would work fine on soft ground (car wheels allow you to easily use self contained hub-bearing assemblies for simplicity). Maybe sand fill the tyres for low maintainance (no tubes, no pump needed, no punctures) and more weight over the contact patch.

All just ideas, I hope some of them are of help.


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## dirtmover (May 10, 2011)

I build and sell plans to a machine that should do what you want. although I am afraid that it would be difficult to get a tractor to Africa. Check out the video: http://www.youtube.com/watch?v=EJGvYYP_wz0

There is more info on my website http://www.thegreensmachines.com/

thank you , Lonnie.


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## Salty9 (Jul 13, 2009)

Another site that discusses alternators used as motors without changing the rotor: http://www.rcgroups.com/forums/showthread.php?t=1123956&highlight=reem

The posts by Ineptone were the most useful to me.


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## JRP3 (Mar 7, 2008)

dirtmover said:


> I build and sell plans to a machine that should do what you want.


Neat machine you have there.


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