Autonomous electric footpath vehicles




1. The problem of village logistics

2. Basic idea and design outline

3. Design details

4. Operation as a logistics system

5. Ideas that extend the concept

1. The problem of village logistics

Over the recent months, I spent quite some hours thinking about adequate logistics systems for rural, hilly Nepal. Especially for the villages not having road connections for now – is getting “the road” really the only way of development? Because with the road comes pollution, road accidents, and a faster pace of life.

Actually, transport for people is not that much of an issue (except for medical emergencies of course): for their occasional travels to the cities, people walk to the next road / bus stop. Means we only need a solution for transporting goods – the big problem is indeed load transportation. Where this takes much effort, access to market is difficult, earning money is difficult, and supply is difficult. Load transport has to be more efficient (in personal time units) than relying on porters, carrying things oneself, or using mules.

2. Basic idea and design outline

Aerial ropeways are one solution for this, but the problem is that they require a lot of additional infrastructure, and the cost of that hinders the widespread deployment (they are also infrastructure with a single point of failure, which was the demise in previous ropeway installations in Nepal). This is not the case when reusing the existing foot path network!

So here is a proposal that I think is my best idea for this so far. It would put Nepal into the same league with the countries most advanced both in electrical transportation and autonomous vehicles, while at the same time needing no additional roads or other infrastructure. The technology is cheap and can be managed locally (given some training).

The basic idea is a narrow (max. 80 cm wide) autonomous vehicle for load transportation on foot tracks. The vehicle would be able to carry 40-100 kg, depending on the exact design, and navigate autonomously using a line on the ground, or optical beacons, or a guide wire. To be able to drive on even narrower footpaths, the vehicle could also have only two in-line wheels, using self-balancing technology as known from motorcycle innovations.

Another advantage of transport on foot tracks is that these transporters can use the small wire bridges which are popular in Nepal’s hilly area and mountains. No need to create much more expensive, heavy-weight bridges for cars.

I’m not saying that constructing such a robot is simple, but it is much simpler than building one for full-scale city traffic. It can completely avoid roads, since there is always a footpath available in Nepal as an alternative route.

3. Design details

I propose it would be a transporter built with bicycle parts like an electric cargo quadracycle, but without a place for a rider. And since standard bicycle parts are used, maintenance and repairs are simple and cheap. For example, wheels should be standard 26" mountain bike wheels. These vehicles will be slow (say 3 km/h uphill, 8 km/h on flat terrain, up to 15 km/h downhill) and can carry much less than trucks, but since they are autonomous, they can drive all day and even through the night (at least the way back downhill, and also uphill if having access to grid-connected charging stations in houses along the way). Also, even with modern jeeps but safe driving you get hardly 8-10 km/h when offroad driving on “roads” in Nepal’s hills (been there, done that) – so the autonomous vehicles will be just a bit slower given that they can shortcut the road with footpaths.

It will be powered by a relatively small Li-Ion battery and recharge with photovoltaic cells that it carries as a roll with it, and deploys on the roadside in sunny spots when it has to charge. (Alternatively, there could be charging stations every few kilometers, but that is less flexible and more expensive for the first few vehicles.) Frequent charging stops are not a problem when transportation is automated.

For energy storage, free, used 18650 Li-Ion cells harvested from notebook batteries, powertool batteries and the like are a more affordable and more economic solution than ultracapacitors – it is more economical even though ultracaps do not wear down. Because to cover 1 km between charging stations at 17% slope uphill with a 80 kg total weight bicycle, about 33 Wh are needed, which cost 430 EUR in supercapacitors at 13 EUR/Wh. Li-Ion cells on the other hand are free when harvesting used ones, and can be used for 1000-2000 cycles if charging to only 3.92 V/cell. Assuming 1500 cycles and one cycles per day on average, that’s 4-5 years on one battery pack until it degraded to 70% its original capacity (and even then, it can still be used).

The Li-Ion battery has to be large enough to allow a 1.5 W load per cell or lower, since that is how used cells last the longest (due to their reduced current carrying capacity). That is easily solved by letting the vehicle go a very slow speed, which is also great for reducing breakage and maintenance anyway. At (say) 3 km/h, driving 15% uphill with a 80 kg total weight vehicle will need about 100 W, so about 66 Li-Ion 18650 cells (very doable). At 2 Wh/cell typical charge capacity (3 Wh/cell remaining capacity, charged to 3.92 V/cell or about 66% capacity), this means 130 Wh total energy content, or 80 minutes of driving, covering 4 km. So a reasonable proposal would be 100-cell batteries and recharging approx. every 5 km (or further, depending on how steep the uphill slope is).

The low power needs of 100 W maximum (or even just 50 W maximum if reducing the uphill speed to half) mean that DC motors from battery power drills or (better) electric wheelchairs can be used. These are available nearly for free second-hand.

In the case of powerdrill motors, no gearbox is needed, since a max. speed of 3 km/h is acceptable and the motor can cover a range of 0-3 km/h by itself by just using a PWM motor controller as integrated in power drills. For a constant reduction gear, one can simply use a bicycle chain gear, a bicycle chain, and a very large (ca. 30-40 cm diameter) DIY gear mounted to the bicycle wheel. Each wheel or each axle can have its own DC motor, and the DC motors incl. the reduction gear mechanism of the front axle would simply move with the wheel when it is steered. This way, the vehicle is a 4x4, making it much more capable on muddy tracks.

4. Operation as a logistics system

To make operating this device possible in the long term (means, incl. maintenance), it would be operated as a service, with village people paying to get items delivered to and from their village, or later also to other places (like, to and from their fields). This is in contrast to people owning their own vehicles.

The vehicle would have a simple display with a selection mechanism so people can select its next destination. This allows to build a network of paths using optical beacons, but also requires that the vehicle can navigate bifurcations etc., and determine its position.

The operators would have to be technologically skilled, perhaps young people from a nearby city creating a startup. Though I am not sure yet what the fees could be and how profitable a company would be offering this as a service. However, such a company has the advantage that scaling comes with cost advantages: one team can operate a fleet of 100-200 of these devices driving around in one district. They will all operate autonomously, until they break (in which case, they can be towed by another device and collected in a workshop until the travelling operators get there).

5. Ideas that extend the concept

Operation as a trailer. In addition, it should be possible to tow this vehicle as a bicycle and motorcycle trailer, allowing to move it faster when accompanied by a person. This is useful to move it around within a settlement, or when it broke down and has to be towed to a workshop.

Combination with aerial ropeways. In addition to using foot tracks and wire bridges, the transporters could even be enabled to use aerial ropes by themselves (hooking themselves to them with an overhead arm, rolling along them, hooking off at the end). This allows shortcutting the way over creeks (where a bridge is not existing or much further) and also to navigate aerial 1-3 km ropeways to go a shortcut over difficult mountain terrain. The cheap battery power enables this new kind of ropeway. What makes it esp. cheap is that it only needs bamboo towers and a single steel rope (or chain or fabric belt), no moving elements at all. The carriages will propel themselves along the rope with rubber wheels on top and below the carrying rope (or, in the case of chains, hard rubber or plastic wheels with cavings to grab the chain elements). Also, since footpaths are used for most of the way, only a bit of new construction is needed, driving down costs further.

Protocol for interaction with humans. For operational safety, the vehicle needs a way to avoid collisions with humans, animals and objects. On footpaths, the worst that can happen is encountering a motorcycle. Having a flashing beacon light on its top will help, and a simple protocol like “autonomous vehicle will stop at the side of the road when you honk three times, so you can overtake it safely”. Which would make it the 1001st use of the horn in Nepal :smiley:

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