Multi pedal vehicles

Multi pedal vehicles

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Nearly every kind of surface vehicle in common use has wheels. While the earliest known vehicles had skids, and some of these designs are still in use today, wheels are so ubiquitous that little or no thought is given to the modern corollary of wheels, namely, paved roads.

This is a complex economic issue. Roads that last a long time, providing a smooth enough surface for comfortable and rapid vehicular movement, are enormously expensive. The only other kind of useful alternative today are tracks, often enough made of steel, whose construction and maintenance is also enormously expensive.

However, there is an obvious alternative to wheels, which is to mimic nature. Apart from the locomotion of very tiny creatures, that move by flexing their bodies, all larger creatures that move on land use legs. The singular major exception to this rule is snakes.

Pedal vehicles, vehicles with legs, have been, in the last couple of decades, a really well known art object. Pioneered by the Dutch artist Theo Janssen Theo Jansen - Wikipedia, the family of Strandbeest have been entertaining and intriguing visitors for years. Many are wind powered, some use feedback sensors, such as the presence of water, to decide the direction of travel.

Another potential use is for exoplanetary land rovers, given the uncertainty of potential terrain to explore. And Boston Dynamics, an American R&D venture Boston Dynamics | Boston Dynamics, has developed several very high performance robotic vehicles (extremely expensive, though), that emphasise the use of legs (and, in some cases, hands).

Is there scope for the construction of practical commonplace human or load carriers that use legs instead of wheels?

What are the main considerations that dictate a successful design?

What are the potential power sources?

What modern materials lend themselves to creating such vehicles?

What other questions need to be asked while venturing on creating such designs, not just for a Maker Lab, but for production?

In the HBCSE Maker Lab, one vehicle was built a couple of years back, whose leg mobility followed the Theo Janssen model. In fact, there are several web sites that offer reasonably well described blueprints for making such devices, which can be found with videos on YouTube as well as in text.

Further thought has distilled some practical ideas for drive mechanisms, using commonplace materials. They will be developed in the near future. More ideas are welcome.

One of the very early ideas was to use a linear motor. Apart from the obvious shape, they have readymade electronic controls that can be enhanced with digital controllers (the software needs to be developed, of course. The software used by Boston Dynamics is proprietary).

However, with a little investigation, it turns out that the motors currently on the market are sophisticated and expensive. It is clear, after discussing the matter with electrical engineers from the industry sector, that this need not be the case, but it is chicken and egg, since there do not seem to be a lot of other applications at present for less sophisticated linear motors.

Another early idea was to use hydraulic pistons. These are fairly easy to couple with hydraulic circuits. However, almost everything needs to be done from scratch, since the industry is heavily focused towards speciality products, made on order for individual developers of various machines.

The same difficulty applies to pneumatic pistons, unfortunately.

The present thinking is helical springs, for which simple levers provide either compressive or expansive motion.

With the Janssen designs, the actual pedal movement often emulates the wheel.

But why should that be? Clearly, that’s not really a need. Rather, much like a ski, the ‘foot’ needs to glide along horizontally to provide maximum contact with the surface, then lift up the minimum amount reasonably necessary to clear all obstacles on an uneven ground, and then come down again to glide.

While this is happening, another leg will be gliding along the ground, and so on.

It so happens that, when 3 or 4 legs are moving in tandem, the resultant motion, or ‘feel’, is indistinguishable from that of a wheel rolling along. This is empirical, and the mathematics for this may or may not be in place.

For any natural stable mobile platform, it is necessary to have at least 3 or 4 pillars.

Putting these two factors together, it becomes clear that a practical mobile device should have 3 or 4 pillars, each made up of 3 to 4 legs, in order to behave like a modern rickshaw or car. In our discussions in the maker space at HBCSE, we have christened this device a ‘chalopede’, while the wheel emulating pillars are called ‘rewheels’. There is nothing particularly unique about either of these names, other than evoking the singularly fresh thinking in this space emerging in India.

There are lots of advantages, in terms of minimising material resources, to using only 3 pillars. However, one must also note that if the vehicle is also intended to be a load carrier, then 4 pillars reasonably compensates for random placement of loads, whereas 3 demands that the overall structure also have a very effective external suspension system, in order to ensure that the support platform remains horizontal no matter how it is loaded.

One major advantage, therefore, of using helical springs in the rewheels, is that each assembly has an inbuilt suspension feature. It is possible that in the finished model, a dampened suspension might not be needed at all. This will be one of the characteristics to explore when building the prototype.

The other mechanism to explore in detail will be the drive system. The initial prototype is intended to be human powered, which avoids the additional complications of external power sources. Those features can be considered if the design proves successful, and leads to further models where higher speeds are possible, with less or no human effort.

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