Multi pedal vehicles

STEM Chat
1

What is the big STEM idea you want to share with us?

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 Robots are making progress on space exploration, along with billionaires | 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.

2

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.

1 Like
3

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.

4 Likes
4

I’m not sure why there are multiple and parallel threads in this discussion area, but this one went much further into the nuts and bolts of putting together a prototype.

Briefly, while the linear helical spring idea has its advantages, I subsequently discovered that a simple geometric assembly of pivoted rods (or flats, whatever can be procured more easily) converts a linear motion into an exactly perpendicular motion. This means, actually, that a single linear drive motion can be divided into two separate perpendicular motions really easily, in a mechanical assembly of very simple (but precise, a good quality maker project) construction.

Such an assembly requires only drive energy, and no dependence on stored energy of any kind.

There might be advantages to stored energy, such as when moving uphill, or to accelerate quickly from a standing start. But they aren’t essential elements of a practical pedal vehicle.

3 Likes
5

A diagram to understand the design in your mind will help.

1 Like
6

I would like a scanner that takes pictures while I am turning the pages and pressing a button alternatively. In the end, I should be able to process the images and get a pdf output. We do not need automating the turning of the page. this is really useful device to build, and a nice challenge for someone to work on.

1 Like
7

Of course a complete drawing would be much more helpful.

The basic geometry of the single perpendicular motion is given in the drawings provided in the link (in the parallel discussion, which is about the idea of building one, as against this thread, which is about the thought going into trying to create an elegant design).

But the complete vehicle is an integrated assembly of the parts that move horizontally, the parts that move vertically, and the linkages that adjust the relative throw of each of them.

For each foot, the linkage should adjust the amount of relative vertical and horizontal movement of the pair.

For each leg, the linkage ensures that all four feet are moving in sync, so that the cumulative motion delivers the comfort of a really large pneumatic tyre.

For the platform, the four legs need to move in sync, with the delivered result being motion a. in a straight line forward; b. in a straight line back; c. in a smooth curve with zero slip (to the left and to the right); d. angle of rotation of curve adjustable in order to allow for balanced turns* at high speed; and finally, of course, e. speed of motion adjustable from zero to maximum for the same amount of energy from the drive energy source, meaning, for a human powered vehicle, the rider.

[right]*For a balanced turn, the dynamic centre of balance (equivalent to the centre of gravity) of the entire vehicle needs to be exactly at the midpoint of the curves drawn by the inner and outer pairs of legs, or else the vehicle will experience unbalanced forces. Achieving this will be a skill that a good driver will probably acquire easily, given a little experience, the way that a good cyclist quickly learns how much to lean over while turning the bicycle at different speeds.[/right]

The control of the linkages need to be handy for the rider, and will probably be efficient if contained in a pair of joysticks. However, it may be as effective to control turning with a wheel, as in a car, but with the wheel mounted on a joystick, which is used to control the ‘transmission’.

The drive itself uses simple pedals operated by the feet, that move in straight, or close to straight, lines back and forth.

Each of these sets of linkages need to be drawn or sketched, which I will attempt, and place them in the design and construction thread.

1 Like
8

A quick update. On reading the other threads (not thread: there are two parallel and related discussions, one that followed the design and engineering of the vehicle, and another on Theo Jansen’s design of strandbeests) I saw that I had dropped the link to the CAD drawings in the Theo Jansen thread, instead of the actual vehicle engineering thread.

Ooops.

Anyway, I’ve put it here now, where it also belongs, without forcing readers and contributors to go read those threads. Although, of course, since I find them interesting, everyone is also welcome to continue to read those parallel and separate thoughts from different contributors.

1 Like
9

You mean turning the pages in a physical book?

As a tool to make PDFs of proprietary format digital pages might be a legal nest of worms.

OCR scans need the pages to be flat, which means the tool also must correct for that distortion.

On reading last week about readymade text from paper applications for the phone, I found that more than one (and this is just one of the reviews) already has this built in, which also means that doing it is very feasible — but which also means that creating it again may not be necessary.

2 Likes
10

Just yesterday, I found that, apart from the convenience of archiving a book, one additional feature makes the phone a very useful tool for a deafblind person. One such tool that uses the feature is an app called SunoDayko, free on both iOS and Android.

Pointing the camera at printed signage yields an output that is directly converted to vibration (Morse) on iOS, and verbal through the speaker on Android. Adding a Braille output device to the Android smartphone, which is anyhow a necessity for many deafblind persons, directly converts the verbal data to Braille. I tested the verbal output on Android, and found it worked pretty well.

2 Likes
11

This post was added to the Theo Jansen tinkering thread, and is being copied here as the nodal point for the engineering inputs to the design.

From separate discussions, we are discovering that there is a clear value contribution from adding intelligence into a mechanism.

The question is, how should this addition take place? The obvious way is to place some kind of computing centre, suitably programmed, to control the movement of the individual segments of the vehicle.

And, following the track of evolution of natural living beings, it turns out that there is a strong value to another approach. This is to add intelligence at each of the individual segments, that takes its data inputs from sensors installed in that segment. Additional data inputs can be added from neighbouring segments.

Rather than developing preconceived coding programmes to transform those data inputs into motion, though, it is meaningful to consider that the computers be programmed to heuristically develop action programs of their own.

The complete vehicle must be allowed to learn, in turn, how to make its segments work in tandem, in order to achieve a given objective (such as, move from here to there without knocking down anything in the way). To do this, perhaps one computing unit can be used to understand an overriding objective, allocating resources to all the segments in order to achieve that purpose.

Of course, in a human powered vehicle, that central computer is the driver/rider, and the subunits in the various segments enable the vehicle rider to optimise the amount of attention paid to achieving the purpose (getting from here to there smoothly and without accidents).

2 Likes
12

Adding to the concept of spare design, I came across another of those space age ideas that ‘moves fast and breaks things’, but the things it breaks are hoary notions of complex and failure prone assemblies.

This is called ‘compliant mechanism design’, mechanisms that incorporate compliance, as against stiffness, parts. The video linked not only describes and demonstrates various really smart ideas, but, importantly, lists 8 critical takeaways from the concept.

In the pedal vehicle, where the transformation of motion in a perpendicular direction is a desired action, using such design will completely simplify the making of one part of a ‘foot’.

It would unify the entire foot, in fact, into one manufactured part, but then the design would lose one important degree of freedom, which is to modify the locus of motion, which is a flattened oval, rather, a D with the flat part lying on the ground (the surface along which the vehicle is moving). The ability to modify the shape of the oval is the equivalent of gear changes in an old fashioned transmission, plus the suspension, so that both the throw of the stride, and the height to which the foot is raised in order to clear uneven parts of the surface, can be modified on demand.

2 Likes