Difftrike Design – the conceptual sketchups

Posted on February 16, 2012


Remember I told you that Manuel started creating designs? Well now is as good a time as any to show you guys what we’ve been playing with. We’ve got six animation videos to show off the ideas we’ve been entertaining. Manuel has been very busy riding his new computer and learning digital 3D, whereas I’ve been riding his designer patience and learning about ergonomy and good taste. 😉

We took the first steps with Google Sketchup because at the time we believed it was good enough for the purpose and it had potential to grow as a technical design and CAM tool. And although it did provide us with a good platform to present and discuss design ideas, it turned out to be too chaotic and not enough mechanical for us – so we’re starting to use Autodesk 123d for the new design phase, and kudos go out to João for having the largeness to teach us 3D engineering design. Autodesk 123d neither Open Source nor Free Software, but hey, at least it’s Gratis. One has to make a few compromises on the road of practical engineering. If anyone knows of an open source alternative to Autodesk 123D (as easy to use and as powerful), please let us know. Thank you.

About the following Dailymotion hosted videos, feel free to use the “Full Screen” and “HD” features so you can better appreciate the details if you wish. The videos are a little fast, but you can use Pause and Rewind to analyse the mechanical details if you’re interested.

The very first sketch we made was merely an attempt to dominate the tool and get the proportions close enough to reality:

Then we procured a human model from the Sketchup on-line warehouse and tried to dimension the protective cage frame around it. We also started studying how to integrate that with some chassis folding. Notice that cage frame is tubular; we were thinking about using natural biodegradable materials like bamboo – but this is an idea that will demand quite a lot of research effort to get right. The initial idea of pantograph-mounted traction wheels is also here in this concept that we affectionately call “the egg”:

One of the ideas that popped up in the process is modularity: instead of having a large multiple-seat vehicle, why not make it so that single-seat vehicles can attach together to make a temporary large vehicle? This would be very efficient in terms of family logistics, for example. Of course, both the mechanics of the frame and the on-board electronics would have to be capable of accommodating such a configuration very easily – only one joystick should be able to control the vehicle, and the wheels facing the center cannot be extended out. Unfortunately, this geometry does not function; the middle wheel axis would then be misaligned with the outer wheels, and the whole thing would not turn:

Again we concentrated on fold-ability of the chassis. This is probably the most crucial point if we ever hope to excite others with our vision, and it is a tough nut to crack. But Manuel came up with a nice scissor-like folding chassis and we forgot the pantographs for a while because of the axis misalignment problem – and also because they would be a weak spot in the chassis. So the main wheels got pulled in to a narrower position, and the front wheel was split into a pair of wheels supported on telescopic arms for a wider base and better stability. At this point we noticed that the vehicle could be ridden while closed, which opens up a whole new world of possibilities for the disabled: how about an electric road-worthy vehicle that is also a wheelchair that will fit in an elevator? With the ability to convert between “road” and “indoor” positions, it would allow disabled people an unprecedented mobility (version without pedals, of course). It also makes it very comfortable for the regular folks to get in and out of the trike.

In these last seconds we study the volume of a “folded” trike by jumbling all the parts together; it’s not really folded, but we needed to get a feeling of what it would look like when compacted into a “suitcase” disposition. And we also revisit the concept of modularity in large scale, showing that nothing really prevents us now from joining 5 vehicles into a five-seat behemoth. 🙂 Yes, that thing would still run and turn – I’m not so sure about mechanical robustness, though.

With a good enough concept of folding chassis, we started looking at a folding canopy. It has to be absolutely integrated with the chassis, so that they fold together without disassembly or any other trouble. Manuel had the neat idea of making the glass canopy open up in the same folding action as the chassis, but I think this will not be practical in all cases.

Anyway, that canopy is waaay to long to be opened like that inside a building… it still needs a lot of work. One of the ideas is to break it into 3 pieces, with the central piece going up and down on pantographs to control the total height when opening. As I said, it’s still a lot of work ahead.

And here is the last version we made in Sketchup, showing the folding chassis and side awning, and then we replaced the glass canopy with the tubular frame. Notice how the red and gray parts of the awning join together when the trike unfolds into action, but separate to allow the driver’s feet to pass when open. The tubular frame is about to be cut into 3 sections and redesigned so that it opens and closes neatly. And again we get to see some vehicle modularity. 3 modules joined together seems to be a good realistic number.

In conclusion, we are obviously just starting in this path of design research. And there are some operational details to solve; like the issue of mass distribution so that the differential traction system is not overworked, or the simple question of “how many wheels does this thing have, again?” 😉 Currently we have 3 applicable answers for this question: 2, 3, or 4, depending on how sophisticated we’d like to get. You’ve seen the 3 and 4 wheel concepts; the 2 wheel concept would depend on balancing technology like Segway’s or have an integrated horizontal flywheel. Either one is less than robust and not as reliable as mechanical hyper-stability.

And there are also other paths of design to explore; we’ve got a bit of a conflict between the “small and light, wheelchair-like foldable trike” and the “fast and performant highway-capable light vehicle”. The first can have a very light and cheap canopy, the second must be crash-worthy, which is a different level of engineering altogether. So yeah, we’ve got plenty to play with for next few months. This, my friends, is just the first step in a very long road. 😉

There is a reason why we are not yet sharing our design files publicly, in this case the Google Sketchup files: they suck. 🙂 We had a hard time trying to make Sketchup do what we wanted it to do, and it won the battle. Sketchup is not an engineering design tool; it is an Architecture design tool. Moving parts don’t fare well inside Sketchup. So fare thee well, Sketchup. As soon as we have some new designs going in Autodesk 123D, we’ll publish them for you to play with.

Now, as the leader of this specific DiffTrike project, I have to take a stand in order to focus our efforts productively and avoid getting ourselves lost in the beautiful dark woods of “what if?” land. I will push the design and engineering trends towards what I originally set this project out to be in the first place: an improvement upon the bicycle that can actually replace the automobile inside the city. This means that the vehicle should have exactly 3 wheels, should manage energy intelligently, should be very light, should protect from most weather conditions, should be highly compactable and foldable, and easy to circulate and store inside buildings. That’s the design problem we must conquer.

Of course, this does not prevent other team members from whipping up their own derivative projects, which we will all be glad to support in the same way. 🙂

Happy Hacking, everyone!

Posted in: Design, DiffTrike