Try refreshing the page to ensure you are enjoying the latest version. I tend to make endless edits and corrections over time. Forgive the sometimes off-topic nature of my blog these days. Walking and enjoying the countryside are vital to my physical and psychological fitness and sense of well-being. They combine to undo the damage caused by an occasional excess of cycling. And, may even stave off another rant! Though I can't promise anything. My long-suffering wife, "The Head Gardener," refers to me as the Imelda Marcos of saddles and saddlebags. She is usually right about almost everything. So it may well be true.


24 Aug 2016

24th August 2016: PodRide quad velo.

00/00

On a lighter note; a Swedish engineer has come up with a fascinating and very clever, little quad velo-car which he hopes to produce as a construction kit:

 JMK-Innovation | Konstruktion och utveckling.

[Construction and development]

The YouTube videos show a remarkable level of stability on ice covered roads and packed snow. It can even manage a BMX course with vicious humps and fierce turns.

The PodRide's turning circle is tiny. A valuable property for any machine used on narrow cycle paths. Particularly if you can't put your feet down and bodily lift the machine! I used to be able to do that with a bare 1WD trike. The mere addition of a saddlebag and U-lock made it much more difficult. Two wheel drive makes it all but impossible!

I have always liked the idea of quadricycles. They make far more sense on corners than a trike with the latter's very marginal stability. Though, ironically, that is precisely why trikes are so much fun! The main downside of the quad is the extra weight of the inevitable, fourth wheel and axle.

The PodRide seems to have ticked an awful lot of the right boxes and is being crowdfunded for future production. The successful prototype has commuted to work for over a year including in icy Swedish winter conditions. It has an aluminium frame with stressed skin cloth covering. A differential, pedals, gears and an electric motor provide the power. The designer seems to have thought of almost everything except the limitations of the short wheelbase for emergency stops. Even here it maintains excellent straight line stability with the back wheels right off the ground!

I have often wondered how well a pedal quad would perform if it was built from a tadpole conversion on a delta racing trike. A Newton/Trykit melding done properly would be fun. Though I fear the trike/quad frame in the middle would suffer from catastrophic twisting loads. [torque] Particularly when all four wheels of a rigid machine were not the ground. Independent suspension on the back wheels would help but increase both weight and complexity. The alternative, using a central, horizontal pivot somewhere between the front and back axles would need careful design not to turn the machine into a useless jelly.

The simple diagram shows the massive stability difference between a trike and a quadricycle. Both machines will tip on corners or adverse camber along a line joining the front and rear wheel contact patches. You can think of this line as a hinge on the ground. When the lateral [centrifugal] forces exceed downward forces from gravity the machine and rider will tip outwards.

The width of the effective track of a trike, at its rider/machine center of gravity, is only a fraction of the quad's. Which is why only a very few enthusiasts drive three-wheeled cars, motorcycle trikes and sporting pedal trikes. All others, very sensibly, choose two, or preferably, four wheels.

Is it really worth the expense and effort of building an upright, pedal driven quad? Even with 20" wheels it will be far heavier than any bike or trike. The quad's potential stability on corners would completely trash any upright trike. It cannot be otherwise. Is the ability to corner like a grinning lunatic worth the hassle and weight handicap? Probably not if the pilot must sit up high in the self-made breeze. A lower, semi-recumbent position makes far more sense from a wind resistance perspective. That fourth wheel and its supporting axle also has to be shoved through the uncompromising air and dragged up steep hills. Electric assistance makes far greater sense than a purist, upright, pedal-driven machine.

The advantages, apart from the 'bomb proof' stability? Massive carrying capacity and being the center of attention wherever you go. Upright trikes attract public attention like a UFO in the high street. People notice you and remember you wherever you go. Then they will stop you outside the shops and tell you about it. Which can be quite handy if you have a poor memory. If you should have to prove your whereabouts on a particular day all you need is a police appeal to be inundated with responses.

Lest thee begin to sneer [out of ignorance] at the whole idea of a quadricycle just remember that the first Mercedes Benz was a motor driven quadricycle. Four wheeled "bikes" were around long before "real" cars. Many different forms of pedal driven machines were tried in their heyday before they were driven off the road by poor [but filthy rich] drivers. Just do a Google Image search for <quadricycle> for examples.

Click on any image for an enlargement.
 00\00