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article 20, issue 07

Leaning Trikes using Rear Axle Pedal Crank Mechanism (condensed version)

Stephen Nurse
December 21, 2013

Abstract

Tilting Delta Trikes with a rear axle made from standard cycle cranks were invented by Mr. Vi Vuong, who calls them "iLean trikes". This article introduces these trikes, shows their relationship to other human-powered vehicles, and considers their tilting and suspension performance. This is a slightly condensed version. Download the complete article PDF (550 kB) and the supplemental spreadsheet  XLS (700 kB).
 

Introduction

Recent internet videos [2, 3] posted by Mr. Vi Vuong astonished the human-powered-vehicle community. He had mounted cycle wheels "in the place of pedals" on cranks on a working bottom bracket and used the resulting assembly as the rear axles of a self-leaning delta trike. See fig. 1.
 
Since seeing the videos I have built my own version of the trike, see fig. 2. Riding it feels just like my equivalent bike [1] with the rear wheels letting the vehicle lean in corners, cope with camber on roads and give a suspension effect. The rear axle makes it feel like there's a "virtual rear wheel" midway between the actual rear wheels. [Editor's note: Steve has documented his progress with his trike then called Vicycle, starting here and in further blog posts.]
 
This rear-wheel mechanism makes braking or driving of the rear wheels difficult, however it seems to be suitable as a variation on most front-wheel-drive recumbent bikes. These include Python and moving-bottom-bracket (Cruzbike) styles as well as fixed-bottom-bracket direct styles (Bevo bike). There's no reason it should not work as well on indirect-drive and other front-wheel-drive recumbents (e.g. Zox, Raptobike, Handcycles).

Photo Vuong Photo Nurse

[Figure 1] Vi Vuong


[Figure 2] Stephen Nurse

Handling

The layout and steering arrangement of these new iLean tilting trikes is shown in fig. 3 together with those of other leaning delta trikes and non-leaning delta and tadpole trikes.
In curves, the axes of all three wheels should meet at a single point. This principle is called Ackermann steering [4], and unless this condition is fulfilled, the tires scrub and resist forward motion. A frequent demonstration of wheel scrub is in a tadpole trike with poorly aligned (toed in or toed out) front wheels. Most delta trikes have innate Ackermann steering, however iLean trikes do not. They have "good enough" Ackermann which is dynamic and depends on the lean of the trike as well as the trike's geometry. With good geometry, the trike's wheel alignment improves when cornering at speed.


[figure 3] screen capture of spreadsheet

[Figure 3] Trike comparison and steering


Handling and behaviour of these trikes include:


[figure 4] screen capture of spreadsheet

[Figure 4] Front wheel drive bikes and their iLean-trike equivalents

Dimensions and Geometry

The relevant dimensions of iLean trikes are:

Notable, changeable influences on the geometry are:

Static Stability

Preventing the rotation of the rear pedal mechanism around the bottom bracket stops the leaning and gives the trike static stability. This allows the rider to be stable when stopped at traffic lights or going very slowly. The iLean trikes seen so far are not equipped with this ability.

Scope

This study only considers trikes where the cranks making up the rear axle are mounted on opposite sides. Other mounts are possible and these can deliver different trike dynamics. One is with the cranks mounted at 90 degrees to each other as shown in S. Alexander Petraj's video.

Photo Petraj

[Figure 5] Alexander Petraj's  iLean trike with cranks at 90. Photo from here.

References

  1. An Illustrated Guide to the Cycle Zoo by Stephen Nurse. ISBN 978-1-921488-08-5 published / available through http://modularbikes.com.au

  2. http://en.openbike.org/wiki/~iLean by Vi Vuong. This website includes photos and links to videos and should be used in conjunction with this article.

  3. Video of Vi Vuong's iLean trike https://www.youtube.com/user/TheFutonExpress

  4. http://en.wikipedia.org/wiki/Ackermann_steering_geometry.


Download the complete article  PDF (1 MB)

Download the supplemental spreadsheet  XLS (650 kB)

 

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