Multi-track Vehicle Projects

Mostly HPV

Rowing Trike

In this project I built a trike frame and steering mechanism specifically designed so that arms and legs could be used to provide power in a rowing fashion, inspired by the Thijs rowbike from the Netherlands (see rowbike details).

The following pictures show the rowing trike in its most advanced state. It was never put to full use, but was tested extensively. Nose and tail sections were to be enclosed. Note the rollcage. A seatbelt was also fitted when test-riding this experimental vehicle.

Rowing trike Click for larger view

My daughter in the rowing trike Click for larger view.

Basically, the steering mechanism here was borrowed from the well-known Varna trike. It is formally known as fixed-ratio tilt steering in which the steering angle corresponds directly to the tilt angle of the frame. That control mechanism is suitable for low-speed use, but is inherently flawed, as I learned in the course of this project. While it is desirable to tilt the frame of a trike while cornering just like a bike, any particular tilt angle is ideal only for a particular speed. Thus, while taking a bend at high speed a bike must lean over more than when taking the same bend at low speed. With fixed-ratio tilt steering you tilt too much at low speed, and too little at high speed.

Although flawed, the steering mechanism used here was highly suitable for use in conjunction with a rowing mechanism: When the two are combined, the limitations of the steering is offset by the ability to use both arms and legs for propulsion.

Gravity-Powered Vehicles for Rapid Prototyping

Most of the experimentation I have done with vehicle steering systems was conducted with gravity as the single means of propulsion!

Downhill coasting provides a simple and quick method of testing lightweight vehicles, while avoiding the need to deal with complications involved in the development of a drive train. If the focus is on experimentation with control systems, then you can save yourself a lot of time in the workshop by using gravity propulsion. However, this option is perhaps only reasonable if your target is a lightweight HPV - some form of transport is required to get to the top of the hill! Below is a view of an experimental 4-wheel vehicle with steering on front and rear, and in the background is the vehicle that was used to take it to the top of the hill.

Vehicles for going uphill and downhill Click for larger view.

Here you see the view from the top, and it should be clear that such downhill runs are not for the faint-hearted, especially when testing prototype rear-wheel steering systems. Good brakes, a roll cage and safety harness are essential. Also note that these tests were all conducted in the wee early hours of the morning - usually on Sundays - to avoid traffic (and the law).

About to run downhill Click for larger view.

FTC Trike

In this project I explored solutions to the steering problems encountered with the fixed-ratio tilt steering mentioned above. Leaving aside the question of propulsion, here the emphasis is on steering control.

The rowing mechanism was removed, and initially the trike was tested on downhill runs only. Later an electric motor was added.

Front view

Note that this is the same frame plus seat I used in the original rowing trike described above, but now there are two wheels at the back and one in front. You might say the whole frame was turned back-to-front with respect to the wheels. It was also raised to give a 50cm seat height, and levers were added to control the tilt, instead of using the Varna-style "hoop".

Side view (Click to see full size)

Free-to-castor (FTC) steering

FTC steering control seems a contradiction in terms: There is no direct manual control of the steering. The steering element (here a single front wheel) is allowed to steer its own path, much like what happens when a bicycle or motorcycle is allowed to go "hands-free". It is well known that one can keep control, and even steer quite effectively in such a situation by shifting one's weight. Steering is under control of the dynamic forces that arise when the wheel rolls and the frame is tilted. Essentially, in contrast to fixed ratio tilt steering, FTC provides a way to get variable ratio tilt steering. Moreover, this happens automatically with no complex control mechanism. Apparently a perfect solution for the kind of steering problems I had encountered with the rowing trike. Such a radical idea called for a practical demonstration, and that is what I set out to do in this project.

Created: January 2008. Updated: November 2011.