Rosco’s LugNet Page
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Adjustable 4-wheel steering
Proof of Concept
| | A diagram of the assembly
Imagine looking down on a fairly standard Lego car, with the front to your right. The front wheels are steered as normal (or a mechanism of your choice!), except an axle from the steering mechanism must be extended to the rear of the vehicle. The axle is connected to this assembly at point “A”. This movement is then transferred to the “open I” link “B”, via a 8 tooth gear and a 24 tooth crown wheel. Thus turning the steering wheel causes link “B” to rotate.
Link “C” is free to slide the length of link “B”. The other end of “C” is connected to link “E”, which is connected to the steering assembly of the rear wheels (not shown).
Rotation of link “D” causes link “C” to slide along the length of “B”. Thus “D” is the control which determines whether the rear wheels turn in unison [1] with the front, or opposed. For this reason, I’ll refer to link “D” as the “control” in the notes.
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Details
Left
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| | Notes
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| | Here we’ve got the control set to neutral. Turning the steering wheel does not move link “E” at all, so you effectively get normal 2 wheel steering.
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| | Here the control is moved to the “unison” position [2]. You can see that the link “E” moves the same way as the link “B”.
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| | Here the control is moved to the “opposed” or “crab” position [2]. You can see that the link “E” now moves in the opposite direction to the link “B”.
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[1] For the purposes of this page, I’ve defined “unison” to be turning the rear wheels in the opposite direction of the front, thus working in unison to turn tighter corners. “Opposed” is the opposite, or “Crab-like” steering. In fact this definition is arbitrary, as explained in [2]
[2] Actually these positions are arbitrary - which direction is unison and which is opposed is determined by:
- The direction of turn of the shaft coming from the front assembly
- The way in which link “E” is connected to the rear assembly
Improvements
This is only an early proof of concept. Many improvements can be seen immediately:
- The assembly is pretty bulky. Some reduction of size is probably possible.
- The link “B” should really be curved, with a radius the length of the link from “C” to “E”. I don’t know if this can be done with Lego, but someone may come up with a way.
- It doesn’t have to be horizontal like this - maybe a vertical layout would be better?
I’ll leave these (and any other) improvements to the (imagination of the) reader...
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Site last modified November 4, 2004 Home
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