This is interesting a real life example and an attempt to minimise some of it's downsides ?
Flevo trike Eric Wannee
Variation number 6: Improved tilt mechanism on trike rear section. | | |
The standard trike rear section contains a ball joint that has a dual function. It is therefore called the duschar (
DU bbel
SCHAR kidney) principle. It pivots vertically to allow for suspension, and in addition it can tilt about the longitudinal axis to allow the bike to tilt relative to the rear section.
This tilting has a few big advantages:
- If you drive around a corner at a reasonable pace, you can lean into the corner to avoid flying out of the corner;
- If you drive diagonally down a sidewalk you will not be thrown from left to right;
- A bump under one rear wheel is only half passed on to the rider, because the height difference is compensated by the other wheel.
But there are a few comments to make with this tilting system:
The rear part (the luggage compartment) does not tilt, and it is not sprung either. That means:
- That the rear wheels have to handle a heavy side load in the bends;
- The luggage in the bin is rattling (be careful if you are transporting 500 eggs!);
- In a bend, the box does not tilt, so that - especially when there is heavy luggage - it tends to tip over towards the outside of the bend.
This last point gave me an ugly crash once: I drove with a bale of 50 kilos of wheat into a right turn. The centrifugal effect made the luggage want to go to the left. But my own weight also pushed the box to the left via the tilting hinge.
These forces combined at the time were great enough to topple the bin, causing me to take an involuntary air trip.
This got me thinking. How can you prevent this?
- Of course you could widen the box considerably. But I just wanted a narrow box to be able to easily drive between posts, to cycle side by side, etc.
- The bucket's center of gravity could be lowered. I have now done this because the rod has disappeared from the box, so that large heavy loads can be lowered.
- The point of application of the tilting mechanism had to be lowered.
The lowering of the point of application of the tilt mechanism, I did by dismantling the dual action of the duschar system.
The detail image on the right shows how. The spring part now works in the same way as with the
bike ; the tilting mechanism is a lot lower (approx. 17 cm above the ground) and is made with the same type of axle as the one used for steering.
The left picture is the system of the standard Flevo-trike. The tipping point (blue dot) is quite high.
The lowered tipping point is used on the right picture.
The trick here is that with the same tilt in the corner, the resulting force due to the weight of the rider (blue arrow) ends up much more in the middle between the two rear wheels (distance 'B' is much greater than 'A' .). Ideally, the pivot point should be on the ground: The blue arrow will then always be exactly in the middle between the two rear wheels. (This is the situation that occurs with the
bike ! You wouldn't be able to feel while riding whether you are riding a bike or a trike.)
Dropping the axle would also lower the pivot ?
I read somewhere the Flevo trikes have a rear track between 15" and 28" with 24" being quite common [ can't find the reference again DOH ]
Paul