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Challenge
Croozer manufactures high-quality and innovative bicycle trailers. In a two-week project, I worked on the topic of caster wheels on the Croozer model. The focus was particularly on the “wheel flutter” and the coupling between the caster wheel and the vehicle.
Research
Research
Why do caster wheels flutter?
Why do caster wheels flutter?
Caster Flutter| Caster wheels start to flutter all by themselves at a certain speed. The smaller the distance between the wheel axle and the steering axle (offset), the earlier the caster starts to flutter. Poor traction and a loose steering axle make wheel flutter even more likely.
Lever Forces| The pin that connects the wheel and the coupling generates strong leverage. Over time, these forces can wear out the coupling. This causes the pin to move freely. The vehicle does not become less safe as a result, but it is perceived as faulty. A moving pin also triggers wheel flutter.
Ideation
Ideation
From cylindric pin to flat mount
From cylindric pin to flat mount
Out of 16 ideas, I chose the most promising solution for wheel flutter and point loads. I replaced the pin that connects the wheel to the mount with a horizontal plate. It is inserted into a rail. This distributes the leverage forces over a wider area.
Conception
Conception
Shaping an idea into a system
Shaping an idea into a system
Base Plate| The base plate is the link between the wheel fork and the bicycle trailer. It also functions as a bearing for the steering axle, i.e. it rotates on the fork.
Support Structure| All functions are connected at the support structure. In addition to the stable connection between the wheel and chassis, it functions as a slot for the base plate.
Locking Mechanism| The wheel must only be released from the mount at the push of a button. There is a latch that hooks into the screw hole in the plate. If you press the button, a wedge slides under the catch and the wheel can be removed.
Case| The outer shape of the coupling is designed to convey stability and dynamics. Round lines and a wide connection to the bumper give an impression of safety. However, the housing also has other important functions: On the inside, it holds the button and latch in position; on the outside, it protects against dirt and water.
Prototyping
Prototyping
From SolidWorks to 3D-Printing
From SolidWorks to 3D-Printing
To test the mechanism and the general function of the design, I 3D-printed and assembled all the components. The locking mechanism was a particular challenge. I iterated and adjusted parts so that the mechanism now works perfectly.
Outlook
Outlook
Small steps towards a holistic solution
Small steps towards a holistic solution
I focused primarily on the redesign of the wheel coupling. However, in order to solve the problems (wheel flutter, lever forces) in a real development process, a complete redesign would be excessive. Strategically, I would therefore first test simpler solutions step by step.
1| A lubricant with high viscosity to dampen the rotation of the steering axle.
2| Cover the axle pin with an elastic coating (rubber) to distribute point forces more evenly.
3| Extend the offset to increase the natural frequency of the wheel and thus reduce wheel flutter.
Learnings
Learnings
The Croozer design is exceptionally well engineered. All components take on several functions. During my research, I was able to learn a lot about design and usability.
I learned valuable product development methods from the professionals at Croozer.
With a product made up of numerous individual parts, there are a multitude of functions to consider. It is easy to overlook important aspects during the design phase that cannot be easily corrected later.
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