Rapid Prototyping as functional element in the R250GP
Introduction:
With these short articles we want to diffuse part of the experience and development acquired by CRP Technology in the functional use of WindformTM parts on a Gran Prix motorbike. In 2005, in fact, the R250GP, built by CRP Technology, was lined up on the starting grid of the road race World Championship with the colours of the famous Fantic Motor brand with the riders Arnaud Vincent (#21) and Gabriele Ferro (#20).
Art.1 Chain slide 11.12.2005
What is it and what’s its use:
The chain pad is a protection placed between the transmission chain and the swing arm (fig.1).
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Fig.1 – R250GP. At the bottom on the right a particular of the chain pad |
The need of this element is due to the fact that when braking the non tensioned side of the chain leans on the upper part of the swing arm caused by the play the chain needs for a correct functioning. Usually this element is made of antifriction material (Teflon®) fully machined if used for small productions or directly hot pressed for big series productions. (fig. 2)
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Fig.2 – Teflon (Yamaha TZ250) chain pad exapmle.
To be noticed: it is necessary to use 4 bolts to assemble the part. |
Although it is made of this specific material to limit the hedgetop attrition, the chain slide is a “sacrificing element” that may last more or less according to the track and to the needs of grip. All the GP bikes, in fact, have a vertical regulation of the swing arm axle (pivot) to conform the bike to the grip conditions which may change between race to race. If the pivot is raised, the chain pad will be more stressed and therefore will have to be changed more frequently.
The first prototype:
CRP, because of the small number of pieces required, decided to realize it in WindformTM taking advantage of the rapid prototyping technology.
Being the R250 bike wholly engineered with the CAD, the geometry of the pad, which had to follow perfectly the profile of the swing arm, was quickly extracted. The problem of the chain wear immediately arose, being the SLS material made of a part of metal and, although it isn’t abrasive it isn’t suitable for creeping phenomenon. A shoal was made to attach (with a specific glue for WindformTM) a Teflon® stripe on which the chain creeps. (fig.3)
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Fig.3 – First pad prototype, on the left CAD image.
Below the pad shaped directly on the swing arm. |
The development:
The first prototype had to have a 3mm thickness of Windform PRO and on it a stripe of Teflon® of 3mm.
When the high pivot was used, this solution brought the whole wear of the Teflon® stripe during a race, and the chain was still having short life due to contact with the WindformTM. The thickness has been reduced for the structural part and the Teflon® one has been increased, saving, also when particularly stressed, the chain and the swing arm.
A forward step was made reducing the thickness in the maximum wear point and leaving a non attached part of Teflon® , in order to absorb the chain shocks during downshift.
In Fig. 4 the last evolution of the piece.
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Fig.4 – Actual chain pad. To be noticed: lower thickness near to the maximum wear point. |
Dr. Eng. Simone Boninsegni
Project Manager 250GP
CRP Technology
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