Reverse Engineering a Better Brake Arm10 Jun, 2009
Racing motorcycle designer CRP Technology uses ergonomics study, CAD, and rapid prototyping to create a custom part.
In the world of motorcycle competition, the braking line is a key factor in which the rider can make a difference. Braking force is controlled by the rider through the pressure applied to the brake handle. For this reason, the "brake feel" needed by the rider is one of the most important aspects in motorcycle racing. The rider must be comfortable with the braking action to perform this task with great confidence.
CRP Racing, an Italian team that has been competing since 2007 in the Italian Road Racing Championship (CIV) and in the Honda Trophy, develops racing motorcycles together with its technical staff.
To enhance the riders' comfort and feel with the vehicle, CRP Racing and CRP Technology has used reverse engineering to carry out research on brake levers. This process involved scanning the hand shape of the rider when braking and creating a tailor-made brake lever for the rider in only a few days.
The Problem and the Solution
As a rider's racing experience increases, the team works to make adjustments to match the motorcycle to the rider. Through testing and experience, the rider realizes areas for improvement that can result in increased comfort and control, thus increasing the performance of both the rider and the vehicle.
During the 2007 season, CRP Racing rider Riccardo Moretti strongly improved his braking line. As he braked later in approaching a corner, the position of his hand and the pressure required became uncomfortable. He asked the team and technical staff to examine the brake lever for possible ways to correct the problem. The problem was bigger at circuits that required dual front brakes. This solution required the use of two disks with a reduced diameter instead of a one disk with a large diameter. This solution improved the vehicle's stability while braking without twisting the fork and also increased the driving efficiency in sudden changes in direction. When the advantages of the dual disk were assimilated, the rider asked for more aggressive braking. The fastest approach is to mount the dual-disk system on larger diameter disks, but they can affect the driving efficiency. To maintain the ability to interchange the pump between the single- and dual-disk system, the braking pressure was increased without increasing the force on the arm by simply modifying the same arm instead.
|Single front disk and dual front disk brakes.|
Braking in Racing
During a race, the rider applies the brake with only two fingers so that he can hold the handlebar with the other fingers, the brake lever is then released when entering a curve. The brake arm used by Moretti is a short standard arm.
|The hand position when using brakes on a handlebar with a short standard arm.|
As illustrated in the picture above, even the shape of the lever arm is important because the rider reaches for the brakes only with his fingers because he must be ready to change direction suddenly or stop in an emergency.
|The hand position when bending using a short standard brake arm|
The Standard Solution and Its Problem
To increase the braking force in the hand of a rider in a settled position, the placement of the pumping element is moved toward the center of the bike by lengthening the brake lever. The chart below shows the balance of the phases: the force that is transmitted from the pump to the brake (F pump) is proportional to the length of the arm brake (L hand); the force of the rider on the brake lever (F hand) is multiplied because of the leverage of a quantity equal to L hand/L pump.
|The force balance of the front brake.|
Usually a series of long, standard brake levers are supplied and should fulfill the need of increasing the braking force, according to the force applied by the rider's hand.
Every person and every rider is different. Moretti's fingers are shorter than the average brake lever allows for; therefore, the position at rest for which the brake lever can be set must be close to this rider's hand.
|The arm brake setup of a front brake is based on rotating pivot.|
During the strongest braking at testing, Moretti noticed that a dangerous situation could occur. The brake lever was so close to the hand grip that he would begin to crush his fingers while holding the handlebar and applying the brakes. In that moment he became aware that he was not able to use his brakes fully, and he began to lose some of his concentration (this also resulted in possible interference with the turn throttle unit). The rider focus shifted from racing and improving speed, to trying to maintain control to avoid overrunning the corner and crashing. The adjustment for the brake feel and control created a situation that was unusable for the rider.
To solve the problem, CRP Technology applied reverse engineering. Starting by digitizing a physical model, CRP Technology obtained a 3D CAD model that represents the starting point for the development of new products.
CRP Technology used an optical scanning system with a seven-axis Platinum Faro arm equipped with an optical Faro laser line probe. The system is fully portable, and it allows operators to scan in 3D and to acquire measurements outside the company facility.
Riccardo Moretti was asked to recreate the ordinary driving position on his bike as it was placed near the laser scanner. CRP Technology was able to optically scan his hand in the driving position while bending and applying the brakes. The data was acquired and translated into a CAD environment.
|Optical laser scanning of the motorcycle rider's hand.|
|The laser line of the scanner on the rider's glove.|
The image below shows some Honda standard parts -- semi-handlebar, handgrip, speed control rapid speed control, brake pump, and short standard brake lever -- that have been scanned and then modeled. The value of this first survey is the ability to see the favorite position of the rider's hand in two different driving conditions and in 3D.
|The short standard arm brake in action.|
|The short brake arm during braking.|
During a second phase, CRP Technology acquired a long standard brake lever and translated into a CAD environment so it could be compared with the short brake lever. By setting up the brake lever according to rider's need, the pump was moved (by only a few millimeters) to increase the braking force. The short and the long levers are different on the end parts that are not used by Moretti. Yet the distance between the rotating pivot and the area of the holding of the index and middle finger is the same.
|The required setup of the short brake arm (light-blue and blue) and long standard brake arm (orange-red) according to the rider's needs.|
If the entire assembly of the brake lever is moved toward the middle of the vehicle (brake pump and lever), the rider might lose his favorite driving position in order to have a stronger braking.
|The translated position of the short standard arm (light-blue and blue) and long standard arm brake (orange-red).|
|The position of the long standard arm brake that crushes the fingers|
|In this long standard arm brake position, there is a risk of interference with speed control.|
After analyzing the functionality and 3D models of the short and long standard brake levers, CRP developed a CRP long ergonomic brake lever that is suitable for the rider and provides a braking force similar to that of the previous long lever.
The resulting geometry (gray parts) is a hybrid that looks like the short standard brake lever in the holding area that is then connected to a translated pump position toward the middle of the handlebar.
|The short standard arm brake (light-blue and blue) and the CRP long arm brake (gray).|
|The short standard arm brake (light-blue) and the CRP long arm brake (gray).|
The new lever must generate increased force to the brake pump. This increase can be checked in CAD environment with the L hand, according to the variation in strength applied by the rider's hand:
- Short arm brake = 95.3 mm
- Long arm brake = 110.7 mm
- CRP long arm brake = 117.4 mm
|Position of the brake pump for short [corta] standard brake arm (blue), long [lunga] standard arm (red), and CRP long [lunga] arm.|
This data means that if the long standard lever is used an increased force (F pump) of only 16% occurs as compared with 23% with CRP long lever.
CRP Technology prepared a prototype of the new brake lever using selective laser sintering and the polyamide Windform GF. With the prototype, CRP could test the geometry and check possible interferences of the new brake lever with the rider's fingers and the speed control. The prototype also was very useful for suggesting some changes.
The CRP brake lever was developed with a few pieces of Ergal 7075 commercial aluminum starting from billet using the following procedure: cutting with wire electric discharge machining (EDM), drilling, reaming, hand finishing/polishing, and black anodizing.
The latest version of the brake lever was mounted on the vehicle, and a second survey was performed to check it in CAD environment using the shape of Moretti's hand with the CRP long brake lever (see images below).
|This view of the CRP long arm brake shows no interference with the speed control.|
|This view of the CRP long arm brake shows that no finger crushing occurs when holding the control on the handlebar.|
|Checking the CRP long arm brake for functionality.|
The two images above show the same setting in a 3D CAD environment and in the real world.
|A comparison of the different brake arms.|
From mechanics to industrial design, it is quite rare that a new part is developed from a clean slate. Many parts come from iterations and improvements made to existing designs and geometry. Reverse engineering can be the most efficient and fastest technology to solve a problem.
In motorsport, time is a precious commodity and it is necessary to avoid any waste in developing and designing as well as in studying the solutions. Here it is the timing of each step:
- Optical scanning and CAD modeling of standard arms: 4 hours
- Vehicle positioning and scanning of the hand and brake arm of the bike: 4 hours
- Modeling the CRP long brake arm, step 1: 8 hours
- Rapid prototyping in Windform GF: 8 hours
- Setting the prototype on the bike, CAD correction, and geometry validation: 8 hours
- Realization of the finished CRP long brake arm: 16 hours
Total: 48 hours, equal to 6 working days.
|The CRP long brake arm on Riccardo Moretti's motorcycle is ready for the next race.|
CRP Racing rider Riccardo Moretti used the CRP brake arm from May 2008 until the end of the championships. It was his favorite compared with standard levers.