A way to fix defects of Shelby Cobra body geometry

Task: To evaluate the accuracy of the Shelby Cobra replica build. To check the geometry of the body for symmetry and obtain the data needed to align the body parts and adjust them in such a way that the joints of the parts are smooth and all the doors of the car are freely opened.

Solution: Rangevision Spectrum, ScanCenter NG, Blender

Summary: The Shelby Cobra car was 3D scanned by RangeVision Spectrum 3D scanner. The obtained 3D model of the car was used to inspect the symmetry of the left and right parts of the car. As a result, a number of body flaws were identified and later corrected during the body work. All parts of the body were adjusted in size, the geometry of the body was aligned by symmetry and the body was painted.

How the project came

We will never know the name of the person who first decided to create in his garage a copy of the car he wanted, but could not afford. Over the years, this activity has spread at a tremendous rate. Right now, the building of car replicas is something that whips up the enthusiasm of thousands of people around the world.

A replica is known to be a self-assembled car that exactly looks like an original model. Car parts can be found at auto-disassemblies or garages, or be supplied as a separate kit of "build it yourself" format. The last variant has recently become very popular. Many companies create their own kits to build replicas of legendary cars and expensive supercars. On average, it takes a person about 1.5 years of slow work to build a copy of a car.

Photo by Oleksandr Zhabin on Unsplash

Admit, it sounds tempting: you can buy a kit car and build the car you want for almost a penny compared to the price you’re asked for the original. But there is also the other side of the coin. When constructing replicas there are often problems with the body: gaps may be uneven, add-on parts often cannot be mounted without fitting, and the edges of the glass may not match the opening. In order to solve such problems, it is necessary to involve professionals.

The famous Russian blogger Ildar, who was working on a project to build a replica of the cult Shelby Cobra 427, faced the same problems.

Shelby Cobra is one of the most multiplied replicas of cars. The legendary racing car was designed by engineer Carroll Shelby and produced from 1962 to 1967. In its short life, it collected a great number of awards and trophies. In 2016 the first car model was sold for an unimaginable sum of $13 million dollars and became the most expensive British car in the world. The movie "Ford v Ferrari" tells the story of the origin of the car. Not surprisingly, it raised a new wave of Shelby Cobra’s popularity in the world.

Photo by Brian Matangelo on Unsplash

In September 2020, Ildar requested help with the alignment of the body of the built replica to our good friend Maxim Tereshchenko, the blogger and the head of the auto body shop named Mashinators. His team specializes in such kind of specific work and has already done similar projects. The Mashinators had the task of identifying and correcting all the car body flaws in just one month.

Car inspection

During the primary inspection of the replica, the Mashinators noticed that some parts of the body did not dock, the left door was crooked, the trunk cover was slightly wider than the gap.

However, it is often not likely to see all the gaps in the body geometry, because the car has many symmetrical points. Without measurements, it is impossible to identify all asymmetries and correct all defects. To see the full picture of the asymmetry of the body, precise measurements must be made.

3D scan

One of possible options for obtaining complete body data is 3D scanning. The result of digitization is a 3D model of the object which is used to check the symmetry of the details and to identify all the defects in the geometry of the body.

Rangevision Spectrum 3D scanner was used for 3D scanning. The scanner combines such features, as high scanning accuracy, large capture area, portability and affordable price. It has proved to be perfect for autotuning.

The Mashinators have been familiar with 3D scanning technology for about two years. Previously, to digitize individual parts of cars, the guys used a low-cost hand-held scanner of another brand which turned out not to be accurate enough. But for 3D scanning large objects like cars, they needed a more appropriate tool. The Mashinators picked Rangevision Spectrum: "We came across Spectrum when we had an order to make a fairing for a Geländewagen. We needed to scan a bumper and addressed our friend Ivan Moskvichev (Plastmaska) who had this scanner. We saw it in action and thought we should have a 3D scanner like this. It is best for our purposes."

The 3D scanning process involved the following steps:

• The 3D scanner calibration

• Preparing the body for scanning

• Sticking markers

• 3D scanning with markers
  
  

Before 3D scanning, the Mashinators carried out some preparatory work. The 3D scanner was assembled and calibrated. To obtain a better result, the shiny chrome parts of the car were covered with matte film and matting powder was applied to the rubber on the wheels. To improve the accuracy of 3D scanning of the object in this project, the Mashinators used a scan mode with markers. For this purpose, markers were applied onto the surface of the car body.

A scanning mode with markers is very popular when digitizing large objects. Markers allow Scancenter NG software to automatically combine the model fragments using markers applied to the object surface, which increases the rate of getting the result and allows achieving greater precision.

It was the first time the guys had scanned the whole car. The entire car was 3D scanned in about 3 hours with all the preparations which was a pleasant surprise to the Mashinators. Maxim admitted that the use of the 3D scanner Spectrum reduced the time required to obtain measurements and improved performance by producing more accurate results in a shorter period.

Alignment of front car 3D scans

Prior to the use of 3D scanners, the Mashinators used t laser-level measurements, which took a long time, and the accuracy of the readings left much to be desired. This method allowed two people to obtain data within seven days of work. It is obvious that using the 3D scanner enables specialists to save time and human resources. The time spent by the Mashinators to take measurements and obtain a processed 3D model was reduced to only a few hours.

Alignment of 3D scans of the left-wing of the car

3D scan result

After scanning, the Mashinators got a highly accurate 3D model of the car. It was exported to Blender for further processing. The specialist dissected the model in half, chose the reference half, and by a mirroring method placed one part on the other to see the match on symmetry, diagonals and planes. According to the 3D model, the left wing of the car was 1.5 cm lower than the right one, the holes on the wings were of different sizes, the gaps between the parts differed, and the trunk lid was slightly larger than the gap.

The Mashinators received the final reference model of the car, which had the necessary symmetry and all the necessary dimensions, which made further work much easier.

Body work

Now the Mashinators got down to the work with the body to correct all the shortcomings. First of all, specialists dismantled all doors and trunk cover to set the main body and front wings correctly.

The following types of body work were carried out by the Mashinators:

• Reduced the trunk lid

• Raised the left wing

• Aligned gaps between the details

• Aligned body surfaces

• Processed all openings 

• Set the loops

• Removed excess materials from a door to make it close freely

• Prepared the body to be painted

• Painted the body

• Put on white vinyl decorative lines

Outcome

The Mashinators have done their job brilliantly! Thanks to 3D scanning, the specialists have made precise measurements and corrected all shortcomings of the body in a short time! Maxim admits: "We’ve had a lot of experience with the car, with the 3D scanner. It’s the first time we’ve ever scanned an object this big. With the help of the 3D scanner, we determined that the body was really uneven. I couldn’t see it in my eyes. Without the scanner, we would have spent a lot of time looking for a reason where something went wrong, or we would have failed at all. The project is now complete. It’s all been successfully assembled. We’re happy with the result. It was interesting!" The owner of the replica has already received it back and is engaged in the further assembly of the car.

It turns out that Maxim and his team use Rangevision Spectrum 3D scanner not only for the tasks of the geometry inspection of car parts and body. A customer once asked them to make a complete copy of a car mirror, but expected it to be 30% bigger than the original. The guys scanned the mirror, scaled up the 3D model, and printed it on a 3D printer. The client was fully pleased with the result. The guys also use the 3D scanner to solve various autotuning problems, such as creating improved fairings based on individual car parts.

The example of this project shows that a 3D scanner is an important 3D technology for a company engaged in tuning, car maintenance and repair. A 3D scanner makes it possible to reduce the time and costs during the preparatory work stage and to improve the quality of the work performed. In fact, a scanner removes many of the limitations of conventional measuring devices. Industry-standard measuring instruments are inexpensive but highly subjective and not suitable for complex measurements. So 3D scanning helps to optimize the whole workflow of the automotive industry, which is very important in the ever-changing world.

RangeVision thanks Maxim Tereshchenko (the Mashinators) and Ivan Moskvichev (Plastmaska) for the assistance in the preparation of the article