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XRAY XB8’16  ‘Making of’  Part 1 – Exclusive story by Martin Bayer

If you think that you can take a rest at XRAY when you finish a project, well… you would be wrong. There is no time for breaks; the working tempo of the entire internal team, and especially of Juraj, is just insane, but, of course, inspiring. After my first full involvement with the XB2 development – which I shared with you in my previous Exclusive store here – I did not want to miss this opportunity, and so I was back in the loop, this time with the XB8 project.

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I was already involved with the XB8 platform in previous years, but this time I took over responsibility for the entire development of this platform from Juraj. Already having extensive experience, I knew exactly what to expect, so I was ready for plenty of work in the office, plenty of travelling, and of course plenty of track time and wrenching. But whatever I was expecting, reality greatly surpassed my expectations.

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As usual we started work by taking the existing car, reading through all the feedback and comments received from customers, team drivers, distributors, and then putting down all my own comments. From this I divided things into a list of details that I would change, details that should be changed, and then also all details that I did not want to change and wanted to carry over. I also had to keep in mind that we needed to use the same platform for the electric version of XB8, and we had to keep everything open for the XT8 truggy version.

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XB8 details I wanted to improve for 2016 version:

  • Eliminate suspension binding in dusty conditions
  • Eliminate vibrations in rear suspension from transferring to the shock tower
  • Gain more steering
  • Increase stability & predictability
  • Improve rear traction
  • Improve the flex
  • Reinforce weak points
  • Improve the performance of the body
  • Test the Lexan wing

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XB8 details I wanted to carry over to the 2016 version:

  • Carry over the entire platform, with maximum parts compatibility
  • Keep most of the layout from the XB8 platform (in general)
  • Keep the reliability of the car
  • Use the same well-proven suspension geometry
  • Continue with the principle of pivot ball suspension

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Task #1:  Eliminate suspension binding in dusty conditions

I was very happy with the performance of the original XRAY pivot ball suspension that we introduced back in 2014; the range of adjustments and how easily all adjustments could be achieved made it a joy to work on the car. However on very dusty tracks we continued to experience problems with binding suspension as the dust blocked the free working of the upper pivot ball.

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Solution:

The first solution I tried was to use small foam pieces that I have installed on the pivot ball which was a slight improvement but certainly far away from a complete professional solution. I tried to increase the play in the upper composite ball joint which of course resulted in wobbly suspension, but still the dust that got inside locked up the movement.

After some brainstorming with Juraj, we were convinced that we needed to change the upper pivot ball from vertical mounting to a horizontal mounting system. This would mean we would have to go in the direction of conventional pivot ball suspension design.

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We worked with Juraj to give this a try and to see if our expectation was correct. The engineers drew the entire front suspension with the conventional pivot ball system, production quickly made a few rapid prototypes for testing, and then we gave it a try. Our expectation was correct: the horizontal pivot ball mounting system worked well in dusty conditions. So despite my wanting to continue to use our unique pivot ball suspension, we would need to change the front end to solve the binding issue.

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Task #2: Eliminate vibrations in rear suspension from transferring to the shock tower

On very rough tracks, vibrations from the rear suspension were transferred to the car. Whatever I did with the shocks and set-up of the rear end, I still could not get the car to stay calm when running over rough terrain.

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I was convinced that the strange handling over rough bumps comes from vibrations when the suspension transfers energy through shocks to the shock tower, and then via rear brace to the chassis. All this has a negative impact on the handling of the car.

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Solution:

This time the solution was straightforward and fairly easy. I redesigned the rear chassis brace, which was mounted to the mounting holder on the rear bulkhead instead of the shock tower. After making a quick prototype from polyamide, I did a quick test which confirmed my theory.

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With the brace not mounted to the shock tower, the car was suddenly very smooth over the rough bumps and finally I had full control over the car no matter how rough the track was. The mounting of the brace is now positioned in a composite holder which has a bit of play so the brace has a minor small side flex which helps the forgiveness of the car for the regular drivers.

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Since we needed to make an all-new mould for the brace, Juraj came up with an idea to make the brace additionally adjustable in the terms of stiffness. After running through a few different alternatives, we came up with the final design that allows to additionally mount graphite inserts into both sides of the rear brace to make it even stiffer.

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Task #3: Gain more steering

Like everyone else in all the categories, we continue to hunt for more steering and more traction, because there is never enough of either. J  The previous XB8 had significantly improved steering characteristics, but I still felt we could get a bit more.

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Solution:

To play around with the steering, we designed & produced several different designs of the steering plate, tested them with different Ackermann and bumpsteer adjustment shims, and tried different height positions of the steering plate.

I spent a few days at the tracks doing back-to-back testing of different designs and alternatives to find the best solution. We came to the point where we needed to redesign the chassis as well, and as such when making different chassis prototypes I also had to produce different chassis with different steering system positions.

Personally I liked the universal drive shafts which gave slightly more steering, as the drive shafts were slightly less binding when the wheels were in full steering lock.

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With the new steering blocks we can now independently change the Ackermann extensions to another adjustment possibility. With previous experience with these steering extensions from XB2, I knew exactly what we wanted to test, so this time it was easy in the design phase but of course time extensive in testing.

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With the combination of different steering plates, steering block extensions, and different chassis with different steering system position, there was a lot of extra work & effort to find the best possible combination that would be a working solution for all different track conditions.

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After extensive testing, I selected the best combinations that I liked and provided them to Juraj for his own testing. Juraj felt pretty much the same differences in steering characteristics, and at the end when we had to choose the final solution we decided on the design with a more forward chassis position. All the new geometry resulted in increased and more smooth steering. I was satisfied, and another checkpoint was made.

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Task #4: Increase stability & predictability

Top drivers are able to race and win with twitchy cars, but for regular drivers the key to success at races is to have a car that is stable & predictable. The XB8 platform has had improved stability, but we still get frequent requests from customers to make the car more stable, especially at rough tracks.

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Solution:

There are several ways to increase the stability of a car, but the tricky part is to find proper balance because a more stable car generally has less cornering speed, and it usually is more ‘square.’  The stability of the new XB8 comes from the several other areas we have worked on and changed, including:

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  • New weight balance: We shortened the chassis by 4mm to make the car easier to control and moved the weight by moving electronics, center diff, fuel tank and engine all frontwards. The wider design of the chassis in the rear helped with stability and the narrower design of the chassis in the front helps to increase traction as well to improve steering.
  • New chassis flex & overall car flex: To get the proper chassis flex, I made and tested several different chassis layouts all with slightly different longitudinal and side-to-side flex characteristics. All these different designs were tested in combination with different chassis braces, different radio boxes from different composite material, and different side guards.

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  • New braces flex: Not only was the rear brace completely redesigned with a new flex characteristics independent from the rear shock tower, but also the front brace was redesigned to be shorter and only with 1-screw mounting to prevent the front brace from negatively influencing the chassis flex.

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  • New side guards: On the previous XB8 we completely removed the reinforcement ribs, which in some track conditions made the car much too stiff. However, the design of the guards was still not optimal at tracks with rough surface; the edges of the guards sometimes got into contact with the ground which of course has a negative influence on performance. As such, we decided to completely redesign the side guard’s layout, to make the edges with large radius so even in the roughest tracks the side guards would not contact the track. The simplified design of the guards made it also easier to predict the flex and of course we tested various composite mixtures all with different hardnesses. I found using a softer composite mixture instantly gave the car more traction.

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  • New radio box flex: I started to test different hand modifications to the radio box already last year, to experience and understand the influence of different modifications of the radio box layouts on the handling of the car. Most tests were made with different positions of the radio box in the chassis to move the balance, but also by making modifications to the radio box to make it either softer or stiffer and to see how each of these would impact the handling of the car.

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  • New universal drive shafts: For a few years I have been testing & comparing the CVD drive shafts used by XB8 platform with universal drive shafts we have used in the early beginnings. In some track conditions – especially on high-traction tracks – I did not see any particular difference. But on low-traction tracks, I felt that the universal drive shafts generate slightly more traction. To verify if it was just a 1-time feeling, I continued to test and compare but my findings seemed to be same in ongoing tests.

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Task #5: Get more traction in the rear

The traction of the car has already improved with the new universal drive shafts, the new weight balance, new flex, and also the new rear brace mounting system. All of these changes have clearly helped with the traction of the car, but I still felt that more traction was possible.

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Solution:

When we changed to the all-new XB8 platform in 2014, I always felt that a bit of rear traction was lost and I was suspicious that it is because of the 2-piece uprights and the upper aluminum bracket which reinforces the whole assembly. That design makes adjustments not that easy, but I felt that the full composite uprights generated a bit more traction.

To prove or deny my feelings, I modified the old previous 1-piece composite uprights, installed them on the car, and ran them for several races at different tracks and checked & compared them back-to-back with the 2-piece uprights. To be sure that this was not only just my personal feelings, we again had Juraj do the same tests. He agreed with my findings, and approved the creation of new 1-piece composite uprights. I was again satisfied when another small improvement part was finished, and we continued to solve the puzzle of what should be changed and improved.


To be continued…