Design

The idea to design a mid motor conversion for the Kyosho Ultima RB5 came at the second round of the BRCA O/R National 2009 in Oswestry while talking with a fellow RB5 racer and seeing how well the prototype for the Atomic Crabon CR2 went for its first official outing.

It was decided right away to design a specific 4-gear gearbox for the car even though it made the task a little bit tougher, the pros highly outweighed the cons.

After a few weeks of CAD work, I had a pretty good base to start with, the main problem was the machining of the plastic chassis, which required quite a bit of machine time and I didn’t have much of that.

After finding out how affordable waterjet cutting was, I decided to change the chassis design to accomodate for the use of this process, which also required a change of material. The idea behind the aluminium chassis was to make up for the lower weight of the Lipo packs. It not only helps bringing the cars back to a more usual weight, but also does that as low as is possible on the car, lowering the CoG, and removing the need to add massive amounts of weight on the car as has become the trend.

During the design process, a lot of focus was put on how to keep the rear end fairly rigid without inducing any tweak. The result is the carbon fibre brace that links the two chassis sides to the gearbox. It allows perfectly symmetrical bending of the T-Plate, which is part of the reasons why the car is so easy and consistent to drive.

Just over 3 months after I started the design, the first prototype was ready to run, just in time for the last round of the BRCA Nationals at Robin hood Raceway.

About the bodyshell, it was pretty clear from the onset that the RB5 shell would not fit, due to the chassis being quite a bit wider. I then had two options, first was to make a specific shell, but that would have added to the cost of the chassis, and the second option was to simply use X-6 compatible shells, which is what I decided to do. Phat bodies were keen enough on the project to offer a special deal on their Zen shell for any MCS owner.

Below are Renderings of the Produced car’s CAD models, along with various design stages.