Jul 07, 2021
For our next project James and I decided to do something a bit more ambitious than the previous projects we have worked on. We wanted to build a racing mower and compete in events in Florida while also providing a test platform for high performance bearings that Boca Bearings supplies. Check out our video!
Our next task was to read over the rules and guidelines for the chassis requirements, as there are certain wheelbase and width requirements to compete. The rules state a 42” minimum wheelbase and a 46” maximum, with a max width of 40” sidewall to sidewall. For wheel sizes it's 6” minimum on all corners.
Keeping this in mind I began to lay out the preliminary designs for the chassis that we will be constructing out of the stock mower frame. The design is subject to change in the near future, but it is good to get ideas down for how it will be constructed so we know what the plan is when it comes time to modify the existing frame. I wanted to get a simple 2d design of the chassis we can go off of for easy reference when it comes to component placement and dimensions. We can also easily go in and adjust the drawing with ease if needed.
For wheels and tires I decided to go with 6” kart wheels with treaded kart tires that can gain traction in hard packed dirt/grass. They can be found here: https://www.bmikarts.com/6-Burris-Treaded-Tires-TX-Series-115-x-85-x-6-_p_7290.html
With the amount of power we are going to eventually push through the rear tires I decided to go with wider rears compared to the front, as traction is going to be our biggest concern. Getting the power to the ground and minimizing wheelspin is going to save us time on the track, as well as increase the longevity of the tires.
For the components of the drivetrain I want to focus on reliability and simplicity as there is less room for things to go wrong when pushed to the limit in competition. A centrifugal clutch will be the main component delivering power from the engine, as it is simple and robust. This will then lead into a right angle transmission or RAGB. The rules state that the mower must have some sort of transmission in order to compete, and this is the simplest form of a transmission. It changes the angle of the output allowing you to run a common vertical shaft engine and be able to easily transfer power to a Kart style rear axle with as little frictional drag as possible.
Rear hydraulic disk brakes are also going to be needed, as we are going to be approaching speeds around 50-70mph. It can be found here: https://www.bmikarts.com/1-or-1-14-Hydraulic-Brake-Kit--Black-Shim_p_10491.html
This should provide us with enough stopping power, although we might want to consider front brakes due to the weight of the chassis.