FTR Heave Spring
After the first rear pushrod failure, at Abingdon, I swapped to some tubular pushrods, which after running through the buckling load calculations, I thought they would be up to the job. Another couple of failures later (at Kirkistown and Castle Combe) I started designing a heave spring for the car. What is a heave spring? A heave spring is a suspension component, also called a "third element," primarily used in high-performance race cars to control vertical movement of the chassis. It is designed to prevent the car from bottoming out, especially due to heavy downforce, and to manage chassis movement during braking, acceleration, and cornering. This allows engineers to achieve specific ride heights and maintain performance by keeping the car's aerodynamic surfaces at an optimal angle relative to the track.
The issue was that no one had ever made one for the Hewland FTR gearbox before. So I couldnt buy an off the shelf kit that would give me the protection against bottoming out, that I needed. I was getting up to speed with Fusion 360 CAD software, and I decided to tackle the project myself, rather than pay someone else a huge amount of money to do it for me.
I decided to 3D print some of the components, prior to getting them milled from aluminium, to ensure the fitment was correct. One of the issues I was facing was that of the oil filler for the Dry Sump tank in the FTR gearbox, was so tall that it sat in the way of the sliding spring that I wanted to fit above it. So I removed the oil filler, reverse engineered it, redesigned it, and sent the drawing off to 3DPeople to sls print in Nylon PA12; when it came back I was very happy to see it was a perfect fit, and one of the obstacles had been removed.
The next task was to model the sliding spring mechanism, and the support posts, to make sure that they would allow a rubber spring to be used, without any of the mechanism binding. In Fusion I drew all of the components, then assembled them, and over several weeks, changed the design of the posts until I was happy that it would work.
I then sent the drawings off to 3DPeople again for printing, and when they returned, I fitted everything to the gearbox and suspension, to ensure it all fitted. I was again very happy to find that it all did.
The next step was to send all the CAD drawings off to my friend, for him to mill from aluminium. I was completely blown away when all the parts came back.
I then fitted everything, after sourcing some appropriately sized fasteners to bolt everything together with. I then drew up the sliding spring mechanism, and Nigel at Altiss Enigneering fabricated it for me; I bought several different rubber springs, and after testing at Blyton Park, settled on the black spring, with some additional spacers, to control when the spring became engaged.
The results were instant. I won a run off with the new setup that very same day, and went on to finish 2nd overall in the championship, without a single pushrod failure, leading to probably the best handling Mygale in the country.
A few videos of the progress
Checking the 3D printed oil filler cap for the Hewland gearbox
Checking the design in Fusion 360
Setting the heave spring up in the garage
The heave spring in action at Blyton Park (May 2023)
Here is the link to the complete model on Fusion. Hewland FTR heave spring model
This is the link to the stubby oil filler that I designed. Hewland FTR stubby oil filler neck
This is the link to the Heave spring base mounts that I designed. Hewland FTR heave spring base mount
The final cost? If you are interested, I can supply a full kit for £1500 + VAT
