In the modern motorsport industry, it is a norm to use paddle shifters to change gears regardless of the class you’re racing in. Paddle shifters let drivers change gears electrically. Having shifters behind a steering wheel is advantageous, especially around corners as they allow drivers to shift gears while holding the steering wheel with both hands.
In racing simulators, paddle shifters are must too because simulators have to cover all – or most of, functions racing cars have in real life.
In this article, I’d like to share how I’ve developed paddle shifters. Hopefully, it’ll be helpful for DIYers as well as for those who are developing Formula Student cars.
In order to avoid confusion, in this article, I shall define ‘Pull’ as a finger movement towards the driver that activates shifters. So you pull the right paddle to shift up, and pull the other one to shift down.
1. Types of Shifters
There are a few types of paddle shifters: standard shifters, magnetic shifters, rocker shifters and push-pull shifters.
Rocker shifters are often used in modern Formula 1 cars and they’re visible when you see the onboard facing to a driver. One of the features of rocker shifters is the ability to shift up and down on each side with the help of see-saw like mechanism. With so many buttons to manipulate while racing at 200+mph, being able to change gears in both ways with only one hand could well be an advantage.
Push-pull shifters are used in Rally cars. You literally push or pull the paddle to change gear. It may sound similar to rocker shifter but the fundamental concept is completely different.
Some steering wheels have standard shifters which use springs to push back a lever that activates a switch inside. High-end wheels are normally equipped with magnetic paddle shifters for positive click feeling and longer durability. Companies like Cosworth, ShifTec and Hewland offer high quality aluminium magnetic shifters.
The image below is an aluminium shifter from Precision Sim Engineering. I bought a pair of them on LeoBodnar store for LMP3 wheels. Decent amount of force is required to activate due to the strong neodymium magnets. Robust aluminium billet construction gives you tactile feedback too.
Aluminium shifters have a more positive click feeling than others in most cases. Use of aluminium adds up the price though. I reckon Ascher Racing offers one of the best Aluminium shifters for simulators.
Many DIYers have been trying to figure out the way to achieve positive click feeling and durability while keeping the cost as low as possible. I wasn’t the exception.
Here I’ll focus on the designing of magnetic paddle shifters.
2. Designing Shifter
When developing paddle shifters, there are a few things to be taken into a thorough consideration: material, travel, force and sensor.
2.1. Choosing Material
In terms of material, 3D printable plastic such as PLA and ABS are a reasonable choice for DIY. If you’re planning on making one from ‘scratch’, then aluminium is a no go, unless you’ve got enough budget and facilities to mill metal. I’ve got an idea to tackle the cost issue in my mind, which I’ll talk about later on.
2.2. Activation and Return Force
Let’s move onto the technical aspect. The schematic diagram below illustrates how magnetic shifter works.
When the paddle is pulled, the lever eventually hits the sensor, then it sends a signal to an electric board. The magnets on the housing and the lever attract each other to bring back the lever to the original position.
Since there’s no complex mechanism, choosing magnets is critical. The amount of force required to activate the shifter only depends on the magnetic forc and the geometry. We’ll go through the calculations of the activation and the return force.
First, you’ll need to calculate the magnetic force. The figures you’ll need are:
- Diameter of magnet : D [mm]
- Thickness of magnet : t [mm]
- Gauss oersted : G [MGOe]
- Distance between the magnets : x [mm]
Generally speaking, calculating magnetic force requires approximations. I’ve tried to calculate using Gilbert Model, but I couldn’t fully trust the figures. After some googling, I’ve found a handy website by K&J Magnetics where you’ll get magnetic forces based on experimental data. Assuming you’re using D=12 mm, t=4 mm and Gauss oersted of 38 (N38) Neodymium magnets placed 3 mm apart, the magnetic force will be about 0.708 kg.
Since you’d likely pull the lever at the tip of the paddle (approx. 10 mm from the edge), you won’t feel the same force as the magnetic field makes (Fm [N]). You’ll need the following figures to calculate the force you feel through your fingers.
- Distance between the centre of the pivot and the centre of the magnet: Lm [mm]
- Distance between the centre of the pivot and the point 10 mm inside from the edge of the paddle: Lp [mm]
- Calculated magnetic force: Fm [N]
When activating shifter, the torque generated by the magnetic force Fm and the torque you’ll apply should be equal. Thus the trigger force can be obtained by the following equation.
The ratio of Lp to Lm plays an important role here. You wouldn’t want to make the lever too long, or place the magnets too close to the pivot.
It’s a slightly different condition when you release the paddle. The image below illustrates a fully activated shifter.
Because of the complexity of the magnetic field, here I’m assuming that the attraction force between magnets is only applied vertically (Fm'[N]), and the opposite poles of the magnets won’t affect the magnetic field. If the tilt of the lever is θ deg, the minimum force required to keep pulling down the lever can be obtained by the following, using torque equation:
Now, if we have a look at the Distance vs Pull Force graph on K&J Magnetics website, the relation between them is obvious; the far the two magnets are separated, the less attraction force they produce. This means if you place the detection point of the sensor too far down, it’ll result in loss of attraction force between the magnets – making it easy to hold the paddle. Large travel (x’) increases θ — i.e., decreases cosθ, although θ would be small enough to be neglected.
The amount of force you want may depend on personal preferences. However, it’s crucial to maintain tactile activation feedback to prevent miss-shifts in intense conditions.
There has to be a way to detect the movement of the lever. Placing a push switch is one of the simpliest idea but it may require a large space. For this reason, a micro switch is commonly used. A microswitch, also known as limit switch, is a tiny switch that is also found in 3D printers, to limit the range of axis’. As far as I know, most of paddle shifter makers implement this solution for their products. The image below is a switch used for shifters from Precision Sim Engineering. Micro switches form DongGuan seem to be quite popular as Ascher Racing use IP67 switch which is also from the Chinese supplier.
Using micro switch is an easy and definite way but there is a risk of troubles. Due to its simple yet delicate mechanism, you may encounter stutterings caused by worn-out switches.
In order to avoid mechanical troubles, some advanced shifters have a hall sensor. Hall sensor is a compact electronic component that detects surrounding magnetic fields. XAP Technology producing electronic components for racing cars is adopting shifters with a hall sensor system for their steering wheels. Magnets you may see on their shifters are for hall sensors; springs are placed beneath the lever.
3. Paddle shifter – Ver.1 (Concept)
I designed the shifter above when I was working on my very first DIY wheel. It looks pretty terrible, doesn’t it? I didn’t even have a 3D printer, so I had to try my best to design one that only comprises panels of plastic attached with adhesive. I’ve prototyped one (I couldn’t find images) with 5mm thick plastic cut into pieces and assembled like a paper-craft. However, it wasn’t hard to list issues the shifter had.
Paddle shifter – Ver.2
I gave it another go after less than a year. This one was for LMP2 ver.1 wheel. I luckily found a company that 3D print things if you send them CAD data. Changes from the predecessor are obvious, compact overall design, much smoother activation with a low-friction shaft from TAMIYA and stronger return force.
Paddle shifter – Ver.3
The ver.3 is the slightly modified version of ver.2 and used for most of Taichi SRW steering wheels. There were some updates though, such as replacing the 3D paddle to 3mm thick twill matte carbon fibre, implementing stronger neodymium magnet and placement of windows on the lever for the ease of maintenance. After many updates, the image below was the final edition of the ver.3 shifter.
The ver.3 shifter was the one that got copied by a dodgy Brazilian company. It was partially my fault for selling the CAD data on Pinshape for just 1 or 2 dollars, for non-commercial use though. Apparently, the restriction was not effective whatsoever.
Paddle shifter – Ver.4 (Concept)
I was working on a ver.4 shifter after the paddle-shifter-gate. The concept is to lower the cost of aluminium shifters. The main reason why billet shifters are so expensive is because of its manufacturing process. They are milled out from a block of metal (billet); more materials are thrown away than that of the actual products.
I’ve come up with an idea, which is to cut out all the parts from a sheet of metal with a laser cut. A similar method is used for CFRP shifters.Since I’d been outsourcing aluminium plates for the wheels, I knew it wouldn’t cost that much.
Sadly though, I didn’t have enough time for further development after making a 3D printed prototype. But I might start working on it again.
Given that Taichi Sim Racing Wheels still exists, I can’t show exact numbers and process we’ve been developing, but I hope you all have found this somewhat interesting and useful.