wheel speed sensors

The Pectel SQ6 has digital input channels for days, way more capability that I will need for trackdays. There are better ECUs out there nowadays but at the time of it's release the SQ6 was positioned right at the top end of the market for professional Motorsport ECUs. 

www.cosworth.com/media/199295/29e-071516.pdf 
http://www.apexspeedtech.com/products-we-love-what-we-like-about-the-pectel-ecus-part-1-hardware
(if anyone's interested!)

I have some previous experience running them in 6 - 12hour Sports Prototype endurance races from 2006 through 2009 and I don't remember us ever having any issues with them. So safe to say pretty robust.

In order to use up some of the digital inputs I decided to run a twin wheel speed sensor setup on the gearbox. This has a number of small advantages over the stock Lotus S1 set-up where there is a single sensor on the nearside rear upright.

• The S1 setup will read different between going left-right on long sweeping corners due to that tyre covering a greater/lesser distance.
• Sensor out on the upright is vulnerable to damage from stones/gravel especially on trackcar.
• Sensor gap is vulnerable to blocking from rubber/grass/gravel especially on a trackcar.
• Sensor/bracket and cable all add to unsprung weight on that corner.

With my twin setup I can get the ECU to average the speeds from the two inputs and display on the Pi Omega digital dash. Even though I don't have as many pulses-per-revolution (6 per side) by running a constant average calculation at high frequency I should be able to get a good refresh rate on the dash.

My setup is also far less vulnerable to damage being on the top of the gearbox and even with two sensors is lighter than the Lotus S1 setup.

 

A good tip for setting up these sensors is to get some thin card and fold to the desired thickness (check with calipers before hand - in my case 1.00mm) insert between sensor and trigger and then clamp up tight in position. I elected to run off the back of the M10 fasteners for the inner CV joint. This is nice and simple and just requires running bolts that are 6-7mm longer than strictly necessary.

Completed sensor in position above drive flange with Torque Seal applied to easily check in future that bolts haven't moved.

Sensors in position either side of rear diff.