Brought to you by TJ13 contributor Iain: R8
So officially, it’s a ‘substance’ that’s used in normal maintenance. Hmm!
The Mercedes steering wheel uses the PCU-8D display module from McLaren Electronics, supplied without connectors. This is a sealed unit, and according to the spec sheet “splash resistant to standard motorsport fluids”.
According to first reports from Toto, the problem was a broken wiring loom. Now the team’s position has changed to it being “a normal servicing substance” which caused a short circuit in the “steering column electronics“. What electronics? There is possibly a position sensor on the column, but what else? The steering wheel controls – and display electronics – connect to both the ECU and the Mercedes local control units for ERS, diff, engine controller etc. Yet the steering wheel was substituted and the problem remained.
So surely, they must be talking about a physical connections between the wheel and the wiring in the column. I would be very surprised if they were using an optical fiber system for the CAN bus, which would require ‘receive’ electronics. So an obvious conclusion to the first Mercedes statement, would be a physical connector malfunction or a broken wire in the connector. However, they now insist that it was a foreign substance to blame.
These photos come courtesy of SPA design and give an idea of how the quick release steering wheel might attach to the column. I would guess that a multi pin connector, like the silver Lemo shown, might be used. What maintenance would you do to that connector?
The recommended product is Isopropyl Alcohol. This evaporates, so it can be be excluded as a cause because it would be very obvious if it was not ‘Iso Al’ that was being used. The wiring would be another potential candidate for failure, if the original claims by Mercedes were true.
But, the only way that a substance could damage the plastic covered wiring is – if it was an acid. Maybe they were using Kapton wiring to save weight. However, using Kapton or Mylar covered wire to save weight, would be extreme, even for F1. Kapton degrades under thermal and mechanical stress, and it is hygroscopic (absorbs fluids).
Now is when we can start making educated guesses. Broken wiring in a connector initially seems the best answer. If it really were a mystery substance problem which caused a short circuit – it would have to be have been conductive.
If it were an open circuit problem, then you could imagine somebody picking up a can of spray lube, by mistake. Surely, they would have noticed immediately. However, that would be obvious the moment the car was started, because the steering wheel is connected when they fire up the engine, and the dash display should show a fault condition.
So what did they do between practice and the start of the race? Why were they doing anything to the connector? I have noticed that the steering wheels are left with the connector uncovered during the race weekend, so this might be a reason to clean the connector pins before practice, qualifying and the race. A better way would be to keep them clean at all times.
It puzzles me that someone introduced a conductive fluid and never noticed. As an engineer, it is just inexplicable at this level. Maybe the Mercedes explanation is just a cover story for bad design. Though the sabotage idea can’t be excluded.
Considering Paddy Lowe’s recent assertions of discovering faults within the Mercedes technical infrastructure at Brackley – it is of particular interest that according to Wiki, Lowe was joint head of electronics at Williams. So shame on him for not spotting this potential issue.