I have wired wheel speed inputs to four digital inputs of the PRO-8. Unfortunately I have an issue in hardware (wiring, frequency divider circuit, etc) that is causing sporadic 40+km/h jumps in speed for 10-15ms. This causes all sorts of havoc with the BMW DCT so I have needed to filter the wheel speeds before sending them to CANTCU.
Herein lies the problem:
- Vehicle speed can (basically) only come from driven/undriven axle speed, which makes sense, except:
- Driven/undriven axle speeds can only come from the individual wheel speeds, which makes sense, except:
- The individual wheel speeds (LF/LR/RF/RR) can only come from a configured sensor, or from a specific CAN protocol, but NOT from a user channel. This is a problem because the filtering on Sensors 1-4 is insufficient.
I did try routing the wheel speeds through Turbo 1/2 freq and Gearbox input/output freq, then having sensors 1-4 use user channels, but unfortunately the resolution for turbo 1/2 frequency wasn’t sufficient for use as a wheel speed.
I guess ideally the wheel speeds (Sensors 1-4) could have stronger filtering (though I realize that would interfere with their effectiveness for traction control). Alternatively, can the individual corners (Wheel Speed / Front Left(etc) / Source) allow the use of a user variable? The consequences aren’t that bad, basically the pit limiter momentarily bounces to “Armed, speed high” state for 10ms due to the incorrect speed), so maybe this is just a “me” problem (the real answer would be to fix the wiring, or maybe connect to the MK60 ABS using CAN).
FWIW I ended up doing the following for filtering:
DeltaLF = ("sensors/wheelSpeed/sensor1/frequency" - FilteredLF)
FilteredLF = clamp(DeltaLF, -8, 8) * 0.200 + FilteredLF
I think I can loosen the filtering but this is working fine for me, mostly because I don’t use traction control. Here’s what the unfiltered axle speed looks like:
