CAN for driver switches

[Jimmy20v]

Hi All,

I am currently working through wiring plans for my newly delivered M150 and had been intending to run most of the driver switches via CAN, however, my MoTec dealer has recommended against doing so.

I was wondering if anyone could point to why that would be a bad idea as when using a D153 or a XAP steering wheel then all driver switching is sent over CAN.

For reference, this is a partner package based on GPR and the switches I am talking about are as follows:
Launch - momentary for activation
Launch Aim - multi position
Traction Aim - multi position
Run switch - via PDM combining both a switch and input from the battery master
Start switch
Upshift paddle
Downshift paddle
Neutral enable

When a CAN receive message is assigned to a driver switch, should the message bus fail for any reason, is the previously received message value retained? Or does the switch revert to a default value?

For example, if Launch Aim is assigned to driver rotary 1, and driver rotary 1 is received on CAN 0 Offset 0. Driver Rotary 1 is configured with cal "CAN Position x 100.1.0" transmitted from the dash.
What would occur should CAN bus communication between the dash and the ECU fail for a period of time?

Or as a second example. If my run switch was assigned to Driver SW 1. Driver SW 1 is received on CAN 0 Offset 2, and CAN communications were to fail. Am I correct in assuming that in this case Driver SW 1 would revert to whatever is configured in "Default" in the switch map. So in this case it could be configured to "on" to ensure the engine continued to run when communications are lost?

I also planned to use the fuel pump output via CAN to enable the fuel pump output within the PDM and things such as the coolant temp to provide pulsed coolant pump control via the PDM.
I assumed these were fairly standard practice nowadays.

Cheers,
James

[Stephen Dean]

Hi James,

As long as the CAN Bus is wired correctly, there should be no issues in using CAN messaging for the buttons. I use CAN messages for most of the inputs on my M150, including the Paddles and Engine Run switch. If the CAN Bus goes down in my car, the engine is going to stop anyway as the Fuel Pumps, ignition coils and injectors are powered through the PDM based off of CAN messages.

The CAN messages will go to 0 if the communications drop out.

[Jimmy20v]

Hi Stephen,

Thanks for confirming that. That's essentially what I thought and I would be in the same position as I too intended to power the fuel pump/coils through the PDM based on CAN messages.

Thanks also for the note that messages will go to 0 with a drop in comms, not quite what I expected but makes sense.

I think I'll double check with the dealer what his concerns are and then weigh up the pros and cons of each route.
With my chosen branch of motorsport (hillclimbing) a run is essentially aborted with any sort of error so either everything works or it doesn't.

Cheers,
James