Transmission speed sensor required? GPS sufficient?

[DParisi]

We are building a transmission and do not have any of the original wiring harness or instruments in the dash.

Can we use a $150 Android tablet (ex. Samsung Galaxy Tab A8 or Huawei MediaPad T5) that has GPS for speed sensing instead of purchasing a speed sensor for the transmission? We plan on running a tablet anyways for display.

Are there any pros or cons to have a transmission speed sensor or would this be redundant?

What are the benefits of running a dedicated GPS to CAN set up? (again, would this remove the need to buy and install a transmission speed sensor?)

[Adamw]

It depends what you want to use the speed sensor for.  GPS would be ok for an idle speed control lockout for example but it wouldnt be any use for gear detection, launch control, cruise control or traction control.  

You will likely need a separate sensor anyhow, it would be difficult to get a GPS signal from a tablet into the ecu.  There are cheap GPS speed sensors that work fine for basic functions like idle speed lockout.  example: https://www.aliexpress.com/item/1005005429092184.html

[Rossobianconero]

On 4/17/2023 at 1:27 PM, Adamw said:

It depends what you want to use the speed sensor for.  GPS would be ok for an idle speed control lockout for example but it wouldnt be any use for gear detection, launch control, cruise control or traction control.  

You will likely need a separate sensor anyhow, it would be difficult to get a GPS signal from a tablet into the ecu.  There are cheap GPS speed sensors that work fine for basic functions like idle speed lockout.  example: https://www.aliexpress.com/item/1005005429092184.html

How would you run traction control on a AWD car?

[Adamw]

2 hours ago, Rossobianconero said:

How would you run traction control on a AWD car?

It's not something I have had a lot to do with as it is pretty rare to do so.  In the OEM world it generally becomes more of a stability control function rather than traction control, where wheel speeds may be manipulated based on yaw, acceleration and other realtime measurements to approximate the level of traction.  In the aftermarket world the strategy would vary with the application and goal, it could be something simple such as a maximum wheel speed acceleration rate or real vehicle speed may be determined from LiDAR/RADAR or there may be GPS-based systems nowadays that incorporate other vehicle dynamics sensors to give a vehicle speed accurate enough to be useful for wheel slip calcs. 

[Rossobianconero]

3 hours ago, Adamw said:

It's not something I have had a lot to do with as it is pretty rare to do so.  In the OEM world it generally becomes more of a stability control function rather than traction control, where wheel speeds may be manipulated based on yaw, acceleration and other realtime measurements to approximate the level of traction.  In the aftermarket world the strategy would vary with the application and goal, it could be something simple such as a maximum wheel speed acceleration rate or real vehicle speed may be determined from LiDAR/RADAR or there may be GPS-based systems nowadays that incorporate other vehicle dynamics sensors to give a vehicle speed accurate enough to be useful for wheel slip calcs. 

For a drag car (AWD), what would be your choice to do this on a link. I do not really want to depend on a fix acceleration rate as a "traction" control, if possible